As-printed Samples Research Articles

On the Grain Microstructure–Mechanical Properties Relationships in Aluminium Alloy Parts Fabricated by Laser Powder Bed Fusion

Recent years witnessed progressive broadening of the practical use of 3D-printed aluminium alloy parts, in particular for specific aerospace applications where weight saving is of great importance. Selective laser melting (SLM) is an intrinsically multi-parametric fabrication technology that offers multiple means of controlling mechanical properties (elastic moduli, yield strength, and ductility) through the control over grains size, shape, and orientation. Targeted control over mechanical properties is achieved through the tuning of 3D-printing parameters and may even obviate the need of heat treatment or mechanical post-processing. Systematic studies of grain structure for different printing orientations with the help of EBSD techniques in combination with mechanical testing at different dimensional levels are the necessary first steps to implement this agenda. Samples of 3D-printable Al-Mg-Si RS-333 alloy were fabricated in three orientations with respect to the principal build direction and the fast laser beam scanning direction. Sample structure and proper-ties were investigated using a number of techniques, including EBSD, in situ SEM tensile testing, roughness measurements, and nanoindentation. The as-printed samples were found to display strong variation in Young’s modulus values from nanoindentation (from 43 to 66 GPa) and tensile tests (from 54 to 75 GPa), yield stress and ultimate tensile strength (100–195 and 130–220 MPa) in different printing orientations, and almost constant hardness of about 0.8 GPa. A further preliminary study was conducted to assess the effect of surface finishing on the mechanical performance. Surface polishing was seen to reduce Young’s modulus and yield strength but improves ductility, whereas the influence of sandblasting was found to be more controversial. The experimental results are discussed in connection with the grain morphology and orientation.

Fabricating Homogeneous FeCoCrNi High-Entropy Alloys via SLM In Situ Alloying

Selective laser melting (SLM) in situ alloying is an effective way to design and fabricate novel materials in which the elemental powder is adopted as the raw material and micro-areas of elemental powder blend are alloyed synchronously in the forming process of selective laser melting (SLM). The pre-alloying process of preparation of raw material powder can be left out, and a batch of bulk samples can be prepared via the technology combined with quantitative powder mixing and feeding. The technique can be applied to high-throughput sample preparation to efficiently obtain a microstructure and performance data for material design. In the present work, bulk equiatomic FeCoCrNi high-entropy alloys with different processing parameters were fabricated via laser in situ alloying. Finite element simulation and CALPHAD calculation were used to determine the appropriate SLM and post-heating parameters. SEM (scanning electron microscope), EDS (energy dispersive spectroscopy), XRD (X-ray diffraction), and mechanical testing were used to characterize the composition, microstructure, and mechanical properties of as-printed and post-heat-treated samples. The experimental results show that the composition deviation of laser in situ alloying samples could be controlled within 20 wt %. The crystal structure of as-printed samples is a single-phase face-centered cubic (FCC), which is the same as those prepared by the traditional method. The mechanical properties of the samples prepared by laser in situ alloying with elemental powder blend are comparable to those prepared by pre-alloying powder and much higher than those prepared by the traditional method (arc melting). As-printed samples can get a homogeneous microstructure under the optimal laser in situ alloying process combined with post-heat treatment at 1200 °C for 20 h.

Compositionally graded joints between magnetically dissimilar alloys achieved through directed energy deposition

Compositionally graded cylinders comprising FeCo-2V, a soft magnetic alloy, and 316L stainless steel, were produced by directed energy deposition incorporating two different gradient lengths. Five distinct regions in the microstructure were observed in both the as-printed and annealed gradients. When normalized for the gradient length, the gradients showed similar grain size and microhardness profiles. In tensile tests, the as-printed samples failed in the 316L region with an effective total “composite” strain of 20-30% and overall strength approaching that of wrought 316L. The annealed samples failed in the FeCo-2V region. Neither exhibited failure in the gradient region. Molecular dynamics simulations were used to calculate tensile strength as a function of composition, showing good correlation to experimental trends but not absolute values. This work demonstrates the tunability of site-specific properties using blown powder directed energy deposition to gradually grade from FeCo-2V to 316L stainless steel in a monolithic component.

Additive manufacturing of TRIP-assisted dual-phases Fe50Mn30Co10Cr10 high-entropy alloy: Microstructure evolution, mechanical properties and deformation mechanisms

Abstract The metastable dual-phase non-equiatomic Fe50Mn30Co10Cr10 high entropy alloy (HEA) was successfully prepared via laser melting deposition (LMD) technique. The phase composition, microstructure and mechanical performance were systematically characterized at different sections of LMDed HEA samples. The as-printed HEA specimens were dominated by FCC γ phase, plate and needle-like HCP e phase, and high density stacking faults and dislocations were observed at high magnification. The as-printed samples exhibited anisotropic mechanical properties, together with the maximum ultimate tensile strength of 760 MPa and maximum elongation of 28%. The fracture surface along X and Z directions exhibit smooth curve shape, while the fracture surface along Y direction shows saw tooth shape, indicating the boundary of melt pool is weakly bounded. After deformation, the deformation bands were observed in the FCC matrix, showing that the plastic strain was controlled by FCC γ phase. In addition, stacking faults, dislocation increase significantly owing to the formation of stacking fault is caused by sliding of Shockeley partial dislocation, and the stacking fault is the core of HCP martensite nucleation.

Additive manufacturing of high strength near β titanium alloy Ti-55511 by engineering nanoscale secondary α laths via in-situ heat treatment

In addition to the great merits of producing three-dimensional complex components from metallic powders in additive manufactured parts, the microstructural features can be tailored by the intrinsic heat treatment (IHT), i.e., cyclic re-heating without any additional post-treatment of the printed samples. Here we report that the microstructural configurations can be widely manipulated in an additive manufactured Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) near β titanium alloy, with an emphasis on the effect of IHT on the in-situ precipitation of α phase. The typical as-printed samples consist of prior-β grains, coarse primary α (α I ) colony and nanoscale secondary α (α II ) laths. Based on automatic quantitative image analysis, the increase of substrate temperature has a remarkable impact on accelerating the precipitation of nanoscale α II laths, while suppressing the precipitation kinetics of the primary α colony, and the corresponding volume fraction of α II laths increases from only 2% to more than 40%, resulting in a tensile strength increment from 900 MPa to 1200 MPa. The enhanced strength derives from those extremely fine α II laths in terms of boundary strengthening. The findings in this work provide a strategy of strengthening additively manufactured components by taking advantage of one step intrinsic heat treatment.

Effects of post-printing heat treatment on the microstructure and mechanical properties of a wire arc additive manufactured 420 martensitic stainless steel part

Abstract In this study, microstructural features and mechanical properties of a wire arc additively manufactured 420 martensitic stainless steel were investigated in as-printed and heat-treated conditions. Initial microstructural investigations on the as-printed part revealed the formation of residual δ-ferrite during the solidification process, which is known as a deleterious phase to both mechanical and corrosion performance of stainless steels. To remove the residual δ-ferrite and obtain a fully martensitic microstructure, the as-printed samples were subjected to different austenitizing temperatures of 950, 1050, 1150, and 1300 °C. Austenitizing at 1150 °C was selected as the optimum cycle due to removal of undesirable phases, such as δ-ferrite and carbides, resulting in a fully martensitic microstructure. Following the austenitizing heat treatment, the samples were tempered at different temperatures including 200, 300, 400, 500, and 600 °C. Increasing the tempering temperature was found to vary the size, morphology, and distribution of chromium carbides precipitated during the tempering process. Although, tempering at lower temperatures (200 and 300 °C) decreased the hardness due to the formation of tempered martensite and stress relieving of the structure, the intermediate temperature of 400 °C increased the hardness value by virtue of the formation of carbides at optimum size and distribution. However, tempering at 500 and 600 °C decreased the hardness as compared to 400 °C due to intergranular segregation and coarsening of carbides. The results of uniaxial tensile testing were consistent with the hardness measurements and confirmed that the tempering temperature of 400 °C led to the optimal combination of strength and ductility ascribed to the formation of fine and homogenously distributed chromium carbides embedded in a moderately tempered martensitic matrix.

Deformation and fracture behavior of a laser powder bed fusion processed stainless steel: In situ synchrotron x-ray computed microtomography study

Tensile plastic deformation and fracture behavior of a laser powder bed fusion processed 316L stainless steel alloy was investigated in situ using high-resolution synchrotron x-ray computed microtomography (sXCT). Three different cases were studied: (1) specimen A1, near full-density with initial porosity of 0.04%, (2) specimen B1, initial lack-of-fusion (LOF) porosity of about 3% with the major axis of defects aligned nearly perpendicular to the tensile loading direction (LD), and (3) specimen B, similar to B1 but with the major axis of LOF defects aligned nearly parallel to LD. The effects of type, density, and orientation of defects in as-printed samples on plastic deformation and failure modes were studied by analyzing sXCT image sequences and quantitative defect properties. Specifically, the evolutions of porosity, size, aspect ratio, and angle of gas pores and LOF defects were characterized as a function of applied strain. Moreover, interactions between as-printed defects and deformation-induced crack propagation were investigated. The tensile behavior of specimen A1 was comparable to that of a commercial wrought plate. The quantitative in-situ sXCT results showed a void-growth phenomenon in A1 but without noticeable coalescence, resulting in a ductile cup-cone failure. Specimen B1 showed damage-driven brittle failure with limited plasticity due to early and rapid propagation of open voids. On the other hand, specimen B, with a similar amount of LOF defects as B1, showed deceivingly strong and ductile tensile behavior similar to A1 without any major crack propagations due to the favorable orientation relationship between LOF defects and the LD.

Effect of heat treatment on microstructural evolution and properties of cemented carbides (WC-17Co) reinforced with 3% volume hexagonal-boron nitride (h-BN) and processed by selective laser sintering (SLS)

In the manufacturing and mining industries, cemented carbides (WC-Co) are desired due to their extraordinary properties such as high strength, good wear resistance and high fracture toughness. Moreover, due to design limitations, such as intricate shapes of parts manufactured using conventional powder metallurgy, metal-3D printing is being sought after for better processing and fabrication of parts with complex shapes and geometries. In this study, a cemented carbide (WC-Co) reinforced with 3% Hexagonal-Boron Nitride (h-BN) was processed using selective laser sintering and heat treated to understand the effect of the elemental composition and post-processing heat treatment on the microstructural evolution and mechanical integrity of processed parts. Generally, the as-printed WC-Co-hBN sample had distinct polyangular WC carbides with sizes between 8 μm to 18 μm, W-C-Co matrix and large areas of fused eta phases (40% area fraction). X-ray diffraction analysis revealed that beside the major hexagonal WC phases, the h-BN breaks down to form minor phases such as CoWB, Co5.47N together with W3Co3C, W3Co3N, W9Co3C4 phases. Post-processing heat treatment at 400 °C resulted in the evolution of well-defined WC carbides and eta phases including reduced W-C-Co matrix when compared with the as-printed samples. X-ray diffraction analysis showed the disappearance of the W3Co3N and W3Co3C4 phases coupled coalescence and coarsening of the WC phases and the minor W9Co3C4, CoWB and Co5.47N phases. However, post-processing at 600 °C resulted in the breakdown of the coarsened WC carbides (~10 μm to 12 μm), evolution of more eta phases (63% area fraction) and more W3Co3C phases when compared with the as-printed sample. Nevertheless, post-processing at 800 °C resulted in extensive depletion of the W-C-Co matrix and the growth of irregular WC carbides and eta phases. At 1000 °C, the relative sizes of the WC carbides were smaller but well-defined and closely packed including large volume fractions of the eta phase when compared with the samples at 800 °C. Also, the h-BN phase appeared, for the first time, in this sample with high characteristic peaks. An inverse correlation was observed with the heat treatment on the residual stresses. Thus, the heat treatment aided in relieving the residual stresses in the heat-treated samples. The as-printed sample recorded the highest average hardness value of 4200 HV which is approximately 200% higher than the SLS printed WC-17Co. The as-printed sample had the highest fracture toughness (7.5 MPa√m) whiles the 600 °C had the lowest fracture toughness. Additionally, the wear properties of the W-C-Co-hBN samples were significantly higher with the 1000 °C having the best wear properties. In general, the h-BN reinforcement in this study demonstrated an improvement and stability in the mechanical properties of fabricated parts even up to 1000 °C.

Microstructure, cracking behavior and mechanical properties of René 104 superalloy fabricated by selective laser melting

Selective laser melting (SLM) is a progressive forming technique for manufacturing complicated components, whereas the microcracks emerge in the preparation process of powder metallurgy (PM) nickel-based superalloy samples undesirably. In this study, René 104 PM nickel-based superalloy samples were prepared by SLM, and the microstructure, cracking behavior and mechanical properties of the as-printed samples were systematically investigated. The results demonstrate that the microstructure of the SLMed René 104 alloy is composed of sub-micron cellular structures on the XY plane, and columnar grains paralleled to building direction on the XZ plane, which is corresponding to the intense<001>fiber texture. Both the solidification cracking and liquation cracking propagate along the high angle grain boundaries (HAGBs) in the SLMed René 104 samples, among which thermal stress and low melting point γ-γ′ eutectics have significant effected on cracking behavior. Additionally, the tensile performance of as-fabricated René 104 samples is obviously anisotropic, which is ascribed to the directional growth of columnar grains with<001>fiber texture and the microcracks are perpendicular to the tensile test direction. This research provides the relationship among the microstructure, microcracks and mechanical properties for the René 104 PM nickel-based superalloy fabricated by SLM and exhibits the potential to fabricate similar alloys without cracks.

Enhancing the FDM infill pattern outcomes of mechanical behavior for as-built and annealed PETG and CFPETG composites parts

Fused deposition modeling (FDM) is the most widely used form of additive manufacturing, a component of the material extrusion, also known as fused filament manufacturing. Recently, in the automotive and aeronautical sectors where FDM is used, polyethene terephthalate glycol (PETG) and carbon fibre-strengthened polyethene terephthalate glycol (CFPETG) composites have developed outstanding material options. In the FDM system, the process parameter influences the behavior of the dimensional stability, consistency, functionality and printed specimen. The present recorded papers address the effects of a number of infill patterns such as grid, honeycomb, rectilinear, cubic on FDM-produced components made of PETG and CFPETG to measure the hardness, tensile, affect, flexural strength of the As-printed and annealing samples. Following the former mechanical properties improved by choosing the right grid pattern infill in PETG and CFPETG samples. In addition, the circulation improved the bonding of the interlayer by the post-processing annealing procedure, which was the secondary objective of this analysis in contrast with the as-printed samples. It is quite clear that the answer to this finding provides a helpful guidance for the development of usable parts by the use of CFPETG, provided the reinforcement present in the PETG.

Effect of Heat Treatment on Microstructures and Mechanical Behaviors of 316L Stainless Steels Synthesized by Selective Laser Melting

In this work, 316L austenite stainless steels were fabricated by the selective laser melting (SLM) technique, and the as-printed samples were then treated by using two various routines, namely the intercritical annealing (IA) and the deep cryogenic treatment (DCT), respectively. Microstructural characterization, nanoindentation creep tests as well as tensile experiments were also performed on the achieved specimens to evaluate the effect brought by the various heat treatment routines. It is found that DCT treatment produces a finer microstructure with higher quantity of homogenous tiny precipitates, compared with the as-printed SLM and single IA counterparts. Such microstructure of the DCT specimen leads to a desirable indentation creep resistance at room temperature as well as a good mechanical performance on tension. In addition, applying a prior deep cryogenic treatment before the intercritical annealing brings more positive effects on the mechanical properties than only using IA. The result indicates that the DCT routine is definitely considerably beneficial for fabricating reliable metallic products fabricated by selective laser melting, and it provides an efficient alternative in real manufactures as well.

Effect of local treatment temperature of ultrasonic nanocrystalline surface modification on tribological behavior and corrosion resistance of stainless steel 316L produced by selective laser melting

In this study, the effects of local treatment temperature of ultrasonic nanocrystal surface modification (UNSM) on tribological behavior and corrosion resistance of stainless steel 316L produced by selective laser melting (SLM) were investigated. The as-printed samples were treated by UNSM at room and high temperatures (RT and HTs) and their strength, tribological behavior and corrosion resistance were compared and discussed. Dry friction coefficient of the UNSM-treated at RT and HT samples was reduced from 0.73 to 0.56 and 0.67 to 0.52, while the dry sliding wear resistance at RT and HT was enhanced from 7.25 × 10−8 to 5.8 × 10−8 and 7.01 × 10−8 to 5.2 × 10−8 mm3/Nmm, respectively. Increase in local treatment temperature of UNSM resulted a lower friction coefficient and higher wear rate compared to that of the UNSM at RT.

Effect of Annealing Heat Treatment on the Microstructural Evolution and Mechanical Properties of Hot Isostatic Pressed 316L Stainless Steel Fabricated by Laser Powder Bed Fusion

In this work, the microstructural features and mechanical properties of an additively manufactured 316L stainless steel have been determined. Three types of samples were characterized: (i) as printed (AP), (ii) annealing heat treated (AHT), and (iii) hot isostatic pressed and annealing heat treated (HIP + AHT). Microstructural analysis reveals that the AP sample formed melt pool boundaries with nano-scale cellular structures. These structures disappeared after annealing heat treatment and hot isostatic pressing. The AP and AHT samples have similar grain morphologies; however, the latter has a lower dislocation density and contains precipitates. Conversely, the HIP + AHT sample displays polygon-shaped grains with twin structures; a completely different morphology compared to the first two samples. Optical micrography reveals that the application of hot isostatic pressing reduces the porosity generated after laser processing. The tensile strengths of all the samples are comparable (about 600 MPa); however, the elongation of the HIP + AHT sample (48%) was superior to that of other two samples. The enhanced ductility of the HIP + AHT sample, however, resulted in lower yield strength. Based on these findings, annealing heat treatment after hot isostatic pressing was found to improve the ductility of as-printed 316L stainless steel by as much as 130%, without sacrificing tensile strength, but the sample may have a reduced (40%) yield strength. The tensile strength determined here has been shown to be higher than that of the hot isostatic pressed, additively manufactured 316L stainless steel available from the literature.

Factors Influencing the Corrosion Behavior of Direct Metal Laser Sintered Ti-6Al-4V for Biomedical Applications

In this study, the effects of microstructure, surface roughness, and surface porosity on the corrosion behavior of direct metal laser sintered (DMLS) Ti-6Al-4V were experimentally investigated. The electrochemical measurements were conducted using a three-electrode setup setting, with the specimens in Ringer’s solution at 37 °C. The acicular microstructure in the DMLS Ti-6Al-4V samples resulted in greater corrosion resistance than that of the Grade 5 alloy with an equiaxed microstructure. Electrochemical study results indicated that microstructure and surface roughness had a significant influence on the corrosion behavior of the samples. Pits and cracks were observed near the edges of the original surface pores in the as-printed samples after a 1-month immersion in simulated body fluid. The results showed that the acicular microstructure with a small number of surface pores and a smooth surface led to more desirable corrosion resistance.

Microstructure Evolution, Mechanical Properties and Deformation Behavior of an Additively Manufactured Maraging Steel.

In this work, the microstructure and mechanical properties of an additively manufactured X3NiCoMoTi18-9-5 maraging steel were determined. Optical and electron microscopies revealed the formation of melt pool boundaries and epitaxial grain growth with cellular dendritic structures after the laser powder bed fusion (LPBF) process. The cooling rate is estimated to be around 106 °C/s during solidification, which eliminates the nucleation of any precipitates. However, it allows the formation of austenite with a volume fraction of about 5% and dendritic structures with primary arm spacing of 0.41 ± 0.23 µm. The electron backscatter diffraction analysis showed the formation of elongated grains with significant low-angle grain boundaries (LAGBs). Then, a solutionizing treatment was applied to the as-printed samples to dissolve all the secondary phases, followed by aging treatment. The reverted austenite was evident after heat treatment, which transformed into martensite after tensile testing. The critical plastic stresses for this transformation were determined using the double differentiation method. The tensile strength of the alloy increased from 1214 MPa to 2106 MPa after the aging process due to the formation of eta phase. The experimental data were complemented with thermodynamic and mechanical properties simulations, which showed a discrepancy of less than 3%.

Effect of Post Processing Heat Treatment Routes on Microstructure and Mechanical Property Evolution of Haynes 282 Ni-Based Superalloy Fabricated with Selective Laser Melting (SLM)

Selective laser melting (SLM) is one of the most widely used additive manufacturing technologies. Fabricating nickel-based superalloys with SLM has garnered significant interest from the industry and the research community alike due to the excellent high temperature properties and thermal stability exhibited by the alloys. Haynes-282 alloy, a γ′-phase strengthened Ni-based superalloy, has shown good high temperature mechanical properties comparable to alloys like R-41, Waspaloy, and 263 alloy but with better fabricability. A study and comparison of the effect of different heat-treatment routes on microstructure and mechanical property evolution of Haynes-282 fabricated with SLM is lacking in the literature. Hence, in this manuscript, a thorough investigation of microstructure and mechanical properties after a three-step heat treatment and hot isostatic pressing (HIP) has been conducted. In-situ heat-treatment experiments were conducted in a transmission electron microscopy (TEM) to study γ′ precipitate evolution. γ′ precipitation was found to start at 950 °C during in-situ heat-treatment. Insights from the in-situ heat-treatment were used to decide the aging heat-treatment for the alloy. The three-step heat-treatment was found to increase yield strength (YS) and ultimate tensile strength (UTS). HIP process enabled γ′ precipitation and recrystallization of grains of the as-printed samples in one single step.

Developing a high-strength Al-Mg-Si-Sc-Zr alloy for selective laser melting: Crack-inhibiting and multiple strengthening mechanisms

To develop high-strength Al alloys for selective laser melting (SLM) additive manufacturing, we designed a series of Al-Mg(-Si)-Sc-Zr alloys and additively manufactured them using atomized alloy powders. In the absence of Si, the developed Al-xMg-0.2Sc-0.1Zr (x = 1.5, 3.0 and 6.0 wt%) alloys are all susceptible to hot cracking and the average crack density increases with increasing Mg content. The addition of 1.3 wt% Si into the Al-6Mg-0.2Sc-0.1Zr alloys effectively inhibits hot cracking during SLM and simultaneously refines the microstructure, and thus leading to enhanced mechanical properties in the as-printed samples. By further fine-tuning the alloy compositions, we designed a new alloy Al-8.0Mg-1.3Si-0.5Mn-0.5Sc-0.3Zr. This new alloy demonstrates significantly refined microstructure consisting of submicron cells with coherent Al3(Sc,Zr) nano-particle (2–15 nm) residing in the cell and intergranular Al-Mg2Si eutectic (Mg2Si diameter 10–100 nm). High-density stacking faults and a unique 9R phase are formed in the as-printed sample. The tensile strength and elongation of the as-printed sample are up to 497 MPa and 11%, respectively. After the aging treatment, the tensile strength reaches 550 MPa, while the ductility ranges from 8% to 17%, depending on the aging conditions. In addition to solid solution strengthening, grain boundary strengthening and nanoparticle strengthening, the high-density stacking faults also contributes to strengthening.

Mechanical Properties of 3D-Printed Maraging Steel Induced by Environmental Exposure

Changes in the mechanical properties of selective laser melted maraging steel 300 induced by exposure to a simulated marine environment were investigated. Maraging steel samples were printed in three orientations: vertical (V), 45° (45), and horizontal (H) relative to the print bed. These were tested as-printed or after heat-treatment (490 °C, 600 °C, or 900 °C). One set of specimens were exposed in a salt spray chamber for 500 h and then compared to unexposed samples. Environmental attack induced changes in the microstructural features and composition were analyzed by scanning electron microscopy and energy dispersive spectroscopy respectively. Samples printed in the H and 45° directions exhibited higher tensile strength than those printed in the V direction. Corrosion induced reduction in strength and hardness was more severe in specimens heat-treated between 480 °C and 600 °C versus as-printed samples. The greatest decrease in tensile strength was observed for the 45°-printed heat-treated samples after exposure. A comparison between additive and subtractive manufactured maraging steel is presented.

An ultra-high strength martensitic steel fabricated using selective laser melting additive manufacturing: Densification, microstructure, and mechanical properties

Martensitic steels have gained renewed interest recently for their use in automotive, aerospace, and defense applications due to their ultra-high yield strengths and reasonable ductility. A recently discovered low alloy martensitic steel, AF9628, has been shown to exhibit strengths greater than 1.5 GPa with more than 10% tensile ductility, due to the formation of ε-carbide phase. In an effort to produce high strength parts with a high degree of control over geometry, the work herein presents the effects of selective laser melting (SLM) parameters on the microstructure and mechanical properties of this new steel. An optimization framework to determine the process parameters for building porosity-free parts is introduced. This framework utilizes the computationally inexpensive Eagar-Tsai model, calibrated with single track experiments, to predict the melt pool geometry. A geometric criterion for determining maximum allowable hatch spacing is also developed in order to avoid lack of fusion induced porosity in the as-printed parts. Using this framework, fully dense samples were successfully fabricated over a wide range of process parameters, allowing the construction of an SLM processing map for AF9628. The as-printed samples displayed tensile strengths of up to 1.4 GPa, the highest reported to date for any 3D printed alloy, with up to 11% elongation. The demonstrated flexibility in process parameter selection, while maintaining full density, opens up the possibility of local microstructural refinement and parameter optimization for improved mechanical properties in as-printed parts. The process optimization framework introduced here is expected to allow successful printing of new materials in an accelerated fashion.

Mechanical properties and microstructures of 3D printed bulk cordierite parts

Abstract In this study, digital light processing (DLP) 3D printing technology is used to prepare cordierite ceramic parts. The quality of the as-printed and as-sintered samples including dimensional accuracy, volume shrinkage, porosity and mechanical properties are determined. The influence of particle size of the prepared cordierite slurries, the predefined sliced layer thickness and the exposure time on the sample quality are evaluated via orthogonal experiments. The study shows that the particle size plays a crucial role in the quality and performance of the bulk samples. Smaller particles often lead to larger volume shrinkage and hence lower porosity. As a result, higher mechanical performance can be reached. Distinct features of cracks are demonstrated on different surfaces of the as-printed samples. Sintering process is found to be responsible for the favorable crack healing. Joint effect of porosity and cracks is believed to account for the mechanical properties measured at different length scales.