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Cold-sprayed coatings: Microstructure, mechanical properties, and wear behaviour
Abstract
Deposition of coatings on the surface of a bulk material is a versatile, economical, and effective strategy to provide additional features to the bulk material, mainly to improve its functionality and extend its service life. Among all the thermal deposition techniques, cold spray (CS) is the only technique in which particles are deposited below their melting point, and therefore, it is a solid-state processing technique. Coatings generated via CS exhibit different characteristics from those of the coatings produced by other methods; this may make CS a competitive technique for the repair and even for the manufacture of self-standing components.
This study presents a basic description of CS and a review of its applications in the deposition of metallic coatings, specifically those based on materials such as Al- and Ti-based alloys, used in aeronautical components. CS is a thermal spray technique that enables the production of coatings with properties and behaviours similar to those of bulk materials with similar compositions.
... During the dry sliding wear of cold sprayed coating, the properties of the interfacial layer have substantial effects on the tribological properties of the coating [9]. The wear rate of the coating is inversely proportional to the hardness of the coating [9,10]. ...
... During the dry sliding wear of cold sprayed coating, the properties of the interfacial layer have substantial effects on the tribological properties of the coating [9]. The wear rate of the coating is inversely proportional to the hardness of the coating [9,10]. But, the high hardness of the coating, associated with a high coefficient of friction, may lead to an increase in the level of wear [9]. ...
... The wear rate of the coating is inversely proportional to the hardness of the coating [9,10]. But, the high hardness of the coating, associated with a high coefficient of friction, may lead to an increase in the level of wear [9]. It has been reported that the wear and friction can be reduced by using a combination of lubricant materials reinforcement with hard materials [9]. ...
A hard and self-lubricious composite coating of tungsten disulfide (WS2) blended Inconel 625 alloy was deposited on AISI 304 stainless steel substrate by laser assisted cold spray (LACS) process through optimizing the laser power and gas pressure of the supersonic jet. Effects of the laser power which determined the deposition temperature and the gas pressure of the cold spray on powder deposition were studied. The surface temperature during laser heating was maintained below the evaporation temperature of WS2 for avoiding depletion of the WS2, but sufficiently high to soften the hard Inconel 625 powder. This facilitated deposition of the blended powder through plastic deformation at a relatively low gas-jet velocity in comparison to that typically employed in a conventional cold spray process. XRD and XPS results confirmed the presence of WS2 in the coating. The coefficient of friction was found to be 5 times lower (0.11) and the wear rate 42 times lower (8.5×10-6 mm3/N-m) than those of the substrate. The coating exhibited a hardness more than two times that of the substrate (490 HV) due to presence of nano-sized tungsten dispersed in the matrix.
... CGS consists of the acceleration of solid powder particles at supersonic velocities, ranging from 500 to 1500 m/s [11][12][13][14]. During the impact, particles undergo plastic deformation, leading to the formation of dense and adherent coatings, maintaining the chemical composition and microstructure of the feedstock powder [15][16][17]. ...
... The high strain suffered by the impinging particles during deposition produces a broadening of the peaks that can be clearly seen in the pattern, making the (111) peak almost no visible. It is also noteworthy that, as expected, oxides or other intermetallic phases are not observed because there is no melting during the CGS process [15,17]. ...
... The distribution of material in AM refers to how layers are built up to form the final part [45][46][47][48][49][50]. Common AM processes include powder bed fusion, material extrusion, Binder Jetting, Directed Energy Deposition (DED), Sheet Lamination, and Vat Photopolymerization [51][52][53][54][55][56]. ...
... More work has to be done on CAD products to accommodate complex structures like porosity and anfractuous for cellular or yarn interweave. [81] examines the controlling thermal stress and sagging is a significant challenge when Table 1 shows the applications and belongings of cold spraying coating materials [53][54][55][56][57][58][59] CS technology is a process which are propelled at very high velocities and then bonded without fusing. This process affects microstructure as a consequence of developing a high density and low porosity of the coatings with fine grain size. ...
Additive Manufacturing (AM) stays gaining popularity in advanced industries like aerospace, automotive, healthcare, and energy outstanding by its ability to create intricate, customized structures. Key drivers include design freedom, light weighting, rapid prototyping, and supply chain optimization. However, the study discusses the challenges of poor surface quality in traditional manufacturing processes and the potential of AM to create advanced thermal spray coatings. It places of interest that need for precise and uniform coatings across industrial components. Surface coating approach permits exact control over coating thickness, microstructure, and fabric composition, upgrading surface quality and encouraging customization for particular applications.s The study also highlights AM’s rapid prototyping and iteration capabilities, accelerating the development cycle and improving coating solutions. This consider analyzes a few sorts of coatings, such as coordinate vitality testimony, cover streaming, powder bed combination, warm splash coatings, and sheet cover. The combination of AM and warm splash coatings empowers engineers and analysts to extend the wear, erosion, oxidation resistance, electrical conductivity, and other key properties of delivered parts. The integration also handles AM difficulties such as roughness of the surface, dimensional precision and material compatibility. This strategy is consistent with the industry’s goal for sustainable and resource-efficient production techniques, optimizing material utilization, minimizing waste, and increasing part longevity through improved surface qualities.
... As a result of the low deposition temperature, defects are not formed that are associated with high temperatures. The use of low temperatures in CS results in unique characteristics [18]. It is possible to maintain the microstructure and properties of the feedstock powders, as well as to prevent oxide formation and any other unfavourable structural changes, thus enhancing the durability of the coatings. ...
... More in detail, the aluminium compositions (Alx) utilised were 0.1, 0.2 and 0.5. The defined process parameters were chosen with the aim of exploring a reasonable Cold Spray temperature range, according to literature [16,18], with an appreciable temperature variation, and to investigate the impact of different chemical compositions. This way, a total number of 10 specimens were generated. ...
A Non-Destructive technique (NDT) based on Active Thermography (AT) is proposed to correlate mechanical properties, process parameters and thermal response for High-Entropy Alloys (HEA) coatings. More in detail, the Pulsed technique is utilised to investigate thermal responses generated by different High-Entropy Alloys (HEA) coatings. In particular, specimens tested in this work are made of several chemical compositions (Al x CoCrCuFeNi and MnCoCrCuFeNi) and are realised by using different Cold Spray temperatures (650°C, 750°C and 850°C), generating coatings with various mechanical properties. This way, results in terms of thermal responses obtained with a Non-Destructive technique are correlated , by means of ANOVA, with the corresponding chemical compositions and process parameters of each specimen. The impact of both roughness and emissivity on the process characterisation was also investigated. ARTICLE HISTORY
... Cold spray technology is considered optimal for repairing large surfaces with complex shapes requiring precise deposition for thin layer repair and uniform coating. Repair of turbine blades is another prominent application of cold spray technology [11]. Key process parameters influencing the CSAM process include gas pressure and temperature, powder feed rate, nozzle design, and standoff distance. ...
... Powder particles are introduced into the gas stream upstream of the nozzle. The high-speed gas flow accelerates the particles to velocities typically between 300 and 1200 m/s [11,12]. When the high-velocity particles collide with the substrate, their kinetic energy is converted into plastic deformation energy. ...
Cold spray additive manufacturing (CSAM) is a cutting-edge high-speed additive manufacturing process enabling the production of high-strength components without relying on traditional high-temperature methods. Unlike other techniques, CSAM produces oxide-free deposits and preserves the feedstock’s original characteristics without adversely affecting the substrate. This makes it ideal for industries requiring materials that maintain structural integrity. This paper explores strategies for improving material quality, focusing on nozzle design, particle size distribution, and fine-tuning of process parameters such as gas pressure, temperature, and spray distance. These factors are key to achieving efficient deposition and optimal bonding, which enhance the mechanical properties of the final products. Challenges in CSAM, including porosity control and achieving uniform coating thickness, are discussed, with solutions offered through the advancements in machine learning (ML). ML algorithms analyze extensive data to predict optimal process parameters, allowing for more precise control, reduced trial-and-error, and improved material usage. Advances in material strength, such as enhanced tensile strength and corrosion resistance, are also highlighted, making CSAM applicable to sectors like aerospace, defense, and automotive. The ability to produce high-performance, durable components positions CSAM as a promising additive-manufacturing technology. By addressing these innovations, this study offers insights into optimizing CSAM processes, guiding future research and industrial applications toward more efficient and high-performing manufacturing systems.
... The key to this process lies in the plastic deformation experienced by the particles upon impact with the substrate, promoting excellent adhesion of the coating. This is how CGS produces high-quality and highly resistant coatings [25]. Fig. 2 shows the starting powder and the coatings obtained with the three different deposition techniques. ...
... The analysis was performed using the software Simapro® release 9.1.1, the most used software for LCA studies in academia that allows the adoption of different impact assessment methods and the access to several databases [25,27], and it was articulated in the four phases defined by the standards and detailed as follows. ...
In this study, an environmental and economic assessment of WC-Co coatings deposited by Cold Gas Spray (CGS), Atmospheric Plasma Spray (APS) and High Velocity Oxy Fuel (HVOF) spray technologies is carried out. Using SimaPro LCA software, several environmental impact categories are analyzed to compare their environmental performance. The economic analysis includes capital and operating expenditures. The results have highlighted that all three processes exhibit low environmental impact in terms of CO2 emissions but the performance of the CGS process is heavily influenced by the low deformability of WC-Co, while the APS process is affected by high electricity consumption. In terms of economic analysis, the HVOF process exhibits the best performance, while the CGS process requires most time to deposit the coating, and consequently, it is the process where the workforce component is most significant. These results depend on the fact that CGS might not be the most suitable deposition technique for fabricating WC-Co coatings.
... All the indentations were carried out under the same conditions. Therefore, the smaller indent on the CS-Ti64-T3000 compared to that on the CA-Ti64 indicates its higher hardness and elastic modulus [21,22]. Ti64-T100, CS-Ti64-T500, CS-Ti64-T1000, and CS-Ti64-T3000, respectively. ...
... Ploughed furrows are clearly seen on their wear morphologies [2,11,28,29,34]. Normally, the repeated dry sliding of the steel ball initiates minute cracks at the interfaces between sprayed Ti64 particles and in the subsurface, propagates them along the interfaces and parallel to a free surface for some extent, and eventually results in a formation of interfacial micro-cracks and a removal of surface materials from deep regions as platelets, respectively [2,11,22,28,36]. The spallation of surface materials can be accelerated by the existence of weak interfacial bonds between sprayed Ti64 particles. ...
The effect of coating thickness (CT) on the microstructures, hardness, and wear of cold sprayed Ti-6Al-4V (CS-Ti64) coatings was systematically investigated since the prolonged high pressure CS deposition could change their microstructures and porosity levels. In addition, the CT was relatively important for their durability, performance, and service life. Therefore, the CS-Ti64 coatings with different CT of 100-3000 µm were prepared on commercially available Ti64 (CA-Ti64) substrates via high pressure CS processes. The CS-Ti64 coatings had low porosity levels wherewith severely deformed Ti64 particles with a crescent-shape could be seen in their cross-sectional microstructures. The hardness of the CS-Ti64 coatings increased with increased CT probably due to their lowered bulk porosity levels associated with longer high pressure CS deposition. As a result, the increased CT from 100 to 3000 µm resulted in a 9.8% decrease in the wear of the CS-Ti64 coatings. The wear of the CS-Ti64 coating with 3000 µm was 16.8% lower than that of the CA-Ti64 as all the CS-Ti64 coatings had lower wear than the CA-Ti64. It could be concluded that the prolonged high pressure CS deposition for the thick CS-Ti64 coatings had an influence on their porosity, hardness, and wear.
... The selection of the appropriate thermal spraying technique and parameters is critical as it directly influences the microstructure, porosity, adhesion, and overall performance of the resulting coating. Factors such as the thermal conductivity, melting point of the coating material, and the operational environment of the substrate must be meticulously considered to optimize the coating's functionality and longevity [166,167]. ...
In the burgeoning energy sector, the deployment of high-temperature resistant coatings is crucial for enhancing the durability and efficiency of components operating under extreme conditions. This research delves into an array of innovative coating materials-ceramics, composites, and metallic alloys-and examines their application through state-of-the-art deposition techniques, including thermal spraying, physical vapor deposition (PVD), and chemical vapor deposition (CVD). Through a synthesis of experimental data and computational modeling (thermodynamic and kinetic modeling, finite element analysis, and molecular dynamics simulations), this study evaluates the coatings' performance in harsh environments. The findings reveal significant improvements in component longevity and functionality; however, issues related to cost-effectiveness, scalability, and environmental impacts are identified. The study highlights the potential of nanostructured materials and green manufacturing processes as viable solutions to these challenges, advocating for their adoption to ensure scal-ability and sustainability in future applications. This research underscores the essential role of advanced coatings in meeting the energy sector's rigorous demands and sets the stage for integrating more sustainable practices into the field's progression.
... Moreover, whether the usage of a 'low-pressure' cold spray system or a 'high-pressure' system generates more performant coatings appears to be application specific. For example, in the case of wear, using a high-pressure system can improve the microstructure of a coating and further increase its wear and disbonding resistance [14], although it is not necessarily true that wear performance is dependent on increasing the coating density (resulting from using higher gas pressures, which subsequently increase particle velocity) [15,16]. Similar findings have been presented for the usage of nitrogen or helium as a carrier gas with the same type of cold spray systemwhile helium can accelerate powder particles to higher velocities based on its lower molecular weight compared to nitrogen gas [17], usage of one carrier gas over the other does not necessarily result in superior mechanical properties or performance in the aforementioned quality assurance tests [11]. ...
... Consequently, the CS manufacturing process is dominated by the plastic deformation of the spraying particles. Then, the processing characteristics by CS do not significantly change the properties of the feedstock powder by heating or melting during the CSAM part fabrication, and also prevents the materials oxidation during the deposition [4,5]. ...
... Finally, a proper surface treatment is applied to reproduce the element's original geometry. Moreover, in the case of particularly harsh operating conditions, the element can be modified by optimizing the chemical composition of the coating or changing the mechanical or tribological properties of the finished element [17][18][19]. The coating's properties can also be changed through technological treatments such as the heat treatment process [5]. ...
In response to environmental issues and the intensive degradation of parts, the civil and military aviation industries have shown increasing interest in developing more sustainable materials and technologies; therefore, this paper proposes the regeneration of structural components by cold spraying. As part of this research, Ti–Al composite powder was deposited by low-pressure cold spraying and then heat treated to obtain a Ti–Al3 intermetallic phase. The Ti–Al3 intermetallic phase is characterized by high hardness and abrasion resistance. The research has shown that at appropriately selected heat treatment parameters, this phase is formed in a certain area of the Ti–Al coating. The presence and morphology of the Ti–Al3 phase were confirmed by X-ray, scanning, and transmission electron microscopy. It has been found that the presence of this phase increases the hardness of coatings and reduces the friction coefficient.
... These fluctuations in the CoF reflect change in actual contact area and presence of wear debris [27]. A sudden increase in CoF can be observed during failure of the coating [28]. The scratch micrographs are observed for a better understanding of the results. ...
Cold spray is a solid-state deposition technique that can be used for both coating and repair applications. Aluminum bronzes are renowned for their excellent corrosion and cavitation resistance in marine environment. Deposition of gas-atomized aluminum bronzes using cold spray is challenging due to the presence of hard martensite. In the present work, gas-atomized nickel aluminum bronze (NAB) powder was heat-treated and segregated according to particle size and subsequently deposited using cold spray. This strategy was successful in enhancing the deposition efficiency (DE) to nearly 100% for the segregated powders from 20% for the as-received powders. Deposition efficiency, hardness, and scratch resistance were used as the parameters to evaluate the inter-splat bonding of the deposits. The bonding state was found to be dependent upon the powder size, as comparatively better properties were achieved for the deposits fabricated with the heat-treated coarser powder.
... Cold spray (CS), an innovative solid-state deposition method, employs high-velocity gas to deposit coatings onto a substrate below the materials' melting point. Its benefits include minimal heat input, low oxygen content, and dense coating microstructure, making it suitable for producing Zn-Al alloy coatings [19][20][21]. Xu et al. [22] used low-pressure CS (LPCS) to prepare pure Zn and Zn-15Al alloy coatings, finding that the addition of Al promoted the formation of dense corrosion products such as Zn6Al2(OH) 16CO3·4H2O and Zn5(OH)8Cl2·H2O while inhibiting the formation of less corrosion-resistant products like ZnO. Zhao et al. [23] used highpressure CS (HPCS) to produce Zn-Al composite coatings with a 1:1 weight ratio of Zn and Al. ...
This study employed a high-pressure cold spray to apply a Zn30Al alloy coating to Q235 steel substrates to provide corrosion protection for steel in marine environments. The corrosion resistance of the coatings was investigated through full immersion tests, and the corrosion mechanisms were further analyzed using electrochemical experiments. The results were compared with those of traditional flame-sprayed Zn30Al alloy coating. The findings indicate that the high-pressure cold-sprayed Zn30Al alloy coating possesses a dense microstructure with a porosity of only 0.32%, providing effective cathodic protection to the substrate during the immersion tests. The cold-sprayed Zn30Al alloy coating maintained good integrity after 720 h immersion in 3.5 wt.% NaCl solution, whereas the flame-sprayed Zn30Al alloy coating exhibited significant pitting corrosion.
... Cold spray additive manufacturing (CSAM) involves the introduction of feedstock in the form of solid particles ranging in size from 10 to 50 µm through a pressurized powder feeder into a high-pressure, hightemperature chamber of a converging-diverging nozzle and subsequent acceleration into a supersonic stream using a carrier gas [1]. The supersonic propulsion of particles upon a suitable substrate results in mechanical interlocking and partial metallurgical bonding [2]. The cold spray (CS) process can be used to produce coatings or self-standing 3D parts from pure metals, blends, alloys and composites [3]. ...
In this study, a novel approach using cold spray additive manufacturing (CSAM) with air as a carrier gas was employed to 3D print a powder mix comprising 90 % Cu and 10 % Al. Two distinct orientations (XY-horizontal and Z-vertical) were examined for microstructural and mechanical properties in both as-printed and heat-treated states. The as-printed components exhibited strong mechanical interlocking and reduced porosity, attributed to the deformation of ductile Al particles by heavier Cu particles. Liquid-phase sintering heat treatment transformed the 3D-printed parts into an Al-bronze alloy, resulting in fully recrystallized microstructures with homogeneous Al diffusion in Cu. Although heat treatment induced a slight increase in porosity (<3.7 %), hardness demonstrated a remarkable up to 58 % improvement. Moreover, elongation increased by up to 10 %, accompanied by a 2-4 times enhancement in tensile strength. This study showcases the potential of CSAM combined with liquid-phase sintering for cost-effective and mechanically stable 3D-printed Al-bronze parts, using compressed air as the sole carrier gas, even at accelerated printing speeds. The process demonstrated excellent dimensional and mechanical reproducibility, with superior performance compared to wrought Cu and as-cast Al-bronze, emphasizing its viability for industrial applications.
... Two of the major surface treatment technologies that have gained widespread application for GCI brake rotors are coatings and ferritic nitrocarburising (FNC) treatment. Surface treatments, such as plasma electrolytic aluminating (PEA) [12,13], laser cladding [14,15], cold spray [16,17], and thermal spray processes [18][19][20], have been examined to address the wear and corrosion issues in GCI brake disc applications. Although these technologies have been developed, they have not yet been widely adopted because of the relatively high production costs and limited availability of specialised coating materials required for most brake system applications. ...
In recent years, the automotive industry has experienced a considerable increase in global sales of electrified vehicles (EVs). This trend is expected to continue as EVs are essential for achieving zero-emission targets by 2050. However, more than 90% of the braking in electric vehicles is performed by the regenerative braking system, which means that the friction brake system is used less frequently. Consequently, friction brakes are prone to surface corrosion over time, resulting in higher PM emissions, brake judder issues, and potential disc failure. To address these challenges, many car manufacturers are exploring ways to improve the corrosion resistance of grey cast iron (GCI) brake rotors. Among the various surface technologies being explored, ferritic nitrocarburising (FNC) treatment is considered a relatively cheap and promising solution for enhancing the corrosion resistance of GCI rotors. This process involves the introduction of nitrogen and carbon onto rotor surfaces to improve their surface functionality and performance. The use of FNC can reduce the formation of oxide buildup on the rotor braking surface, resulting in improved corrosion performance. However, the application of FNC in GCI brake rotors presents several challenges, including inhomogeneous microstructure, interference from graphite flakes, and fulfilment of the tight geometric tolerance requirements of the rotors. This study highlights the technical and practical challenges faced in treating GCI rotors. Potential solutions to overcome these problems are discussed to achieve high-quality FNC-treated brake discs suitable for EV applications.
... The formation of cold-sprayed deposits relies on high kinetic energy rather than thermal energy, which helps to minimize thermal influences (e.g., oxidation, phase transformation, residual thermal stress and grain growth) [16]. In addition, the working hardening effect induced by the severe plastic deformation of particles leads to a significant increase in hardness, implying the superior wear-resistant properties of the deposits [17,18]. Moreover, cold spray deposition process does not produce any harmful fumes or gases, making it more environmentally friendly compared with thermal spray and other melting-solidification manufacturing techniques. ...
... The phase distribution of the feedstock powder and that of the three obtained coatings were analyzed using the XRD technique. As widely confirmed by existing literature data [36], the mechanism of the CGS process is based on the plastic deformation of the feedstock powder, not giving rise to new oxides or carbides during the deposition process that could worsen the coating properties. Instead, changes in crystalline size are appreciable, highlighted by the broadening of some peaks [37]. ...
In this research, a life cycle inventory (LCI) is developed for tungsten carbide–cobalt (WC-Co) coatings deposited via atmospheric plasma spray (APS), high-velocity oxy-fuel (HVOF), and cold gas spray (CGS) techniques. For the APS process, a mixture of Ar/H2 was used, while the HVOF process was fueled by H2. The carrier gas for CGS was N2. This study aims to determine and quantify the inputs (consumption of inputs and materials) and outputs (emissions to air, soil, water, and waste generation) that could be used in the life cycle analysis (LCA) of these processes. The dataset produced will allow users to estimate the environmental impacts of these processes using WC-Co feedstock powder. To obtain a complete and detailed LCI, measurements of electrical energy, gas, WC-CO powder, and alumina powder consumption were performed (the use of alumina was for sandblasting). Furthermore, emissions like carbon dioxide (CO2), carbon monoxide (CO), and noise were also measured. This practice allowed us to determine the input/output process quantities. For the first time, it was possible to obtain LCI data for the APS, HVOF, and CGS deposition processes using WC-12Co as a feedstock powder, allowing access to the LCI data to a broader audience. Comparisons were made between APS, HVOF, and CGS processes in terms of consumption and emissions. It was determined that the APS process consumes more electrical energy and that its deposition efficiency is higher than the other processes, while the HVOF process consumes a large amount of H2, which makes the process costlier. CGS has comparatively low electricity consumption, high N2 consumption, and low deposition efficiency. The APS, HVOF, and CGS processes analyzed in this study do not emit CO, and CO2 emissions are negligible.
... CS can be used for depositing protective coatings [2], as well as for depositing bulk components [3]. The deposition is made by accelerating micron-sized powder to supersonic velocities with the help of a pressurised and hot gas, expanding through a de Laval (converging-diverging) nozzle [4]. The highvelocity particles bond cohesively or adhesively due to severe plastic deformation upon impact [5]. ...
Porosity poses a challenge to the mechanical properties of cold sprayed coatings, especially when it is open or surface-connected, limiting the coatings’ capabilities to act as a barrier. The porosity formation is dependent on the feedstock powder characteristics and the cold spray process parameters. We present a machine learning-based approach to predict porosity based on the above-mentioned factors. Nine different machine learning models based on linear regression (LR), decision trees, random forests, gradient boosting, support vector machine (SVM), and neural networks were explored. Considering the excellent properties of high entropy alloys, Cantor alloy was taken as the consumable. Our dataset, derived from the literature and experiments, identified SVM with a linear kernel and LR as the top-performing models based on the Pearson correlation coefficient (PCC) and root mean square error, where the PCC values exceeded 0.8. The SHapley Additive exPlanations method helped in identifying that the type of gas and powder are the top two factors in pore formation.
... The plastically deformed regions on the LPCS coating surface were likely a result of the ploughing effect during repetitive sliding motion. A similar mechanism was reported by Poza et al. [56] for cold sprayed Al-based coatings, further supporting these findings. Notably, the LPCS coatings exhibited the highest wear rates for both temperature conditions in comparison to the FS and HVOF coatings. ...
The remarkable mechanical and wear properties of high entropy alloys (HEAs) have opened up exciting possi-
bilities for their use in aerospace applications. This study explores the potential of AlCoCrFeMo high entropy
coatings (HECs) fabricated using three thermal spray techniques, namely low-pressure cold spray (LPCS), flame
spray (FS), and high-velocity oxy fuel spray (HVOF) as wear resistant surfaces. The coatings were investigated in
terms of their microstructures, phases, mechanical properties, and sliding wear characteristics from room tem-
perature up to 350 ◦C. Ex-situ characterization was performed using XRD for phase analysis and SEM-EDS for
cross-sectional microscopy and phase compositions of the coatings. All three coatings exhibited a typical lamellar
structure with the formation of BCC solid solution phase and variations in porosity and oxide content. The HVOF
sprayed coatings showed higher hardness values compared to the FS and LPCS coatings, which can be attributed
to their fine splats microstructure, lower porosity, and oxide inclusions compared to the other two coatings. In
terms of tribological performance, the LPCS coatings exhibited overall lower frictional coefficient than the FS and
HVOF coatings at both tested temperatures. However, the HVOF coatings exhibited relatively lower wear rates,
correlating well with observations from ex-situ analysis, highlighting lower material transfer and decreased
formation of debris particles compared to LPCS and FS coatings. These findings suggest that the HEA materials
have great potential as next-generation tribological interfaces under high-temperature wear conditions,
emphasizing the importance of designing materials with improved microstructural features.
The cold gas spray (CS) technique has emerged as a promising coating deposition method in the last decades for many materials, including Ti and most recently metal matrix composites, such as graphene-reinforced Ti. In this study, CS Ti coatings reinforced with two types of carbon nanofibers (GFs), HCNFs and MWCNTs, were evaluated regarding their electrochemical, electrical, and thermal properties before and after heat treatments (HT) at 700 and 1000 °C. The results indicated that incorporating GFs did not alter the CS Ti coatings deposition efficiency, porosity, or hardness in as-sprayed condition. HT reduced the CS Ti and Ti-GFs coatings resistivity by 21 and 23%, respectively, as well as improved their thermal conductivity by 25 and 32%, respectively. CS Ti-GFs coatings demonstrated an impressive reduction in corrosion rate of up to 80% compared to unreinforced Ti. These findings highlight the potential of CS Ti-GFs composite coatings applied through CS for industrial applications requiring high corrosion resistance. However, improvements by incorporating GFs in Ti powder in thermal and electrical properties were limited, indicating the need to optimize matrix–reinforcement interaction and CS process parameters to maximize their performance in these areas.
Surface coating technologies have become fundamental in modern industrial development, offering effective methods to enhance material surface properties while maintaining bulk characteristics. These technologies span from traditional methods like electroplating to advanced techniques such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and atomic layer deposition (ALD), serving crucial functions in corrosion protection, wear resistance, and various specialized applications across industries. The field has witnessed significant advancement in both process sophistication and application scope, driven by increasing demands for enhanced material performance and environmental sustainability. The integration of nanotechnology and smart materials has led to the development of multifunctional coatings with unprecedented properties, while emerging technologies (such as smart manufacturing and biomedical coatings) like cold spray and biomimetic surface modification continue to expand the possibilities for surface engineering applications. Bearing it in mind, we would like to offer a timely and concisely summary for the recent representative progress of surface coating technology, hoping to provide basic understanding and fundamental guidance for the development of the field.
This thesis deals with Life Cycle Assessment (LCA) and Life Cycle Cost Analysis (LCCA) applied
to three thermal spraying technologies: Cold Gas Spray (CGS), Atmospheric Plasma Spray (APS)
and High Velocity Oxy-Fuel (HVOF). The main objective is to analyze their environmental impact
and assess their economic implications. A key focus is the use of cobalt tungsten carbide powder
(WC-12Co), selected for its properties and wide applicability in these technologies. Specific Life
Cycle Inventories (LCI) were developed for the CGS, APS, HVOF and pre-blasting processes on
the substrate, essential to improve adhesion of coatings. This effort contributes to filling a data gap
in the industry and in the existing literature, allowing for an accurate environmental assessment.
The methodology used is based on ISO 14040 international standards, ensuring consistency and
comparability in LCA and LCCA studies. Another outstanding contribution is the implementation
of a cyclone-type collection system in the CGS process, which facilitates the recovery and reuse of
316L stainless steel metal powder. This system reduces material waste and allows characterisation
of the recovered powder and evaluation of the properties of the coatings obtained. Overall, this
research not only provides a fundamental data basis for the coatings industry, but also promotes
sustainability through resource optimization and waste reduction. The results have a significant
impact on the economic and environmental efficiency of thermal spraying technologies, establishing
a solid basis for future research in this field.
This thorough analysis examines the opportunities and difficulties related to improving the microstructure and functional characteristics of materials. Phases, grain boundaries, dislocations, and other flaws are examples of the microstructure, which is an essential component in defining the functional properties of a material, such as its electrical conductivity, mechanical strength, thermal stability, and resistance to corrosion. The production of materials with improved performance for a range of applications has been made possible by improvements in materials processing methods, such as severe plastic deformation and additive manufacturing, which have provided previously unheard-of control over microstructural properties. On the other hand, maintaining stability under operating circumstances, comprehending the intricate relationships inside microstructures, and generating uniform microstructures on a broad scale continue to be formidable problems. This study gives a comprehensive summary of the most recent developments in microstructure engineering, the ways in which microstructural features affect material properties, and the potential paths for future research in this area.
This chapter reviews various process and parameters optimization techniques. Further, focusing on the latest coating materials, including ceramics, metals, and composites, with a focus on their improved performance, the research also examines cutting-edge coating quality diagnostics and characterization methods. Finally, the different applications of coatings in various sectors, such as wear resistance, thermal insulation, mechanical strength and corrosion protection etc. are explored and highlighted their critical roles in industries like aerospace, automotive, energy and constructions.
This chapter provides the depth overview of distinct process elements that affect the quality of thermal spray coating. These factors include stand of distance, the rate at which the material is supplied, the surface’s temperature that is being sprayed from, and the particle velocity. Additionally, various post-processing and surface finishing techniques are discussed. Finally, the effects of different thermal spray processes on the quality of coatings are analyzed. Thus, this chapter becomes useful for the researchers studying the effects of various processes as well as parameters on the coating quality.
Thermal spray methods have grown in popularity across various sectors due to their ability to deposit protective coatings on surfaces. These coatings improve the surface qualities of substrates, including resistance to wear, corrosion, and thermal insulation. However, a number of crucial elements impact the quality and function of the coated substrate surface. This chapter provides a thorough evaluation and effects of significant factors on the coated substrate surface using a range of thermal spray techniques. Powder characteristics, process parameters, substrate preparation, and post-treatment techniques are some of these crucial elements. The effects of several factors, such as powder characteristics, process parameters, substrate preparation, and post-treatment processes, are explored in relation to the coating's microstructure, adhesion, and overall performance. The objective of this study is to examine the effects of various factors influencing the coated substrate’s surface and to provide suggestions for future investigations aimed at improving thermal spray methods.
As technology advances, tribo-coupling components, viz. gears, seals, bearings etc., frequently function under severe conditions, and this enhanced the demand of effective lubrication for reduced friction and wear of contacting interfaces. The optimal content of solid lubricants in the matrix is a viable alternative to acquire the desired lubrication in extended regime of temperatures. The present work investigates the tribological characteristics of cold sprayed Ni-based self-lubricating composite coatings with varying content of Ag (5, 10, 12.5 and 15 wt.%) and fixed concentration of MoS2 (10 wt.%). The mechanical, microstructural and the tribological properties were evaluated from room temperature (RT) to 800 °C. The results revealed that the coating having 12.5 wt.% of Ag along with 10 wt.% of MoS2 has delivered superior lubricity among all compositions in terms of lower coefficient of friction COF (0.18) and wear rate 5 × 10-5 mm3/Nm at 800 °C. The average COF, without the use of Ag and MoS2, has attained (0.49) at 800 °C. However, the coating containing 12.5 wt.% of Ag has attained increased COF (0.38) and wear rate 7.1 × 10-5 mm3/Nm at 400 °C; thereafter, a declining trend was observed. The improved frictional properties were accredited to the synergistic effects of impregnated solid lubricants and novel lubricious phases (Ag2MoO4, Ag2Mo2O7, Ag2Mo4O13 NiO, etc.) formed on the worn surface. The observed wear mechanisms were correlated with the morphologies and tribo-chemical reaction between the contacting interfaces.
In this paper, the influence of Ti-TiC satellite powder obtained in situ by the CVD method on the microstructure, properties, and residual stress of titanium cold-sprayed coatings was studied. A commercially available titanium powder was subjected to a satelliting process using the CVD process, where TiC particles were in situ formed on titanium granules. Then, a powder mixture of pure Ti and 20 wt.% of Ti-TiC satellite powder was obtained. Cold spray coatings of Ti-(Ti-TiC) sat powder mixtures were applied to Ti6Al4V substrates with carrier gas temperatures of 900 °C and 1100 °C. The coating characterization included microstructural analyses by SEM, hardness measurements, determination of Young’s modulus, phase composition by XRD, and residual stress measurements. Cross-sectional analysis revealed good cohesion between Ti and TiC during the satelliting process, which survives coating deposition. Moreover, the higher spraying temperature resulted in TiC crystallite size reduction, higher hardness, and Young’s modulus, decreasing linear and shear stresses.
Cold spray is a solid-state additive manufacturing technology and has significant potential in component fabrication and structural repair. However, the unfavourable strength–ductility synergy in cold spray due to the high work hardening, porosity and insufficient bonding strength makes it an obstacle for real application. In recent years, several methods have been proposed to improve the quality of the cold-sprayed deposits, and to achieve a balance between strength and ductility. According to the mechanism of how these methods work to enhance metallurgical bonding, decrease porosity and reduce dislocation densities, they can be divided into four groups: (i) thermal methods, (ii) mechanical methods, (iii) thermal–mechanical methods and (iv) optimisation of microstructure morphology. A comprehensive review of the strengthening mechanism, microstructure and mechanical properties of cold-sprayed deposits by these methods is conducted. The challenges towards strength–ductility synergy of cold-sprayed deposits are summarised. The possible research directions based on authors’ research experience are also proposed. This review article aims to help researchers and engineers understand the strengths and weaknesses of existing methods and provide pointers to develop new technologies that are easily adopted to improve the strength–ductility synergy of cold-sprayed deposits for real application.
Functional coatings, including organic and inorganic coatings, play a vital role in various industries by providing a protective layer and introducing unique functionalities. However, its design often involves time‐consuming experimentation with multiple materials and processing parameters. To overcome these limitations, data‐driven approaches are gaining traction in materials science. In this paper, recent advances in data‐driven materials research and development (R&D) for functional coatings, highlighting the importance, data sources, working processes, and applications of this paradigm are summarized. It is begun by discussing the challenges of traditional methods, then introduce typical data‐driven processes. It is demonstrated how data‐driven approaches enable the identification of correlations between input parameters and coating performance, thus allowing for efficient prediction and design. Furthermore, carefully selected case studies are presented across diverse industries that exemplify the effectiveness of data‐driven methods in accelerating the discovery of new functional coatings with tailored properties. Finally, the emerging research directions, involving integrating advanced techniques and data from different sources, are addressed. Overall, this review provides an overview of data‐driven materials R&D for functional coatings, shedding light on its potential and future developments.
This comprehensive book explores the techniques, materials, and real-world applications of thermal spray coatings across various industries, including power generation, aerospace, medical, and automotive sectors. Readers will learn about the basic science and engineering aspects of thermal spray technology, its historical developments, and the diverse range of materials used, from metallic to ceramic materials, and nano-crystallization materials. Distinct thermal spray techniques are explained (flame spray, detonation-gun spray, high-velocity oxy-fuel spray, electric arc spray, plasma spray and cold spray). Chapters on advanced topics also give an understanding of crucial material properties such as high temperature corrosion, oxidation, erosion or wear resistance, and biocompatibility. Key features - Contributions from materials science experts with references for each topic - Gives a comprehensive overview of materials and distinct spray techniques used in thermal coatings - Dedicated chapters for applications of thermal coatings in different industries - Covers recent trends and new advances such as surface modification techniques to improve functionality and performance This book is intended as a resource for an in-depth understanding of the fundamentals and applications of thermal spray coatings for students, professionals and researchers in materials science and chemical engineering disciplines.
Voids are a common issue in cold-sprayed coatings, negatively impacting their mechanical properties and bonding strength. In this study, we report an efficient void healing approach for cold-sprayed coatings via pressure-free low-temperature sintering, and unveil the void healing mechanism at the atomic level. Sintering at 500°C (∼0.59 Tm) for 20 hours effectively reduces the porosity in the cold-sprayed CuCrZr coating, leading to a significant enhancement in shear bonding strength with an Al2O3 dispersion-strengthened copper substrate by a factor of 3.5. It is found that an intermediate nanograined layer formed between the coating and the substrate plays a crucial role in the subsequent void healing process during sintering. This nanocrystalline layer, a byproduct of continuous dynamic recrystallization activated by high strain-rate deformation of powders during cold spray, demonstrates thermal instability and high grain growth capability, thereby accelerating the void healing process. In-situ TEM observations unveil the growth of nanograins along with the in-situ generation of Cr2O3 oxides, gradually filling the voids and contributing to the void healing process. Molecular dynamics simulations indicate that grain boundary (GB) migration in nanograins facilitates atom diffusion, enhancing GB-voids interaction. The GB structural transformation during heating provides an efficient diffusion channel for transporting vacancies, thereby accelerating the closure of voids.
Cold spray is a solid-state powder deposition technique and has evolved into an additive manufacturing process. Unlike conventional additive manufacturing technologies that rely on melting and solidification, cold spray additive manufacturing (CSAM) forms components at low temperatures at a relatively high build rate. This article introduces the technical principles, process parameters and typical microstructure of cold spray, as well as its applications in the fabrication of 3D components and damaged component repair. Current issues faced in cold spray research and future development directions in CSAM are also discussed.
Nickel-based coatings provide outstanding wear and erosion resistance making them particularly suitable for several applications, from aerospace and naval to automotive, energy, and electrical. Cold spray (CS) is encountering a growing interest as a promising technology to deposit thick and dense coatings for components used in energy power generation systems, such as the concentrating solar power (CSP) plants. In this article, nickel coating was deposited onto steel substrates by using a low-pressure CS. The erosion behaviour of the coating was evaluated by a solid particle impact test at two different impact angles. The coating erosion rate was 10 × 10 ⁻⁴ at a 60° impact angle, showing a combination of ploughing and cutting mechanisms.
The present work focuses on exploring the effect of thermal treatment on HVOF thermally sprayed rGO-reinforced alumina-based coatings on 17-4 PH steel. Based on the previous study, an optimized coating composition (Al2O3-0.8CeO2-0.2 rGO) is selected for exploring the effect of flame heat treatment in terms of physical, tribological, mechanical, and electrochemical properties. The hardness (Vickers and scratch) and tribological responses are recorded using a CETR-UMT tribometer. The as-coated, treated, and worn surfaces are analyzed using Goniometer, Scanning electron microscope (SEM), Energy dispersive spectroscopy (EDS), Raman spectroscopy, and 3-D optical profilometer. Corrosive degradation is studied using Potentiodynamic polarization and Electrical impedance spectroscopy (EIS). The results revealed that the thermal treatment severely deteriorates the coating properties. The Vickers hardness and scratch hardness of the as-sprayed coating were reduced to one-third and one-ninth respectively, after the post-treatment process. The specific wear rate and corrosion rate increased by ≈165 times and ≈1500 times, respectively. Furthermore, the Raman, SEM, and EDS analysis of the corroded region of the heat-treated coating confirmed the formation of iron oxides. This deterioration in the heat-treated coating properties is attributed to the evaporation of the reinforced rGO from the as-sprayed coating making the coating highly porous. So, it is not advisable to heat treat the above-mentioned coating composition above 400 °C.
Cold spray is a coating deposition technique that enables to produce a large variety of metallic coatings using supersonic powder particles. Pure copper (Cu) has been used as a model material for cold spray due to its high deposition rate. Nevertheless, many Cu alloys that are broadly used in engineering applications, including Cu-10wt%Ni (CuNi), Cu-10wt%Sn (CuSn) and Cu-7wt%Ni-2wt%Si-0.9wt%Cr (MoldMAX V® High Strength Cu), have not been fully investigated in the cold spray process. Thus, there is still a lack of understanding of their deposition process, microstructure evolution and mechanical properties in these Cu-alloy coatings made by cold spray. In this study, we study the deposition efficiencies, porosities, microstructures and hardness of the cold sprayed Cu alloys and elucidate their deformation mechanisms. Our results show that all the coatings have high densities above 99 % and deposition efficiencies ranging from 73 % (CuSn), 80 % (CuNi) to 99.9 % (HS Cu). The average Vickers hardness of the CuNi, CuSn, and HS Cu coating samples are about 130 HV, 160 HV, and 190 HV, respectively, with HS Cu showing the highest work hardening rate. We find that these Cu coatings, particularly CuNi, exhibit heterogeneous microstructures with relatively large grains in the particle interiors and fine grains at the particle-particle interfaces, which are due to serve plastic deformation at the interfacial regions. Nanoindentation maps also show that the local nanohardness distributions are correlated to the heterogeneous microstructure observed.
Polymer matrix composites are finding never-ending widespread uses in the last decades; one recent tendency is to metallize their surface to further widen their field of application. Cold-spray deposition is one of the most promising techniques that can be adopted to this aim. Cold-spray deposition on polymers is in its early stage and more experimental work is required to fully understand the phenomena ruling the deposition. In this paper, the results of nanoindentation measurements on cold-spray coatings on various substrates will be presented and discussed. Polypropylene was used as matrix while carbon and glass fibers have been used as reinforcement, both steel and aluminum have been used as feedstock material for the cold-spray deposition. Nanoindentations tests have been then carried out on all the different samples; the influence of the fibers and of the powders sprayed on the behavior of the coatings is discussed in light of the experimental outcomes.
Cold spray (CS) is an emerging coating technology that makes use of a converging/diverging nozzle, a high pressure and a heated gas source to create a high‐velocity gas flow. Coating deposition occurs at relatively low temperatures compared to other spray technologies, therefore the sprayed particles remaining in the solid-state. The process can produce dense coatings when the process parameters are optimized. Despite the incredible advantages of CS and the established knowledge of CS considering metal substrates, some questions like the bonding mechanism and the adhesion/cohesion strength of the coating with polymeric substrates remain an open research topic. In this paper, a metal coating (AlSi10Mg) was deposited on a plate in polypropylene by cold spray in order to increase the properties of the surface. Metallic particles, in the range of 20-40 µm, were injected into gas flow and propelled to supersonic velocities. Polymers require a deposition technique in which the substrate remains at relatively low temperatures during the whole process in order to avoid plastic deformation or degradation. Determination of the mechanical properties of thin films on substrates by indentation has always been difficult because of the influence of the substrate on the measured properties. In order to evaluate the local properties of the deposited coating, microindentation tests and DMA were carried out. In particular hardness values by microindentation tests and values of elastic modulus by DMA were calculated.
The deformation behaviour of particles and substrate in cold spray is dictated by the intrinsic properties of both materials, and their bonding directly affects the resulting properties of the deposited coating. The processing through heat treatment of aluminium alloy powders has only recently been developed for both cold spray and additive manufacturing, hence the necessity to evaluate and further understand the evolution of their properties. In this study, an Al 7075 gas-atomised powder was solution heat treated, quenched and subsequently aged. The powder in its as-quenched, T4 (natural ageing at room temperature for 21 days) and T6 (artificial ageing at 120 C for 24 h) condition was characterised through differential scanning calorimetry and scanning electron microscopy to evaluate the precipitation kinetics. Powders were cold sprayed using heated N2 at 500 C and 6.0 MPa and the resulting deposits were evaluated using tubular coating tensile and pull-off bond strength tests. The precipitation development in the gas atomised powder was found to be similar to the bulk alloys, with development of η′ precipitates during artificial ageing and Guinier-Preston zone formation and development during natural ageing. A relationship between the deposition efficiency of the powders and the coating properties was discovered and explained through an adapted densification mechanism based on powder tamping.
Single-component tin coatings have successfully been cold sprayed onto carbon fiber reinforced polymers in previous studies at McGill University. Coatings with mixed metal powders were also sprayed to improve the deposition efficiency and coating conductivity. The results indicated a noticeable improvement in deposition efficiency related to the addition of a secondary metallic powder (aluminum, copper and zinc); this study is focused on the effect of aluminum. Following cold spray of various Sn/Al mixtures over a wide range of gas pressures, unusual coating morphologies were observed. The study of these morphologies leads to the description of two distinct deposition phases depending on the spray pressure: a direct deposition effect and an indirect deposition effect. The presence of submicron particles also supports the occurrence of a powder melting phenomenon during the process. Numerical simulations were conducted to support the description of these phenomena.
Ti6Al4V coatings were cold sprayed onto the same bulk alloy at standard conditions, using 800 °C as gas temperature, and a set of new conditions, using 1100°C as gas temperature, which improved coatings performance. Some of these coatings, processed with innovative parameters, were heat treated to promote adhesion and reduce porosity. Scratch tests were performed using a nanoindenter Agilent G200 and the effect of both normal load and scratch velocity were explored. The different mechanisms responsible of wear were evaluated, identifying ploughing and cutting as the main abrasion mechanisms. The wear rate measured in the standard coating was the highest, indicating that this material could not be used to repair the bulk component. However, the abrasion resistance measured in the coatings sprayed at 1100°C was similar to that found in the bulk substrate. Therefore, cold spray could be used for repairing using the new conditions evaluated in this work.
Metallic infrastructures suffer deterioration during their service life. When the metallic component reaches a limit level of damage, it is replaced by a new one. This generates high costs of maintenance and residues management. However, the deposition of coatings by the cold spray technique would allow the repairing of these damaged components and extent their service life. In this work the effect of the spraying temperature and pressure on the mechanical behavior of 316L stainless steel coatings deposited on carbon steel by the cold-spray technique has been analyzed. Spraying gas temperatures of 800oC, 900oC and 1000oC combined with gas pressures of 50 and 60 bars were selected. Indentation stress-strain curves were determined for each spraying conditions. The results showed a significant effect of both spraying parameters on the work hardening of the coatings.
Ti6Al4V coatings were cold sprayed onto the same bulk alloy using standard conditions and a set of parameters developed to improve the coating’s performance. In addition, the enhanced coating was heat treated to improve coating adhesion and reduce porosity. Wear tests were performed, onto the coatings and the substrate, in oscillating conditions, which simulate wear induced by the contact with bearing parts during vibration. Wear behaviour at room temperature is dominated by a mixed mechanism, which involves plastic deformation and transference from the counterbody forming mechanically mixed layers. As temperature is increased, the formation of mechanically mixed layers dominates wear. The wear resistance of the enhanced coatings is similar to the bulk alloy, or even better in some conditions. Consequently, cold sprayed improved coatings could be used for repairing titanium components from the contact wear point of view.
When metallic microparticles impact substrates at high enough velocity, they bond cohesively. It has been widely argued that this critical adhesion velocity is associated with the impact velocity required to induce adiabatic shear instability. Here, we argue that the large interfacial strain needed to achieve bonding does not necessarily require adiabatic shear instability to trigger. Instead, we suggest that the interaction of strong pressure waves with the free surface at the particle edges—a natural dynamic effect of a sufficiently rapid impact—can cause hydrodynamic plasticity that effects bonding, without requiring shear instability. We proceed on this basis to postulate and confirm a proportionality between critical velocity and the bulk speed of sound, which supports the viewpoint that shear instability is not the mechanism of adhesion in cold spray.
Cold spray technology has been in significant development since the early 1990s, however, not until recently has it begun to approach near wrought like properties for metals and alloys of aluminum, copper, nickel, titanium, as well as steels, stainless steels, superalloys, and refractory metals like niobium and tantalum. These advancements have come through the use of high pressure cold spray equipment and a greater fundamental understanding of the process variables. As a result, numerous applications have been developed for repairing high cost and long lead time parts for the aerospace and defense market, as well as a broad range of commercial markets such as oil & gas, transportation, and heavy industry. In particular, parts with lead times in excess of 12 months have been successfully repaired and re-introduced into service. This saves not only the direct cost of the part, but also returns the system to service much sooner. Cold spray is an additive manufacturing technology that uses heated high-pressure inert gas to accelerate metal powders through a converging-diverging de Laval nozzle above the critical velocity for deposition onto a substrate. The process produces only mild heating of the substrate compared to most conventional metal deposition or welding technologies, hence the nomenclature of “cold” in cold spray, even though there is heating of the gas in almost all cases. There are also no toxic fumes or other harmful emissions from cold spray because the accelerant gases are: 1) inert (helium, nitrogen, or air), and 2) the heating source is electric and is controlled at temperatures below the melting temperature of the material being sprayed. Furthermore, because parts are being repaired and refurbished rather than replaced, there is tremendous cost, energy, and overall environmental benefit, making cold spray a very “green” technology and an excellent technology for enhancing the long-term sustainability of high value assets.
Understanding and linking mechanical properties obtained by spherical indentation experiments to uniaxial data is extremely challenging. Since the first attempts in the early 20th century numerous advances gradually allowed to expand the output of indentation tests. Still, the extraction of flow curves from spherical nanoindentation has not yet been fully established, as tip shape problems and size effects impede a straight-forward implementation. Within this study, we show new calibration procedures originating from fundamental geometrical considerations to account for tip shape imperfections. This sets the base for strain-rate controlled tests, which in turn enables us to measure rate-dependent material properties either with constant strain-rate or by strain-rate jump tests. Finally, experimental evaluation of the constraint factor in consideration of the mechanical properties and induced strain enables the extraction of flow curves. Testing materials with refined microstructures ensures the absence of possible size-effects. This study contributes to a significant improvement of current experimental protocols and allows to move flow curve measurements from single spherical imprints one step closer to its implementation as a standard characterization technique for modern materials.
This book serves as a comprehensive resource on various traditional, advanced and futuristic material technologies for aerospace applications encompassing nearly 20 major areas. Each of the chapters addresses scientific principles behind processing and production, production details, equipment and facilities for industrial production, and finally aerospace application areas of these material technologies. The chapters are authored by pioneers of industrial aerospace material technologies. This book has a well-planned layout in 4 parts. The first part deals with primary metal and material processing, including nano manufacturing. The second part deals with materials characterization and testing methodologies and technologies. The third part addresses structural design. Finally, several advanced material technologies are covered in the fourth part. Some key advanced topics such as “Structural Design by ASIP”, “Damage Mechanics-Based Life Prediction and Extension” and “Principles of Structural Health Monitoring” are dealt with at equal length as the traditional aerospace materials technology topics. This book will be useful to students, researchers and professionals working in the domain of aerospace materials.
Previous results have shown that metallic coatings can be successfully cold sprayed onto polymeric substrates. This paper studies the cold sprayability of various metal powders on different polymeric substrates. Five different substrates were used, including carbon fiber reinforced polymer (CFRP), acrylonitrile butadiene styrene (ABS), polyether ether ketone (PEEK), polyethylenimine (PEI); mild steel was also used as a benchmark substrate. The CFRP used in this work has a thermosetting matrix, and the ABS, PEEK and PEI are all thermoplastic polymers, with different glass transition temperatures as well as a number of distinct mechanical properties. Three metal powders, tin, copper and iron, were cold sprayed with both a low-pressure system and a high-pressure system at various conditions. In general, cold spray on the thermoplastic polymers rendered more positive results than the thermosetting polymers, due to the local thermal softening mechanism in the thermoplastics. Thick copper coatings were successfully deposited on PEEK and PEI. Based on the results, a method is proposed to determine the feasibility and deposition window of cold spraying specific metal powder/polymeric substrate combinations.
Cold spray is a remarkable coating technology that has wide-ranging applications, including additive manufacturing and repair of aerospace components. The primary class of materials used for cold spray is metal, but more recently, one finds researchers preparing metal matrix composites that are useful for tribological applications. This chapter will review briefly fundamentals of tribology and processing principles for deposition of metal matrix composites by cold spray. The primary focus will be a review of the tribology of composite coatings manufactured by cold spray that include ceramic reinforcements (e.g., Al2O3, WC) and solid lubricants (e.g., MoS2, h-BN). A discussion of the future directions for metal matrix composites made by cold spray and their usefulness for tribological applications is also presented.
We study supersonic impact of individual metallic microparticles on metallic substrates, that is, the unit process of materials buildup in cold spray coatings/additive manufacturing. We resolve the moment of impact bonding through real-time observations of single particle impacts with micron-scale and nanosecond-level resolution. We offer the first in-situ observation of a material-dependent threshold velocity, above which the particle undergoes an impact-induced jet-like material ejection and adheres to the substrate. We report direct measurements of critical velocities for structural metals, which unlike in nozzle experiments, are not affected by process-related complexities obscuring particles' kinetic and thermal histories. Text Understanding material behavior under high velocity impact is the key to addressing a variety of fundamental questions in areas ranging from geological cratering [1] to impact-induced phase transformations [2], spallation [3], wear [4], and ballistic penetration [5]. Recently, adhesion has emerged in this spectrum since it has been found that micrometer-sized metallic particles can bond to metallic substrates under supersonic-impact conditions [6-11]. The phenomenon of impact
Fiber reinforced polymer composites are an important class of structural materials. They possess high strength-to-weight ratios and high rigidities. However, for man ' applications heir wear resistance is less than desirable. Wear resistant thermal spray coatings can enhance the surface of these materials. Coatings on some composites have satisfactory adhesion without a bond coat, but others needed an appropriate bond coat. Polymer and o her bond coats have been used to enhance he adhesion of thermal spray coatings on composites. The present study was conducted to find one or more suitable bond coat materials. Materials such as polyamides, polyimides, polyether-etherketone or simply aluminum or nickel were found to be suitable bond coats for man ' different composite substrates.
Ti6Al4V alloys are widely used in components of the aeronautical industry. Consequently, impact erosion with small particles in suspension has revealed to be one of the most common damage processes during its service life. In order to study the possibility of repairing these components by spraying coatings, in this work, the behavior against erosion by the impact of abrasive particles of Ti6Al4V coatings manufactured by cold spray has been analyzed. The work includes the comparison between the responses of the coating and the bulk alloy, analyzing the effect of the speed and the angle of impact of the erosive particles on the erosion rate. The values of the spraying parameters used in this work have allowed obtaining coatings that showed a behavior against erosion similar to that of the bulk material. It has been possible to identify a ductile behavior of the coating and alloy dominated by plastic deformation. Through the study of erosion scars, two damage processes, microploughing and microcutting, have been identified as the dominant mechanisms responsible for the erosion process.
The novel mechanical, microstructural, and functional properties associated with nanocrystalline metal materials has brought about interdisciplinary interest and curiosity. Nanostructured metals can be manufactured by way of multiple methods; however, during the course of this research the method studied herein is employs severe plastic deformation processing via cold spray powder deposition. TEM and SEM analysis confirmed the noteworthy grain refinement brought about by cold spray for two copper feed stocks. More specifically, the two types of copper powders were that of conventional gas atomized Cu as well as nanostructured Cu powders produced by way of spray drying and agglomeration. As such, the classical nanoindentation properties of hardness and Elastic modulus are experimentally determined using both static and dynamic nanomechanical testing. Dynamic spherical nanoindentation methodologies are employed to unveil the cold spray consolidated coating's stress-strain response and flow behavior. The mechanical flow curves extracted herein suggest that the protocol refinements proposed by Leitner, Maier-Kiener, and Kiener may have fundamentally advanced spherical nanoindentation testing at large.
Different types of metallic infrastructures are exposed to atmospheric conditions and, consequently, suffer deterioration over the years. The metallic structures can be repaired by replacing the components by new ones. This increment the maintenance costs. However, the damaged components can be repaired by depositing a coating on their surface. Traditionally, the technique used to deposit steel coatings has been High Velocity Oxi-Fuel (HVOF). However, this high temperature thermal spray method presents some problems due to the possible oxidation of the powder during the spraying process. Additionally, the reparation of a metallic structure could require thickness unattainable by this technique. An alternative could be the Cold Spray (CS) deposition. CS constitutes a coating deposition technology that permits in-situ repair of structures, with little or no detrimental effects to the main component. For these reasons, this research compares the performance of 316L coatings processed by CS with those traditionally deposited by HVOF onto a S355-J2 structural steel. Adhesion tests were planned to quantify the adherence of the coatings. Additionally, the mechanical response of coatings and substrate was measured by nanoindentation tests. Finally, the microstructure of the coatings was correlated with their mechanical response.
Additive manufacturing potential of cold spray technology was used to fabricate freestanding samples of a copper alloy.. Different volume fractions of micro and nanocrystalline powder particles were used to obatin a bimodal structure with heterogeneous arrangement of crystalline phases. The effects of volume fractions of each phase were investigated on the microstructural arrangement, porosity, microhardness, residual stresses, and mechanical strength of the deposited materials. A series of finite element simulations were developed and validated by experimental data to describe the influence of volume fraction, morphology, and spatial distribution of the phases on the global strength of the samples under tensile loading. The obtained results evidence the possibility of tailoring the mechanical response of freestanding cold spray deposits, adopting a heterogeneous phase structure. Optimized fabrication parameters and post-processing strategies should be studied to further enhance the performance of the designed bimodal materials and overcome the intrinsic brittleness of cold spray deposits.
Compared to conventional high temperature processes, e.g. arc additive manufacturing, thermal spraying and laser/electron-beam cladding/additive manufacturing, coatings of Ti and its alloys with cold spraying (CS) are increasingly attracting attention from researchers and industries, because of the low temperature and high velocity characteristics of sprayed particles, which strictly restrict the oxidation of the sprayed powder and bring about prominent metallurgical benefits. However, coatings of Ti and its alloys by CS have been found limited industrial applications compared to other materials (e.g. Cu and Al), partly due to the special particle deposition behavior of Ti and its alloys and the lack of comprehensive knowledge of its control. This review therefore focuses on the deposition characteristics of Ti and its alloys during CS in an effort to shed light on them and expand their applications. The first part presents a brief introduction of CS and the basic characteristics of Ti and its alloys coatings by CS. The second part describes the effects of CS process parameters on the deposition characteristics of Ti and its alloys. The third part discusses the bonding mechanisms of Ti and its alloy particles during CS. The fourth part discusses the strengthening methods such as in-situ shot peening and laser-assisted CS. The coating properties can also be improved with post-spray treatment, such as heat treatment, laser treatment, hot rolling, hot isostatic pressing and friction stir processing. In addition, further applications are suggested, such as protective coatings, biocompatible coatings, and additive manufacturing. Finally, the summary and prospects for the deposition of Ti and its alloys are presented.
Ti-6Al-4V components are widely used in the aircrafts engine or airframe parts, as landing gears or wing boxes, where the wear by unidirectional sliding or oscillating relative motion is one of the most recurrent damage processes. Recently, the deposition by Cold-Spray (CS) has been revealed as a promising alternative to repair these damaged components, increasing their useful time and decreasing the maintenance costs. Consequently, the wear resistance of the coatings could be improved by optimizing the CS processing parameters. In this work, oscillating and unidirectional sliding wear tests were planned to determine the wear resistance of Ti-6Al-4V coatings deposited onto substrates of the same Ti alloy by CS. The coatings were sprayed using two different values for two of the main spraying parameters. First, values of 800 °C and 40 bars were used for the process gas temperature and pressure, respectively, which are widely used spray conditions by researchers; and secondly, values of 1100 °C and 50 bar were used for both parameters, respectively. Unidirectional sliding and oscillating wear tests were performed and the effect of the testing temperature was studied. The main wear mechanisms in room temperature (RT) were abrasion and adhesion, while oxidation was also distinguished during the high temperature tests. In addition, the wear processes were more severe during the unidirectional sliding tests as compared to the oscillating tests. The results showed that the coatings deposited using the first spraying conditions presented a poor wear resistance as compared to the substrate and thus they are not adequate for repairing purposes. However, the coatings deposited using higher values of gas temperature and pressure showed a comparable, or even better, wear resistance to that of the substrate under oscillating movement.
The feasibility of depositing aluminum onto thermoplastic substrates via cold spray (CS) was investigated. Dense coatings of 7075 Al and CP Al (commercial purity) were achieved on three substrates—polyetheretherketone (PEEK), polyetherimide (PEI), and acrylonitrile butadiene styrene (ABS) using an iterative optimization process. 7075 Al deposition yielded low deposition efficiencies (DEs) and low thicknesses but high adhesive strengths, while CP Al deposition led to high DEs and thicknesses but relatively low adhesive strengths. PEEK and PEI were more suitable substrates for cold spray than ABS, which suffered from surface erosion and substrate distortion. Two key factors were identified that influenced the DE and adhesive strength of the coating. The first factor was the bond layer, the initial few particle layers that fused with the substrate to allow subsequent buildup. The bond layer was influenced by the substrate hardness, yield strength, glass transition temperature, and impact strength, as well as the differences in thermal expansion coefficients of Al and the polymer substrates. The second factor was the CS process parameters selected, as the bond layer and the build-up layers may require different process conditions in order to optimize both bonding strength and coating strength, respectively.
The paper has taken a fundamental approach to study the nano-scale deformation behavior of Al-Al2O3 cermet coatings deposited by low-pressure cold spraying (LPCS) on AZ31 magnesium and Al6056 lightweight alloy substrates. Coating microstructural characteristics were first evaluated and correlated with LPCS process parameters using metallurgical characterization techniques: SEM, 3D optical profilometry, and XRD, followed by their microhardness and wear depth measurements and comparing with uncoated substrates under three-body abrasion wear. These properties were analyzed/mapped against probable deformation scenarios for nano-scale yield strength determination using the combined experimental nanoindentation load-depth curve method and computational expanding cavity models (ECMs). Obtained yield strength with key coating parameters like hardness and Young’s modulus were taken for modeling and simulation of strain-hardening effect under a peak loading of 165 mN in ABAQUS finite element (FE). Results from both combined experimental/computational and FE approaches indicate a progressive elasto-plastic mode being the dominating coating deformation mechanism with a strain hardening exponent of 0.15, under the studied loads.
Aluminium-Silicon alloys, like Al C355, are extensively used in aeronautical applications, where light materials are required. Consequently, it is necessary to develop maintenance and overhaul technologies to extend the life of metallic components used in the aeronautical sector. Cold Spray (CS) represents a promising alternative to repair damaged light alloys surfaces. However, the repaired component should exhibit similar properties as the original substrate. In particular, degradation by erosion is usual during service in aeroplane operation. This is precisely the aim of this research: to evaluate the erosion performance of Al C355 coatings cold sprayed onto the same bulk alloy. Air jet-erosion tests were performed on the coatings and substrate, according to ASTM G76 standard. Coatings processed by CS using standard parameters exhibit lower erosion performance than the substrate. However, the erosion resistance of coatings deposited using improved conditions was similar to that observed in the uncoated substrate.
This paper examines the single particle impact process for a series of Al-Cu alloy powder particles with 2–5 wt% copper, performed using a low-pressure cold spray system with helium as the carrier gas. The cold spray deposition process is fundamentally controlled by the deformation processes, which occur during single particle impacts. Single particle depositions on steel substrates were produced for each composition over a range of gas temperatures (225–325 °C). Cross sections from single, impacted particles were produced using focused ion beam methods. The deformation microstructure in individual cold sprayed particles was studied using precession electron diffraction (PED) and transmission Kikuchi diffraction (TKD) techniques. For Al-Cu alloy particles, the amount of deformation estimated using a compression ratio did not show a significant difference with varying copper alloy additions. The single particles experienced large deformation upon impact, and ultrafine grains were formed at the particle/substrate interface via dynamic recrystallization. The particles were bonded to the steel substrate via a thin amorphous layer at the interface.
A new method which allows the development of Low Pressure Cold Sprayed copper coatings on PEEK (Poly-Ether-Ether-Ketone) based composites reinforced by carbon fibers is investigated. Due to the solid state and high velocities of impacting particles, cold spraying involves a high erosion on composite materials, leading to an absence of coatings and sometimes damaged carbon fibers. As a result, few dozen micrometers of pure PEEK matrix have been added on the surface of the composite to act as an interfacial layer between composite and coating. Optimization of the LPCS parameters has been carried out, using a careful choice of powder size distribution in order to avoid substrate damage, erosion and coating delamination. Dense copper coatings exceeding 100 μm thick have been obtained. SEM observations have been carried out to evaluate the microstructure of coatings, and the minimal required matrix thickness regarding the size distribution of the powder.
In our original paper, Acta Materialia 158 (2018) 430–439, we showed that adiabatic shear instability is not necessary for impact-induced jetting and bonding to occur in cold spray. We also developed a mechanistic framework to estimate the critical velocity for jetting on the basis of a hydrodynamic spall process. In their comment, Scripta Materialia xx (2018) xx-xx, Assadi et al. raised several questions about the versatility of our framework in capturing cold spray-related physical phenomena. Here, we demonstrate that not only can our mechanistic framework explain cold spray physical phenomena such as particle size effects, strength effects and temperature effects, but also it can be used to quantify them.
The cold gas dynamic spraying process provides an advantageous solution to the deposition, and additive manufacturing, of metals. Namely, it provides a reduced reactive environment, simple operation, and high deposition rates. It is known that the deposition efficiency of the cold spray process can be substantially increased using helium instead of nitrogen as the process gas. However, the use of pure helium can be cost prohibitive and commercially available helium recovery systems constitute a major capital investment and cannot be used with portable systems. This work focuses on the development and use of a novel, in-line gas mixing system, designed to provide a blend of nitrogen and helium at any ratio. Deposits produced with different gas ratios are investigated through particle velocity measurements, deposition efficiency, coating porosity, and coating hardness. The experimental results show that helium, even in lower percentages, can have a significant effect on deposition efficiency and coating quality. From the results, a cost model is presented which, when provided experimental values and user costs, can be used to identify the nitrogen–helium ratio that will produce the lowest overall coating cost.
The Cold Gas Dynamic Spray technology, generally referred as Cold Spray, is a relatively new additive manufacturing technique able to produce fully dense coatings through the deposition of particles on a substrate. Fine powders are accelerated to high velocity and projected onto a substrate, upon impact with the target surface, conversion of kinetic energy to plastic deformation occurs and the solid particles deform and bond together. During the cold spray deposition process, the particles remain in a solid state during the deposition, resulting in high-quality coatings with low residual stresses and oxide inclusions. The relative lower process temperatures allow the cold spray to manufacture coatings on high temperature-sensitive materials. It could also be a valid method for deposition of a wide variety of materials, from metallic alloys up to ceramics and composites. Depending on the materials employed as substrate and coating, different bonding mechanisms can occur during the deposition. The present review aims to summarise the main bonding theories proposed up to now for the cold spray, focusing on both the particle deformation behaviour during the contact with the surface and the interfacial bonding mechanisms. The available theories for different substrate/coating configurations will be discussed and compared. The effects of deposition parameters, the substrate’s surface and microstructure of feedstock powders on the bonding mechanism will also be discussed.
The relationship between the cold spray deposition mechanism, microstructure, and strength of the resulting film must be understood for this innovative process to be practical. Previous studies have suggested that the coating mechanism is reliant on breaking the natural oxide film such that metallic bonding occurs through direct contact between the metal surfaces. In this study, the proposed model was experimentally verified by a small tensile adhesion test and auger electron spectroscopy analysis of the bonding interface. Since shear deformation does not occur at the tip (south pole) of the incoming particle, the oxide film is not broken, such that the bonding strength is weak. In contrast, at the outer edge of the particle, metallic bonding occurs, attaining a level of strength that exceeds that of the base material due to the huge plastic deformation. This phenomenon is known as the “south-pole problem,” and can lead to a decrease in the overall adhesion strength despite the local adhesion being strong. However, detailed observations revealed, in parts of the deposits, particles that had adhered across their entire surface. This suggests that, provided the collision state can be controlled, it is possible to overcome the south-pole problem and improve the adhesion strength.
Recent advances in the field of cold spray have put forward the potential of this deposition technique to be used as a non-thermal additive manufacturing process with significantly high deposition rates. In this study, we use the additive manufacturing potential of cold spray for fabrication of freestanding three-dimensional Inconel 718 samples, which is a challenging material for cold spray due to its high hardness and limited deformability. Additionally, we fabricated samples with similar geometry using one of the most common additive manufacturing methods, i.e. selective laser melting. Microstructural characteristics, distribution of residual stresses, porosity and structural integrity of the cold spray deposited samples were compared with those obtained by selective laser melting before and after different heat treatments. The results of the first time study of axial fatigue strength of cold spray deposited freeform samples indicate the notable efficiency of cold spray for fabrication of freestanding objects for structural components, with similar characteristics to those obtained from laser based additive manufacturing technique and even comparable to bulk material properties. The low working temperature of the cold spray method, suggests it as a promising additive manufacturing technique with a high potential to address many challenges regarding laser based approaches.
Cold spray is a coating technology that works at temperatures below the melting point of the initial powder and appears to be an interesting alternative to repair aeronautical components. This work evaluates the effect of temperature on the quality and properties of the aluminum alloy 2024 coatings deposited by cold spray. The coatings were sprayed at a conventional temperature of 350 °C and at a non-conventional one of 500 °C on aluminum 2024 T351 substrates. Electron microscopy was used to analyze the microstructure. Depth sensing indentation and Vickers microhardness tests were conducted to determine the elastic modulus and hardness. Both coatings exhibited a work hardened microstructure, and no modifications in phase composition were observed. However, the coating processed at 500 °C presented hardness values lower than those obtained for the coating processed under conventional conditions. The hardness of the coatings increased regarding to the initial powder particles due to the plastic deformation induced during spraying. Comparing both coatings, the study indicates that cold spray at 500 °C could be adequate for maintaining and overhauling aluminum components used in the aeronautical industry.
Continuous development of cold spray technology, resulting in better mechanical properties, enables extension of cold spray application to components carrying loads. As a new subject, no standard procedures to assess fatigue life of repaired parts are available. Here, we propose new specimen for axial fatigue test to simulate behaviour of parts with localized damage and repaired with cold spray, which are subjected to cyclic loading. The specimen includes a cavity representing spray bed machined around the damage to permit cold spraying. The geometry of the specimen was based on coating quality and stress analysis, which are both discussed in this study. Specimen, produced from A357 aluminum alloy, was successfully tested and can be used as a part of standard procedure for mechanical testing of structural repairs. Moreover, fatigue limit obtained on repaired specimens corresponds to the limit obtained on bulk material, which proves potential of cold spray for restoration of structural parts.
Al–Cu alloys, like Al 2024, and Al–Si alloys, like Al F357 and Al C355, are used in aeronautic gearboxes and fuselage parts operating in severe conditions. It is necessary to develop maintenance and overhaul technologies to extend the life of metallic components used in the aeronautical sector. Cold Spray (CS) could be an alternative as it is real solid-state processing technique. However, the repaired component should exhibit similar properties as the original substrate. This paper evaluates the wear performance of Al coatings CS onto the same Al substrates in sliding and oscillating conditions. The results were compared with the corresponding substrates. The wear rate of coatings processed using new conditions, developed to enhance the coatings performance, was similar or smaller than that measured in the substrate bulk alloys. For Al 2024 and Al C355 CS could be used for repairing, from the tribological point of view.
A high pressure cold spray system was used to deposit three Ti-6Al-4V feedstock powders (i.e., hydride de-hydride, plasma atomized, and gas atomized) on Ti-6Al-4V substrates while varying gas temperature and nozzle length. Particle impact temperature and particle velocity were calculated using a 1-D axial model. The microstructure of the feedstock powders and the cold spray depositions were characterized via optical and scanning electron microscopy. The hardness of the as-received powders was determined using nanoindentation. To assess deposition quality, coatings were characterized in terms of porosity, microhardness, and adhesion strength. Results showed that hydride de-hydride powders were characterized by an equiaxed alpha grain structure with intergranular beta phase regions while atomized powders were characterized by martensitic α phase structures. Cold sprayed coatings revealed two distinct microstructures. Regions that experienced low/moderate plastic strain retained the as-received powder microstructure while regions that experienced significant plastic strain were characterized either by a featureless microstructure (atomized coatings) or the presence of fine, elongated beta precipitates (hydride de-hydride coatings). Depositions performed using a long nozzle resulted in the best deposition quality, with porosity as low as 0.3% and adhesion strengths > 69 MPa. While atomized powders resulted in comparatively higher quality coatings for all process conditions, hydride de-hydride coatings of excellent quality (average porosity ≈ 0.6%, adhesion strength > 65 MPa) were achieved under optimal conditions. Thus, hydride de-hydride powders may hold promise as a cost effective alternative to atomized powders for Ti-6Al-4V cold spray depositions.
Today, cold gas dynamic spray (CGDS) technology has thrived with considerable capabilities for manufacturing various technological depositions. The deposition conditions have been developed through many years and that have led to produce ample experimental data which is available in the literature. But, recent research and development activities also reveal innovative findings regarding various deposition conditions. This paper contains a review of experimental deposition procedures for the cold spray additive manufacturing. Details of processing conditions are reported and classified into various categories of baseline working conditions, specific processing including deposition of nanotechnological components, composites-based structures and hybrid coating with substrate deposition. Available substrate treatments and their contributions on the deposition capability were also included. A large collection of experimental data from the literature is addressed in the Appendices A1–A6 in Supplementary material.
Cold spray, originally developed as a coating technique, is now applied as an additive manufacturing process to fabricate freestanding components and restore damaged components. Having low working temperature, cold spray additive manufacturing (CSAM) and cold spray restoration (CSR) have the ability to retain the original feedstock properties and prevent adverse influence on the underlying substrate materials. These superior merits are not achievable through conventional high-temperature additive manufacturing processes, thereby CSAM and CSR are attracting great attentions from both scientific and industrial communities. During the past decade, investigations of CSAM and CSR have been widely conducted. Existing works mainly focused on applications, product properties, processing parameters optimization, spray strategy, and robot control. Despite having a large number of reports, a systematic summarization and review on these works has yet to be carried out. Therefore, in this chapter, the existing CSAM and CSR works were summarized and reviewed for the purpose of systematically introducing the progress of CSAM and CSR techniques.
In the cold spray (CS) process, deposits are produced by depositing powder particles at high velocity onto a substrate. Powders deposited by CS do not undergo melting before or upon impact with the substrate. This feature makes CS suitable for deposition of a wide variety of materials, most commonly metallic alloys but also ceramics and polymers or composites of those materials. During processing, the particles undergo severe plastic deformation, and both components of bonding, i.e., mechanical and metallurgical, are achieved with the underlying material, depending on the material type and impact velocity. The deformation behavior of powder particles depends on multiple material and process parameters. Changing to these parameters leads to the evolution of different microstructures and consequently changes the mechanical properties in the deposit. While CS technology has matured during the last decade, the process is inherently complex, and thus the effects of deposition parameters on particle deformation, deposit microstructure, and mechanical properties are not always clear. The purpose of this chapter is to describe the existing relationships between microstructure and mechanical properties of various CS deposits to illuminate what has been discovered to date.
This chapter will present various cold spray applications developed by the US Army Research Laboratory (ARL) associated with the repair of parts from aircraft and ships by providing actual examples and their relevance toward the advancement and implementation of cold spray technology. It is not an all-inclusive by any means, but it serves to illustrate that cold spray (CS) can be used across very diverse industry sectors. It is important to note that most cold spray applications today are for dimensional restoration of parts that have experienced wear and/or corrosion in service. Significant points of interest associated with the development of these CS applications will be highlighted. Emphasis will be placed on important aspects of process development and optimization, testing and evaluation, and qualification and specifications. The methodology and essential technical data for the transition of cold spray technology for these select applications will be discussed and illustrated by actual case studies. The substrate materials represented will include aluminum, magnesium, and titanium. The focus application will involve the restoration of magnesium aerospace components where much data will be presented, while the remaining case studies cannot be so inclusive due to page restrictions.
Cold spray coatings have shown great corrosion protections due to the intrinsic dense character of the sprayed material. However, these types of coatings do not get wide application in low-temperature corrosion for their economical inferiority compared to other alternative coating technologies. For this reason, the other possible application for cold spray corrosion coatings needs to be developed, such as high-temperature oxidation resistance coatings on titanium-based alloys. The titanium-based alloys such as orthorhombic Ti2AlNb and γ-TiAl-based alloys are considered as potential structural materials for high-temperature applications in aeroengines, but they still suffered from oxidation and environmental embrittlement at elevated temperatures. Coatings represent an effective way to solve the problems. However, the available coatings do not meet the requirements of titanium-based alloys for many reasons. In this chapter, the use of cold spray technology for preparing TiAl3, TiAl3/Al, TiAl3/Al2O3, and TiAlSi coatings on titanium-based alloys and their behaviors at high temperatures are reviewed. This chapter is mainly divided into four parts, including the background of the study, the coating preparations, the coating characterization, and the high temperature performance of the coatings. The main results of the investigations showed that the TiAl3 composite coatings prepared by cold spray exhibited great improvement for the oxidation of substrate alloys, which is different from those prepared by other available technologies. The coating protection and degradation mechanisms are analyzed. Comparison of TiAl3 composite coatings prepared by cold spray and other technologies is also discussed.
This chapter presents the corrosion properties of cold-sprayed coatings. Cold spraying has shown its potential producing corrosion-resistant coatings for several operation conditions due to the fact that dense and protective metallic and composite coatings can be manufactured by using cold spray processes, examples are presented in Fig. 13.1. This enables the use of cold-sprayed coatings as corrosion barrier coatings. In addition to corrosion resistance, other advantages of cold-sprayed coatings are dealing with high strength, electrical conductivity and minimal or compressive residual stresses as well as repairing and additive manufacturing (Papyrin et al., Cold spray technology, 1st edn. Elsevier, printed in the Netherlands, 328 p, 2007; Champagne and Helfritch, Int Mater Rev 61(7):437–455, 2016; Champagne, The cold spray materials deposition process: fundamentals and applications. Woodhead Publishing Ltd., Cambridge, 362 p, 2007; Koivuluoto, Microstructural characteristics and corrosion properties of cold-sprayed coatings, Doctoral Thesis, Tampere University of Technology, Tampereen Yliopistopaino Oy, Tampere, 153, 2010; Villafuerte, Modern cold spray – materials, process, and applications. Springer International Publishing, p 429, 2015). Corrosion properties and behavior of the cold-sprayed coatings are increasingly reported in the literature during last years. Recently, review papers concerning corrosion properties of cold-sprayed coatings have been published by Bala et al. (Surf Eng 30(6):414–421, 2014), Koivuluoto and Vuoristo, (Surf Eng 30:404–414, 2014) and Hassani-Gangaraj et al. (Surf Eng 31(11):803–815, 2015). Furthermore, cold spraying can be used for corrosion protection as well as repairing of corrosion defects (Vardelle et al., J Therm Spray Technol 25(8):1376–1440, 2016).
The Chapter “Low-Pressure Cold Spray” presents a description of basics of LPCS technology, bonding mechanisms, temperature effects and LPCS localization processes. To illustrate the main aspects of LPCS system parameters determination, the numerical simulation and experimental data are presented. The emphasis is placed on the proper development of the cold-sprayed metal matrix composite coatings and their structure and properties, which are of paramount importance to the success of LPCS. Processes such as bonding, hardening and softening of the coating materials during cold spraying and coating structure formation at following heat treatment (sintering) are dealt with from the theoretical as well as practical aspect.
Cold gas dynamic spraying (CGDS) is an emerging technique that involves the surface modification in order to provide enhanced surface properties on material substrates. Particles, with size in the range of 1–50 μm, are accelerated by a supersonic jet gas up to 1200 m/s and impact on the substrate surface. Under specific conditions, the metal powders undergo a severe plastic deformation and adhere to the substrate. In the last decades, the cold spraying of several materials, like copper, aluminium and iron, has been widely explored providing optimal processing windows for a wide range of material pairs. Titanium and its alloys are finding a widespread use in many strategic industries, namely, aeronautic and aerospace field, due to the lightweight, high corrosion resistance and compatibility with polymer-reinforced composites, as well as in the biomedical sector, due to their biocompatibility. However, the high cost of raw materials and the manufacturing issues put severe restrictions to their wider use. On the other hand, replacement of titanium bulk with multilayer material, consisting in a cold sprayed titanium coating on aluminium components, could be a promising alternative and an advantageous trade-off between the cost compression and the higher surface properties of titanium alloy. The present chapter deals with the analysis of the deposition of pure titanium coatings on aluminium alloy substrate by means of low-pressure cold gas spray technique and deals also with the study of the properties of multilayer material. A post-deposition process to further improve the properties of the coating itself was also analysed.
Cold gas dynamic spraying, or cold spraying (CS), is a solid-state coating process wherein powders in a carrier gas are accelerated toward a substrate. Under sufficiently high impact velocities, the powder particles deform plastically and adhere to the substrate. Metals, ceramics, polymers, and composites can be deposited using CS. Among currently available surface coating technologies, CS offers several advantages over thermal spraying, because it utilizes kinetic rather than thermal energy for deposition. This avoids residual stresses, oxidation, and undesirable chemical reactions. The intent to develop new material systems with enhanced properties that fulfill the required surface and interface functionalities for components with many applications has inspired CS investigations of many material combinations. The number of studies and patents on CS and CS-related technologies has increased exponentially in recent years, establishing much new information in a short time. In this chapter, the process of CS is discussed from mechanistic and technological perspectives, including its general operating parameters, current applications to specific material systems, and ongoing research increasing the scope of the technique. A critical discussion on developing CS technologies examines the microstructural bonding mechanisms utilized in variations on the process. Future investigations are suggested, particularly in quantitatively linking CS processing parameters to the behaviors of material systems during impact. This chapter briefly summarizes the rapidly expanding common knowledge on CS to assist researchers and engineers in future endeavors with this technology.
Cold spray coating deposition is an innovative thermal spray technique, which addresses some of the shortcomings of several traditional thermal spray processes. The cold spray method can be used for coating deposition at ambient temperature that leads to near-negligible phase transformation during the process, which indicates no particle melting. Therefore unlike other thermal spray techniques, the harmful reactions such as oxidation, nitriding, decarburizing, and other types of decomposition mechanism in general are avoided in this process. These attributes offer significant advantages and new possibilities. The cold spray is applicable to corrosion protection where absence of process-induced oxidation may offer improved performance. The coatings produced by typical thermal spray methods like atmospheric plasma spray (APS) and high velocity oxygen fuel (HVOF) spraying contain comparatively higher porosity and possible oxides, which may lead to a decline of corrosion resistance of the as-sprayed coatings. Efforts are going on for the development of a more comprehensive scientific basis for the cold spray process and a broader range of appropriate materials along with their applications for corrosion protection. This chapter presents a tutorial introduction to the process of cold spray coating. It includes the comparison of cold spray coating process with some popular thermal spray techniques. The studies from various researchers have been reported with regard to use of cold spray coatings for corrosion protection. These studies clearly signify that the cold spray coatings have already proved successful for erosion-corrosion protection. A thorough survey on various coating compositions deposited by cold spraying on different substrates along with their properties has also been detailed with emphasis on corrosion prevention. It has been concluded that the cold spray technology has great prospective for future research especially with reference to its application to actual industrial solutions.
Tremendous attention has been given to the cold spray process, even more today with the emergence of additive manufacturing, worldwide. Several inventions related to the cold spray technology have been patented for over a century and mostly since a couple of decades. But the cold spray technology knows a period of great innovations due to recent and current substantial explorations. Various technological solutions have been developed. The technical dimension, and particularly in terms of manufacturing method, has also always been a major genesis of progresses and novelties. This chapter is a technological survey of the cold spray additive manufacturing and reports variant methods and innovative contributions. Through an introduction section, the chapter begins by a depiction of cold spraying (CS) that addresses a review of distinctive deposition methods based on a capability variance. Then, a section reports a brief chronology of cold spraying towards the generic modern deposition method as it stands nowadays. A concise survey of material aspect is addressed, this showing the current capability of cold spraying prior to a brief overview of various deposit possibilities and applications. Stand-alone sections will be focused on modern variances of cold spraying, viz. the low-pressure cold spray method bringing new benefits and the very-low-pressure cold spray manufacturing for the development of advanced technological solutions. Since combination of cold spray with another process for various innovations represents a new added value, such approach merits to be highlighted among modern trends of the cold spray use. For that purpose, this book chapter also addresses an overview of hybrid combinations based on the cold spray technology, including novel hybrid variant for 3D submicron architecturation and laser-assisted cold spray method that enables positive thermal effect, viz. improved deposition and increased deposit features. Combining high-temperature deposition and high kinematic conditions, a new cold spray variant, denoted pulse gas dynamic spraying capable of thermal improvement is also reported. Together, all these achievements reveal a great flexibility of the cold spray additive manufacturing in terms of material possibilities, deposition methods and technological solutions.
The majority of the mechanical components in aeronautical applications show a reduction of their performance during their service life. Sometimes the component replacement is necessary, with the consequent cost of material and time. An alternative is to repair the component depositing a coating onto the metallic alloy. In this work, a cold spray technique was used to generate Ti6Al4V coatings onto a bulk of the same material. The mechanical response of these coatings was investigated by instrumented indentation tests. Additionally, instrumented indentation tests were also conducted on the particles used for the spraying process and on the substrate. The Young’s modulus and the hardness of the coatings were compared to those obtained on the particles and on the substrate. The mechanical properties obtained on the coatings presented values similar to those obtained on the substrate. Also, the sprayed particles showed a hardness significantly lower than that obtained on the coatings.