No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Effect of nanostructuring and Al alloying on friction and wear behaviour of thermal sprayed WC–Co coatings
Abstract
Nanostructured WC–Co and WC–Co–Al coatings, with about 300-μm as-deposited coating thickness, were deposited by high velocity oxy-fuel (HVOF) spraying. Agglomerated nanostructured cermet powders produced by the Mechanomade® process was used for HVOF spraying. Dense and well-adherent coatings with crystal sizes below 30 nm were deposited on stainless steel 304 substrate. Porosity was less than 5% and the bond strength with the substrate was around 60 MPa. Experimental data on friction, wear, and abrasion resistance revealed that nanostructured WC–Co based coatings containing some Al as alloying element, exhibit improved tribological characteristics in comparison to nanostructured and micron-sized WC–Co coatings. This was attributed to a carbide particle distribution within the coating revealed by SEM, the absence of brittle W2C-like phases revealed by XRD, and the presence of Al at particle/matrix boundaries revealed by TEM.
... Among different coating deposition processes, high-velocity oxy-fuel (HVOF) spraying and air plasma spraying (APS) are widely used. In recent years, thermal spraying using nanostructured feedstock powders has yielded coatings with higher hardness, strength, and corrosion resistance than the corresponding conventional coatings (Basak et al., 2012). Moreover, materials in their wrought or cast form (e.g., stainless steel) are generally less wear resistant than their thermally sprayed counterparts (Basak et al., 2007). ...
... Thermal spraying is very flexible and allows buildup of thick coatings from many materials, as shown in Figure 14.3. During such deposition, a very limited crystal growth can be achieved that allows for a buildup of coatings with a refined structure, down to a size of 30 nm in the case of nanostructured WC-Co-based coatings (Basak et al., 2012). ...
... Figure 14.5 shows the polished sections of APS nanostructured Fe-Al-Al 2 O 3 coatings (Basak et al., 2008). Basak et al. (2008) has done extensive studies on this and proven the superiority of nanostructured WC-12Co coatings compared with microsized counterparts (Basak et al., 2008(Basak et al., , 2010(Basak et al., , 2012. ...
The quest for advanced functional materials with superior functionality is being driven in various frontiers of engineering materials. One such frontier is the research of metal matrix composites (MMCs), which has already been proven as one of the most productive fields. With advance technology, it is possible to reinforce the MMCs with nanosized particles compared with conventional micron-sized counterparts. However, the addition of nanoparticles to MMCs to improve their mechanical properties is not unconditional, and there are several factors that should be taken into consideration. This present chapter gives an overview of such considerations along with recent trends in this field.
... However, the main drawbacks of thermal-sprayed coatings were their high porosity [3], common characteristic of all ceramic coatings elaborated by thermal spraying, and especially in the case of carbide cermets, the decarburization/ dissociation of the carbide particles due to the high temperatures developed during deposition. The issue of high porosity was tackled in a satisfactory way in the one hand by applying High Velocity Oxy-Fuel (HVOF) spraying and in the other hand by employing powder feedstocks of sub-micron and nano-size [4][5][6][7][8]. In HVOF spraying, oxygen and fuel gas are mixed and burnt in a combustion chamber at high flow-rates and pressures up to 12 bar, producing a high-speed jet. ...
... Recent studies, addressing this issue are focused on the optimization of the deposition process parameters (e.g. spray distance, oxygen and flue flow rates) via Taguchi analysis using as a criterion the coating hardness values achieved [25,26] Studies on the tribological performance of WCbased cermets concern abrasion, sliding friction and fretting wear testing [4,5,[8][9][10]12,15,19,[21][22][23][24][25][26][27][28] according to the ASTM G65, G99 and D6037 specifications, respectively. Relevant research findings demonstrated high wear resistance comparable to that of sintered cermets [9]; thus these coatings are the most widely considered as being capable of replacing hard chromium electrodeposits on a variety of industrial components, especially in automotive applications [3,15,27]. ...
... Such coatings often operate in corrosive environments, where the chemical passivity of the metal binder is a demand to avoid coatings total failure through electrochemical reactions or pitting. Relevant works concern the comparative study of influence of various types of binders, as Ni, Co, or Ni-Cr, Co-Cr mixtures [4,5,13,17] in percentages lower than 20 %, on the anticorrosive resistance of WC-based cermet coatings, each one inhibiting different corrosion type. Especially, alloys of the Ni-Cr system exhibit excellent corrosion resistance in aqueous environment, as well as high temperature wear resistance and can be directly deposited as dense and well-adhered coatings onto steel substrates by HVOF spraying [29][30][31][32][33]. ...
The influence of the cermet fraction in cermet/ metal composite coatings developed by High-Velocity Oxyfuel Flame (HVOF) spraying on their tribological behaviour was studied. Five series of coatings, each one containing different proportion of cermet-metal components, prepared by premixing commercially available feedstocks of NiCrFeBSiC metallic and WC-Co/Cr cermet powders were deposited on AISI 304 stainless steel substrate. The microstructure of as-sprayed coatings was characterized by partial decomposition of the WC particles, lamellar morphology and micro-porosity among the solidified splats. Tribological behavior was studied under sliding friction conditions using a Si3N4 ball as counterbody and the friction coefficient and volume loss were determined as a function of the cermet fraction. Microscopic examinations of the wear tracks and relevant cross sections identified the wear mechanisms involved. Coatings containing only the metallic phase were worn out through a combination of ploughing, micro-cracking and splat exfoliation, whilst those containing only the cermet phase primarily by micro-cracking at the individual splat scale. The wear mechanisms of the composite coatings were strongly affected by their randomly stratified structure. In-depth cracks almost perpendicular to the coating/ substrate interface occurring at the wear track boundaries resulted in cermet trans-splat fracture.
... However, with the decreases of carbide size, nanostructured WC-Co powder decarburized in the spraying process, which should be avoided as much as possible. Bimodal powders have been produced to minimize this effect, keeping higher resistance to corrosion when compared with conventional ones [22][23][24]. ...
... Moreover, the nano-sized WC particles are evenly distributed around the WC, which acts as a dispersion strengthening and fine grain strengthening. In addition, the bond strength test of the WC-10Co4Cr coatings shows that the average bond strength is approximately 68 MPa, indicating the WC-10Co4Cr coatings prepared by HVOF have a good bond strength [24]. ...
Two kinds of WC-10Co4Cr composite coatings with conventional (micron-sized WC particles) and bimodal (a mixture of nano-sized and micron-sized WC particles) structures were successfully prepared on 35CrMo steel (ANSI/ASTM 4135) substrate by high velocity oxygen fuel (HVOF) technology. Scanning electron microscope (SEM) equipped with the energy dispersive spectroscopy (EDS), mechanical testing machine, microhardness tester were used to analyze the characteristics of the coatings. The coatings were immersed in the simulated seawater drilling fluid under the high pressure to simulate the deep-sea environment, and then electrochemical impedance spectroscopy (EIS), potentiodynamic polarization were carried out to investigate the electrochemical properties of the coatings and substrate. The results show the WC-10Co4Cr coating has excellent corrosion resistance and can effectively protect the substrate under the high pressure. Besides, compared with the conventional coating (CC), the bimodal coating (BC) has a denser microstructure, superior mechanical properties, lower porosity, and better corrosion resistance. The corrosion mechanism of the coatings in the simulated seawater drilling fluid under high the pressure is as follows: The micro-galvanic corrosion between the WC phase and the CoCr binder phase is the primary corrosion mechanism. Besides, the electrolyte under the high pressure is more penetrable, so the crevice corrosion also exists.
... Great efforts have been made to improve the wear resistance of WC-Co coatings in order to satisfy the growing demands for high-performance surface protection materials. The methods that are used to enhance the properties of WC-Co coatings can be summarized as (i) introduction of metals or ceramics to the starting powder [5][6][7][8][9][10], (ii) decreasing the WC grain size [11][12][13] or optimizing the combination of WC grains with different sizes [14][15][16], (iii) structural modification and improvement of the physical properties of the spray feedstock [17][18][19][20], (iv) innovation of thermal spraying technologies and optimization of spray parameters [21][22][23][24][25], and (v) post-treatments for coatings [26][27][28]. In most cases, these methods were used in combination. ...
... Basak et al. demonstrated that the wear resistance of the nanostructured WC-Co coating with 1 wt.% Al was more than twice as high as that without Al, and three times higher than that of the micron-sized WC-Co coating [8]. The presence of Al mainly increases the cohesion within the coating, forms Al 2 O 3 as well as reduces the porosity of the nanostructured coating. ...
A new type of WC-based coating with high oxidation- and wear-resistance at elevated temperature was fabricated by thermal spraying the pre-treated WC-Co powder doped with WB. Addition of WB led to in situ formation of WCoB, which acted as a substitute for Co in the powders and the resultant coatings. It was shown by thermal analysis that WCoB has obviously higher oxidation resistance at high temperatures than that of WC and Co. Thus, the oxidation of the WC-WCoB coating was mainly initiated from WC, rather than from Co in the conventional WC-Co coatings. Most of WCoB was preserved in the coating after high-temperature wear tests. Particularly, with an addition of 40 wt.% WB, the wear rates of the WC-Co coating were dramatically decreased by 90% and 77% at the room and elevated temperatures, respectively.
... The present paper aims to characterize the properties of coatings obtained by High-Velocity Oxygen Fuel (HVOF) spraying of a TiC-based hardmetal powder with Fe-based alloy matrix, produced through an industrial high-energy ball milling process already in use for large-scale powder production, as previously illustrated in [42,43]. The production of the feedstock presented in this study is therefore amenable for direct, cost-effective scale-up. ...
... As a term of comparison, commercially available WC-10Co-4Cr [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] (WOKA 3652) and Cr 3 C 2 -25(Ni-20Cr) (WOKA 7102) powders (both from Oerlikon Metco WOKA GmbH, Barchfeld, Germany) were also sprayed by the same HVOF torch, using previously optimized process parameters listed in Table 1. ...
As an alternative to WC-CoCr and Cr3C2-NiCr coatings for wear and corrosion protection, a TiC – 25 vol% (Fe-20 wt%Cr-5 wt%Al) powder, free from hazardous and/or supply-critical elements (Ni, Co, W), was produced by high-energy ball-milling and processed by High Velocity Oxygen-Fuel (HVOF) spraying, obtaining dense (<1 vol% porosity), hard (HIT > 12 GPa) layers with reasonably good deposition efficiency of ≈ 54%.
Tribological testing revealed that the TiC-FeCrAl coatings are particularly promising for sliding contacts, as their ball-on-disc wear rates against an Al2O3 counterpart were lower than those of an HVOF-sprayed Cr3C2-NiCr reference, both at room temperature and at 400 °C, although they could not match the performance of WC-CoCr. At room temperature, brittle fracture along oxidized lamellar boundaries caused localized spallation, releasing debris in the contact region, but, in the incubation period before spallation cracks could propagate, remarkably low friction (≈0.27) was recorded. At 400 °C, spallation was largely suppressed by thermal softening, whilst coarser abrasive grooving became the dominant wear mechanism.
TiC-FeCrAl coatings appeared less suited to high-stress abrasion, since extensive brittle fracture resulted in higher wear rates than HVOF-sprayed Cr3C2-NiCr, and to (acidic) corrosive environments. Electrochemical polarisation tests in 0.1 M HCl indeed revealed limited corrosion resistance of the FeCrAl matrix.
... Z uwagi na szczególne właściwości fizyczne i mechaniczne znacznie przekraczające właściwości materiałów krystalicznych i mikrokrystalicznych, materiały nanostrukturalne i nanopowłoki stanowią od wielu lat przedmiot wszechstronnych badań [13,14]. Na przestrzeni minionych lat wielokrotnie wykazano, że zastosowanie materiałów nanostrukturalnych do wytwarzania wysokojakościowych powłok zapewnia im dużą odporność na ścieranie, niski współczynnik tarcia (również w wysokich temperaturach) i odporność na chemiczne oddziaływanie środowiska [9,13]. ...
... 7a) wskazują, że powłoki te charakteryzują się również znacząco mniejszym zużyciem ściernym (wyrażonym przez głębokość wytarcia) niż inne badane materiały odniesienia. Szczegółowe wyniki badań przedstawiono we wcześniejszych publikacjach autorów [9,14]. Testom odporności na zużycie ścierne poddano również powłoki cermetalowe WC-CoAl natryskiwane zimnym gazem (rys. ...
... However, decomposition and decarburisation of the WC still occur during the spraying process. The undesirable W 2 C phases, tungsten oxide, and amorphous or nanostructured Co-W-C compounds are formed during decarburisation of the WC leading to brittleness coating [15][16][17]. Several investigations have been conducted to evaluate the harmful effects of these phases on the friction properties and thus suggested many solutions for reducing these harmful effects [15][16][17][18][19]. ...
... The undesirable W 2 C phases, tungsten oxide, and amorphous or nanostructured Co-W-C compounds are formed during decarburisation of the WC leading to brittleness coating [15][16][17]. Several investigations have been conducted to evaluate the harmful effects of these phases on the friction properties and thus suggested many solutions for reducing these harmful effects [15][16][17][18][19]. Some of these solutions include the usage of the inert gasses [20,21] and optimisation of HVOF parameters such as in-flight particle velocity and fuel/oxygen ratio [22,23]. ...
In this study, electroless nickel–phosphorus plating was optimised for WC–Co powder using different bath loads and then subjected to a high-velocity oxygen fuel process. The produced Ni–P-coated WC–12Co powders were subsequently used as HVOF feedstock materials. Based on the SEM results, an increase in the bath load resulted in a decrease in the thickness of the Ni–P coating formed on the WC–12Co powders. Moreover, applying the HVOF process led to a lower porosity and roughness and a higher thickness of nickel coating, whereas applying a suitable thickness of this coating can prevent the destructive W2C phase. Finally, a bath load of 16 g L–1 was determined as the optimum value to achieve a proper thickness of the Ni–P, extremely low porosity (0.3%), good surface roughness (5 μm), and high microhardness (1112 Hv) in the produced coating.
... Great efforts have been made to improve the wear resistance of WC-Co coatings in order to satisfy the growing demands for high-performance surface protection materials. The methods that are used to enhance the properties of WC-Co coatings can be summarized as (i) introduction of metals or ceramics to the starting powder [5][6][7][8][9][10], (ii) decreasing the WC grain size [11][12][13] or optimizing the combination of WC grains with different sizes [14][15][16], (iii) structural modification and improvement of the physical properties of the spray feedstock [17][18][19][20], (iv) innovation of thermal spraying technologies and optimization of spray parameters [21][22][23][24][25], and (v) post-treatments for coatings [26][27][28]. In most cases, these methods were used in combination. ...
... Basak et al. demonstrated that the wear resistance of the nanostructured WC-Co coating with 1 wt.% Al was more than twice as high as that without Al, and three times higher than that of the micron-sized WC-Co coating [8]. The presence of Al mainly increases the cohesion within the coating, forms Al 2 O 3 as well as reduces the porosity of the nanostructured coating. ...
A new kind of WC-based coating with superhard WCoB compound as the binder was fabricated by the high velocity oxy-fuel spraying of WC-WB-Co powder. The microstructure, mechanical and tribological properties of the WC-WCoB coating were investigated, together with those of the conventional WC-Co coating for comparison. The results demonstrated that the WC-WCoB coating has simultaneously improved hardness and fracture toughness, and thus remarkably decreased wear rate as compared to the conventional coating. The enhanced tribological properties of the WC-WCoB coating are attributed to the low plastic deformation and the resultant inhibition of the micro-ploughing wear and the increased fracture toughness and interfacial bonding, which can reduce the amount of large cracks. Moreover, the high intrinsic hardness of WC and WCoB, as well as their good interfacial bonding, are more effective in resisting against wear as compared with the conventional coating.
... The mechanism of W 2 C formation in mc-WC coating is delineated by schematic in Fig. 4d. The extensive grain growth of WC in nc-WC coating is caused by the high temperature of HVOF flame resulting in the coalescence of adjacent nano-sized WC to form larger particles (more details on grain growth mechanisms of nano-sized WC are provided in [36,37]). Despite the decarburized region that indicated a core-shell structure of mc-WC (Fig. 4), W-2 region of nc-WC coating is characterized by a large number of discrete W 2 C particles with a rounded morphology (Fig. 5b). ...
... Apart from the protective role of the Ni layer against decarburization, this layer was found to be effective in suppressing WC grain growth during HVOF spraying of Ni/mc-WC and Ni/nc-WC as compared to mc-WC and nc-WC ( Supplementary Information, Fig. S3). The reason is that, due to the presence of Ni outer layer, WC-Co particles located in the core position of Ni/mc-WC and Ni/nc-WC powders experience lower temperatures during HVOF process causing the WC grain growth, which mainly occurs by coalescence mechanism [37], to be highly retarded. ...
In this study, we addressed the effects of Ni-plating and nanostructuring of WC-Co powders on the microstructure-property relations and WC decarburization of WC-Co composite coatings. By high velocity oxygen fuel (HVOF) spraying, the coating materials were produced from four different powders, referred to as microstructured WC-Co (mc-WC), nanostructured WC-Co (nc-WC), Ni-plated microstructured WC-Co (Ni/mc-WC) and Ni-plated nanostructured WC-Co (Ni/nc-WC). We found that the coatings, deposited from Ni-free powders, undergo a high level of decarburization, thereby yielding W2C phase formation in brittle amorphous W-rich Co matrix that could be preferential site for crack propagation. On the contrary, the Ni-plating treatment could reduce the amount of decarburization of the coatings, resulting in the uniform distribution of WC phase in the W-depleted Co matrix. Consequently, we revealed the underlying mechanisms responsible for WC decarburization in the coatings, and further suggested that the coating deposited from Ni-plated and nanostructured powders exhibits a superior combination of hardness and fracture toughness as compared to other coatings.
... Recently, a great interest has been taken in nanostructured WC-Co based thermal spray coatings, which possess superior hardness, fracture toughness and correspondingly improved wear resistance compared to the conventional counterparts as a result of the high density of grain boundaries. However, the nanostructured WC-Co based coatings with a greater surface area of WC particles have higher tendency toward decarburization and dissolution during the thermal spraying process that can degrade mechanical properties [4][5][6]. It is therefore worthwhile to select a proper thermal spraying process for preparing the nanostructured coatings. ...
... Therefore, many attempts have been made to investigate the wear resistance of HVOF sprayed nanostructured WC-Co based coatings. Most investigations [4][5][6][10][11][12] revealed that HVOF sprayed nanostructured WC-Co based coatings were superior in wear resistance compared to conventional ones, while other authors [13,14] held the opposite opinion. Furthermore, the influence of the spray parameters (e.g. ...
In this paper, the Taguchi method was employed to optimize the spray parameters (spray distance, oxygen flow and kerosene flow) to achieve the highest hardness and, in turn, the best wear resistance of the high-velocity oxygen-fuel (HVOF) sprayed nanostructured WC-10Co-4Cr coating by investigating the correlation between the spray parameters and the hardness. The important sequence of spray parameters on the hardness of the coatings is kerosene flow > oxygen flow > spray distance, and the kerosene flow is the only significant factor. The optimal spray parameter (OSP) for the coating is obtained by optimizing hardness (330 mm for the spray distance, 2000 scfh for the oxygen flow and 6.0 gph for the kerosene flow). The coating deposited under the OSP with low porosity and high microhardness consists predominately of WC and a certain amount of W2C phases. The coating deposited under the OSP exhibits better wear resistance compared with the cold work die steel Cr12MoV. The material removal of the coating is the extrusion of the ductile Co-Cr matrix followed by the crack and the removal of the hard WC particles.
... Nanostructured WC-Co based thermal spray coatings have attracted much attention in recent years due to their superior hardness, fracture toughness and correspondingly improved wear resistance compared to the conventional counterparts. However, a longstanding problem for nanostructured WC-Co based coatings is that they suffer from high tendency toward decarburization and dissolution during the thermal spraying process that can lead degradation of their mechanical properties [11][12][13]. To avoid this weakness, HVOF spraying has the potential to develop near-nanostructured cermet coatings with reduced percentage of coating decarburization and/or dissolution. ...
... A large number of studies have focused on the microstructure and performance of HVOF sprayed nanostructured WC-Co based coatings. Many investigations revealed that HVOF sprayed nanostructured WC-Co based coatings were well bonded to the substrate with high fraction of retained near-nano WC grain, low porosity and quantity of detrimental reaction products, and possessed higher wear, corrosion, and cavitation erosion resistance than the conventional ones [12][13][14][15][16][17][18]. For example, Thakur and Arora [18] compared the characteristics and cavitation erosion behavior of HVOF sprayed nanostructured and conventional WC-10Co-4Cr coatings. ...
... The addition of the Al in a small amount into the nanostructures WC-Co coatings improved the wear resistance of the coatings. Al helps to improve the cohesion between the coatings resulting in the reduction of porosity, and also helps by forming Al 2 O 3 [123]. ...
Components working under harsh environments in power generation, marine, and aerospace sectors are subjected to severe surface degradation because of wear, corrosion, and erosion by solid particles, slurry, silt, and cavitation. Carbide-based materials exhibit high resistance to degradation under such conditions because of their high hardness and chemical stability. These carbides can be effectively deposited as coatings on the components using advanced thermal spray techniques such as plasma spraying, HVOF, and HVAF. The carbide-based thermal spray coatings are majorly based on either WC or Cr3C2 or a combination of these materials. However, the composition of the carbides, the type and percentage of binders, and process parameters significantly affect the performance of these coated components. In this article, the degradation behavior and performance of the different carbide-based coatings as a function of carbide grain size and type of metallic binders, spray process parameters, and working conditions have been critically reviewed. On the other hand, the post-processing of carbide coatings is also emerging as a promising strategy to enhance the performance by modifying and refining the structure of coatings. Hence, a comprehensive summary of the post-processing techniques such as heat treatment, laser treatment, and cryogenic treatment of the carbide coatings is also provided.
... Application of suitable tribological coatings (including engineered soft coatings and solid lubricants) on the mating components [9]; and iii. ...
To simulate today’s complex tribo-contact scenarios, a methodological breakdown of a complex design problem into simpler sub-problems is essential to achieve acceptable simulation outcomes. This also helps to manage iterative, hierarchical systems within given computational power. In this paper, the authors reviewed recent trends of simulation practices in tribology to model tribo-contact scenario and life cycle assessment (LCA) with the help of simulation. With the advancement of modern computers and computing power, increasing effort has been given towards simulation, which not only saves time and resources but also provides meaningful results. Having said that, like every other technique, simulation has some inherent limitations which need to be considered during practice. Keeping this in mind, the pros and cons of both physical experiments and simulation approaches are reviewed together with their interdependency and how one approach can benefit the other. Various simulation techniques are outlined with a focus on machine learning which will dominate simulation approaches in the future. In addition, simulation of tribo-contacts across different length scales and lubrication conditions is discussed in detail. An extension of the simulation approach, together with experimental data, can lead towards LCA of components which will provide us with a better understanding of the efficient usage of limited resources and conservation of both energy and resources.
... Qiao et al. [20] reported that the hardest and toughest WC-Co coatings with superior tribological performance are obtained with a hot, neutral flame during the HVOF spraying process. Furthermore, the addition of Al into an HVOF-sprayed nanostructured WC-12Co coating is an effective method to enhance wear resistance [21]. However, till now, there is only limited works focus on sliding wear of HVOF-sprayed WC-based coatings at different temperatures [22,23]. ...
The main objective of this study was to develop an efficient coating to increase the wear resistance of cold work die steel at different temperatures. The microstructures of high-velocity oxygen-fuel (HVOF)-sprayed WC-CoCr coatings were evaluated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of temperature on the tribological properties of the coatings and the reference Cr12MoV cold work die steel were both investigated by SEM, environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD), and a pin-on-disk high-temperature tribometer. The coating exhibited a significantly lower wear rate and superior resistance against sliding wear as compared to the die steel at each test temperature, whereas no major differences in terms of the variation tendency of the friction coefficient as a function of temperature were observed in both the coatings and the die steels. These can be attributed to the presence of nanocrystalline grains and the fcc-Co phase in the coating. Moreover, the wear mechanisms of the coatings and the die steels were compared and discussed. The coating presented herein provided a competitive approach to improve the sliding wear performance of cold work die steel.
... In terms of substance, these various thermal spraying processes are all based on the same spraying principle: the coating material is rapidly heated in a hot gaseous medium while being projected onto the surface at a high speed to create a coating. The reason why thermal spray coatings are used to prevent fretting damage is generally that some oxides in the coating can prevent or delay adhesion between the two contact surfaces; the laminated structure of the coating also delays the expansion of the fatigue crack from the fretting site [25]. ...
This paper summarises the regulation mechanism of the traditional and emerging surface strengthening treatments – mechanical shot peening (SP) and laser shock processing (LSP) treatment, respectively – on the fretting fatigue behaviour of the tenon joint materials of aero-engine cold-end parts, as surface strengthening treatment contributes to the improvement of service performance. From the point of view of the actual service environment of turbine components, this paper also expounds on the key problems faced by surface strengthening treatments in improving the mechanical properties of joint materials for aero-engine hot-end components. The application of LSP in the fretting fatigue life extension of turbine joint materials has strong feasibility and development prospects.
... In the case of carbide coatings, feedstock powders of tungsten carbide (WC) with a 10-15 wt % Co-based metal binder fraction [21][22][23] and chromium carbide (Cr 3 C 2 ) with a 25-35 wt % NiCr-based metal binder fraction [24][25][26][27] are used to elaborate extremely wear-resistant and ultra-hard coatings, via High Velocity Oxygen Fuel spraying, a process that controls the in-flight carbide decomposition phenomena. Although these coating types can provide excellent anti-wear protection of metallic components, their deposition processes require large, stationary installation facilities, a fact that limits their industrial applications to parts of relevant small dimensions and hinders their in-situ deposition on non-removable metallic systems. ...
The technique of thermal spraying has been proposed since several years ago, as an alternative to Cr electrodeposition, a process characterized by the need of post-deposition handling of a large amount of toxic slurry wastes. Chromium oxide and chromium carbide coatings, as well as Cr electrodeposits find applications, mainly, on the wear protection of metallic components participating in several tribosystems. In the present study, three different thermal spraying techniques were applied for the deposition of such ceramic coatings onto stainless steel substrates; namely, Flame Spraying (FS) and Atmospheric Plasma Spraying (APS) were employed for the deposition of chromium oxide coatings, whilst High Velocity Oxygen Fuel (HVOF) technique for the elaboration of chromium carbide ones. Post-deposition evaluation of the coatings with respect to dry sliding against an Al2O3 ball and a cBN-coated conical insert, as well as three-body abrasion performance according to the ASTM G65 technical specification, demonstrated that the APS oxide coatings exhibited superior tribological behavior during both tests, despite the fact that their microstructure was not free of flaws. Compared to APS ones, FS oxide coatings exhibited lower three-body abrasion resistance; however, their dry sliding wear resistance was of the same order of magnitude, being only marginally lower. This last characteristic advocates for the use of the much more flexible FS technique for the elaboration of chromium oxide coatings for applications where relatively low shear stresses are expected to be encountered. Finally, the HVOF carbide coatings showed intermediate three-body abrasion resistance but high sliding wear, the latter attributed to both microstructure flaws and in-flight decomposition of the feedstock carbide powder during deposition.
... 1. Running-in: During this stage, the sliding occurs between the ceramic coating and the abrasive ball surface. As seen in Figure 5, the surface of the coatings has primarily some microscopic asperities due to the differences in particles melting points and splats flattening degrees [44,45]. At the initial stage of the wear test the COF value is high, due to the high coating roughness and the smaller contact areas between the ball and coatings and therefore higher applied stress on the contact surface. ...
In this study, the microstructure and mechanical properties of the atmospheric plasma-sprayed Cr2O3 (C), Cr2O3-20YSZ (CZ), and Cr2O3-20YSZ-10SiC (CZS) coatings were evaluated and also compared with each other, so as to explain the coatings wear behavior. Microstructural evaluations included X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDX) and porosity measurements. Mechanical tests including bonding strength, fracture toughness, and micro-hardness tests were used to advance our understanding of the correlation between the coatings properties and their wear behavior. The sliding wear test was conducted using a ball-on-disk configuration against an alumina counterpart at room temperature. Addition of multimodal YSZ and subsequent SiC reinforcements to the Cr2O3 matrix resulted in an increase in the fracture toughness and Vickers micro-hardness, respectively. It was found that the composite coatings had comparable coefficients of friction with pure Cr2O3 coatings. When compared with the C coating, the CZ and CZS composite coatings with higher fracture toughness exhibited superior wear resistance. Observation of the wear tracks of the coatings indicated that the lower wear rates of the CZ and CZS coatings were due to the higher plastic deformation of the detached materials. In fact, improvement in the wear resistance of the composite coatings was attributed to a phase transformation toughening mechanism associated with tetragonal zirconia which created more ductile tribofilms during the wear test participated in filling the pores of coatings.
... Hong et al. [10] prepared nanostructured WC-10Co-4Cr coating by adjusting HVOF process, and the coating exhibited better corrosion resistance in 3.5% NaCl solution. Investigation by Basak et al. [11] showed nanostructured WC-Co coatings (with and without Al) exhibited better corrosion in comparison with micron-sized coating. Reference [12] reported that the addition of TiC improves the corrosion resistance of WC-Co in 1 mol L −1 NaOH compared with the base alloy. ...
There is an urgent need to improve the corrosion resistance of WC-based cermet coatings in different corrosive environments. The main objective of this work was to investigate the microstructure and evaluate the corrosion resistance in neutral, acidic, and alkaline electrolytes of the WC-based cermet/Fe-based amorphous alloy composite coating. Thus, a composite coating of WC–CoCr/Fe-based amorphous alloy and a single WC–CoCr coating were fabricated using the high-velocity oxygen fuel (HVOF) process. The phase composition, microstructure of the original powders, and as-sprayed coatings were studied. The detailed interface information between different compositions of the composite coating was observed by high-resolution transmission electron microscopy (HRTEM). The corrosion resistance of the coatings was studied comparatively by electrochemical tests in 3.5 wt % NaCl, 1 M HCl and 1 M NaOH solutions, respectively. Results showed that the composited coating had a dense layered structure with a composition of WC, Fe-based amorphous alloy, and small amount of W2C. It was revealed that obvious inter-diffusion exists between the interfaces of tungsten carbide/Co, Cr binder and WC–CoCr/Fe-based amorphous alloy. The electrochemical test results showed that the composite coating displayed better corrosion resistance than single WC–CoCr coating both in 3.5 wt % NaCl solution and in 1 M NaOH solution.
... The recent studies have reported that the hardness and toughness of the nanostructured WC-based coatings can be simultaneously improved [10][11][12][13], indicating the very promising applications of the nanostructured WC-based coatings. However, there is still much uncertainty regarding the wear resistance property and its influencing factors of the nanostructured cermet coatings [14][15][16][17][18]. The challenge is to disclose which kind of interfacial bonding state is beneficial to enhance the wear resistance of the nanostructured cermet coatings. ...
Dense near-nanostructured WC-Co coatings with hardness above 1400 HV0.3 were fabricated by high velocity oxy-fuel spraying using the in situ synthesized WC-Co composite powders containing VC and Cr3C2. The carbide additives inhibited WC coarsening effectively and facilitated formation of the clustered structures consisting of WC grains and amorphous Co. Owing to the dragging effect of clusters, the connected WC particles are much more difficult to be peeled off than the isolated WC particles. Therefore, the wear resistance of the near-nanostructured coating was significantly enhanced. The mechanisms proposed the importance of interfacial characteristics for the wear resistance behavior of the cermet coatings.
... Furthermore, pores and voids are unavoidable in plasma sprayed coatings, decreasing the coating performance [12]. In such a case, metals such as Cr, Co, Ni and Al are widely used as a binder metal in ceramic coatings because of its good wetting behavior [13][14][15], with the aim to enhance bonding strength between ceramic phases as well as the coating/substrate interface, and low porosity of coating is also achieved. ...
Nanostructured TiCN based composite coatings with various Cr content were prepared by reactive plasma spray (RPS) from mixed powder (Ti-graphite + Cr) under nitrogen atmosphere. Results showed that composite coatings consisted mainly of TiC0.7N0.3 phase and residual metal Cr. Metal Cr plates were homogeneously embedded in TiCN matrix with good interface bond. The TiCN-Cr composite coatings exhibited lower porosity than TiCN coatings, but increasing porosity with excess Cr addition (30 wt.%). The TiCN–20 wt.% Cr coating showed the highest hardness (1309 HV0.2) among composite coatings, slight lower than the TiCN matrix coating (1526 HV0.2). Compared with the TiCN matrix coating, the TiCN-Cr composite coatings showed higher variability in surface microhardness distribution. The TiCN-Cr composite coatings showed slight higher friction coefficients (0.4–0.6) than TiCN matrix coating (0.35). The wear resistance of TiCN-Cr composite coatings was improved with less mass loss compared with TiCN coating under the test load of 400 N. The TiCN-Cr composite coatings with high Cr content showed the mixture of abrasive and adhesive wear.
... Various thermal spray techniques including atmospheric plasma spray (APS) and high velocity oxygen fuel (HVOF) have been employed to deposit WC-Co coatings. The HVOF spraying provides several advantages over APS, such as higher velocity and lower temperature, resulting in the deposition of a highly compacted coating with negligible porosity, a very high adhesive strength to the substrate and limited WC decomposition during spraying [6][7][8][9][10]. ...
WC-Co coatings with low degree of WC decomposition were deposited from electroless Ni-plated micro- and nano-structured feedstock powders using high velocity oxygen fuel (HVOF) spraying. Dry sliding friction and wear behavior of the resultant coatings, referred to as Ni/mc-WC and Ni/nc-WC, were investigated by using sintered alumina (Al2O3) as the mating material at 700 °C. For the purpose of comparison, similar experiments were carried out on conventional micro- and nano-structured coatings, denoted as mc-WC and nc-WC. The worn scars were examined by field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS). The wear resistance of Ni/mc-WC and Ni/nc-WC coatings at 700 °C was found to be 45% and 72% greater than that of mc-WC and nc-WC coatings, respectively. Moreover, Ni/mc-WC and Ni/nc-WC coatings exhibited a significantly lower friction coefficient with negligible fluctuations as compared to mc-WC and nc-WC. The microscopic analyses of mc-WC and nc-WC worn surface revealed the presence of plastically deformed and discontinuous tribofilms, made up of a mixture of MWO4/WO3 (M = Co) and Al2O3, severe cracking and delamination especially at the interface of tribofilm and the underlying surface. In contrast, examination of Ni/mc-WC and Ni/nc-WC substantiated that a large area of the coatings surface is covered by a dense and adhered MWO4-type oxide layer (M = Co, Ni), which provides a more protection against wear at elevated temperature.
... Recently, Wu et al. [18] reported an Al/WC composite coating prepared by high energy milling and found that Al can react with WC, which was beneficial to bond Al and WC. Basak et al. [19] also reported that Al alloying can improve the wear resistance of the WC-Co coatings. However, there is still no evidence in literature regarding the deposition behavior of nanostructured WC-Co/Al powder and the details of the microstructural evolution during preparation of these powders. ...
Nanostructured WC-Co/Al powder was synthesized from WC-12Co powder and pure Al powder by mechanical alloying (MA). The morphology and microstructural evolution of WC-Co/Al powder were investigated by a series of characterization methods. The results showed that the β-Co phase in the initial WC-12Co powder was replaced by the Al
xCo phases (such as Al9Co2 and Al13Co4). As the ball milling time increased, the average grain size of WC in the WC-Co/Al powder decreased firstly and then remained at a constant value of around 40 nm. The deposition behavior of powders sprayed by high velocity oxygen fuel (HVOF) spraying was investigated. During spraying, the WC-Co/Al powder had a better flattening than the WC-12Co powder without ball milling, which is beneficial to fabricate compact coatings with lower porosity.
... In the case of oxide coatings, alumina (Al 2 O 3 ) ones are the most widely investigated with respect to both the quality of the feedstock powders used, as well as their wear resistance under various tribo-pairs configurations [11][12][13][14][15] whilst the most suitable thermal spraying technique to obtain oxide coatings is Atmospheric Plasma Spraying (APS). In the case of carbide coatings, feedstock powders of tungsten carbide (WC) with a metal binder fraction of ~10% are used to elaborate extremely wear-resistant and ultra-hard coatings, via High Velocity Oxy-Fuel (HVOF) spraying [16][17][18][19][20][21], a process that controls the in-flight carbide decomposition phenomena. Although these coating types can provide excellent anti-wear protection of metallic components, their deposition processes require large, stationary installation facilities, a fact that limits their industrial applications to parts of relevant small dimensions and does not allow in-situ deposition on non-removable metallic systems. ...
Abstract: The paper presents the applications of thermal spray (TS) coatings, when a high tribological performance (wear resistance, friction, lubrication) is necessary. For many decades Cr plating was applied when high wear resistance was requested. However this technique is characterized by the hazardous emission of Cr6+ ions, and the need of management of a large amount of toxic wastes. Several coating techniques are proposed as alternative to hard Cr. Among them, thermal spray seems to be the most appropriate, since it combines cost effectiveness, short production time and a large flexibility in the choice of coating material. In addition, the use of nanostructured materials in TS adds a new dimension.
Keywords: Coatings, Thermal spray, Tribological performance, Cr replacement, Industrial applications
... In the case of oxide coatings, alumina (Al 2 O 3 ) ones are the most widely investigated with respect to both the quality of the feedstock powders used, as well as their wear resistance under various tribo-pairs configurations [4][5][6][7][8] whilst the most suitable thermal spraying technique to obtain oxide coatings is Atmospheric Plasma Spraying (APS). In the case of carbide coatings, feedstock powders of tungsten carbide (WC) with a metal binder fraction of ~10% are used to elaborate extremely wear-resistant and ultra-hard coatings, via High Velocity Oxy-Fuel (HVOF) spraying [9][10][11][12][13][14], a process that controls the in-flight carbide decomposition phenomena. Although these coating types can provide excellent anti-wear protection of metallic components, their deposition processes require large, stationary installation facilities, a fact that limits their industrial applications to parts of relevant small dimensions and does not allow in-situ deposition on non-removable metallic systems. ...
Abstract: The present study is focused on the evaluation of the in-service tribological performance of Cr2O3 coatings deposited by Flame Spraying, a method that allows in-situ deposition and surface enhancement of metallic components of large dimensions. The relevant experimental results concern ball-on-disc and three-body abrasion testing and are compared to those obtained for APS Cr2O3 and HVOF Cr3C2 coatings. The strategic target of the work is to investigate the feasibility of replacing Cr electrodeposition, a technique characterized by the need of post-deposition management of a large amount of toxic slurry wastes, by thermal-sprayed Cr compounds using flexible and mobile spraying equipment.
Keywords: Thermal spraying, Cr-oxide coatings, Cr-carbide coatings, Tribological performance.
... Nanostructuring of the cermet coating is recognized as an important approach for further improving its mechanical properties. Over the past decade, many efforts have been made to fabricate ultrafine and even nanostructured WC-Co coatings with enhanced performance as compared with conventional coarse-grained coatings [1][2][3][4][5][6][7][8][9][10]. ...
... Moreover, the major differences in the wear mechanisms of both types of coatings gave rise to an improvement of toughness and strength as a result of small WC grain size. Basak et al. [27] showed that nanostructured WC-12Co coatings demonstrate superior wear resistance compared to micron sized ones. They further improved the coating by addition of small amount Al as alloying element. ...
Investigation of HVOF thermal sprayed
nanostructured WC-12Co mixed with
A. Al-Hamed1, H. Y. Al-Fadhli2, S. Al-Mutairi3, B. S. Yilbas4,
M. S. J. Hashmi1 & J. Stokes1
1National Centre for Plasma Science and Technology,
School of Mechanical and Manufacturing Engineering,
Dublin City University, Ireland
2Non-Metallic and Protective Coating Unit,
Consulting Services Department, Saudi Aramco Dhahran, Saudi Arabia
3Research and Development Centre Unit, Saudi Aramco Dhahran,
Saudi Arabia
4Mechanical Engineering Department, King Fahd University of
Petroleum and Minerals, Saudi Arabia
Abstract
Different machine parts in oil and gas industries suffer from erosion-corrosion
degradations due to the impact of small solid particles entraining a liquid stream
during transportation. To overcome such a tribological problem, the demand for
WC-12Co and Inconel-625 HVOF thermal spray coatings is becoming more and
more stringent. To date, the development of nanostructured WC-12Co feedstock
materials have significantly improved the mechanical property performance of
such coatings over conventional micro-structured coatings. This paper identifies
the recent developments of WC-12Co nanostructured coatings and how they
have performed when deposited using different thermal spray techniques. The
research focuses also on the modification of WC-12Co by the addition of
Inconel-625 against erosion-corrosion. The results demonstrate that the
significant improvement in nanostructured WC-12Co coating performance can
be achieved by utilizing proper controlling parameters for HVOF technique.
Keywords: nanostructure, HVOF, thermal spray, WC-Co, erosion, Inconel-625.
... An example of this finding is illustrated in flank-worn SEM images in Fig. 14, which shows an improvement in wear resistance achieved by increasing C/N. Weight loss of the cermets can be inversely proportional to the bulk hardness based on Archard's law [96][97][98]. ...
Cermets, particularly those based on TiC, are receiving considerable attention because of their unique properties, including high hardness and resistance to thermal deformation. However, TiC-based cermets lack sufficient toughness. To improve the performance of these cermets, numerous studies have been conducted to determine the factors that can be manipulated to improve their toughness. However, the results of these studies vary. This paper summarizes the studies to improve cermet design via chemical compositions and microstructures. Critical issues including the effects of grain size and sintering temperature on the mechanical properties (i.e., toughness, hardness, and wear resistance) of TiC-based cermets are also discussed.
In this study, the Stellite 6 coating was applied on 316 stainless steel substrates through the high-velocity oxygen fuel method (ST-HVOF). Then, the laser-glazed sample (ST-Glazing) was deposited on the as-sprayed Stellite 6 coating using optimal conditions. Afterward, the Stellite 6 powder was optimized on the stainless-steel substrate by laser cladding process (ST-Clad) using 300 W and 5 mm/s of laser power and beam scanning speed, respectively. The microstructural characterization and phase analysis of ST-HVOF, ST-Clad, and ST-Glazing coatings were performed by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques. The microscopic observation results revealed that laser glazing significantly decreased the porosity of ST-HVOF (from about 2.3% to about 0.3%) and formed a dense coating with a uniform microstructure and strong adhesion to the substrate. Also, ST-Clad coating showed a porosity of 0.2% and a compact and uniform microstructure with a high-strength bonding to the substrate. Tribological evaluation of the coatings indicated a 67% and 58% increase in wear resistance of ST-Clad and ST-Glazing coatings compared to ST-HVOF coating, respectively. The high-temperature wear results suggested the following mechanisms for the studied coatings: plastic deformation mechanisms, wear adhesion, brittle fracture, and delamination.
Ball end magnetorheological finishing (BEMRF) is a nanofinishing process for finishing 3D surfaces of a large variety of materials such as glass, steel, copper, polycarbonates, silicon, etc. Under the influence of magnetic field, abrasive-laden ball of magnetorheological polishing fluid present at the tip of the tool removes material from the workpiece surface. The knowledge of forces associated with the process aids in understanding the material removal mechanism and the process physics. Also, the prediction of finishing spot plays a vital role in increasing the process capabilities of BEMRF process in the area of localized/selective finishing. In this work, a theoretical model of finishing forces is presented that helps in improving the in-depth understanding of the nanofinishing process. In addition to it, a theoretical model of finishing spot size is also proposed. Depending upon the area of workpiece to be finished locally/selectively, the finishing spot model provides a deterministic way to alter the size of finishing spot of BEMRF process by changing the finishing parameters.
During the machining of hard coatings, debris generated due to machining causes abrasive wear of machine components as well as workpiece. The present chapter investigates such abrasive wear effect by simulating such conditions that took place during machining in sand abrasion test instruments. Hard nanostructured cermet coatings, namely nanostructured WC-Co and FeCu/Al2O3/Al, with about 250 μm thickness, were deposited by high velocity oxy-fuel (HVOF) and atmospheric plasma spraying techniques on stainless steel 304 substrate. Experimental data on abrasive wear of such coatings were reported under both dry and lubricated abrasion conditions. Relatively higher abrasion resistance of such coatings, compared to reference metallic materials, is due to the formation of small debris that rolls between the moving surfaces and thus limits the wear of the workpiece materials. Another aspect of higher abrasive wear resistance is homogeneous distribution of hard (WC and Al2O3) particles within relatively soft matrix (Co and FeCu) as revealed by scanning electron microscopy investigation on wear scars of the samples after abrasion tests.
The tribological properties and behaviors in the nanometric machining play a critical role in the high surface quality and low subsurface damage for the machined materials. However, in situ TEM experiments have the limitation of length and time scales to investigate the dynamic nanomachining process. Molecular dynamics (MD) simulation is widely employed to describe the nanomachining at atomic scale, and provides some dynamic deformation details which can be hardly revealed by the experiment. In this chapter, we review recent works on the nanometric machining to understand the tribological behaviour. The fundamentals of nanometric machining in term of the friction, material removal, tool wear, and lubrication, are discussed for deeply understanding of the physical mechanisms of nanomachining induced tribological behaviour.
Abrasive wear behaviour of WC-Co and Fe/Cu-based nanostructured coatings has been investigated under dry and slurry conditions in this study. The retention of nanostructured coating constituents was confirmed together with the formation of various metallic and ceramic phases. Abrasive wear rate of nanostructured WC-Co coating was one order lower than that of micro-structured coatings in both conditions. Relatively higher abrasion wear resistance of such coatings compare to reference metallic material was because of comparatively smaller debris formation. These debris roll in between the moving surfaces and thus limit the wear of coating materials. Another aspect of higher abrasive wear resistance is homogeneous distribution of hard (WC and Al2O3) particles within relatively soft matrix (Co and FeCu) as revealed by SEM investigation.
Recent work indicates that the high-velocity oxy-fuel (HVOF) thermal spraying WC–Co coatings have been used to enhance the wear resistance of various engineering components in a variety of industrial environments. In the present work, WC–Co powder, containing Cr particles in an amount of 10%, was deposited on ductile cast iron with the HVOF thermal spray coating technique. An investigation was conducted to determine the role of Cr particles in the WC–Co coating produced with the HVOF technique on microstructure, mechanical, and wear properties in a system of type: WC-Co coating/ductile cast iron. The microstructure of the HVOF-sprayed WC–Co + Cr coating was characterised by light microscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and energy-dispersive X-ray spectroscopy (EDS). The analysis of the microstructure showed the formation of a coating with low porosity, compact structure, and good adhesion to the substrate with a typical lamellar structure composed of fine molten Cr particles and finely fragmented WC grains embedded in a Co matrix, reaching the size of nanocrystalline. The scratch test was applied for the analysis of the adhesion of coatings to the substrate. The erosion behaviour and mechanism of material removal was studied and discussed based on microstructural examinations. Moreover, the results were discussed in relation to the bending strength test, including cracks and delamination in the system of the WC–Co + Cr/ductile cast iron, as microhardness and erosion resistance of the coating. It was found that the addition of Cr particles to the WC–Co powder, which causes hardening of the binder phase is a key influence on increased mechanical and wear properties in the studied system. Additionally, due to the construction of nanostructured coatings, suitable proportion of hard and soft phases, the technique sprayed HVOF coatings have advantageous properties such as high density and good slurry erosion resistance.
In this study, nanostructured WC-12Co powder was produced by ball milling and then agglomerating by spray drying. The produced nanostructured WC-12Co powder was used for laser cladding of AISI 321 stainless steel substrate. In order to evaluate the effect of argon shroud protection, the cladding process was performed with and without argon shroud protection. Microstructural and phase characterization showed that argon shroud protection can reduce the WC decarburization and the relative fraction of WC phase in clads reached up to 74%. In addition, microhardness and porosity percentage of the clads with argon shroud protection showed a significant improvement in comparison with the clads without argon shroud protection. The microhardness (to 2200 HV) and wear resistance increased and the porosity percentage decreased to less than 1%.
In this study, the effect of TiCN and WC-Co coatings on the tribological performance of spheroidal graphite cast iron materials was investigated by wear tests under dry and lubricated conditions. The mechanical and physical effects of the coating processes were analysed by microhardness measurements and visual methods (SEM, EDX, XRD). The tribological effect of WC-Co and TiCN coated specimens were investigated by ball-on-plate wear tests carried out under dry and boron oil emulsion (5% concentration) conditions at 50 N load and 60 rpm sliding speed parameters. The friction coefficient and wear volume results were obtained to investigate the effect of the coating process and boron oil emulsion on friction and wear behaviour. The wear mechanisms were determined with SEM images obtained from the worn surfaces and surfaces analysed elementally with EDX images. Additionally, surface morphology was examined with surface roughness measurements and 2D-3D topography images. According to the microhardness measurement results, it was observed that the spheroidal graphite cast iron with 290 HV hardness reached 1559 HV with TiCN coating and 1440 HV with WC-Co coating. According to the wear test results, it was determined that TiCN and WC-Co coatings decreased the friction coefficient by 32.51% and 12.80%, respectively. When the effect of boron oil usage compared to dry environmental conditions, it was concluded that the friction coefficient and wear volume decreased by a maximum of 54.80% and 53.70%, respectively. Additionally, the roughness values decreased in the experiments where the boron oil emulsion was used. However, although the TiCN coating improved the surface quality, the WC coating negatively affected the surface quality. Surface form images obtained with 2D and 3D topography also support the alteration in roughness values.
A Ni-20 wt% Sn coating was deposited by the cold spraying method on steel substrate. The thickness of the deposited coating was approximately 50 μm and porosity was <1%. The coating microstructure consisted of a Ni solid solution with the presence of various intermetallics, which was confirmed by x-ray diffraction and electron microscopy. Stress-strain behaviour of this coating, both in planar and cross-sectional direction, was investigated under in-situ micro-pillar compression. It was found that strength and elastic modulus was slightly higher in the cross-sectional direction of the coating compared to that of the planar direction. The presence of intermetallics in the coating microstructure acts as a reinforcement medium to allow effective load bearing capacity of the coating. Loading direction during compression with respect to splat boundary orientation plays an important role in the mechanism of coating deformation. There was no substantial work hardening, due to the lubricating effect of SnO2 in the coating system.
A WC-17 wt % Co coating was deposited onto a ST37 mild steel substrate by HVOF-spray technique and then vacuum heat treated at 1100°C. The cross sectional microstructure of the produced coating was characterized before and after heat treatment by optical microscopy. X-ray diffraction (XRD) was also utilized to evaluate the effects of heat treatment on the phase composition of the WC-17Co coating. To study the electrochemical corrosion behavior of both as-produced and heat treated samples, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods were performed in 3.5 wt % NaCl solution. Our results reveal that the WC-17Co coating had a dense structure with an average thickness of about ~500 μm. However, heat treating the coating resulted in an adhesion failure and therefore partial separation of the coating from the substrate. The as-produced coating was also composed of both crystalline WC and amorphous phases whilst the heat treated layer was fully crystalline. According to the corrosion tests, the WC-17Co coating improved the corrosion resistance of the substrate. However, heat treating the coating at 1100°C decreased anticorrosion performance which was due to the precipitation of η-phases with different electrochemical potential than the WC phase together with the formation of microgalvanic cells between the crystalline phases with different compositions.
Mechanical equipment operating in the ocean is vulnerable to cavitation erosion damage. The coatings fabricated by high velocity oxygen fuel (HVOF) spraying technology can remarkably improve the resistance of cavitation erosion. In this study, WC-10Co4Cr coatings with two structures (conventional and bimodal) were prepared on 35CrMo steel substrate, respectively. The morphologies and structures of the powders and as-sprayed coatings were analyzed by SEM and XRD, and microhardness, porosity and surface roughness were also studied. The corrosion resistance of the coatings was evaluated by using potentiodynamic polarization. More importantly, the cavitation erosion resistance in simulated sea water was studied by the ultrasonic cavitation vibratory apparatus and the cavitation erosion failure mechanisms were also explored. The results show that the bimodal coating has better quality and cavitation erosion resistance. Moreover, the effect of corrosion on cavitation erosion is not obvious.
In this research, plasma nitridation is carried out on the as-sintered and hardened Astaloy Mo in order to improve the wear behavior of PM parts. The starting materials including pre-alloyed powders with 0.8% graphite were pressed at different pressures. Next, the specimens were sintered at 1120 °C for 30 min, in the N2/H2 atmosphere. The effects of density and cooling rate were studied on the microhardness, microstructure, and wear performance of as-sintered and hardened specimens. X-ray technique, scanning electron microscopy, and energy dispersive spectroscopy were used for phase transformation, morphology characterization, and elemental analysis, respectively. The results showed that plasma nitridation and an increase in cooling rate and density up to 6.8 g/cm³ resulted in a change in wear resistance. Moreover, the wear performance of dense samples was decreased due to the enhanced three-body abrasive mechanism.
The flexural strength and residual stresses significantly influence the mechanical, structural and tribological performance of the coatings/claddings on metallic substrates. In this study, micrometric and nanometric WC-12Co clad were developed on stainless steel substrates using microwave hybrid heating technique. The flexural strength of the WC-12Co clads was evaluated using a three-point bend test. The nanometric clads exhibited approximately 14% higher flexural strength compared to the micrometric clads. The presence of eutectics of nanocarbides in the nanometric clads restricted crack propagation in the decohered ductile metallic matrix. The residual stresses in the micrometric and nanometric clads were evaluated through the sin2ψ technique using X-ray diffraction. The nature of residual stresses was observed to be compressive in the micrometric and nanometric clads. However, the magnitude of the stresses in the nanometric clads was observed to be ~ 68% higher than the micrometric clads.
The nanostructured WC–10Co–4Cr coatings were fabricated by high velocity oxy-fuel spraying using the in situ synthesized WC–Co nanocomposite powder with size of 70–200 nm and Cr addition. Through optimization of the processing conditions, the nanostructured WC–Co–Cr coating has only a small amount of decarburized phase, a dense microstructure and an excellent combination of hardness, fracture toughness and wear resistance. A series of sliding wear tests were performed to investigate the wear behavior of the nanostructured cermet coating. The evolution of the friction coefficient, wear characteristics and their mechanisms were studied for the nanostructured WC–Co–Cr coating with the change of the load. The present study proposes a new understanding of the occurrence and the related mechanisms of the wear of the cermet coatings.
Conventional and nanostructured WC-12 %wt Co powders were HVOF sprayed on Al 7075-T6. The nanocoatings presented slightly less microporosity, higher microhardness, higher fracture toughness but higher decarburization, than the conventional ones. The nanocoatings exhibited greater resistance to general corrosion and localized corrosion in 3.5% NaCl than their conventional counterparts. Other than an occasional removal of WC nanoparticles, corrosion modes appeared similar for both types of coatings, characterized by selective dissolution of Co, formation of protective surface films and crevice corrosion along interlayer boundaries. Both types of coatings exhibited high dry sliding wear resistance. Nevertheless, the wear performance of the nanocoatings was even superior than that of their conventional counterparts. Main wear modes included plastic deformation of binder, oxidative wear leading to the formation of lubricating oxides and adhesive wear leading to the formation of alumina-rich surface depositions. Coating of Al 7075 with nano WC-12Co was proved effective in terms of microstructural features, corrosion and wear behaviour.
Cermet/iron alloy cladding layers were coated on the surface of Al-Mg-Si alloy (A6061) plates by resistance seam welding method with tungsten carbide (WC) and high-carbon iron alloy (SHA) powders. The cladding layer consisted of WC reinforcement, SHA binder, A6061 and FeAl3. The effect of WC ratio (30 wt%, 50 wt% and 70 wt%) on the microstructure and wear behavior of the cladding layers was investigated in detail. Abrasive wear test was performed under two kinds of load condition by using a rubber wheel apparatus to evaluate wear resistance. The results showed that the wear resistance of the cladding layer was improved by 3.5-5 times than that of the substrate. At lower load, the wear resistances of the samples 30% and 70% WC were nearly the same, which suggested that FeAl3 played an important role in improvement of the wear resistance instead of WC. While at higher load, the amount of WC determined the wear resistance of the cladding layer. Furthermore, wear behavior of these cladding layers was explained with reference to the observed microstructure of the worn surface.
The aim of this work was to study the detailed microstructures, thermostability and microhardness distribution of high velocity oxygen fuel sprayed WC-10Co-4Cr coating using X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, differential scanning calorimeter and high resolution transmission electron microscope. The coating has a dense structure and is well bonded to the substrate. The coating is mainly composed of WC phase and W2C phase. Owing to the high cooling rates of molten droplets and the multicomponent system of feedstock powder, amorphous phase is obtained in the coating. The crystallisation temperature of the amorphous phase is 651°C. The Weibull analysis of Vickers microhardness of the coating exhibits a bimodal distribution under indentation load of 300 g and a monomodal distribution under indentation load of 100 g. Such distribution is attributed to the presence of the poorly bonded splats and pores within the coating.
In this study, two kinds of WC–Co coatings with different decarburization levels were deposited by high-velocity oxy-fuel (HVOF) spraying using the ultrafine WC–Co composite powder and commercial micronsized powder, respectively. The hardness and elastic modulus were measured on the top surface and cross sections of the prepared coatings by the nanoindentation method. The results show that the ultrafine-structured coating has much higher density and inhibited decarburization than the conventional coating, which thus results in higher hardness and elastic modulus values than the micronsized coating. The wear resistance of thermal-sprayed cermet coatings greatly depends on the cross-sectional hardness and elastic modulus which reflects the bond strength between splats to some extent. Based on the analysis, a better understanding of the microstructure and properties in cermet coating materials was obtained.
In this research, a novel nickel-coated nanostructured WC-12Co powder (Ni/nc-WC) was developed and used as feedstock material for high velocity oxygen fuel process. The Ni/nc-WC powders with average WC grain size of ~15 nm were produced by mechanical milling and electroless plating processes. The microstructural and tribological characteristics of Ni/nc-WC coating were investigated and compared with those of microcrystalline WC-12Co (mc-WC) and nanostructured WC-12Co (nc-WC) coatings. X-ray diffractometry, high-resolution field emission scanning electron microscopy, and transmission electron microscopy were used to evaluate the microstructure of the powders and coatings. A ball-on-disk technique was used to probe the wear behavior of the coatings. The Ni/nc-WC coating showed negligible decarburization of ~5.4%, while mc-WC and nc-WC coatings suffered from higher decarburization levels of 16.3 and 36.8%. The wear rate of Ni/nc-WC coating was 2.5 × 10−4 mg/m indicating ~ 75 and 82% increase in wear resistance compared with mc-WC and nc-WC coatings. The wear track analysis of mc-WC and nc-WC coatings showed evidences of delamination mechanism. Besides, a severe carbide pullout mechanism was operative in wear of nc-WC coating. As for Ni/nc-WC coating, individual carbide pullout following the elimination of Ni(Co) matrix was the predominant wear mechanism.
Nanostructured WC–12Co coating with crystal sizes below 30 nm were deposited on low carbon steel substrate by high velocity oxy-fuel spraying. In this study, corrosion behavior of such coatings was investigated in artificial sea water electrolyte and compared with micron-sized (internal structure) coating of similar composition. Besides that, role of small amount Al alloying on corrosion behavior of such nanostructured coating was also investigated. Nanostructured WC–12Co coatings with or without Al exhibit lower corrosion potential and lower polarization resistance compared to micron-sized (internal structure) coating as well as higher Co dissolution as revealed by electrochemical impedance spectroscopy (EIS) together with other complementary electrochemical techniques.
Al2O3, Cr2O3, and Al2O3-Cr2O3 composite coatings were produced by plasma spraying. Their tribological properties were evaluated at high load conditions. The average friction coefficients, wear rates, and worn surface temperatures of the coating/graphite pairs were measured. Compared with the single coating/graphite pairs, the friction coefficients of composite coating/graphite pairs are more stable. The corresponding wear rates and worn surface temperatures are lower, which may be conducive to the formation of more effective and stable graphite transfer film on the surface of the coating subjected to abrasion. Especially, 10wt.%Al2O3-90wt.%Cr2O3 (AC90) composite coating shows better anti-wear performance, which may be attributed to its higher thermal conduction.
A nanostructured cermet coating consisting of alumina dispersed in a Fe–Cu–Al matrix was deposited by supersonic spraying. The experiments revealed a strong effect of deposition parameters and chemical composition of the powders on the structural characteristics of the Fe–Cu–Al + Al2O3 sprayed cermet. This cermet is made up of complex metallurgical phases as revealed by electron microscopy and X-ray diffraction. The mechanical properties of the different phases detected were determined by nanoindentation. Finally, the friction and wear behavior of this nanostructured sprayed cermet were compared to the ones of benchmark materials. It was found that the Fe–Cu–Al + Al2O3 cermet coating exhibit better tribological properties than the benchmark materials thanks to an appropriate balance of hard and soft phases, and a nanostructuring. The wear mechanism was investigated to establish a ‘structure–property’ relationship for this type of nanostructured cermet coatings.
WC–Co coatings obtained by high velocity oxy fuel spraying (HVOF) are widely used in applications where good abrasion, erosion or sliding wear resistance is required, due to the high toughness that the cobalt matrix provides combined with the wear resistance that the hard carbides give to the coating. The sliding properties of this coating are excellent due to the formation of oxides during the sliding process which act as a solid lubricant and give the coatings low friction coefficients. In the present paper the effect of the counterfaces (Al2O3, hard metal, Si3N4 and martensitic steel) on the friction coefficient and wear damage of the coating in the sliding tests carried out have been studied. For this purpose SEM and atomic force microscopy (AFM) were used to obtain information on the wear mechanisms. Also the results of friction coefficients and wear damage for both the balls and the coating are reported. A relationship between the quantity of debris produced by the counterfaces during sliding and the friction coefficient and wear resistance of the coating was found.
Comparative wear and corrosion properties of Cr3C2-NiCr (CC-TS) (a high-velocity oxyfuel [HVOF]) and hard chromium (HC) coatings obtained on a steel substrate have been studied.
The structural characterization was done before and after measurements by optical microscopy, scanning electron microscopy,
and scanning white light interferometry. Wear and corrosion properties were evaluated by ball on disk (ASTM G99-90), rubber
wheel (ASTM G65-91), and electrochemical measurements of open circuit and polarization curves. The best corrosion and wear
resistance was for the CC-TS obtained by HVOF. The open-circuit potential values measured for both samples after 18 h of immersion
were: −0.240 and −0.550 V, respectively, for CC-TS and HC, versus Ag/AgCl,KClsat. Three orders of magnitude lower volume loss were found for CC-TS (HVOF) after friction tests compared with HC.
The effect of carbon addition on tribological properties of a series of Fe-Al alloys was discussed. The addition of carbon in Fe-Al alloys resulted into the formation of Fe3AlC0.5 or graphite in the matrix, depending on the Al content. The tribological properties of high carbon Fe-Al alloys were compared with those of cast iron. Optical micrographs of the carbon-added Fe-Al alloys after homogenizing treatment were also presented. The addition of carbon was found to be effective in improving the room-temperature tribological properties of Fe-Al alloys, but had negative effect on the tribological properties at elevated temperatures.
It is proposed that a correlation exists between the d state electronic configuration of transition metal based hardmetals and the thermokinetic reactions that take place between binder and hardmetal during sintering.MST/1749
The tribological behavior of Al2O3/TiO2 and WC/Co plasma-sprayed coatings was studied under dry sliding conditions. X-ray photoelectron spectroscopic analyses have shown the presence of graphite in WC/17 wt% Co coatings and a thin WO3 layer in the contact. These phases could explain the improvement in the friction behavior of the cermet/ceramic couples versus the ceramic/ceramic couples.
Materials can be processed by grinding not only for comminution, but also to obtain a variety of structures (amorphous, nanophased), fine mixing of phases, alloys and to directly synthesize compounds such as carbides. Nanocomposites can also be synthesized by reduction, exchange and mixing reactions driven by grinding, as well as by combining the above processes. Large scale economical production of such materials is feasible by grinding in mills designed for that purpose. The mechanical properties of materials are enhanced by the nanophase structure.
Conventional and nanostructured WC–12%Co coatings were deposited on 1Cr18Ni9Ti stainless steel substrate using air plasma spraying. The hardness of the coatings was measured, while their friction and wear behavior sliding against Si3N4 at room temperature and elevated temperatures up to 400 °C was comparatively studied. The microstructures and worn surface morphologies of the coatings were comparatively analyzed as well by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDXA). It was found that the as-sprayed WC–12%Co coatings were composed of WC as the major phase and W2C, WC1−x, and W3Co3C as the minor phases. The plasma sprayed nanostructured WC–12%Co coating had much higher hardness and refined microstructures than the conventional WC–12%Co coating. This largely accounted for the better wear resistance of the nanostructured WC–12%Co coating than the conventional coating. Besides, the two types of WC–12%Co coatings showed minor differences in friction coefficients, though the nanostructured WC–12%Co coating roughly had slightly smaller friction coefficient than the conventional coating under the same sliding condition. Moreover, both the conventional and nanostructured WC–12%Co coatings recorded gradually increased wear rate with increasing temperature, and the nanostructured coating was less sensitive to the temperature rise in terms of the wear resistance. The worn surfaces of the conventional WC–12%Co coating at different sliding conditions showed more severe adhesion, microfracture, and peeling as compared to the nanostructured WC–12%Co coating, which well conformed to the corresponding wear resistance of the two types of coatings. The nanostructured WC–12%Co coating with a wear rate as small as 1.01 × 10−7 mm3/Nm at 400 °C could be promising candidate coating for the surface-modification of some sliding components subject to harsh working conditions involving elevated temperature and corrosive medium.
Mechanical alloying is a method of synthesis of advanced materials, often with non-equilibrium structures, and, remarkably, of crystalline materials with nanometersized grains. Grinding is also a way of inducing or activating chemical reactions. After having described some general characteristics and some applications of high-energy ball-milling, we sketch out some contributions which Mssbauer spectroscopy has made to gaining a deeper understanding of synthesis mechanisms and of mechanosynthesized materials.
Ten WC–Co (12, 17, and 20 wt.% Co) powders manufactured by different techniques (sintering, atomization, coating) were studied. Both open atmosphere Ar–H 2 plasma spraying and controlled atmosphere Ar–He chamber plasma spraying were performed. Pressures of 60, 150, 400, and 700 Torr were employed. To optimize controlled atmosphere spray conditions, particles splatted on glass slides rapidly traversing the jet at different distances from the nozzle exit were studied. The melting conditions were determined as a function of the plasma power level, the particle composition, and structure for particles with the same size distribution. Crystal structure analysis showed a strong decomposition of the carbides when sprayed in open atmosphere. Less decomposition occurred in the coated or atomized particles. The decomposition was reduced and coating density increased by reduced pressure spraying. The best results were obtained at 60 Torr. The hardness depended on the cobalt content, the degree of decomposition and on the density of the coatings.
WC–Co cermets have been used traditionally as wear-resistant materials. Recent work has shown that nanostructured cermets offer improved properties over their conventional counterparts. This work examines the performance of such conventional and nanostructured materials in the form of coatings deposited by high velocity oxy-fuel (HVOF) thermal spraying. WC–Co coatings were deposited under identical conditions using both conventional sintered and crushed and nanocomposite powder feedstocks. Both powders consisted of tungsten carbide (WC) grains in a cobalt binder. Characterisation of the coatings by a range of techniques showed that both coatings not only contained WC but also reaction products such as tungsten hemicarbide (W2C) and W and an amorphous Co-rich binder phase containing W and C. Due to differences in the morphology of the powder feedstock and the WC grain size, the nanocomposite coating contained a smaller fraction of unreacted WC than the conventional coating. Three body abrasive wear tests were performed using a modified dry sand rubber wheel apparatus with alumina and silica abrasives. A range of abrasive particle sizes and loads were used to assess the wear resistance of both coatings. It was found that the nanocomposite had a poorer wear resistance than the conventional coating under all the conditions examined. Wear was dominated by the loss of ductility in the Co-rich binder phase due to its amorphisation. The differences in the wear behaviour of the coatings could, thus, be explained in terms of differences in powder characteristics, the extent of reaction and decarburisation during spraying, and the subsequent development of the microstructure in the coating during splat solidification at high cooling rates.
The plasma spraying of TiC-reinforced wear resistant coatings, and a study of their structure and tribological behaviour are the subject of this paper. HVOF WC-Co coatings, which are well established hard facing coatings, were investigated for comparison with the coatings tested in the present study. Based on scientific criteria, modifications of the carbide and the binder phase of the NiCrTiC system were realised. Strengthening of the NiCr matrix, achieved by alloying the matrix with Fe, Al and Ti, proved to be beneficial for the coating tribological behaviour, as evaluated by pin-on-disk tests. The NiCr-based coatings reinforced with a solid solution (Ti,Ta)C showed better tribological behaviour than the coatings reinforced with just TiC particles. In unlubricated sliding under ambient conditions, the WC-Co coatings showed better tribological behaviour than the TiC-based coatings. The coating structure, wear track, counterbody and debris investigation contributes in better understanding the coating wear performance.
WC–Co hardmetals have been used traditionally as wear resistant materials and a significant body of research has demonstrated that sintered hardmetals with WC particles in the nanoscale range offer improved properties over their conventional counterparts. This work examines the performance of such conventional and nanostructured materials in the form of coatings deposited by high velocity oxy-fuel (HVOF) thermal spraying. WC–Co coatings were deposited using both conventional (sintered and crushed) and nanostructured powder feedstocks. Characterisation of the coatings by a range of techniques showed that both coatings not only contained WC but also reaction products such as W2C and W and an amorphous Co-rich binder phase containing W and C. The nanostructured coating exhibited higher levels of these decomposition products due to the enhanced kinetics of dissolution of the small WC particles into the molten binder during HVOF spraying. The performance of the coatings were examined under sliding wear conditions against an alumina ball and compared with the behaviour of a conventional sintered WC–Co hardmetal. It was found that the nanostructured coating exhibited the highest wear rate of the three materials examined. Microstructural examination showed that wear was dominated by the loss of ductility in the Co-rich binder phase (due to decomposition during spraying) leading to subsurface fracture and the generation of wear debris.
In order to examine the effect of carbide grain size on the wear behavior of WC–Co coatings, coatings with low degree of decomposition of WC were thermally sprayed by a high-velocity oxy-fuel (HVOF) system from three agglomerated WC–12% Co powders with various carbide size distributions. Characterization of the coating showed that the average carbide grain sizes of the coatings were 0.8, 1.4 and 2.8 μm and that a decrease in carbide grain size led to slightly higher degree of decomposition of WC. Dry sliding friction and wear tests using sintered alumina (Al2O3) as the mating material were performed. The coefficient of friction of the coatings was nearly constant regardless of the test conditions and carbide grain sizes. The specific wear rate of the coatings was very low ∼10−6 mm3/(Nm) and increased with increasing carbide grain size. The microscopic analyses of the worn tracks have shown that binder extrusion followed by carbide removal or carbide fracture are the dominant material removal mechanisms. The extruded cobalt acts as binder to form a ductile, dense and well cohered tribofilm on the worn surface to protect the surface from further wear, decreasing the wear rate of the coatings. Because a pull-out of single carbide particle provides less damage to the finer coating and also because the debris consisting of finer carbides are less effective as the third-body abrasions, the wear rate decreases with decreasing carbide size in the coatings.
The sliding wear mechanisms of cemented carbide and the effects of the microstructure scale on the wear resistance were investigated by performing a series of unlubricated sliding wear tests in air with pins of WCCo composites sliding against silicon nitride disks. In the first approximation, the wear rate is proportional to the hardness with a wear coefficient k = 6.9 × 10−6 for all materials. In the conventional cermets, the wear coefficient k also depends on the grain size; materials with smaller WC grains exhibit a smaller wear resistance. This reduction, however, does not extend to the nanostructured materials which exhibit the above value for k: their wear resistance is higher than that of conventional cermets in proportion to their hardness. The data can also be expressed in terms of cobalt content; the lower the cobalt content, the lower the wear; but two different such dependencies exist, one for the conventional and one for the nanostructured materials with lower wear. The sliding wear of WCCo composites occurs on a very small scale: the worn surfaces show no evidence of fracture or plastic deformation. This wear behavior is explained by the hexagonal structure and the anisotropic mechanical behavior of the WC grains that are capable of shear in a limited number of planes but are not capable of triaxial deformation. The higher wear resistance of the nanostructured composites is related to their hardness which decreases the real area of contact.
Nanophase materials can be synthesized by high energy milling. However, processing of large quantities finds a limitation in the devices available commercially, which are usually designed mainly for comminution and for laboratory-scale operations. We propose the design of a high energy, high capacity ball-mill which can be easily scaled up. An experimental device capable of processing up to about 250 g of powders with about 5 kg of balls has been realized. Impact velocities of about 3.5 m s−1 has been measured with operating frequencies of 17 Hz. The synthesis of nanophase iron carbides (assumed as a test system) is shown to be feasible with the new mill, with kinetics comparable with the best obtained in a Spex mill.
Nanostructured and conventional WC–Co coatings were deposited by vacuum plasma spraying. The wear and friction properties of the two coatings against alumina under dry friction conditions were comparatively studied. It was found that the wear resistance of the nanostructured WC–Co coating is superior to that of conventional WC–Co coatings, especially under high load conditions. The improved wear resistance of the nanostructured coating is attributed to its higher hardness and toughness. The wear mechanism of the nanostructured WC–Co coating is plastic deformation with slight surface fracture, whilst that of a conventional WC–Co coating is the initial removal of a binder phase followed by fragmentation or uprooting of carbide grains. Their tribological properties are discussed in relation to the microstructure of the two coatings. It is concluded the decomposition is a fatal factor influencing the wear resistance of thermal sprayed nanostructured WC–Co coatings.
Processing of cermet such as WC–Co is not easy by cold spray deposition, although cold spray process can eliminate the degradation of the WC phase as compared to conventional high velocity oxygen fuel (HVOF) or plasma spraying process. In this study, WC–12%Co powders with nano-sized WC were deposited by cold spray process using helium gas. Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out by SEM and XRD. The results show, as expected, that there is no detrimental phase transformation and/or decarburization of WC by cold spray deposition. It is also observed that nano-sized WC in the feedstock powder is maintained in the cold sprayed coatings. It is demonstrated that it is possible to fabricate the nano-structured WC–Co coatings with low porosity and very high hardness (∼2050 HV) by cold spray deposition with reasonable powder preheating.
A conceptually new simulation system for the laboratory investigation of fretting wear is described. Fretting vibrations are generated either directly by oscillating a linear relative displacement device of constant stroke between the contacting bodies or indirectly by oscillating the applied contact load resulting in a cyclic radial expansion of the contact zone. The principles of both actuation mechanisms are outlined in detail, indicating the precision and performance range of the simulation system. A data acquisition and evaluation strategy has been developed for the on-line characterization of the mechanical contact response. It is based on the measurement of the contact displacement, tangential force and normal load. Typical experimental results obtained under different testing conditions are presented for hard coatings such as TiN and diamond deposited on flat samples and vibrating against corundum counterbody balls.
In this paper we propose a prefetching algorithm called STAP (Spatial and Temporal Association based Prefetching algorithm).
Our methods are based on the analysis of the spatial and temporal associations of the user’s request using data mining techniques.
First, we exploit an ”associative class set” consisting of an itemset of service classes that is close both spatially and
temporally and frequently requested together. With the first method, our prefetching algorithm can select a candidate set
that is spatially and temporally associated with the previous request of a user. It is shown that through performance experiments
STAP is effective in improving system performance.
Nanostructured WC-Co based coatings were investigated. The main focus was given to the effect of Al and Cr addition on their tribological behaviour. These coatings were successfully deposited from engineered nanosized powders using high velocity oxy fuel (HVOF) and atmospheric plasma spraying (APS). Porosity level was < 3%. Crystal sizes of around 20-30 nm determined by TEM in such coatings, confirm the retention of a nanosize after thermal spraying. The nanostructured coatings were tested for their tribological characteristics and compared to industrial micrometre sized WC-Co coatings and common wear resistant engineering materials. It was found that decarburisation of the coating constituents is a critical issue and has a large impact on the tribological behaviour of the coatings. Proper selection of spraying technique, spraying parameters and distribution of phases are shown to be key factors for achieving nanostructured coatings with high wear resistance.
High-velocity oxyfuel (HVOF) spraying of WC-12Co was performed using a feedstock in which the WC phase was either principally in the micron size range (conventional) or was engineered to contain a significant fraction of nanosized grains (multimodal). Three different HVOF systems and a wide range of spray parameter settings were used to study the effect of in-flight particle characteristics on coating properties. A process window with respect to particle temperature was identified for producing coatings with the highest resistance to dry abrasion. Although the use of a feedstock containing a nanosized WC phase produced harder coatings, there was little difference in the abrasion resistance of the best-performing conventional and multimodal coatings. However, there is a potential benefit in using the multimodal feedstock due to higher deposition efficiencies and a larger processing window.
Doctor in de ingenieurswetenschappen Afdeling Chemische Materiaalkunde Departement MTM Faculteit Ingenieurswetenschappen Doctoral thesis Doctoraatsthesis
- A K Basak
- P Matteazzi
- M Vardavoulias
- J.-P Celis
A.K. Basak, P. Matteazzi, M. Vardavoulias, J.-P. Celis, Surf. Coat. Technol. 206
(2012) 3508–3516.
- Giovanni Bolelli
- Roberto Giovanardi
- Luca Lusvarghi
- Tiziano Manfredini
Giovanni Bolelli, Roberto Giovanardi, Luca Lusvarghi, Tiziano Manfredini,
Corros. Sci. 48 (2006) 3375–3397.
- Jianhong He
- Julie M Schoenung
Jianhong He, Julie M. Schoenung, Mater. Sci. Eng. A 336 (1–2) (2002)
274–319.
- C Liu
- A Leyland
- S Lyon
- A Matthews
C. Liu, A. Leyland, S. Lyon, A. Matthews, Surf. Coat. Technol. 76-77 (1995)
615–624.
- C Monticelli
- A Frignani
- F Zucchi
C. Monticelli, A. Frignani, F. Zucchi, Corros. Sci. 46 (2004) 1225–1234.
- A M Human
- H E Exner
A.M. Human, H.E. Exner, Int. J. Ref. Met. Hard Mater. 15 (1997) 65–76.
- V S Saji
- J Thomas
V.S. Saji, J. Thomas, Curr. Sci. 92 (1) (2007) 51–55.
- S P Pednekar
S.P. Pednekar, Corrosion 53 (10) (1997) 813–821.
- C H Hsu
- F Mansfeld
C.H. Hsu, F. Mansfeld, Corrosion 57 (2001) 747–757.
- G C Saha
- T I Khan
- G A Zhang
G.C. Saha, T.I. Khan, G.A. Zhang, Corros. Sci. 53 (6) (2011) 2106–2114.
Thermal Spray 2003: Advancing the Science and Applying the Technology
- J Kawakita
- S Kuroda
- T Fukushima
J. Kawakita, S. Kuroda, T. Fukushima, Thermal Spray 2003: Advancing the
Science and Applying the Technology, in: C. Moreau, B. Marple (Eds.), ASM
International, Materials Park, Ohio, USA, 2003, p. 353.
- A Collazo
- X R Novoa
A. Collazo, X.R. Novoa, C. Pé rez, Electrochim. Acta 44 (1999) 4289–4295.
- R Saengera
- D Martina
- C Gabriellib
R. Saengera, D. Martina, C. Gabriellib, Surf. Coat. Technol. 194 (2005)
335–343.
- V Fervel
- B Normand
- C Coddet
V. Fervel, B. Normand, C. Coddet, Wear 230 (1999) 70–77.
- A Neville
- T Hodgkiess
A. Neville, T. Hodgkiess, J. Am. Ceram. Soc. 62 (8) (1999) 2138–2145.
- J R Macdonald
- W R Kenen
J.R. Macdonald, W.R. Kenen, Impedance Spectroscopy Emphasizing Solid
Materials and Systems, Wiley-Interscience, 1987.
- S F Mertens
- C Xhoffer
- B C De Cooman
- E Temmerman
S.F. Mertens, C. Xhoffer, B.C. De Cooman, E. Temmerman, Corrosion 53 (1997)
381–387.
- Y Xie
- H M Hawthorne
Y. Xie, H.M. Hawthorne, Wear 225 (1999) 90–103.
- S Skale
- V Doleček
- M Slemnik
S. Skale, V. Doleček, M. Slemnik, Corr. Sci. 49 (2007) 1045–1055.
- G O Ilevbare
- J R Scully
G.O. Ilevbare, J.R. Scully, Corrosion 57 (2001) 134–141.
- H.-J Kim
- C.-H Lee
- S.-Y Hwang
H.-J. Kim, C.-H. Lee, S.-Y. Hwang, Mater. Sci. Eng. A 391 (1-2) (2005) 243.
- V Fervel
- B Normand
- H Liao
- C Coddet
- E Beche
- R Berjoan
- J M Guilemany
- J M Miguel
- S Vizcaino
- F Climent
V. Fervel, B. Normand, H. Liao, C. Coddet, E. Beche, R. Berjoan, Surf. Coat. Technol.
111 (1999) 255.
[24] J.M. Guilemany, J.M. Miguel, S. Vizcaino, F. Climent, Surf. Coat. Technol. 140
(2001) 141.
- B R Marple
- R S Lima
B.R. Marple, R.S. Lima, J. Therm. Spray Technol. 14 (1) (2005) 67.
- X Zhao
- H Zhou
- J Chen
X. Zhao, H. Zhou, J. Chen, Mater. Sci. Eng. A 431 (2006) 290.