As-printed Samples Research Articles

Microstructural evolution and high strain rate deformation response of SLM-printed CoCrFeMnNi after annealing and deep-cryogenic treatment

This study examines the microstructural evolution and high strain rate deformation response of Selective Laser Melted (SLM) CoCrFeMnNi high-entropy alloys (HEAs) after annealing and deep cryogenic treatment. Annealing treatment has traditionally improved the ductility of SLM materials. However, in this work, a significant improvement in strength was observed in the annealed SLM CoCrFeMnNi after high strain rate deformation testing. TEM/HRTEM investigations revealed the formation of refined oxides, generated from the processing chamber environment and constituent powder feedstock. These oxides were homogenously distributed within microstructure, reinforcing its structural integrity. Initial microstructural analysis of the as-printed samples showed Mn2O3 oxides sparsely distributed within a cellular dislocation structure and significant Mn segregation. Unique grain growth with a less prominent cellular dislocation structure was observed in the annealed specimen. Deep cryogenic treatment induced oriented cellular structures with higher dislocation density and rounded oxides that were 56 % smaller. High strain rate impact tests (up to 6500 s-1) demonstrated that the as-printed sample was sensitive to the strain rate and reached a yield strength of ∼920 MPa at 6000 s−1 and a strain deformation of ∼55 % making it desirable for high strain rate applications. Remarkably, up to 22 % higher strength and ∼10 % greater ductility were achieved after annealing. The strengthening mechanisms in the samples and their contributions to the overall material strength were thoroughly analyzed. It was determined that a substantial portion of the strength in the annealed samples was due to the contributions of the precipitates within the alloy. The observed increase in strength was primarily attributed to the presence of two distinct nano-precipitates in the annealed specimens. However, there was no change in ductility after the deep cryogenic treatment but ∼10 % higher yield strength values at equivalent strain rates also attributed to the increased dislocation density.

Heat treatments-induced wear resistance of Inconel 718 superalloy fabricated via Laser based Powder Bed Fusion

Laser based Powder Bed Fusion (LPBF) stands out among Additive Manufacturing (AM) techniques for its ability to fabricate intricate geometries with high precision. However, LPBF produced parts, particularly Inconel 718 (IN718) superalloys, demand further exploration in microstructural and mechanical properties aspect. This study explores the effect of heat treatments on LPBF fabricated Inconel 718. Three distinct heat treatments involving diverse solutionizing temperatures and ageing steps were applied to the LPBFed IN718 alloy. As-printed samples showed columnar dendritic microstructure. The heat treatments led to precipitation of strengthening γ′′ and γ′ phases. A substantial increase in microhardness was observed after heat treatments. Wear tests revealed as-printed specimens suffered higher wear loss (∼889 μm) and coefficient of friction (COF) (∼0.627) attributed to Laves phase and low hardness of the matrix. However, heat-treated specimens exhibited substantially lower wear loss (∼217 μm) and COF (∼0.342), with HT2 condition demonstrating superior wear resistance attributed to a homogeneous microstructure.

Microstructure, mechanical properties, and shape memory behavior of laser-directed energy deposited Co–20Fe–18Cr–19Mn high-entropy alloy

Laser additive manufacturing has become a powerful tool in modern production processes, and the additive manufacturing of Cantor-type high-entropy alloys has attracted considerable attention owing to its unique properties. In this study, we successfully utilized a laser-directed energy deposition (L-DED) process to fabricate a Co–20Fe–18Cr–19Mn, wt.% (Co40Fe20Cr20Mn20, at.%) alloy and analyzed its microstructure, room temperature mechanical properties, and shape memory effect. Microstructural analysis revealed a dense microstructure of the alloy. Before heat treatment, the alloy exhibited a microstructure consisting of both columnar and equiaxed dendrites with a hexagonal close-packed structure (HCP). However, post-treatment led to a completely different microstructure owing to recrystallization with a face-centered cubic (FCC) structure. Tensile testing results indicated a subtle anisotropy in the yielding, and after heat treatment, a significant enhancement in ductility was observed. A study of the shape memory effect demonstrated that the as-printed samples exhibited an FCC-HCP dual-phase structure, which transformed into an FCC single-phase structure after heat treatment. The application of external loading induced reformation of the HCP phase, successfully demonstrating the shape memory effect in the alloy, with a maximum recovery strain of 0.79 %.

Effect of Printing Parameters and Heat Treatments on Microstructure Development of LPBF Manufactured Inconel 718 Alloy

Abstract Processing parameters of the laser powder bed fusion (LPBF) technique strongly govern achieved performances and manufacturing defects of printed alloys. In this work, it was aimed to study the effects of LPBF printing parameters and subsequent heat treatments on resulted microstructure characteristics and tensile properties of Inconel 718 alloy. Inconel samples were fabricated using three different energy densities. Then, microstructure features such as Lave phase, primary dendrite arm spacing, and internal residual stresses as microstrains of both as-built and heat-treated specimens were determined. It was found that in the range of used energy densities, alterations of phase fractions and average sizes of the Laves phase were insignificant. Decreased energy density led to microstructures with smaller primary dendrite arm spacing and thus principally contributed to enhanced yield and tensile strengths of as-printed samples, whereas increased porosity greatly deteriorated elongation. Moreover, their flow stress curves could be significantly increased by direct aging; however, typical cellular and columnar substructures occurring during the LPBF printing remained. Homogenization treatment could entirely eliminate such substructures and otherwise caused different formations of delta phase when it was performed prior to a delta process.

Revealing the microstructural evolution and mechanical response of repaired Fe–Cr–Si based alloy by directed energy deposition

This study investigates the microstructure and mechanical properties of wear-resistant hardfacing structures fabricated on an AISI 1045 carbon steel substrate using a specially designed Fe–Cr based powder for directed energy deposition (DED). Electron backscatter diffraction (EBSD) analysis reveals that the texture predominantly consists of cube rotated {001}<110> and cube {001}<110> textures, in addition to weaker Brass {112}<111> texture components. These textures contribute to the random orientations of martensitic grains and facilitate the tracing of austenite reconstruction. Notably, the as-printed samples exhibited superior yield strength (999.4 ± 86.3 MPa) and ductility (9.6 ± 2.6%) along the build direction (BD), compared to conventional samples, which demonstrated a tensile strength of 790 MPa and ductility of 2%. This improvement is primarily attributed to the hardening effects associated with a low volume fraction of retained austenite and the precipitation of Cr carbides. Comprehensive mechanical response, nanoindentation hardness profile across the interface, and microstructural analyses were conducted to confirm the feasibility of using a Fe-based hardfacing alloy for DED. The findings underscore the outstanding balance of strength and ductility exhibited by as-printed hardfacing alloy, further enhanced by its high printability, highlighting its potential in producing wear-resistant structures for repair applications.

On the microstructural evolution and mechanical property development of additively manufactured AlCoCrFeNi2.1 eutectic high-entropy alloy with aging temperature

In this study, the microstructure and mechanical properties of a laser powder bed fusion processed eutectic high-entropy alloy, AlCoCrFeNi2.1, and the influence of aging temperature have been investigated. The as-printed material consists of a hierarchical cellular eutectic microstructure with γ cells and a B2 network along the cell boundaries. The γ matrix contains homogeneously distributed Al2O3 nanoparticles and sporadically distributed L12 long-range ordered (LRO) domains. Some B2 grains contain ultrafine body-centred cubic Cr-rich precipitates. Aging at 500–700 °C leads to disruption of the B2 network and coarsening of the B2 grains at the intersections of several cells and thinning of the rest of the regions. At 800 °C, the B2 cellular network completely disappears and turns into large isolated spherical or near-spherical B2 particles with the original γ cells being fully integrated. At 600 °C, numerous ultrafine γ′ nanoparticles form from the γ matrix and turn into elongated γ′ at 700 °C but completely disappear at 800 °C due to the formation of thermally more stable B2 precipitates. The as-printed samples show a high yield strength (YS∼ 1050 MPa) and good ductility (elongation ∼ 20 %) due to the strengthening effects from the LRO domains and the less deformable B2 and Al2O3 particles. Aging at 600–700 °C leads to significant strength improvement mainly owing to the γ′ particles. Aging at 800 °C results in a considerable decrease in YS but improves the ductility due to the disappearance of γ′ precipitates and the B2 cellular network.

Effect of HIP Treatment on the Evolution of Texture and Microstructure of LBPF Fabricated Pure Ni

Microstructure and texture analysis were conducted employing electron backscatter diffraction (EBSD) technique on laser powder bed fusion (LPBF) fabricated pure Ni. The texture analysis of the hot isostatic pressed (HIP) and as-printed (AP) samples were done utilizing orientation distribution function (ODF) maps. The AP sample comprises mostly of &amp;lt;110&amp;gt;||BD fiber texture with insignificant presence of twins. In contrast, the HIP sample has &amp;lt;111&amp;gt;||BD grains. It was found that the development of the texture &amp;lt;111&amp;gt;||BD was due to the deformation linked to the HIP process. In addition, HIP generated a substantial fraction of Σ3 coincident site lattice boundaries (CSL) because of pure Ni which is a medium stacking fault energy (SFE) element.

Post-Processing Effect on the Corrosion Resistance of Super Duplex Stainless Steel Produced by Laser Powder Bed Fusion.

This study examines the microstructural characteristics and corrosion resistance of super duplex stainless steel (SDSS) produced through laser powder bed fusion (LPBF). The analysis shows that the as-printed samples mainly exhibit a ferritic microstructure, which is due to the fast-cooling rates of the LPBF technique. X-ray and microstructure analyses reveal the presence of minor austenite phases in the ferritic matrix. The process of solution annealing led to a more balanced microstructure. Analyses of corrosion resistance, such as potentiodynamic polarization tests and EIS, indicate that heat treatment has a significant impact on the corrosion behavior of SDSS. Solution annealing and stress relieving at 400 °C for 1 h can improve corrosion resistance by increasing polarization resistance and favorable EIS parameters. However, stress relieving at 550 °C for 5 h may reduce the material's corrosion resistance due to the formation of chromium nitride. Therefore, stress relieving at 400 °C for 1 h is a practical method to significantly enhance the corrosion resistance of LPBF-printed SDSS. This method offers a balance between microstructural integrity and material performance.

Wet chemical surface functionalization of AA2017 powders for additive manufacturing

Laser Powder Bed Fusion (L-PBF) is an important route for processing aluminum alloys, nevertheless, the high laser reflectivity and thermal conductivity and lower powder flowability of the aluminum alloys remain a challenge for their processing. Aiming to overcome these issues, AA2017 powders were surface-functionalized using chemical etchings. The powders' physical and rheological characterization revealed a decrease in the laser reflectance and an improvement in the flowability of the surface-functionalized powders, when compared to the gas-atomized powder. The higher amount of keyhole porosity in the as-printed L-PBF samples using the surface-functionalized powders also suggests an improvement in the laser absorption of these powders. However, the formation of a thick oxide layer on the surface-functionalized powders led to oxidation porosity in the as-printed samples. Therefore, the chemical etching should be improved to avoid the formation of a thick oxide layer on the powder surface and oxidation porosity in the as-printed L-PBF samples.

Binder-jet 3D printing of pea-based snacks with modulated texture

This paper demonstrates, for the very first time, 3D printing of pea-based snacks with tunable texture using the binder jetting (BJT) method, pea flour as the print powder, and an aqueous binder solution. The binding mechanism was studied by performing both Hele-Shaw cell experiments and confocal microscopy on the printed samples. As the pea flour was exposed to an aqueous binder, the starch granules swelled. These granules remained swollen but were further joined by a network of protein-rich bridges as the sample dried. Inclusion of sugar and post-printing baking tended to strengthen the as-printed samples, and the resultant mechanical properties were on par with commercial snacks that are not 3D printed. By controlling the amount of aqueous binder dispensed from the inkjet print heads, more than one order of magnitude differences in compressive strength and modulus were achieved, demonstrating the exciting potential of using 3D printing for texture modulation of plant-based snacks.

Microstructure and mechanical properties of a hypereutectic Al–Si–Cu alloy manufactured by laser powder bed fusion

A novel Al–Si–Cu alloy was designed for additive manufacturing of automotive components, such as pistons and supercharger rotors, requiring a combination of elevated temperature properties and high cycle fatigue strength. The alloy was designed with an Al–Si hypereutectic chemistry to exploit the formation of primary Si nucleants to enable an equiaxed as-printed microstructure during laser powder bed fusion (LPBF). The alloy design space was assessed using a combined integrated computational materials engineering (ICME) approach with melt-spinning experiments to select a chemistry exhibiting primary Si nucleants acting as heterogeneous grain nucleation sites. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) of the LPBF as-printed samples revealed primary Si particles with a fully equiaxed grain structure and no apparent texturing as evaluated using electron backscatter diffraction (EBSD). High-resolution scanning transmission electron microscopy (STEM) revealed sub-micron Si particles and Al2Cu θ-phase precipitates which result in enhanced room and elevated temperature mechanical strength (room temperature: UTS: 449 ± 10 MPa, YS: 336 ± 12 MPa) as compared to commercial Al10SiMg (UTS: 417 ± 3 MPa, YS: 236 ± 6 MPa).

Multiscale characterisation study on the effect of heat treatment on the microstructure of additively manufactured 316L stainless steel

Additively manufactured 316L components are known to exhibit complex three-dimensional microstructures on multiple length-scales. The effect of heat treatment on the stability of grains and dislocation cell structures within the microstructure has previously been investigated but there are appreciable disagreements surrounding the nature of the texture that is present in the specimens, and there is also limited published work on the compositional homogeneity of specimens, particularly on the atomic scale, after heat treatments. In this study, we investigate the effect of applying two different heat treatments to 316L components produced by laser powder bed fusion before characterising them using a combination of electron microscopy and atom probe tomography. The importance of using multiple characterisation techniques, which span from the nanometre to micrometre scale, in addition to carefully and accurately describing analysis methods when investigating the evolution of the microstructure of additively manufactured 316L steels is demonstrated. Our EBSD (Electron Back Scatter Diffraction) results show the presence of a strong texture in the build direction of the samples, and a reduction in morphological texture as a result of heat treatment. TEM (Transmission Electron Microscopy) results indicate a dissolution of the dislocation cell structure that forms during solidification. Atom probe tomography was used to investigate compositional homogeneity in the samples and indicated that there are regions enriched in Cr, Mn, Mo, and Ni in the As-Printed samples that are likely associated with the dislocation cell walls. The atom probe results also reveal the presence of impurities, such as Co, which were not detected in the feedstock powder.

Additive manufacturing Ti-22Al-25 Nb alloy with excellent high temperature tensile properties by electron beam powder bed fusion

Additive manufacturing of TiAl alloys remains challenging due to their poor high-temperature tensile properties. In this work, electron beam powder bed fusion (PBF-EB) was applied to fabricate Ti-22Al-25 Nb alloy with a high pre-heating temperature (830℃), achieving a breakthrough in improving the tensile properties of TiAl alloys by additive manufacturing. The microstructure and tensile properties of Ti-22Al-25 Nb fabricated by laser beam powder bed fusion (PBF-LB) and PBF-EB were investigated. Excellent tensile strength (803 MPa) at 650℃ was obtained by PBF-EB, which was attributable to the precipitation and growth of the O phase at a suitable pre-heating temperature. An in-depth microstructure analysis of the deformation and fracture mechanisms of the as-printed samples was performed via Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM). The area fraction of the O phase in the PBF-EB sample was approximately 6 times higher than that of the PBF-LB sample. The PBF-EB sample exhibited transgranular fracture at 650 °C, in contrast to the PBF-LB samples. The shape and quantity of the O phase and β phase played an important role in improving the tensile properties of the Ti-22Al-25 Nb alloys at high temperature.

Crystal Plasticity Modeling to Capture Microstructural Variations in Cold-Sprayed Materials

The high-velocity impact of powder particles in cold-spray additively manufactured (CSAM) parts creates intersplat boundaries with regions of high dislocation densities and sub-grain structures. Upon microstructure and mechanical characterization, CSAM Aluminum 6061 showed non-uniformity with spatial variation in the microstructure and mechanical properties, affecting the overall response of the additively manufactured parts. Post-processing treatments are conducted in as-printed samples to improve particle bonding, relieve residual stresses, and improve mechanical properties. In this work, we attempt to implement the effects of grain size and distribution of smaller grains along the intersplat boundaries using the grain size distribution function and powder size information to accurately predict the deformation response of cold-sprayed material using a mean-field viscoplastic self-consistent (VPSC) model. The incorporation of an intersplat boundary term in the VPSC model resulted in a stress–strain response closely matching the experimental findings, preventing the superficially high stresses observed due to Hall–Petch effects from ultra-fine-grain structures. Likewise, the results from the grain analysis showed the combined effects of grain size, orientation, and intersplat mechanisms that captured the stresses experienced and strain accommodated by individual grains.

How to characterise the anisotropy of laser powder bed fusion-processed parts? Towards a surrogate, non-destructive indentation-based approach

This work proposes a non-destructive indentation (NDI)-based surrogate mechanical testing framework for anisotropy and mechanical property evaluation of LPBF processed Inconel 718 superalloy. A Knoop-hardness tester was employed to develop the surrogate framework. Further post-heat treatments (PHTs) were performed at various cooling rates. The as-printed and PHT (SA, SB, SC, and SD) samples were characterized using X-ray diffraction (XRD) optical microscopy (OM), scanning electron microscopy (SEM), and electron back-scattered diffraction (EBSD) techniques. The yield locus plots show strong anisotropy for the as-printed sample. The IPF maps and pole figures for the as-printed samples showed elongated columnar grains with strong fiber texture along the (001) plane parallel to the build direction. They corroborated sufficiently with XRD, grain boundary map (GBM), and Kernel average misorientation (KAM) analysis. The yield locus shape of samples subjected to homogenization treatment becomes a nearly uniform ellipse with a reduction in the difference between σx and σy values, which can be attributed to the recrystallization of grains as observed by the transition from low-angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs). The PHT samples show a further increase in yield loci size due to the precipitation of γ’ and γ” strengthening phases due to aging treatment and corroborated with higher Taylor factor and dislocation density than the as-printed samples. The yield loci were sensitive to the PHT's cooling rates. Notably, among PHT ones, ‘SA’ samples exhibited a strong correlation (R2 ≈ 97.5 %) between the Taylor factor and yield locus. It was attributed to slower cooling rates (furnace cooled) with noticeably enhanced precipitation of strengthening phases, an increase in the volume fraction of recrystallized grains (from grain orientation spread (GOS) map), corroborating with higher dislocation density due to local strain as inferred from EBSD analysis. The proposed NDI surrogate approach was initially validated on an as-printed Inconel 718 stator blade. The yield locus showed a strong correlation between the stator blade and the as-printed sample, indicating the effectiveness of the proposed methodology.

Exploring How LPBF process parameters impact the interface characteristics of LPBF Inconel 718 deposited on Inconel 718 wrought substrates

This work investigates the interface properties of LPBF Inconel 718 deposited on Inconel 718 wrought substrates fabricated using the laser powder bed fusion (LPBF) technique. The as-printed (S1, S2, S3, and S4) samples were characterized using optical microscopy (OM),scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and micro-hardness techniques.The samples showed the development of a melted interface zone (MIZ) at the wrought substrate-deposition interface for all processing conditions. The developed interface showed a dendritic grain structure, signifying the remelting of the wrought substrate followed by rapid solidification. The MIZ thickness increased with an increase in laser power and scan speed (28.5 % increase in the MIZ thickness with a ∼ 12 % increase in normalized enthalpy). The assessment of the MIZ showed a high-quality interface. However, with an increase in scanning speed, the density of the MIZ decreases owing to increased porosity and lack-of-fusion (LOF) defects. The S1 condition (250 W and 850 mm/s) resulted in a highly dense part with no visible porosity, LOF defects, and a high relative density (∼99.9 %) in the MIZ region. The S4 condition showed the presence of large porosities and LOF defects at the deposition-MIZ interface, signifying an inferior bond between the deposition and substrate. The microstructural characterization of the LPBF-processed and MIZ region showed an increase in the primary dendritic arm spacing (PDAS) with increasing laser power due to a reduced cooling rate. The micro-hardness characterization of the sample shows a decrease in the hardness of the MIZ attributed to the dissolution of strengthening phases due to remelting. The present work outcome demonstrates the effectiveness of the proposed methodology for manufacturing high-quality parts using LPBF technology.

Effect of Build Orientation and Heat Treatment on Erosion Behavior of Al10SiMg Fabricated Using Laser Powder Bed Fusion

Laser Powder Bed Fusion (LPBF) is a form of additive manufacturing that can directly make metal components and has begun to be employed in a variety of industrial situations. Moreover, the erosion characteristics of SLM-produced items have been documented relatively infrequently. In the current work, the erosion behavior of a heat-treated Al-Si-10% Mg alloy generated via laser powder bed fusion (LPBF) has been investigated. The samples were printed in three directions (horizontal (0o), vertical (90o), and inclined (45o) on the build platform using the Direct Metal Laser Sintering (DMLS) system (EOS M 290) machine. Al%Si-10%Mg samples were given treatment (T5, T6). Optical and scanning electron microscopes (SEM) were used to examine the microstructure under both printed and heat-treated conditions. Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) were used to investigate the alloy's elemental composition and compound production. The erosion test was executed in each of the three orientations, plus heat-treated samples and as-printed samples. The selected input parameters were impingement angle and flow velocity. The erosion rate was examined and contrasted across orientations for printed and heat-treated conditions to establish the best orientation. The post-eroded surface was analysed using SEM, EDS, and XRD to evaluate possible erosion processes. The key findings were: T5 heat-treated samples sustain well and have the least mass loss; Horizontal (0°) oriented samples undergo less erosion compared to other orientations; T6 heat-treated samples show maximum erosion on printed samples, and hence it is not recommended. T5 heat treatment is proven to be superior in providing high erosion resistance, followed by printed and T6 heat-treatment, respectively. The heat treatment effects are more significant than the orientation effects in determining the erosion resistance of the Al10SiMg alloy. The erosion mechanisms, such as ploughing, melting, and cratering, were identified.

Topological fidelity of additively manufactured AlSi10Mg gyroid structures

Additively manufactured Triply Periodic Minimal Surfaces (TPMS), walled gyroid structures (WGS) in particular, have garnered research and industry attention recently, especially in realizing compact and efficient heat exchangers. Methodologies for topological and geometric fidelity assessment of as-printed samples against their as-designed models are pertinent to predict and evaluate their performance, as deviations can impact heat transfer rates and energy dissipation. In this study, 7 WGS samples with cell sizes and relative densities ranging from 3 mm to 7 mm and 8.5 % to 26.2 % respectively were manufactured via laser powder bed fusion (LPBF) in AlSi10Mg. Geometric (3D) and layer-wise (2D) topological fidelity analyses were done by comparing micro x-ray computed tomography (μ−CT) scans of the WGS samples with corresponding computer-aided designed (CAD) models. Metrics such as the degree of overlap, underprint, overprint, and percentage deviation were defined and quantitatively assessed. Results show bonded partially melted powder particles on downfacing surfaces resulting in higher average surface roughness of up to 41μm in these regions. Topological conformities in terms of the degree of layer-wise overlap, and the degree of overprint and underprint improve as the ratio of the relative density to cell length increases from 2 to 5 (% per mm) for a cell size of 5 mm.

Material extrusion additive manufacturing of AISI 316L pastes

Material extrusion (MEX) processes that employ metal-polymer composites to 3D print “green” parts offer an economical and user-friendly alternative to melt-based additive manufacturing. Leveraging existing powder metallurgy knowledge permits the fabrication of functional parts with predictable microstructures and properties. However, the large fractions of binder, typically 45 to 55 vol%, introduce the need for specialized debinding procedures that significantly prolong the total manufacturing time, limit geometrical capabilities, and negatively affect mechanical properties if not adequately removed. To address these limitations, this paper presents a MEX framework that involves (1) synthesis of a 316L stainless steel paste with just 3.2 vol% binder, (2) design and implementation of a synchronized two-stage extrusion mechanism, (3) an experimentally-driven approach to evaluate the effects of MEX parameters on extrudate morphology, density, and surface roughness, (4) multi-objective optimization, and (5) evaluation of thermal post-processing strategies. The as-printed samples displayed densities of 4.67 g/cm3 and 21.54 μm areal surface roughness. The framework permitted the fabrication of increasingly complex geometries and sintered densities measuring 91.8–97.9%TD after just 22 h of thermal post-processing (including approx. ten hours of cooling time in the furnace).

Influence of post-heat treatment with super β transus temperature on the tensile behaviour of LPBF processed Ti6Al4V

This paper investigates the tensile behaviour of Laser powder bed fusion (LPBF) processed Ti6Al4 V samples under three build orientations. The effect of microstructural changes from the post-heat treatments (PHTs – 850 °C, 950 °C 1050 °C) was assessed. The microstructural characterization was performed using optical microscopy, X-ray diffraction, and SEM techniques. The tensile tests were performed using a uniaxial universal testing machine (UTM). The fractal dimension analysis was performed on the fractured surfaces using ImageJ software integrated with an open-source MultiFrac plug-in. The PHT at a higher temperature (i.e., 1050 °C) induces a higher amount of β phase than the other PHTs. The PHT performed at 1050 °C exhibited α-Widmanstatten microstructure consisting of elongated β and a small amount of α. The PHT induces an isotropic behaviour in the LPBF-processed samples. However, the ductility of specimens subjected to PHT at 1050 °C showed ∼ 67%, 40%, and 177% improvement under horizontal (0°), inclined (45°), and vertical (90°) orientations than as-printed samples. Further fractal dimension analysis corroborates well with the ductility values of PHT samples. Therefore, the combination of fractography analysis and fractal dimension approach can be a promising methodology towards fractured surface characterization of additively manufactured metal parts.