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Damage-tolerant metallic composites via melt infiltration of additively manufactured preforms
Abstract
A356/316L interpenetrating phase composites were fabricated by infiltrating additively manufactured 316L lattices with molten A356. Measurements of the thermal conductivity of the composites showed an inverse rule-of-mixtures dependence on the 316L volume fraction. Compression tests revealed that the stress-strain response of the composites can be tailored by adjusting both the volume fraction and the topology of the 316L reinforcement. Tension tests on composites with 39 vol% 316L showed a strain to failure of 32%, representing an order of magnitude improvement over the strain to failure of monolithic A356. Inspection of the as-tested tensile specimens suggested that this exceptional damage tolerance is a result of the interpenetrating structure of the constituents. These results together demonstrate that this infiltration processing route avoids problems with intermetallic formation, cracking, and poor resolution that limit current fusion-based additive manufacturing techniques for printing metallic composites.
... PrintCasting is an emerging technology that combines a directed energy (laser or electron beam)based additive manufacturing (AM) approach with conventional metal casting to create composites with metallic constituents [1,2]. This method consists of a two-step processing approach. ...
... superior mechanical properties including a light weight (density < 4 g/cm 3 ), good tensile strength (up to 400MPa), considerable ductility (with strains-to-failure > 30%) and exceptional energy absorption during hypervelocity impact [1][2][3][4][5][6]. ...
... Despite the attractive performance of PrintCast composites, the understanding of the relationship between the lattice design, processing conditions and mechanical properties is inadequate. It has been shown that PrintCast composites can exhibit ductility and energy absorption properties over an order of magnitude greater than the matrix material (as-cast A356) [1]. However, these improvements do not follow a linear relationship with reinforcement (i.e. ...
A356/316 L interpenetrating phase composites can be fabricated by infiltrating additively-manufactured 316 L stainless-steel lattices with a molten A356 aluminum alloy, a new process termed PrintCasting. This work investigates the mechanical properties of PrintCast composites and their relation to the volume-fraction of 316 L reinforcement. Uniaxial tension experiments were conducted with A356/316 L PrintCast composites that had either 30 vol%, 40 vol% or 50 vol% 316 L. When 316 L reinforcement increased from 30 vol% to 40 vol%, a > 200% increase in ductility and 400% increase in absorbed-energy were observed, while a much lower increase was exhibited when reinforcement increased from 40 vol% to 50 vol%. The failure of the 30 vol% sample occurred by localized deformation and a single failure initiation region, in contrast to the 40 vol% and 50 vol% samples which failed by delocalized damage in the entire gauge section. To understand this transition phenomena, digital image correlation (DIC) was coupled with finite element (FE) analysis to capture the deformation and failure processes. The results revealed that, for all samples, stress concentrated and failure initiated in a 316 L strut near the lattice nodes, where the strut underwent localized bending-dominated deformation. In the high 316 L volume-fraction composites, the increase in 316 L-strut diameter reduced local bending stress and stabilized the deformation, leading to improved damage tolerance. Based on the presented analysis, local modifications to the PrintCast structure are suggested.
... In a recent study we demonstrated a two-step approach for fabricating net-shaped metallic composites with tailorable thermal and mechanical properties [1]. First, selective laser melting is used to create a lattice preform that defines the shape of the component and the position of the reinforcement. ...
... We prepared IPCs consisting of 316 L (Fe-18Cr-12Ni-2Mo, wt%) and A356 (Al-7.6Si-0.25Mg-0.2Fe, wt%) following the procedure described in our previous work [1]. First, we fabricated the lattice preform on a Renishaw AM250 selective laser melting system using gas-atomized 316L powder with a particle size distribution between 15 and 45 μm. ...
... The lattice had an initial relative density of 0.43 and body-centered cubic symmetry, with a unit cell size of 2.5 mm. The shape of the lattice preform was the same as that shown in Fig. 1 of Pawlowski et al. [1]. Next, we used centrifugal casting to infiltrate the lattice with molten A356. ...
We have investigated the relationship between structure and thermal conductivity in additively manufactured interpenetrating A356/316L composites. We used X-ray microcomputed tomography to characterize the pore structure in as-fabricated composites, finding microporosity in both constituents as well as a 50 μm thick layer of interfacial porosity separating the constituents. We measured the thermal conductivity of a 43 vol% 316L composite to be 53 Wm⁻¹K⁻¹, which is significantly less than that predicted by a simple rule-of-mixtures approximation, presumably because of the residual porosity. Motivated by these experimental results we used periodic homogenization theory to determine the combined effects of porosity and unit cell structure on the effective thermal conductivity. This analysis showed that in fully dense composites, the topology of the constituents has a weak effect on the thermal conductivity, whereas in composites with interfacial porosity, the size and structure of the unit cell strongly influence the thermal conductivity. We also found that an approximation formula of the strong contrast expansion method gives excellent estimates of the effective thermal conductivity of these composites, providing a powerful tool for designing functionally graded composites and for identifying mesostructures with optimal thermal conductivity values.
... However, limited research has been conducted in this area. Pawlowski et al. [24] conducted a two-step process to fabricate Al-Si (A356) matrix composites reinforced with AM 316L SS lattices. Firstly, they created the AM 316L SS lattices using SLM system. ...
... The improved mechanical properties of the composite can be attributed to the reinforcement provided by the lattice structure of 316L SS. This observation aligns with the findings reported by Pawlowski et al. [24], who investigated the mechanical behavior of Al-Si matrix Fig. 11. True stress-strain curves obtained from Gleeble compression testing at a constant strain rate of 0.001 s − 1 for the 316L lattice structure reinforcement, composite (Al/AM 316L), and pure Al at room temperature. ...
... Materials for IPCs typically adopt metal-ceramic combinations [1][2][3][4][5][6][7][8][9], the most common being Al-Al2O3 composites, as well as metal-metal (e.g. stainless steel/bronze) [10,11], metal-polymer, ceramic-polymer and polymer-polymer pairings (e.g. polystyrene/poly(ether-ester)) [12][13][14][15][16][17][18]. ...
... They are generally fabricated by infiltrating a molten matrix into stochastic foams or 3D printed scaffolds, which serve as the reinforcement phase [5,9] [11]. ...
The elastic modulus of interpenetrating phase composites (IPCs) was analyzed through a theoretical model that accounted for bending deformation of the reinforcement phase. The model was validated against literature data, as well as simulation and experimental results of IPCs that were constructed from 3D-printed polymeric reinforcements embedded in a polydimethylsiloxane (PDMS) matrix. The reinforcements were in the form of Octet Truss and Kelvin Cell lattices, which are known to exhibit very different degrees of bending during elastic deformation. When the matrix modulus was relatively low, the model was able to explain how the bending of reinforcement struts caused the overall IPC modulus to be much lower than those predicted by other theoretical models. As the matrix modulus increased to beyond 20% that of the reinforcement material, however, the different lattice designs were found to have no significant influence on the IPC modulus. Further increase in matrix modulus pushed the elastic response of IPCs towards the isostrain limit, as the matrix helped to distribute the load more evenly and suppress the bending of struts, especially for lower density lattices. The model was able to account for a wide range of different constituent moduli and was also applicable to IPCs which utilized stochastic foams for reinforcement. The insights derived in this study is expected to be particularly useful for designing polymer-based IPCs where the elastic moduli of the reinforcement and matrix can differ over several orders of magnitude.
... These alloys offer low density, minimal thermal expansion, high thermal conductivity, excellent castability, and high corrosion and wear resistance, ensuring durability and longevity in challenging environments. [9][10][11][12] Moreover, in the car industry, there is a requirement to improve the properties of aluminium alloys to make vehicles lighter. It helps to save fuel and reduce emissions. ...
This study investigates the dry sliding wear behaviour of Al–7.6Si–xZr (x = 0.0, 0.1, 0.2, and 0.3) alloys under different applied loads of 19.6 N, 39.2 N, and 58.8 N, aiming to understand the underlying wear mechanism of the alloys. The inclusion of Zr in the Al–7.6Si alloy led to the formation of in situ ZrSi and ZrSi2 compounds, serving as nucleation sites that result in finer and granular α-Al and acicular and fibrous eutectic Si formation. This Zr modification also contributed to improving the alloy’s bulk hardness. Wear test results indicated that the proportion of Zr and wear test loads was important factors influencing the cumulative wear loss (CWL) and coefficient of friction (COF). The wear resistance of the Al–7.6Si–xZr alloys decreased with an increase in the wear test load but increased with an increase in the sliding distance. The primary wear mechanisms were abrasive, adhesive, and oxidative wear, and they exhibited significant variations depending on the concentration of Zr in the alloy. The addition of Zr significantly improved the wear resistance of the Al–7.6Si alloy, and the wear resistance increased as the Zr concentration increased. The wear maps depicted the transitional stages between different wear mechanisms under varying loads and sliding distances.
... Moreover, wear and ballistic resistant IPC materials [12] with enhanced thermal conductivity [13], as well as characteristic failure progression patterns [14] have been engineered through metal-ceramic interpenetrating phase composites [15,16]. What is more, enhanced strength upon reduced specific weight has been achieved through the combination of aluminum-aluminum alloys [17,18] or Al-Si and Al-TiC alloys [19,20]. ...
A hybrid manufacturing process for the fabrication of architected metal-ceramic and metal-metal interpenetrating phase composites (IPCs) is elaborated and employed to assess the mechanical performance of novel, advanced composite materials. In particular, aluminum-based co-continuous composites, reinforced with triply periodic minimal surface (TPMS) steel and ceramic (zirconia) phases are engineered, combining 3D-printing and investment casting techniques. The hybrid process results in excellent wettability between the ceramic-Al and steel-Al phases, characterized through Scanning Electron Microscopy (SEM) and micro-CT scanning analysis. The arising IPCs yield mechanical properties that utterly differ from the performance of the base ceramic or steel TPMS reinforcement topologies, with the ceramic-Al composites to furnish a highly ductile response and steel-Al IPCs a remarkable post-elastic stiffening performance. Ceramic-based IPCs yield a specific energy absorption (SEA) that is more than 400 times higher than the one of single-phase ceramic metamaterials, while steel-based IPCs allow for SEA values in the order of 50 J/g, values which rank among the highest ever reported for architected IPCs. A broader Ashby-type classification is provided, while the efficiency of the IPC plastification process is associated with the obtained SEA values. Moreover, experimental results are complemented by finite element analysis insights in the effect of the interpenetrating phase design on the inner stresses developed. The hybrid manufacturing process and the co-continuous composites investigated open novel pathways in the engineering of next-generation multifunctional architected IPCs for base material combinations beyond the ones here considered.
... Infiltration casting is an effective means of preparing interpenetrating structures with in situ bonded interfaces, which is one of the favorable prerequisites for the formation of metallurgical bonding interface [31,32]. Pawlowski et al. [33] infiltrated liquid A356 into additively manufactured 316L lattice, and obtained A356/316L interpenetrating phase composites. Results showed that the thermodynamic and mechanical properties of the composites can be regulated through changing the content of 316L. ...
... Our scientific interest was sparked by an experiment studying the response of a heterogeneous medium with an adapted interpenetrating mesostructure. This mesostructure was fabricated using the hybrid additive technology known as PrintCast [15][16][17]. The experiment focused on investigating the impact loads that arise during high-velocity interactions, which can be utilized as one of the spacecraft protection options [18]. ...
A series of calculations has been conducted to study the high-speed interaction of space debris (SD) particles with screens of finite thickness. For the first time, taking into account the fracture effects, a numerical solution has been obtained for the problem of high-velocity interaction between SD particles and a volumetrically reinforced penetrating composite screen. The calculations were performed using the REACTOR 3D software package in a three-dimensional setup. To calibrate the material properties of homogeneous screens made of aluminum alloy A356, stainless steel 316L, and multilayer screens, methodical load calculations were carried out. The properties of materials have been verified based on experimental data through systematic calculations of the load on homogeneous screens made of aluminum alloy A356, stainless steel 316L, and multilayer screens comprising a combination of aluminum and steel plates. Several options for the numerical design of heterogeneous screens based on A356 and 316L were considered, including interpenetrating reinforcement with steel inclusions and a gradient distribution of steel throughout the thickness of an aluminum matrix. The study has revealed that the screens constructed as a two-layer composite of A356/316L, volumetrically reinforced composite screens, and heterogeneous screens with a direct gradient distribution of steel in the aluminum matrix provide protection for devices from both a single SD particle and streams of SD particles moving at speeds of up to 6 km/s. SD particles were modeled as spherical particles with a diameter of 1.9 mm made of the aluminum alloy Al2017-T4 with a mass of 10 mg.
... AM is used to form interpenetrating phase composites (IPCs), for instance, where the ability to control geometric features, such as mesoscale phase distribution and interface configuration, influences quasi-static mechanical properties. 1,2 The dynamic response of such novel IPCs with complex internal geometries is of current interest, where, similarly, control of internal mesoscale geometry via AM gives influence over shock response. [3][4][5] This ability to tailor the shock response of IPCs has broad implications for high-performance structural and reactive material applications. ...
In this work, we examine the macroscale and fine-scale shock responses of interpenetrating phase composites comprising a body-centered cubic steel lattice embedded in an aluminum matrix. Through plate impact simulations, we find that the complex mesoscale geometry reduces shock velocity relative to monolithic constituents, slowing and spreading the shock front via reflection and redirection. The periodicity of the mesoscale composite geometry is also reflected by quasi-steady-wave behavior. On the fine-scale, we can predict several aspects of the oscillatory pressure and longitudinal velocity responses by tracking internal wave reflections. We also observe that the post-shock maximum temperature increases with structural openness and temperature hotspots form at interfaces parallel to the shock direction. The findings in this work provide novel structure–property linkages in the dynamic response of architectured interpenetrating phase composites.
... Other SS are also included in the second generation of AHSS, like metastable austenitic and TWIP SS [403][404][405], while the third generation includes medium-Mn TRIP SS and quenching and partitioning (Q&P) SS [406][407][408]. To elaborate interpenetrating multiphase structured materials (Fig. 11(d)) with SS as matrix [409][410][411], reinforcement [412,413,[422][423][424][425][414][415][416][417][418][419][420][421] or coating [426], preform porous structures can be done by PM methods [409,411,419], AM [412,416-418, 420,423], pressing and sintering [410,[413][414][415]422,424], squeeze casting [422], welding of mesh [421], freeze-casting, or replication process, etc. Those preforms will be lately infiltrated with molten alloy by high pressure die casting (HPDC), spring-driven centrifugal casting, capillarity-driven infiltration, vacuum-assisted melt infiltration, etc. Different modelling efforts have been done to study the elastoplastic behaviour and its relationship with different properties and damage evolution of interpenetrating arrangements with SS as matrix or reinforcement [427,428]. ...
The study of heterostructured materials (HSMs) answered one of the most pressing questions in the metallurgical field: “is it possible to greatly increase both the strength and the strain hardening, to avoid the “inevitable” loss of ductility?”. From the synergy between the deformation modes of zones with greatly different flow stress, low stacking fault energy (SFE) alloys can reduce their typical trade-off between strength and ductility. Stainless steel (SS) is a low-SFE material, which is widely applied for structural, biomedical, biosafety, food-processing, and daily applications. The possibility to combine its corrosion resistance and biocompatibility with the outstanding mechanical behaviour of HSMs can convert SS into a promising option for low-cost and high-effective advanced material. This paper reviews all the microstructural aspects of HS SS obtained by different processing methods and their correlation with crystallographic texture and properties such as mechanical, corrosion, biological, and magnetic characteristics. The critical comparison between experimental and modelling findings is also presented in terms of the deformation mechanisms, microstructural and texture features. Thus, the processing-microstructure-properties relationship in HS SS is the focus of this publication. The multi-disciplinary perspectives of HS SS are also discussed. This review paper will serve as a reference for understanding and designing new multi-functional HS SSs.
... [47] These machines have also been used to make composites materials. [42,48] As discussed earlier, these conventional methods have the advantages of being relatively simple and highly scalable. However, they are less effective in controlling the internal architecture of the composites, which is known critical to affect the toughness of a material system. ...
To address the strength–toughness dilemma, various techniques for the preparation of ceramic–metal composites have been proposed. Utilizing stereolithographic additive manufacturing and centrifugal infiltration, a method for the preparation of bio‐inspired ceramic–metal composites is proposed. The proposed method offers flexibility in the design of individual phases of ceramic–metal composites architecturally, with the benefits of scalability and individual phase dimensional control. The versatility of this approach is demonstrated by fabricating silica–aluminum composites with structures inspired by mineralized layers in bivalve mollusk shells, including both 2D prismatic and 3D interpenetrating composites. For composites in compression, the measured specific strength is as high as 169% than that of the base metal (monolithic 6061 aluminum alloy). The highest crack growth toughness of 12.89 MPa m1/2 is recorded. The crack growth sequence shows crack deflection at ceramic–metal interfaces. Based on the tomographic structural analysis of the ceramic parts, the porosity of the green and sintered parts are 9% and 15%, respectively. It is believed that the strength and fracture toughness of these ceramic–metal composites could be further improved if the mechanical properties of the ceramic components can be improved by reducing porosity and structural defects during printing and sintering steps.
... This latticed composite contains two parts, namely the lattice and the matrix, in which another material is filled into the lattice gaps. There is also much research on the microstructure and mechanical properties of bimetallic lattice structures manufactured by SLM, such as CuSn/18Ni300 bimetallic porous structures [47], and A356/316L interpenetrating phase composites [48,49], in which [49] investigated the mechanical properties of PrintCast composites through finite element analysis (FEA), coupled with digital image correlation (DIC) to capture the deformation and failure processes. ...
This study reports fabrication, mechanical characterization, and finite element modeling of a novel lattice structure based bimetallic composite comprising 316L stainless steel and a functional dissolvable aluminum alloy. A net-shaped 316L stainless steel lattice structure composed of diamond unit cells was fabricated by selective laser melting (SLM). The cavities in the lattice structure were then filled through vacuum-assisted melt infiltration to form the bimetallic composite. The bulk aluminum sample was also cast using the same casting parameters for comparison. The compressive and tensile behavior of 316L stainless steel lattice, bulk dissolvable aluminum, and 316L stainless steel/dissolvable aluminum bimetallic composite is studied. Comparison between experimental, finite element analysis (FEA), and digital image correlation (DIC) results are also investigated in this study. There is no notable difference in the tensile behavior of the lattice and bimetallic composite because of the weak bonding in the interface between the two constituents of the bimetallic composite, limiting load transfer from the 316L stainless steel lattice to the dissolvable aluminum matrix. However, the aluminum matrix is vital in the compressive behavior of the bimetallic composite. The dissolvable aluminum showed higher Young’s modulus, yield stress, and ultimate stress than the lattice and composite in both tension and compression tests, but much less elongation. Moreover, FEA and DIC have been demonstrated to be effective and efficient methods to simulate, analyze, and verify the experimental results through juxtaposing curves on the plots and comparing strains of critical points by checking contour plots.
... Additive manufacturing (AM) offers a potential solution to this problem, since it can be used to fabricate complex structures with well-controlled geometries that impart specific, desirable failure behaviors. For example, AM has been used to precisely arrange the spatial distribution of constituents in interpenetrating phase composites [10,11], which enables tailored crack bridging [12] and damage delocalization [13,14]. Additionally, by patterning porosity in a single material, AM has been used to form interpenetrating lattices which extend the range of available mechanical properties beyond those of conventional lattices [15]. ...
This paper introduces the chain lattice, a hierarchical porous structure comprising two interpenetrating cellular solids. One constituent toughens the material and prevents catastrophic localized failure while the other serves as a porous matrix which densifies to absorb energy during tensile loading. Through tension testing, we demonstrate 3D-printed plastic chain lattices that exhibit delocalized damage and an order of magnitude increment in strain-to-failure over the fully dense base material. These experiments validate a micromechanics-based model of tensile specific energy absorption, which we then use in a parametric study on the effects of chain geometry and matrix properties on tensile behavior. We find that ceramic chain lattices can achieve an order of magnitude improvement in tensile specific energy absorption over the fully dense material, in line with the improvement seen when forming monolithic ceramics into fiber-reinforced ceramic matrix composites. The experiments and analysis highlight the ability of the chain lattice to impart damage-tolerance to 3D-printable materials that are normally brittle and flaw-sensitive.
... This explains the extensive research conducted on the fabrication of alloy 316L by laser powder-bed fusion (LPBF), also commonly referred to as selective laser melting (SLM) [9][10][11][12][13][14][15][16][17][18]. LPBF has also created new opportunities for 316L steel in the automotive and aerospace industry with hybrid manufacturing and in the hydrogen industry with new electrolyzer designs [19][20][21]. Significant effort on optimizing the 316L LPBF processing parameters and scan strategies has led to the repeatable fabrication of material >99% dense [11,12,18], and standard fabrication parameters for 316L are typically provided by LPBF machine manufacturers. The suppression of large defects in LPBF 316L material has led to a significant increase in reported ductility [22][23][24][25], with several recent articles highlighting the desirable combination of strength and ductility achievable for LPBF 316L at room temperature [14,16]. ...
316L stainless steel fabricated by laser powder-bed fusion (LPBF) has attracted significant attention due to a unique combination of strength and ductility at room temperature. Understanding of high temperature tensile properties of LPBF fabricated 316L is, however, limited. In the present investigation, tensile testing was conducted at 20–700ºC on LPBF 316L in as printed condition and after annealing for 5 h at 500–800ºC. Room temperature data confirmed the excellent ductility of the LPBF-processed 316L steel due to the cellular structure with high dislocation density. However, a significant decrease in ductility was observed at temperatures above 200ºC. These results are consistent with a change of deformation mechanisms observed in wrought 316L, with twinning playing a key role at room temperature. Microstructure characterization and tensile testing revealed that the cellular structure is stable up to 500ºC, but a decrease of yield strength was observed at temperatures above 600ºC likely due to a decrease in dislocation density via annealing.
... The composites in our previous studies were manufactured through a two-step additive manufacturing process termed PrintCasting, which is fully described in Cordero et al. [4]. Briefly, a lattice preform is fabricated through selective laser melting (SLM) and is infiltrated with a second phase that has a lower melting point than the reinforcement. ...
Recently developed hybrid additive manufacturing techniques can create architectured composites where the constituents are patterned in a periodic array, with a characteristic length scale on the order of several hundred microns. This control over mesostructure can be used to fabricate materials with precisely controlled shock dynamics tailored for a specific response e.g., shielding, munition casing, etc. In the present work, we use hydrocode simulations to determine the structure of planar impacts in periodic two-dimensional composites and to assess their ability to dissipate shock compression. Additionally, localized, geometry-induced wave scattering is related to the bulk dispersive properties of the material.
... Fundamental to all assembled systems, contact mechanics is integral to mechanical design. This is evident in many applications, such as: jointed structures (Brake, 2016), electrical contacts (Ghaednia et al., 2014), thermal contacts (Jackson et al., 2012), collision mechanics (Brake, 2012(Brake, , 2015Ghaednia et al., 2015;Gheadnia et al., 2015;Brake et al., 2017), continum mechanics (Golgoon et al., 2016;Yavari, 2017, 2018), biomechanics (Zhao et al., 2007;Borjali et al., 2017Borjali et al., , 2018Borjali et al., , 2019Langhorn et al., 2018;Mollaeian et al., 2018), turbines (Firrone and Zucca, 2011), additive manufacturing (Kardel et al., 2017;Pawlowski et al., 2017), bearings (Sadeghi et al., 2009), particle and powder interactions (Christoforou et al., 2013;Rathbone et al., 2015), and seals (Green and Etsion, 1985;Miller and Green, 2001) amongst other applications. Contact mechanics can be categorized into both single asperity and rough surface contact, where single asperity models are usually used in rough surface models. ...
Indentation measurements are a crucial technique for measuring mechanical properties. Although several contact models have been developed to relate force-displacement measurements with the mechanical properties, they all consider simplifying assumptions, such as no strain hardening, which significantly affects the predictions. In this study, the effect of bilinear strain hardening on the contact parameters for indentations is investigated. Simulations show that even 1% strain hardening causes significant changes in the contact parameters and contact profile. Pile-up behavior is observed for elastic-perfectly plastic materials, while for strain hardening values greater than 6%, only sink-in (i.e., no pile-up) is seen. These results are used to derive a new, predictive formulation to account for the bilinear strain hardening from elastic-perfectly plastic to purely elastic materials.
... The layered and interpenetrating composites were 7.5 mm thick with 40 vol% 316L. The interpenetrating composite was prepared using PrintCasting [1] and possessed a body centered cubic (BCC) lattice symmetry. The structures of the recovered test specimens were characterized using optical and electron microscopy. ...
Shielding elements used to protect against micrometeoroids and orbital debris (MMOD) (e.g., Whipple shields, multi-shock shields, stuffed Whipple shields) typically incorporate thin bumper sheets that intercept and vaporize incident MMOD traveling at speeds in excess of several km/s. In some applications, however, space limitations prevent the use of large stand-offs, and components must instead be protected by a single monolithic shielding element. Electronics, for example, are often only protected by their housing. With such applications in mind, we describe a class of spatially efficient composite shielding elements fabricated using a hybrid additive manufacturing approach termed PrintCasting. The PrintCast process consists of two steps: First selective laser melting is used to fabricate a lattice preform in the shape of the final component. Next this preform is infiltrated with a liquid metal that has a melting point lower than that of the lattice. The resulting solidified part is a periodic interpenetrating composite in which each constituent forms a continuous network. Using a combination of hypervelocity impact experiments and shock transmission calculations, we demonstrate that these interpenetrating composite shielding elements mitigate spallation and other failure modes through multiple internal shock reflections at the buried heterophase interfaces.
... Instead, these FGMs should be processed using specialized additive manufacturing techniques that suppress intermetallic formation and cracking by avoiding rapid liquid-phase mixing of the constituents. Such processes include solid-phase additive manufacturing techniques, such as ultrasonic additive manufacturing [33], as well as hybrid additive manufacturing techniques, such as PrintCasting [34][35][36], in which a net-shaped additively manufactured preform of one constituent (e.g., stainless steel) is liquid metal infiltrated with a second constituent that has a lower melting point (e.g., an aluminum alloy). ...
Functionally graded metals fabricated using high-temperature additive manufacturing can form intermetallics that fracture during printing due to thermal stresses generated by the heat source. To address this problem, we introduce a new class of non-equilibrium phase diagrams, termed Scheil Ternary Projection (STeP) diagrams, for designing optimal composition gradients that avoid brittle phases. Using the Fe-Cr-Al ternary as a model system, we compare the phase fields in equilibrium and STeP diagrams to show that intermetallic phase fields are dramatically expanded under the rapid solidification conditions in melt-based additive manufacturing, an important effect that must be accounted for when designing composition gradients.
... Two different layered composites were tested: in one composite, the strike face was a 4.5 mm thick A356 layer with a 3 mm thick 316L backing (Fig. 1a); in the other specimen, the layer order was reversed so the strike face was a 3 mm thick 316L layer. The interpenetrating composite was prepared using PrintCasting [13]. A 316L lattice preform was prepared on a Renishaw AM250 selective laser melting (SLM) system using gas-atomized 316L (Fe-18Cr-12Ni-2Mo, wt%) powder feedstock. ...
Shielding elements used to protect against micrometeoroids and orbital debris (MMOD) (e.g., standard and stuffed Whipple shields, multi-shock shields) typically incorporate thin bumper sheets that intercept and vaporize incident MMOD traveling at speeds in excess of several km/s. In some applications, however, space limitations prevent the use of large stand-offs, and components must instead be protected by a single monolithic shielding element. Electronics, for example, are often only protected by their housing. With such applications in mind, we describe a class of spatially efficient composite shielding elements fabricated using a hybrid additive manufacturing approach termed PrintCasting. The PrintCast process consists of two steps: First selective laser melting is used to fabricate a lattice preform in the shape of the final component. Next this preform is infiltrated with a liquid metal that has a melting point lower than that of the lattice. The resulting solidified part is a periodic interpenetrating composite in which each constituent forms a continuous network. Using a combination of hypervelocity impact experiments and shock transmission calculations, we demonstrate that these interpenetrating composite shielding elements mitigate spallation and other failure modes through multiple internal shock reflections at the buried heterophase interfaces.
... However, this kind of approach is limited on resolution and the different compositions in feedstock that can react with each other and form inter-metallics, which further leads to generation of cracks under thermal stress [47,48]. To address this challenge, Pawlowski et al reported a two-step AM approach to overcome the intermetallic formation [49]. First, selective laser melting was used to fabricate a skeleton with the composition. ...
The rapid development in materials science and engineering requests the manufacturing of materials in a more rational and designable manner. Beyond traditional manufacturing techniques, such as casting and coating, digital control of material morphology, composition, and structure represents a highly integrated and versatile approach. Digital manufacturing systems enable users to fabricate freeform materials, which lead to new functionalities and applications. Digital additive manufacturing (AM), which is a layer-by-layer fabrication approach to create three-dimensional (3D) products with complex geometries, is changing the way materials manufacturing is approached in traditional industry. More recently, digital printing of chemically synthesized colloidal nanoparticles has paved the way toward manufacturing a class of designer nanomaterials with properties precisely tailored by the nanoparticles and their interactions down to atomic scales. Despite the tremendous progress being made so far, multiple challenges have prevented the broader applications and impacts of the digital manufacturing technologies. This review features cutting-edge research in the development of some of the most advanced digital manufacturing methods. We focus on outlining major challenges in the field and providing our perspectives on the future research and development directions.
... Contact mechanics is one of the most common problems in mechanical engineering and tribology, with a variety of applications in collision mechanics [3][4][5], joint structures [6,7], electrical contact [8], thermal contact [9], solid mechanics [10][11][12][13], seals and bearings [14], biomechanical systems [15,16], turbines [17], and additive manufacturing [18,19]. The studies in contact mechanics can be categorized into: single asperity spherical, elliptical, cylindrical and flat contacts, with single asperity spherical contact being the most employed one [20][21][22][23][24]. ...
For elastic contact, an exact analytical solution for the stresses and strains within two contacting bodies has been known since the 1880s. Despite this, there is no similar solution for elastic-plastic contact due to the integral nature of plastic deformations, and the few models that do exist develop approximate solutions for the elastic-perfectly plastic material model. In this work, the full transition from elastic-perfectly plastic to elastic materials in contact is studied using a bilinear material model in a finite element environment for a frictionless dry flattening contact. Even though the contact is considered flattening, elastic deformations are allowed to happen on the flat. The real contact radius is found to converge to the elastic contact limit at a tangent modulus of elasticity around 20%. For the contact force, the results show a different trend in which there is a continual variation in forces across the entire range of material models studied. A new formulation has been developed based on the finite element results to predict the deformations, real contact area, and contact force. A second approach has been introduced to calculate the contact force based on the approximation of the Hertzian solution for the elastic deformations on the flat. The proposed formulation is verified for five different materials sets.
... Such design approach can provide reduced material weight and improved mobility for users. Furthermore, additive manufacturing has made sophisticated new composites possible [17,18]. ...
... While these problems may be resolved in the future, for near-term mass production, it is desirable to combine the possibilities and flexibility of AM with faster and scalable production processes like casting. Recent work performed at Oak Ridge National Laboratory (ORNL) and Rice University demonstrates that such hybrid processing schemes are possible and can achieve unique hybrid materials [8] . ...
The ORNL/Rice team proof of concept work has demonstrated how AMIPCs can enable new opportunities in the world of industrial design and materials selection by combining AM with casting technology. In particular, this processing strategy can be used to pattern the components at the sub-millimeter scale, providing exceptional control over microstructure and significant advantages over conventional processing technologies for manufacturing high-performance materials systems. By tuning the local geometry of a part, rather than the chemical composition of each layer, it is possible to reduce the formation of intermetallic phases that are often present in functionally graded materials produced using only fusion-based AM processes, avoiding a major challenge in the creation of functionally graded parts and increasing the potential number of applications of multi-material solutions. Further, while steel and aluminum were chosen for the initial work in AMIPCs, this processing strategy can be extended to many other materials combinations where the components possess dissimilar melting temperatures. In this proof of concept work, the lattice configuration used by the ORNL/Rice team was selected for its simplicity and ease of infiltration. Another opportunity for improving the performance of AMIPCs is shown through recent work in mechanical metamaterials[17], which suggests that the lattice configuration can strongly influence the observed tradeoffs in material properties. Such approaches could be incorporated into the AMIPC manufacturing process, further expanding the range of potential material properties. The authors anticipate several developments in the field of additive manufacturing as AM processes continue to mature. Improved surface finishes realized by using powders with finer sizes will enable finer details in 3D-printed parts as well as in AMIPCs. Further advances in AM will reduce cost and increase throughput and these benefits will extend to AMIPCs as well. AMIPCs have the unique ability to tailor properties of interest in specific locations where required, greatly expanding the variety of parts that may be produced through hybrid materials and manufacturing approaches, integrating additive manufacturing into conventional industries and manufacturing processes.
... Lattice structures have also been used to create locally variable material properties by modifying the relative density of a part and creating site-specific stiffness and yield strength [2,5,11]. This has also been taken one step further to include creation of printed lattice preforms to reinforce cast metal components [12]. ...
Additive manufacturing (AM) of metal components is characterized by the joining of material particles or feedstock to make parts described by 3D model data in typically a layer by layer fashion [1]. These modern and constantly improving manufacturing techniques inherently allow far more geometric freedom than traditional “subtractive” manufacturing processes, and thus necessitate novel approaches to component design. Careful utilization of this geometric freedom can be translated into products characterized by improved functionality and performance, simplified assemblies, are customizable, and/or lightweight [2-5]. This paper provides a brief overview design approaches, manufacturing limitations, and available tools for successful design of additive manufactured components, with special attention paid to the selective laser melting (SLM) approach.
In this paper, bi-continuous interpenetrated porous composites (BIPCs) were prepared with the combination of melt foaming and infiltration casting process. All BIPCs exhibited superior mechanical performance than aluminum foam (AF) and the sum of their components. Among them, 4# BIPC (with 75 struts) showed the highest specific energy absorption which is 2.70 times that of AF, and 3# BIPC (with 48 struts) presented the best improvement in terms of structural strength, while 2# BIPC (with 27 struts) exhibited the largest enhancement of energy absorption. The results indicate that the in situ interface of AF and ordered lattice structure contributes to the enhanced strength of BIPCs, while pores in AF prolongs the stress plateau stage. This research provides a novelty method to solve the trade-off between different mechanical property indicators.
We report a process route to fabricate an Al-Al interpenetrating-phase composite by combining the Al-Mg-Mn-Sc-Zr lattice structure and Al84Ni7Gd6Co3 nanostructured structure. The lattice structure was produced by the selective laser melting and subsequently filled with the Al84Ni7Gd6Co3 amorphous powder, and finally the mixture was used for hot extrusion to produce bulk samples. The results show that the composites achieve a high densification and good interface bonding due to the element diffusion and plastic deformation during hot extrusion. The bulk samples show a heterogeneous structure with a combination of honeycomb lattice structure with an average grain size of less than 1 µm and nanostructured area with a high volume fraction of nanometric intermetallics and nanograin α-Al. The heterogeneous structure leads to a bimodal mechanical zone with hard area and soft area giving rise to high strength and acceptable plasticity, where the compressive yield strength and the compressive plasticity can reach ∼745 MPa and ∼30%, respectively. The high strength can be explained by the rule of mixture, the grain boundary strengthening, and the back stress, while the acceptable plasticity is mainly owing to the confinement effect of the nanostructured area retarding the brittle fracture behavior.
Architected metals and ceramics with nanoscale cellular designs, e.g., nanolattices, are currently subject of extensive investigation. By harnessing extreme material size effects, nanolattices demonstrated classically inaccessible properties at low density, with exceptional potential for superior lightweight materials. This study expands the concept of nanoarchitecture to dense metal/ceramic composites, presenting co-continuous architectures of three-dimensional printed pyrolytic carbon shell reinforcements and electrodeposited nickel matrices. We demonstrate ductile compressive deformability with elongated ultrahigh strength plateaus, resulting in an extremely high combination of compressive strength and strain energy absorption. Simultaneously, property-to-weight ratios outperform those of lightweight nanolattices. Superior to cellular nanoarchitectures, interpenetrating nanocomposites may combine multiple size-dependent characteristics, whether mechanical or functional, which are radically antagonistic in existing materials. This provides a pathway toward previously unobtainable multifunctionality, extending far beyond lightweight structure applications.
Both strain hardening and indenter elastic deformation are unavoidable in most engineering contacts. By the finite element (FE) method, this paper investigates the unloading behavior of elastic-power-law strain hardening half-space frictionlessly indented by elastic sphere for systematic materials. The effect of indenter elasticity on the unloading curve, cavity profile during unloading and residual indentation of strain hardening contact are analyzed. The unloading curve is observed to follow a power-law relationship, whose exponent is sensitive to strain hardening but independent upon indenter elastic deformation. The indenter elasticity hugely affects the residual indentation of strain hardening materials. Based on the power-law relationship of the unloading curve and the expression of the residual indentation fitted from the FE data, an innovative contact unloading law of strain hardening materials considering the indenter elasticity effect is developed. Its suitability is validated numerically and experimentally by strain hardening materials contacted by elastic indenter or rigid flat.
A unique microstructural feature often referred to as “fish-scale” has been reported in 316L austenitic stainless steel parts made by laser powder bed fusion (L-PBF) technique. Because the final microstructure is predominantly austenitic, with a face-centered cubic (γ-fcc) crystal structure, the “fish-scale” structures were originally assumed to be based on etching response due to crystallographic orientations of the solidified γ grains. This research evaluated this assumption through multi-length scale and site-specific characterization using optical microscopy, hardness mapping, X-ray diffraction, electron back-scattered diffraction imaging, and scanning transmission electron microscopy. The nanoscale compositional measurements suggest that the “fish-scale” structures are related to a phase selection phenomenon that occurs during solidification due to spatial and temporal variation of thermal gradients and liquid–solid interface velocity. This phenomenon triggers the transition from γ-fcc to body-centered cubic (bcc) δ-ferrite solidification and then subsequent solid-state phase transformations of this bcc to fcc at low temperature. The significance of these phase transformation pathways with reference to deployment of additively manufactured 316 stainless steel components for harsh environments relevant to power generation is discussed.
This research elucidated the mechanism for the “fish-scale” microstructure evolution in 316L additively manufactured stainless steel builds based on phase selection—either body- or fcc solidification—as a function of spatially varying thermal gradient and liquid–solid interface velocity within a single melt pool based on multi-length scale characterization and computational modeling.
The increasing demand for geometrically complex structures—specifically, higher-inlet-temperature turbine blades for the fifth-generation or other high-generation machines of advanced fighter aircrafts—has made the development of more complex double-walled three-layer hollow-cavity structures a necessity. However, this requires the preparation of complex ceramic cores and advanced, integrated technologies. Stereolithographic three-dimensional printing (SLA-3DP) technology, with digital control upon material morphology, composition, and structure, is a high integration and versatile technique that is superior to the traditional manufacturing techniques for ceramic cores, including gel casting, injection molding, and hot pressing. The latent capacity of this technique is contingent on the progress of processing routes that significantly reduce the distortion and defect formation in response to the elimination of the reacted organic monomer phase during photo-curing. Despite the tremendous progress in the field, multiple challenges remain, such as the preparation of high-solid-content and low-viscosity suspensions, SLA-3DP of large double-walled ceramic cores with complex structures, and process optimization and sinter strengthening for the fabrication of ceramic cores. These challenges have prevented the broader applications and reduced the impact of the SLA-3DP technology. This review discusses cutting-edge research on the crucial factors governing this production method. Specifically, we outline the existing challenges within the field and provide our perspective on the upcoming research work and progress.
Alloy design is an important step in realizing the optimal microstructure in a manufactured metallic component. Attaining the right microstructure distribution within a component is necessary for ensuring mechanical and functional performances that is expected in service. The inspiration for alloy design by empirical experimental observations has always been part of the human evolution. In the modern times, the alloy design methodologies have evolved into materials as system. This system level concept relies on the linkage between process, structure and properties based on data streams from numerical models and characterization. In this article the role of computational thermodynamic and kinetic models to describe process-structure linkages are discussed with a few case studies with specific application to manufacturing.
In this study, Mg17Al12/Al ordered structure composites were prepared by infiltrating the ordered porous aluminum with the intermetallic compound Mg17Al12 under gravity condition. Their compressive properties and energy absorption behavior were investigated by quasi-static compression tests. The results showed that Mg17Al12/Al ordered structure composites exhibited distinctly different compressive stress-strain curves with a prominent linear elastic stage and had an advantage over ordered porous aluminum and Mg17Al12/Al composites with irregular structures on mechanical properties. Moreover, Mg17Al12/Al composites with strengthened truss structure showed better compressive properties than Mg17Al12/Al composites with basic truss structure. The ordered porous aluminum that acted as matrix skeleton showed great plasticity and ductility while the intermetallic compound Mg17Al12 as filler exhibited high compressive strength and obvious brittleness. The improvement of mechanical properties of Mg17Al12/Al ordered structure composites was attributed to the ordered composite structure and the distinct mechanical property of co-continuous intermetallic compound Mg17Al12 and pure Al.
La recherche constante d’allégement de structure et d’optimisation des performances est à l’origine des matériaux hybrides. Ils sont définis comme la combinaison de deux matériaux (ou plus), ou la structuration d’un matériau dans un volume donné, selon une organisation et une échelle prédéterminée en vue de répondre à une application spécifique. De plus, l’essor récent de la fabrication additive permet d’entrevoir une liberté de conception inégalée. Ceci est à l’origine de matériaux hybrides tels que les structures lattices ; il s’agit d’un assemblage de micro-poutres ordonnées ou non visant à remplir un volume donné. Ce travail de thèse porte sur l’élaboration d’un matériau hybride métallique à squelette architecturé optimisé. Dans un premier temps, nous nous intéresserons à l’optimisation du squelette. Pour ce faire un modèle original de génération de structures lattices périodiques inspiré de la cristallographie sera proposé. Il permettra la génération d’une base de données de structures à laquelle seront ajoutées des structures lattices quasipériodiques. Dans un second temps, nous nous intéresserons aux performances de ces structures du point de vue du comportement mécanique et de l’infiltration de réseau poreux par un liquide. Dans les deux cas, des relations phénoménologiques seront déterminées afin de relier la rigidité à la densité relative, ou la remonté d’un front d’infiltration en fonction des caractéristique géométrique d’un squelette. Ces relations, via les paramètres qui les gouvernent, permettent de dégager l’influence de la topologie et donne lieu à des outils de sélection sous forme de cartes 2D. Les étapes de contrôle des structures par tomographie X, d’évaluations des propriétés mécaniques expérimentales et d’infiltration de réseaux poreux, rendent possible la confrontation avec les modèles proposés. Ces différents outils valident la topologie et l’échelle du squelette optimisé du point de vue mécanique et de l’infiltration. Pour finir, des composites associant un alliage d’aluminium et un squelette en Ti- 6Al-4V produit par fusion laser sélective, sont élaborées par creuset froid. Une analyse des porosités et de la métallurgie à l’interface Ti/Al révélera la viabilité du procédé, ainsi que l’influence des conditions d’élaborations sur les microstructures.
The infiltration of aluminum melts into porous metal skeletons produced by powder metallurgy methods, including 3D printing, under a pressure gradient was studied. The densification of compacts made of iron powder with various blowing additions was examined. The minimum pressures at which 35–40% porosity was reached were found to be 150–200 MPa. The use of metal iron shavings allowed a porous skeleton to be formed at a lower pressure (100 MPa). The minimum pore size (400 μm) ensuring complete filling of the porous skeleton with an aluminum melt heated to 760–780°C under a pressure gradient was established. The potential production of iron–aluminum composites without the formation of chemical compounds was shown. A thin discrete layer 5–10 μm thick was observed at the interface between iron and aluminum, where the iron skeleton became saturated with aluminum. This layer provides better adhesion between the iron skeleton and the aluminum melt. The absence of chemical compounds in the Fe–Al system in impregnation conditions is explained by the process kinetics: the components cannot react with each other within several seconds. The effect exerted by the type of porous skeletal structure on the compressive strain of the iron–aluminum composites was established. The greatest compression strength (~400 MPa) was shown by the samples produced from 3D skeletons. The stress–strain curves for the samples with 3D skeletons show two bends: one is in the range 60–70 MPa (beginning of plastic deformation) where strain hardening occurs and strain increases to 20–22% and the other begins at 230–240 MPa and determines the bulk deformation of the samples. The highest yield stress was observed for the samples with shavings-based skeletons (115.2 MPa), which is associated with a high contact surface area of the shaving particles that are randomly intertwined. Accordingly, the lowest characteristics were shown by the samples with skeletons consisting of powder particles with the minimum contact area.
Additive Manufacturing (AM) of metals by the Selective Laser Melting (SLM) process has attracted wide attention in recent years due to its potential to increase specific properties of metals and alloys beyond the capacity of bulk materials. SLM can be used to fabricate cellular lattice 3D structures from a wide variety of metals. This research has applied these structures as the basis for the fabrication of a new type of Interpenetrating Phase Composites (IPCs). IPCs were fabricated by filling titanium cellular lattice structures with hardmetal (WC-Co) powder and subsequent consolidation by Spark Plasma Sintering (SPS). A special attention was drawn on the influence of the interphase between titanium and WC-Co phases. In order to alter the extent of chemical reactions and diffusion during the consolidation process, surface nitriding and carburizing of the titanium lattice were carried out. The present research findings demonstrate that by applying AM, metal - ceramic IPCs can be fabricated. The developed IPCs manifest unconventional mechanical properties such as decreased elastic modulus and high strain values, which have not been observed for hardmetals so far made by conventional means. Under compressive loading ~10% of the deformation was observed in the IPCs before a catastrophic failure. The principal constituents of hardmetals (tungsten carbide and cobalt) are defined by the EU as critical and in the case of cobalt as dangerous to health. Usage of both of these elements will be considerably decreased in wear resistant parts, if standard hardmetal tools are replaced by such novel IPCs.
A metallic hybrid structure, consisting of an Inconel-718 matrix and a Co-Cr internal structure, was successfully manufactured using laser direct energy deposition process. Characterizations were performed using energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), neutron-computed tomography (nCT), and electron back-scatter diffraction (EBSD) to verify the interfaces between Co-rich and Ni-rich phases. nCT revealed the internal structures to be continuous without cracking or significant intermixing due to inter-diffusion of Co and Ni (i.e., dissolved boundaries between the two structures). Minor porosity was detected. EBSD confirmed a good bond at the granular level. No precipitate phases were detected with XRD. EDS revealed dilution/intermixing between the Co and Ni interfaces presumably due to melt-pool overlay between the matrix and the internal structures. © 2018 The Minerals, Metals & Materials Society and ASM International
Complex shaped boron carbide with carbon (B4C/C) at near-full densities were achieved for the first time using negative additive manufacturing techniques via gelcasting. Negative additive manufacturing involves 3D printing of sacrificial molds used for casting negative copies. B4C powder distributions and rheology of suspensions were optimized to successfully cast complex shapes. In addition to demonstrating scalability of these complex geometries, hierarchically meso-porous structures were also shown to be possible from this technique. Resorcinol-Formaldehyde (RF) polymer was selected as the gelling agent and can also pyrolyze into a carbon aerogel network to act as the sintering aid for B4C. Due to the highly effective distribution of in situ carbon for the B4C matrix, near-full sintered density of 97–98% of theoretical maximum density was achieved.
Selective Electron Beam Melting (SEBM) is a promising powder bed Additive Manufacturing technique for near-net-shape manufacture of high-value titanium components. However without post manufacture HIPing the fatigue life of SEBM parts is currently dominated by the presence of porosity. In this study, the size, volume fraction, and spatial distribution of the pores in model samples has been characterised in 3D, using X-ray Computed Tomography, and correlated to the process variables. The average volume fraction of the pores (< 0.2%) was measured to be lower than that usually observed in competing processes, such as selective laser melting, but a strong relationship was found with the different beam strategies used to contour, and infill by hatching, a part section. The majority of pores were found to be small spherical gas pores, concentrated in the infill hatched region; this was attributed to the lower energy density and less focused beam used in the infill strategy allowing less opportunity for gas bubbles to escape the melt pool. Overall, increasing the energy density or focus of the beam was found correlate strongly to a reduction in the level of gas porosity. Rarer irregular shaped pores were mostly located in the contour region and have been attributed to a lack of fusion between powder particles.
It is known that heat treatment causes the spheroidization of eutectic silicon. This paper presents the influence of T6 heat treatment on the microstructures, tensile properties, and fracture behavior of the A356 alloys modified by mischmetal containing La and Ce elements. Microstructural analysis showed that the size of eutectic silicon particles was greatly reduced and the extent of speroidisation of Si particles was remarkably improved for the modified A356 alloys. Comparison between the unmodified and modified alloys suggested that the values of mean diameter, roundness, and aspect ration of eutectic silicon particles were decreased by 48.10–56.85%, 49.55–54.52%, and 13.36–30.17%, respectively. The tensile properties of the modified A356 alloys can be enhanced, especially the ductility. These could be associated with the decrease of secondary dendrite arm spacing, spheroidization of fine eutectic silicon and precipitation hardening. Scanning electron microscopy (SEM) examination indicated that the ductile fracture mechanism was responsible for the modified alloys due to the existence of a couple of fine and uniformly distributed dimples. And the eutectic silicon particles and RE-containing intermetallic compounds provide the weak locations during the fracture process.
Interest in additive manufacturing (AM) has dramatically expanded in the last several years, owing to the paradigm shift that the process provides over conventional manufacturing. Although the vast majority of recent work in AM has focused on three-dimensional printing in polymers, AM techniques for fabricating metal alloys have been available for more than a decade. Here, laser deposition (LD) is used to fabricate multifunctional metal alloys that have a strategically graded composition to alter their mechanical and physical properties. Using the technique in combination with rotational deposition enables fabrication of compositional gradients radially from the center of a sample. A roadmap for developing gradient alloys is presented that uses multi-component phase diagrams as maps for composition selection so as to avoid unwanted phases. Practical applications for the new technology are demonstrated in low-coefficient of thermal expansion radially graded metal inserts for carbon-fiber spacecraft panels.
A developing SLS process, known as Multiple Material Selective Laser Sintering, will allow the material composition of a component to be varied in a controlled manner. This process could allow the fabrication of functionally gradient materials (FGMs) in which a blended interface exists. Two potential applications of FGMs are the reduction of thermal stresses in metal/ceramic joints and the matching of material properties to functional requirements. A tungsten carbide/cobalt system has been examined in which the ceramic/metal ratio has been varied in an attempt to control the hardness/fracture resistance _ratio. An FGM powder bed was manually fabricated using a discrete banding technique. Results of traditional SLS processing of this powder bed are presented.
In modern thermal analysis and design involving thermal transport in solid components it is necessary to apply different modeling of the thermal heat flow in bulk material and across solid surface interfaces either in shape of a layer or a solid-solid interface. Similar differences occur when applying different measurement techniques. Some techniques have been developed specifically for the purpose of performing measurements of bulk properties by removing the influence from thermal contact resistance between the measurement probe and the sample material. Thermal conductivity measurements on metal and ceramic objects of various geometries such as thin bars, thin sheets as well as coatings or layers are here described when using the Transient Plane Source technique. A summary overview of the recent developments of this technique, including its ability to be applied in measurement situations covering a wide range of length and time scales, is also presented. Structural changes in anisotropy can be recorded with high sensitivity by comparative measurements. The technique may be applied in situations requiring non-destructive testing, e.g. samples of particular geometry used for mechanical or tensile testing.
Three-dimensional printing or rapid prototyping are processes by which components are fabricated directly from computer models by selectively curing, depositing or consolidating materials in successive layers. These technologies have traditionally been limited to the fabrication of models suitable for product visualization but, over the past decade, have quickly developed into a new paradigm called additive manufacturing. We are now beginning to see additive manufacturing used for the fabrication of a range of functional end use components. In this review, we briefly discuss the evolution of additive manufacturing from its roots in accelerating product development to its proliferation into a variety of fields. Here, we focus on some of the key technologies that are advancing additive manufacturing and present some state of the art applications.
The influence of casting defects on the room temperature fatigue performance of a Sr-modified A356-T6 casting alloy has been studied using un-notched polished cylindrical specimens. The numbers of cycles to failure of materials with various secondary arm spacings (SDAS) were investigated as a function of stress amplitude, stress ratio, and casting defect size. To produce pore-free samples, HIP-ed and Densal™ treatments were applied prior to the T6 heat treatment. It was observed that casting defects have a detrimental effect on fatigue life by shortening not only the crack propagation period, but also the initiation period. Castings with defects show at least an order of magnitude lower fatigue life compared to defect-free ones. The decrease in fatigue life is directly correlated to the increase of defect size. HIP-ed alloys show much longer fatigue lives compared to non-HIP-ed ones. There seems to exist a critical defect size for fatigue crack initiation, below which fatigue crack initiates from other competing initiators such as eutectic particles and slip bands. A fracture mechanics approach has been used to determine the number of cycles necessary to propagate a fatigue crack from a casting defect to final failure. Fatigue life of castings containing defects can be quantitatively predicted using the size of the defects. Moreover, the fatigue fracture behavior of aluminum castings is well described by Weibull statistics. Crack originating from different defects (such as porosity and oxide films) can be readily identified from the Weibull modulus and the characteristic fatigue life. Compared with oxide films, porosity is more detrimental to fatigue life.
Robotic deposition was used to create an alumina structure with three-dimensional periodicity and submillimeter feature size. Liquid metal infiltration of this structure resulted in an Al2O3–Al interpenetrating-phase composite exhibiting low thermal expansion and high compressive strength.
In this paper, we examine prospects for the manufacture of patient-specific biomedical implants replacing hard tissues (bone), particularly knee and hip stems and large bone (femoral) intramedullary rods, using additive manufacturing (AM) by electron beam melting (EBM). Of particular interest is the fabrication of complex functional (biocompatible) mesh arrays. Mesh elements or unit cells can be divided into different regions in order to use different cell designs in different areas of the component to produce various or continually varying (functionally graded) mesh densities. Numerous design elements have been used to fabricate prototypes by AM using EBM of Ti-6Al-4V powders, where the densities have been compared with the elastic (Young) moduli determined by resonant frequency and damping analysis. Density optimization at the bone-implant interface can allow for bone ingrowth and cementless implant components. Computerized tomography (CT) scans of metal (aluminium alloy) foam have also allowed for the building of Ti-6Al-4V foams by embedding the digital-layered scans in computer-aided design or software models for EBM. Variations in mesh complexity and especially strut (or truss) dimensions alter the cooling and solidification rate, which alters the alpha-phase (hexagonal close-packed) microstructure by creating mixtures of alpha/alpha' (martensite) observed by optical and electron metallography. Microindentation hardness measurements are characteristic of these microstructures and microstructure mixtures (alpha/alpha') and sizes.
In functionally graded materials (FGMs), the elemental composition, or structure, within a component varies gradually as a function of position, allowing for the gradual transition from one alloy to another, and the local tailoring of properties. One method for fabricating FGMs with varying elemental composition is through layer-by-layer directed energy deposition additive manufacturing. This work combines experimental characterization and computational analysis to investigate a material graded from Ti-6Al-4V to Invar 36 (64 wt.% Fe, 36 wt.% Ni). The microstructure, composition, phases, and microhardness were determined as a function of position within the FGM. During the fabrication process, detrimental phases associated with the compositional blending of the Ti-6Al-4V and Invar may form, leading to cracking in the final deposited part. Intermetallic phases (FeTi, Fe2Ti, Ni3Ti, and NiTi2) were experimentally identified to occur throughout the gradient region, and were considered as the reason that the FGM cracked during fabrication. CALPHAD (CALculation of PHase Diagrams) thermodynamic calculations were used concurrently to predict phases that would form during the manufacturing process and were compared to the experimental results. The experimental-computational approach described herein for characterizing FGMs can be used to improve the understanding and design of other FGMs.
A series of Ti-6Al-4V wall structures were additively manufactured (AM) using directed energy deposition (DED) with similar processing parameters and build paths to investigate the role of geometry on the resulting as-deposited microstructure and mechanical properties.While the aggregated tensile strengths (1049 ± 37 MPa), yield strengths (936 ± 43 MPa), and elongations (18 ± 4%) were relatively consistent, a more in-depth statistical analysis revealed statistically significant relationships between the resulting mechanical properties and the orientation with respect to the build direction.Tensile samples with the long dimension parallel to the substrate exhibited a higher average tensile strength than samples with the long dimension perpendicular to the substrate.In addition, the tensile strengths from thick multi pass wall structures were significantly higher than thin single pass wall structures.Finally, the tensile strengths decreased with increasing height above the substrate within the wall structures.Most of the observed differences in mechanical behavior can be attributed to differences observed in the average prior β grain sizes and shapes that impact the amounts of boundary strengthening within the structures.Qualitative differences within the microstructure were observed at different locations within individual and correlated with changes in tensile strength.
Selective electron beam melting (SEBM) belongs to the additive manufacturing technologies which are believed to revolutionise future industrial production. Starting from computer-aided designed data, components are built layer by layer within a powder bed by selectively melting the powder with a high power electron beam. In contrast to selective laser melting (SLM), which can be used for metals, polymers and ceramics, the application field of the electron beam is restricted to metallic components since electric conductivity is required. On the other hand, the electron beam works under vacuum conditions, can be moved at extremely high velocities and a high beam power is available. These features make SEBM especially interesting for the processing of high-performance alloys. The present review describes SEBM with special focus on the relationship between process characteristics, material consolidation and the resulting materials and component properties.
Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.
Many engineering applications, particularly in extreme environments, require components with properties that vary with location in the part. Functionally graded materials (FGMs), which possess gradients in properties such as hardness or density, are a potential solution to address these requirements. The laser-based additive manufacturing process of directed energy deposition (DED) can be used to fabricate metallic parts with a gradient in composition by adjusting the volume fraction of metallic powders delivered to the melt pool as a function of position. As this is a fusion process, secondary phases may develop in the gradient zone during solidification that can result in undesirable properties in the part. This work describes experimental and thermodynamic studies of a component built from 304L stainless steel incrementally graded to Inconel 625. The microstructure, chemistry, phase composition, and microhardness as a function of position were characterized by microscopy, energy dispersive spectroscopy, X-ray diffraction, and microindentation. Particles of secondary phases were found in small amounts within cracks in the gradient zone. These were ascertained to consist of transition metal carbides by experimental results and thermodynamic calculations. The study provides a combined experimental and thermodynamic computational modeling approach toward the fabrication and evaluation of a functionally graded material made by DED additive manufacturing.
This study evaluates the mechanical properties of Ti-6Al-4 V samples produced by selective laser melting (SLM) and electron beam melting (EBM). Different combinations of process parameters with varying energy density levels were utilized to produce samples, which were analyzed for defects and subjected to hardness, tensile, and fatigue tests. In SLM samples, small pores in amounts up to 1 vol.% resulting from an increase in energy density beyond the optimum level were found to have no major detrimental effect on the mechanical properties. However, further increase in the energy density increased the amount of porosity to 5 vol.%, leading to considerable drop in tensile properties. Samples produced using lower-than-optimum energy density exhibited unmelted powder defects, which, even at 1 vol.% level, strongly affected both tensile and fatigue properties. In EBM, insufficient energy input was found to result in large, macroscopic voids, causing serious degradation in all mechanical properties. These findings are helpful in process optimization and standardization of SLM and EBM processes.
This study evaluates the mechanical properties of Ti–6Al–4 V samples produced by selective laser melting (SLM) and electron beam melting (EBM). Different combinations of process parameters with varying energy density levels were utilized to produce samples, which were analyzed for defects and subjected to hardness, tensile, and fatigue tests. In SLM samples, small pores in amounts up to 1 vol.% resulting from an increase in energy density beyond the optimum level were found to have no major detrimental effect on the mechanical properties. However, further increase in the energy density increased the amount of porosity to 5 vol.%, leading to considerable drop in tensile properties. Samples produced using lower-than-optimum energy density exhibited unmelted powder defects, which, even at 1 vol.% level, strongly affected both tensile and fatigue properties. In EBM, insufficient energy input was found to result in large, macroscopic voids, causing serious degradation in all mechanical properties. These findings are helpful in process optimization and standardization of SLM and EBM processes.
Manufacturing businesses aiming to deliver their new customised products more quickly and gain more consumer markets for their products will increasingly employ selective laser sintering/melting (SLS/SLM) for fabricating high quality, low cost, repeatable, and reliable aluminium alloy powdered parts for automotive, aerospace, and aircraft applications. However, aluminium powder is known to be uniquely bedevilled with the tenacious surface oxide film which is difficult to avoid during SLS/SLM processing. The tenacity of the surface oxide film inhibits metallurgical bonding across the layers during SLS/SLM processing and this consequently leads to initiation of spheroidisation by Marangoni convection. Due to the paucity of publications on SLS/SLM processing of aluminium alloy powders, we review the current state of research and progress from different perspectives of the SLS/SLM, powder metallurgy (P/M) sintering, and pulsed electric current sintering (PECS) of ferrous, non-ferrous alloys, and composite powders as well as laser welding of aluminium alloys in order to provide a basis for follow-on- research that leads to the development of high productivity, SLS/SLM processing of aluminium alloy powders. Moreover, both P/M sintering and PECS of aluminium alloys are evaluated and related to the SLS process with a view to gaining useful insights especially in the aspects of liquid phase sintering (LPS) of aluminium alloys; application of LPS to SLS process; alloying effect in disrupting the surface oxide film of aluminium alloys; and designing of aluminium alloy suitable for the SLS/SLM process. Thereafter, SLS/SLM parameters, powder properties, and different types of lasers with their effects on the processing and densification of aluminium alloys are considered. The microstructure and metallurgical defects associated with SLS/SLM processed parts are also elucidated by highlighting the mechanism of their formation, the main influencing factors, and the remedial measures. Mechanical properties such as hardness, tensile, and fatigue strength of SLS/SLM processed parts are reported. The final part of this paper summarises findings from this review and outlines the trend for future research in the SLS/SLM processing of aluminium alloy powders.
Unlike conventional materials removal methods, additive manufacturing (AM) is based on a novel materials incremental manufacturing philosophy. Additive manufacturing implies layer by layer shaping and consolidation of powder feedstock to arbitrary configurations, normally using a computer controlled laser. The current development focus of AM is to produce complex shaped functional metallic components, including metals, alloys and metal matrix composites (MMCs), to meet demanding requirements from aerospace, defence, automotive and biomedical industries. Laser sintering (LS), laser melting (LM) and laser metal deposition (LMD) are presently regarded as the three most versatile AM processes. Laser based AM processes generally have a complex non-equilibrium physical and chemical metallurgical nature, which is material and process dependent. The influence of material characteristics and processing conditions on metallurgical mechanisms and resultant microstructural and mechanical properties of AM processed components needs to be clarified. The present review initially defines LS/LM/LMD processes and operative consolidation mechanisms for metallic components. Powder materials used for AM, in the categories of pure metal powder, prealloyed powder and multicomponent metals/alloys/MMCs powder, and associated densification mechanisms during AM are addressed. An in depth review is then presented of material and process aspects of AM, including physical aspects of materials for AM and microstructural and mechanical properties of AM processed components. The overall objective is to establish a relationship between material, process, and metallurgical mechanism for laser based AM of metallic components. © 2012 Institute of Materials, Minerals and Mining and ASM International.
The current work provides an overview of the state-of-the-art in polymer and metal additive manufacturing and provides a progress report on the science and technology behind gradient metal alloys produced through laser deposition. The research discusses a road map for creating
gradient metals using additive manufacturing, demonstrates basic science results obtainable through the methodology, shows examples of prototype gradient hardware, and suggests that Compositionally Graded Metals is an emerging field of metallurgy research.
In order to produce serial parts via additive layer manufacturing, the fatigue performance can be a critical attribute. In this paper, the microstructure, high cycle fatigue (HCF), and fracture behavior of additive manufactured AlSi10Mg samples are investigated. The samples were manufactured by a particular powder-bed process called Selective Laser Melting (SLM) and machined afterwards. 91 samples were manufactured without (30 °C) and with heating (300 °C) of the building platform and in different directions (0°, 45°, 90°). Samples were tested in the peak-hardened (T6) and as-built condition. The Wöhler curves were interpolated by a Weibull distribution. The results were analysed statistically by design of experiments, correlation analysis, and marginal means plots. The investigations show that the post heat treatment has the most considerable effect and the building direction has the least considerable effect on the fatigue resistance. The fatigue resistance of the samples, however, is high in comparison to the standard DIN EN 1706. The combination of 300 °C platform heating and peak-hardening is a valuable approach to increase the fatigue resistance and neutralize the differences in fatigue life for the 0°, 45°, and 90° directions.
This paper presents a thorough literature review of the powder-based electron beam additive manufacturing (EBAM) technology. EBAM, a relatively new additive manufacturing (AM) process, can produce full-density metallic parts directly from the electronic data of the designed part geometry. EBAM has gained broad attentions from different industries such as aerospace and biomedical, with great potential in a variety of applications. The paper first introduces the general aspects of EBAM. The unique characteristics, advantages and challenges of EBAM are then presented. Moreover, the hub of this paper includes extensive discussions of microstructures, mechanical properties, geometric attributes, which impact the application ranges of EBAM parts, with focus on commonly used titanium alloys (in particular, Ti-6Al-4V). In the end, modeling work of the EBAM process is discussed as well.
Selective laser melting, as a facile method, was successfully used in this paper to manufacture perfect Ti6Al4V parts. Based on a series of single tracks, the processing windows were firstly proposed, corresponding to different melting mechanisms. And selective laser melted Ti6Al4V parts using various parameters within the processing map were investigated in terms of microstructure, roughness, densification and microhardness. It was found that the microstructure, roughness, densification and microhardness of Ti6Al4V parts were a strong function of processing parameters. An excellent Ti6Al4V part with the high microhardness and the smooth surface can be manufactured by selective laser melting using preferable laser power 110 W and scanning speed 0.4 m/s, corresponding to continuous melting mechanism. The density is so high that it can be comparable to that of bulk Ti6Al4V alloy.
The principal difficulty in fabricating 3-3 composites is in controlling the connectivity and spatial distribution of two or more component phases. Fabrication of 3-3 mullite�Al or alumina�Al composites via fused depostion (FD) has several inherent advantages over some of the other approaches for processing similar composites. Using FD processes not only can the shape or macrostructure of the part be controlled via CAD, but also the microstructure. This approach can help to design and develop an optimal microstructure for any specific application.
The rapid manufacturing process of selective laser melting has been used to produce a series of stainless steel 316L microlattice structures. Laser power and laser exposure time are the two processing parameters used for manufacturing the lattice structures and, therefore, control the quality and mechanical properties of microlattice parts. An evaluation of the lattice material was undertaken by manufacturing a range of struts, representative of the individual trusses of the microlattices, as well as, microlattice block structures. Low laser powers were shown to result in significantly lower strand strengths due to the presence of inclusions of unmelted powder in the strut cross-sections. Higher laser powers resulted in struts that were near to full density as the measured strengths were comparable to the bulk 316L values. Uniaxial compression tests on microlattice blocks highlighted the effect of manufacturing parameters on the mechanical properties of these structures and a linear relationship was found between the plateau stress and elastic modulus relative to the measured relative density.
Interpenetrating composites are created by infiltration of liquid aluminum into three-dimensional (3-D) periodic Al2O3 preforms with simple tetragonal symmetry produced by direct-write assembly. Volume-averaged lattice strains in the Al2O3 phase of the composite are measured by synchrotron X-ray diffraction for various uniaxial compression stresses up to −350MPa. Load transfer, found by diffraction to occur from the metal phase to the ceramic phase, is in general agreement with simple rule-of-mixture models and in better agreement with more complex, 3-D finite-element models that account for metal plasticity and details of the geometry of both phases. Spatially resolved diffraction measurements show variations in load transfer at two different positions within the composite.
The fracture toughness properties of two interpenetrating phase composites (IPCs)—a bronze-infiltrated porous 420 stainless steel and a polymer resin-impregnated porous 316L stainless steel—have been measured using ASTM Standard E 813-89. Both IPCs exhibited stable crack growth at all volume fractions, resulting from an increase in toughness with crack growth (R-curve behaviour). Initiation toughness, JIc, increased and R-curve behaviour became more pronounced with increasing volume fraction of the more ductile constituent phase. R-curve behaviour is attributed to the mechanisms of crack bridging and unloading in the wake of a process zone, which is characterized by secondary cracking and plasticity. The importance of an interpenetrating phase morphology is dependent upon the combination of materials, but it appears that interconnecting the more ductile phase will result in increased toughness, particularly if this is the stronger and stiffer phase. The application of ASTM Standard E 813-89 to the IPCs investigated was found to result in a large number of validity criterion failures. The implications of these failures are discussed.
The effect of microporosity on the tensile properties of A356 alloy was investigated through systematic experimental approaches, with a consti-tutive prediction that takes into account the strain rate sensitivity and strain-hardening exponent. The strain rate sensitivity was measured through the incremental strain rate change method, and the volumetric porosity and fractographic porosity were obtained from the measurements of bulk density and the quantitative fractography analyses on the fractured surface, respectively. The UTS and elongation exhibit a strong dependence upon the variation in microporosity, with a linear and inverse parabolic relationship, respectively. The constitutive prediction based on the fracto-graphic rather than the volumetric porosity can more accurately predict the overall tensile properties of A356 alloy. The constitutive model should necessarily take into account the strain rate sensitivity and strain-hardening exponent for an exact theoretical prediction of the tensile properties.
A comprehensive methodology that takes into account solidification, shrinkage-driven interdendritic fluid flow, hydrogen precipitation,
and porosity evolution has been developed for the prediction of the microporosity fraction and distribution in aluminum alloy
castings. The approach may be used to determine the extent of gas and shrinkage porosity, i.e., the resultant microporosity which occurs due to gas precipitation and that which occurs when solidification shrinkage cannot
be compensated for by the interdendritic fluid flow. A solution algorithm in which the local pressure and microporosity are
coupled is presented, and details of the implementation methodology are provided. The models are implemented in a computational
framework consistent with that of commonly used algorithms for fluid dynamics, allowing a straightforward incorporation into
existing commercial software. The results show that the effect of microporosity on the interdendritic fluid flow cannot be
neglected. The predictions of porosity profiles are validated by comparison with independent experimental measurements by
other researchers on aluminum A356 alloy test castings designed to capture a variety of solidification conditions. The numerical
results reproduce the characteristic microporosity profiles observed in the experimental results and also agree quantitatively
with the experimentally measured porosity levels. The approach provides an enhanced capability for the design of structural
castings.
The general theory of the transient plane source (TPS) technique is outlined in some details with approximations for the two experimental arrangements that may be referred to as ‘‘hot square’’ and ‘‘hot disk.’’ Experimental arrangements and measurements on two materials, Cecorite 130P and Corning 9606 Pyroceram, using a hot disk configuration, are reported and assessed.
Laser assisted direct metal deposition refers to the additive layered manufacturing technology for building components from a computer-aided design (CAD) model. A motion control program is used to control the motion of a laser focal spot to trace all areas of the part, typically a planar layer at a time. Metal powders, injected into the laser focal zone, are melted and then re-solidify into fully dense metal in the wake of the moving molten pool created by the laser beam. The practical considerations and capabilities of the laser assisted directed metal deposition are further explored.
Brittle solids can be toughened by incorporating ductile inclusions into them. The inclusions bridge the crack and are stretched as the crack opens, absorbing energy which contributes to the toughness. To calculate the contribution to the toughness it is necessary to know the force-displacement curve for an inclusion, constrained (as it is) by the stiff, brittle matrix. Measured force-displacement curves for highly constrained metal wires are described and related to the unconstrained properties of the wire. The constraint was achieved by bonding the wire into a thick-walled glass capillary, which was then cracked in a plane normal to the axis of the wire and tested in tension. Constraint factors as high as 6 were found, but a lesser constraint gives a larger contribution to the toughness. The diameter of the wires (or of the inclusions) plays an important role. Simple, approximate, models for the failure of the wires are developed. The results allow the contribution of ductile particles to the toughness of a brittle matrix composite to be calculated.
The use of rapid prototyping (RP) technology for rapid tooling and rapid manufacturing has given rise to the development of application-oriented composites. The present paper furnishes succinct notes of the composites formed using main rapid prototyping processes such as Selective Laser Sintering/Melting, Laser Engineered Net Shaping, Laminated Object Manufacturing, Stereolithography, Fused Deposition Modeling, Three Dimensional Printing and Ultrasonic Consolidation. The emphasis of the present work is on the methodology of composite formation and the reporting of various materials used.
Crack-free functionally graded TiC/Ti composite materials were fabricated by laser engineered net shaping (LENS), with compositions changing from pure Ti to approximately 95 vol% TiC. By delivering the constituent materials from different powder feeders and through process control, the LENS process can be used for the fabrication of functionally graded materials.
Compositionally graded binary titanium–vanadium and titanium–molybdenum alloys have been deposited using the laser engineered net-shaping (LENS™) process. A compositional gradient, from elemental Ti to Ti–25at.% V or Ti–25at.% Mo, has been achieved within a length of ∼25 mm. The feedstock used for depositing the graded alloy consists of elemental Ti and V (or Mo) powders. Though the microstructural features across the graded alloy correspond to those typically observed in α/β Ti alloys, the scale of the features is refined in a number of cases. Microhardness measurements across the graded samples exhibit an increase in hardness with increasing alloying content up to a composition of ∼12% in case of Ti–xV and up to a composition of ∼10% in case of the Ti–xMo alloys. Further increase in the alloying content resulted in a decrease in hardness for both the Ti–xV as well as the Ti–xMo alloys. A notable feature of these graded deposits is the large prior β grain size resulting from the directionally solidified nature of the microstructure. Thus, grains ∼10 mm in length grows in a direction perpendicular to the substrate. The ability to achieve such substantial changes in composition across rather limited length makes this process a highly attractive candidate for combinatorial materials science studies.
The microstructure and mechanical behavior of simple product geometries produced by layered manufacturing using the electron beam melting (EBM) process and the selective laser melting (SLM) process are compared with those characteristic of conventional wrought and cast products of Ti-6Al-4V. Microstructures are characterized utilizing optical metallography (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and included alpha (hcp), beta (bcc) and alpha(') (hcp) martensite phase regimes which give rise to hardness variations ranging from HRC 37 to 57 and tensile strengths ranging from 0.9 to 1.45 GPa. The advantages and disadvantages of layered manufacturing utilizing initial powders in custom building of biomedical components by EBM and SLM in contrast to conventional manufacturing from Ti-6Al-4V wrought bar stock are discussed.
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