The demand for miniaturized high-temperature components necessitates advanced additive manufacturing techniques, yet the microstructural and mechanical consequences of scaling down the laser powder bed fusion (LPBF) process remain poorly understood. In this study, we systematically investigate the scaling effects of micro laser powder bed fusion (μ-LPBF) versus conventional LPBF on the phase transformation kinetics and performance of the near-α Ti65 alloy. Results demonstrate that μ-LPBF significantly enhances surface integrity, reducing the arithmetic mean roughness (Ra) by 59.5%. Microstructural characterization reveals that the extreme cooling rates intrinsic to the microscale melt pool induce a massive refinement of hierarchical α′ martensite and promote a highly randomized variant selection. Consequently, the strong building-direction crystallographic texture typical of LPBF is substantially weakened, and the proportion of high-angle grain boundaries increases to 91.6%. This microstructural homogenization effectively mitigates mechanical anisotropy, reducing the directional variance in the Schmid factor by 35%. In terms of mechanical properties, μ-LPBF demonstrates exceptional strengthening at both room temperature and 600 °C, achieving a room-temperature yield strength of 1297 MPa and an ultimate tensile strength of 1514 MPa, which represent increases of 16.5% and 8.6%, respectively, compared to those of conventional LPBF. These findings provide critical insights into defect suppression and multiscale microstructural control under extreme thermal gradients, paving the way for the fabrication of isotropic, high-strength micro devices.

The rapid development of the aerospace industry has increased the demand for lightweight materials with high-temperature performance. Ti-22Al-25Nb intermetallic compound alloys are promising candidates for such applications. However, their practical use remains limited by the intrinsic trade-off between strength and ductility. Therefore, overcoming this limitation through advanced manufacturing technologies is highly important for the structural design of high-performance aerospace components. In this study, micro-laser powder bed fusion (μ-LPBF) was employed to fabricate near-net-shaped Ti-22Al-25Nb alloys. The microstructural evolution, tensile properties, and electrochemical corrosion behavior were comprehensively investigated. The results show that the optimized as-printed sample exhibited excellent mechanical properties at room temperature, with an ultimate tensile strength of approximately 1188 MPa and an elongation of approximately 22.3%, exceeding those of most conventional counterparts. This improvement is attributed mainly to the synergistic effect of grain boundary strengthening and high-density dislocation strengthening. In addition, the sample under optimized conditions exhibited excellent corrosion resistance in chloride-containing environments, which is mainly associated with the formation of a dense and protective passive film dominated by TiO2/Nb2O5.

In this study, FeCoCrNiMo high-entropy alloy coatings were prepared using the high-speed laser cladding (HSLC) technique, and their microstructure, Vickers hardness, wear resistance, and corrosion resistance were examined. The results showed that the FeCoCrNiMo coating comprised a face-centered cubic (FCC) phase and a sub-micronsized sigma phase. The Vickers hardness of the FeCoCrNiMo coating increased with depth, which was attributed to the reduction in width of the plastically deformable FCC subcrystals. Additionally, the FeCoCrNiMo coating exhibited a maximum Vickers hardness values that were 77.1 %, 44.8 %, and 18.8 % higher than those of the 304, 431, and Ni60 coatings, respectively. The superior wear resistance of the FeCoCrNiMo coating was evidenced by its wear rate, which was 51 % to 511 % lower than that of the Ni60, 431, and 304 coatings. This improved wear resistance was mainly attributed to MoO3 functioning as a solid lubricant and MoO2 imparting a toughening effect to the oxide layer, resulting in predominantly oxidative wear in the coating. The Ecorr of the FeCoCrNiMo coating was 1.5-1.7 times higher than the 304, 431, and Ni60 coatings, while its Icorr was only a quarter of 304's, half of 431's, and slightly above that of Ni60. Therefore, the FeCoCrNiMo coating exhibited wear-corrosion resistance, making it a promising material for demanding service environments.

Ti65 high-temperature titanium alloy, known for its exceptional high-temperature mechanical properties and oxidation resistance, demonstrates considerable potential for aerospace applications. Nevertheless, conventional manufacturing techniques are often inadequate for achieving high design freedom and fabricating complex geometries. This study presents a systematic investigation into the process optimization, microstructure characterization, and mechanical performance of Ti65 alloy produced by laser powder bed fusion (LPBF). Via meticulously designed single-track, multi-track, and bulk sample experiments, the influences of laser power (P), scanning speed (V), and hatch spacing (h) on molten pool behavior, defect formation, microstructural evolution, and surface roughness were thoroughly examined. The results indicate that under optimized parameters, the specimens attain ultra-high dimensional accuracy, with a near-full density (>99.99%) and reduced surface roughness (Ra = 3.9 ± 1.3 μm). Inadequate energy input (low P or high V) led to lack-of-fusion defects, whereas excessive energy (high P or low V) resulted in keyhole porosity. Microstructural analysis revealed that the rapid solidification inherent to LPBF promotes the formation of fine acicular α′-phase (0.236–0.274 μm), while elevated laser power or reduced scanning speed facilitated the development of coarse lamellar α′-martensite (0.525–0.645 μm). Tensile tests demonstrated that samples produced under the optimized parameters exhibit high ultimate tensile strength (1489 ± 7.5 MPa), yield strength (1278 ± 5.2 MPa), and satisfactory elongation (5.7 ± 0.15%), alongside elevated microhardness (446.7 ± 1.7 HV0.2). The optimized microstructure thereby enables the simultaneous achievement of high density and superior mechanical properties. The fundamental mechanism is attributed to precise control over volumetric energy density, which governs melt pool mode, defect generation, and solidification kinetics, thereby tailoring the resultant microstructure. This study offers valuable insights into defect suppression, microstructure control, and process optimization for LPBF-fabricated Ti65 alloy, facilitating its application in high-temperature structural components.

Due to their light weight and outstanding mechanical properties at high temperatures, Ti3Al-based intermetallic alloys have driven increasing interest from both academia and industry; however, when additive manufacturing (AM) is applied to them, the outcome is hardly satisfying. In this work, we report a crack-free Ti3Al-based alloy fabrication by laser powder bed fusion (LPBF) using a mixture of a commercial Ti-48Al-2Cr-2Nb powder and a pure Ti powder. With the aid of a high cooling rate during LPBF, the as-built sample shows a ductile β phase with some partially-melted particles. After the heat treatment, partially-melted particles were dissolved, and the sample showed equiaxed α2 precipitates in the β matrix. The hardness was 515 ± 38 HV in the as-built sample and 475 ± 37 HV in the heat-treated sample. This study shows a novel strategy to fabricate crack-free Ti3Al-based alloy using LPBF from powder blends.

The application of Ti-48Al-2Cr-2Nb (TiAl-4822) produced by laser powder bed fusion (LPBF) is hindered by its severe cold cracking susceptibility caused by the intrinsic brittleness of alpha 2 and gamma phase. Although the high cooling rate of LPBF is normally deemed detrimental for brittle materials, the present study proposed a counterintuitive strategy to mitigate cold cracking, by taking advantage of the high cooling rate rather than suppressing it. By reducing laser input energy, the cooling rate of LPBF increased, which led to the formation of a massive ductile beta phase. The unique beta and alpha 2 phase distribution and the transition of beta -> alpha 2 were also revealed, further proving the presence of the massive beta phase. Compared with the sample without beta phase, the beta-containing sample success-fully mitigated cold cracking. This study shows a novel method to alleviate the cracking problem of LPBF-processed TiAl-4822, providing new insights into the future LPBF process design of TiAl-4822 and other TiAl-based alloys.

Single-crystal-like stainless steel 316L (SS316L) was tailored by laser beam powder bed fusion (PBF-LB). Tensile responses along the <100>, <110> and <111> crystallographic directions show considerably different strength ratios in different orientations from a standard face-centered cubic (FCC) alloy. A multi-scale crystal plasticity modelling methodology is developed to simulate and understand such unique orientation-dependent plastic deformation behaviour. The polycrystal model, based on the visco-plastic self-consistent (VPSC) formulation, considers deformation by slip and twinning, adapting a dislocation-based approach with latent hardening at single crystal level, including slip-slip, slip-twin, twin-slip and twin-twin interactions, to account for the orientation-dependent strain hardening behaviour. Based on the proposed multi-scale model, the orientation-dependent superior strength-ductility behaviour of textured PBF-LB SS316L can be attributed to the beneficial effects of deformation twinning and the cellular sub-grain structure.

The study demonstrates that the presence of sharp notch-like features on the as-built surface of microstruts fabricated via laser powder bed fusion (LPBF) results in reduced mechanical performance under quasi-static tensile loading. 3D models of 250 mu m diameter cylinders textured with uniform surface features of 25 mu m, 45 mu m, 65 mu m, and 85 mu m heights were designed to mimic the typical as-built surfaces of LPBF microstruts. Finite element analysis was utilized to simulate the tensile plastic flow interaction with the respective surface morphologies of the microstruts. The localized increase in uniaxial stress at the roots of notches associated with the induced surface features causes an overall strengthening effect in the microstruts, which increases with increasing feature heights. As a result, the ultimate tensile strength increases from 533 MPa for the plain (notch-free) microstrut to a maximum of 760 MPa for the surface textured microstruts. Further, local increase in triaxiality at notch roots restrict plastic flow. As a result, the uniform elongation strain decreases from similar to 0.52 for the plain microstrut to a range of 0.36 - 0.38 for the surface textured microstruts. Post UTS, increasing localization of strain and shifting of maximum triaxiality to notch roots of the surface textured microstruts initiates the final failure.

In the present study, dense and crack-free Hastelloy X (HX) thin cylindrical struts with diameters ranging from 0.25 mm to 2 mm were fabricated through laser powder bed fusion (LPBF). Their crystallographic texture was found to transition from a < 110 > || building direction (BD) fiber texture in the 2 mm strut, to a single crystal in the 0.25 mm strut with < 110 > || BD. The size of the cellular sub-grain microstructure increased as the strut diameter decreased and was linked with an inverse trend in microhardness, which was the highest in the 2 mm strut due to a smaller cell size. Lower hardness measurements in the regions close to the strut edges was also related to larger cell size observed in these regions. From tensile testing, elongation to fracture values were measured in the range of 35-50%. Deformation twinning and lattice rotation after testing were observed. Differences in strength from between different struts of different diameter are also discussed. Finally, fractography analysis further confirmed the ductile fracture behavior. (c) 2022 Elsevier B.V. All rights reserved.

The corrosion behavior of the {100}, {110}, {111} planes of a single-crystalline-like stainless steel 316L (SS316L) produced by laser powder bed fusion (LPBF) was investigated in 3.5 wt% aqueous NaCl and compared with their LPBF-polycrystalline and wrought counterparts. The general corrosion resistance followed: wrought & AP; {110} < polycrystalline < {100} < {111} trend, which was rationalized by the surface atom density and corrosion activation energy. All LPBF samples exhibited a significantly higher pitting corrosion potential than the wrought SS316L due to the lower concentration of oxygen vacancies in their passive oxide films. These findings provide insights into improving the corrosion performance by tailoring the crystallographic texture of LPBFSS316L.

In the present study, solid solution strengthened Ni-based superalloy Hastelloy X (HX) parts were fabricated using the laser powder bed fusion (LPBF) additive manufacturing process with the intent of developing a strong crystallographic texture. Their tensile properties at room temperature were investigated along the < 100 > , < 110 > , and < 111 > crystallographic orientations. Tensile behavior was found to be highly dependent on the crystallographic orientation and present unique combinations of strength and ductility when compared with other LPBF-HX counterparts. EBSD (Electron backscatter diffraction) analysis after fracture revealed deformation twinning in the < 110 > and < 111 > samples, but not in the < 100 > orientation. It was observed that crystallographic orientation had a great impact on the effective stacking fault energies. Critical stress for deformation twinning was also observed to be crystallographic orientation-dependent. It was close, if not below the yield strength (YS) for < 110 > and < 111 >, while it was well above the ultimate tensile strength (UTS) of the < 100 > orientation. The YS value of < 111 > (807 +/- 28 MPa) was higher than that of < 100 > (693 +/- 8 MPa) and < 110 > (648 +/- 13 MPa). The results suggest that deformation twinning can occur in solid solution strengthened Ni-base superalloys at room temperature, and their formation does not mandatorily require the presence of gamma' precipitates or thermally assisted mechanisms. In contrast to the < 100 > and < 111 > orientations, rotation of the lattice after deformation was found for the < 110 > . (C) 2021 Published by Elsevier B.V.

Metal additive manufacturing techniques have been recognized for their capability of controlling the crystallographic orientations of stainless steels. However, the inherent anisotropic corrosion behavior has not been extensively studied. In this study, the corrosion properties of 316L stainless steels prepared by Laser Powder Bed Fusion (LPBF) additive manufacturing were investigated. The effects of different crystallographic textures, namely {100}, {110} and {111} on both general and pitting corrosion were characterized by several electrochemical measurements, including Electrochemical Impedance Spectroscopy (EIS), potentiodynamic polarization and Mott-Schottky analysis. The results were also compared to the polycrystalline and wrought 316L counterparts. It was found that the LPBF-{111} sample offered the highest general corrosion resistance, followed by the LPBF-{100}, LPBF-polycrystalline and LPBF-{110} samples (Figure 1). The origin of this trend was related to the atomic surface density. The LPBF-{111} surface exhibited a stronger atomic bonding than that of LPBF-{100} and LPBF-{110} samples, resulting in a higher corrosion activation energy and thus a higher general corrosion resistance. All the LPBF samples also offered a significantly higher pitting corrosion resistance (Figure 2), which was attributed to the lower concentration of oxygen vacancies (donor levels) in the passive film that serve as pits nucleation sites, as observed by the Mott-Schottky analysis (Figure 3). Figure 1

In the present study, single-crystalline-like bulk stainless steel (SS316L) specimens with a {110} <001> Goss texture were produced by laser powder bed fusion (LPBF). The tensile behaviours of the LPBF-fabricated SS316L along the <100>, <110> and <111> crystallographic directions were systematically investigated. The samples along the three crystallographic directions enabled a broader strength-ductility paradigm of LPBF-fabricated SS316L and exhibited a superior strength-ductility synergy over their traditionally manufactured counterparts. The tensile responses of the SS316L samples were highly dependent on their crystallographic orientations. The <111> orientated samples exhibited higher yield strength (YS) than those of the <100> and <110> orientated samples, which was mainly attributed to the lower Schmid factors of the <111> grains along their tensile axes (TAs). The dominant deformation mechanisms were found to be dislocation slip and deformation twinning for the <100> and <111> orientated samples, respectively. For <110> orientated samples, significant deformation twinning as well as evident lattice rotation were observed simultaneously. The higher tendency towards deformation twinning of the <110> and <111> orientated samples arose from the larger separations between the partial dislocations in these samples, which reduced the effective stacking fault energies as well as the critical stresses for deformation twinning significantly. Due to the higher propensity towards deformation twinning, the <110> and <111> orientated samples showed better ductility over the <100> orientated samples by facilitating twinning-induced plasticity (TWIP) effect. Furthermore, the lattice rotation of the <110> samples during tension featured a modest TWIP effect which enabled a more prolonged strain hardening rate uphill than that of the <111> samples, resulting in a superior ductility with a total elongation (TE) of ~100 %.

Current quantitative X-ray microanalysis methods are only available for homogeneous materials. This paper presents a newly developed inverse modeling algorithm to determine both the structure and composition of twodimensional (2D) heterogeneous materials from a series of X-ray intensity measurements under different beam energies and beam positions. It utilizes an iterative process of forward modeling to determine the optimal specimen to minimize the relative differences between the simulated and experimental characteristic X-ray intensities. The Monte Carlo method is used for the forward modeling to predict the X-ray radiation for a given specimen and experimental setup. Several examples of applications are presented for different types of samples with one-dimensional (1D) and 2D structures, in which the simulated X-ray intensities from phantom samples are used as input. Most of the results obtained from our algorithm agree well with the phantom samples. Some discrepancies are found for the voxels located at deeper depths of the 2D samples. And the discrepancies may be attributed to errors from the Monte Carlo simulations and from the variation of the X-ray range with beam energy. As a proof-of-concept work, this paper confirms the feasibility of our inverse modeling algorithm applied to 2D heterogeneous materials.

In this study, dense and crack-free specimens were fabricated from the solid-solution strengthened nickel-based superalloy Hastelloy X (HX) through laser powder bed fusion (LPBF) in both horizontal and vertical build orientations. Samples were subjected to one of three conditions: as-built (AB), hot isostatic pressing treatment (HIP), and conventional heat treatment (HT). Tensile testing was carried out for every orientation and condition at room temperature (RT) and an elevated temperature of 750 degrees C (ET). AB samples showed columnar grains and a partial fiber texture aligned with the build direction, which is reduced after HIP and HT, where partial recrystallization occurred. Mo and Cr carbides, as well as Al-O enriched precipitates were found in the RT microstructures, and were seen to increase in size after ET exposure. AB samples displayed high strength (up to 924 +/- 10 MPa ultimate tensile strength), while HIP and HT samples maintained strength values close to a reference HX wrought alloy. Although lower ductility was observed for the AB samples when testing at ET, the elongation was improved after HIP and HT. Strength and elongation comparable to that of the wrought alloy at RT can be obtained by performing just HT, without the need of HIPing.

In electron probe microanalysis or scanning electron microscopy, the Monte Carlo method is widely used for modeling electron transport within specimens and calculating X-ray spectra. For an accurate simulation, the calculation of secondary fluorescence (SF) is necessary, especially for samples with complex geometries. In this study, we developed a program, using a hybrid model that combines the Monte Carlo simulation with an analytical model, to perform SF correction for three-dimensional (3D) heterogeneous materials. The Monte Carlo simulation is performed using MC X-ray, a Monte Carlo program, to obtain the 3D primary X-ray distribution, which becomes the input of the analytical model. The voxel-based calculation of MC X-ray enables the model to be applicable to arbitrary samples. We demonstrate the derivation of the analytical model in detail and present the 3D X-ray distributions for both primary and secondary fluorescence to illustrate the capability of our program. Examples for non-diffusion couples and spherical inclusions inside matrices are shown. The results of our program are compared with experimental data from references and with results from other Monte Carlo codes. They are found to be in good agreement.

Ti-6Al-4V and Ti-6Al-7Nb were manufactured with laser powder bed fusion (LPBF). Microstructural comparison study between Ti-6Al-4V and Ti6Al-6Nb was used to understand processability similarities between two different titanium alloys. Quantitative similarities between two alloys revealed that Ti-6Al-4V processing parameters can be used for optimization of Ti-6Al-7Nb. The microstructure, processing, properties relationship and the influence of heat treatments were investigated for Ti-6Al-7Nb. The as-built microstructure was composed of a columnar prior beta grains with fine acicular alpha' martensite resulting in a yield strength of 1082 MPa and an ultimate tensile strength of 1160 MPa with an elongation of 9.7%. Solutionizing at 1055 degrees C and aging at 540 degrees C completely transformed the columnar structure of the prior beta grains to equiaxed via phase transformation and grain growth, solutionized the alpha' martensite into beta and then created a fine lamellar alpha + beta structure with air cooling. The resultant microstructure had reduced strength and hardness but increased ductility. The reduction in yield (871 MPa) and ultimate tensile (940 MPa) strength would be positive to minimize stress shielding of orthopedic implants. The improved elongation of 11.5% meets the requirements for biomedical applications which stipulates an elongation of at least 10% according to the ISO 5832-3 Standard.

In this study, we explored the feasibility of fabricating single-crystalline or single-crystalline-like stainless steel 316L (SS316L) with different geometries (thin struts, cubes, walls and a simulated pump impeller) using laser powder bed fusion (LPBF). The LPBF-fabricated SS316L thin struts possessed a single-crystalline core featuring a 〈110〉 ∥ building direction (BD) crystallographic texture. The cubes, walls and the pump impeller preserved this 〈110〉 ∥ BD texture and also exhibited a well-defined single-crystalline-like {110}〈001〉 Goss texture. Cellular sub-grain structures with their primary dendrite arm spacing (PDAS) values smaller than 1 μm were discovered in all the samples with their growth directions showing a 45° angular deviation from the BD. Nanoscale precipitates and dislocations were also found in the cellular sub-grain structures of the thin struts. The mechanical properties of different geometries (the thin struts, the walls, and the simulated pump impeller) were studied and compared. The anisotropic mechanical responses of the walls and the simulated pump impeller were correlated with their crystallographic textures.

Single crystalline austenitic stainless steel struts with a diameter of 250 μm were successfully fabricated using laser powder bed fusion (LPBF). The struts exhibited a strong 〈110〉 texture parallel to the building direction (BD). Excellent strength-ductility combination was achieved for the struts, which is attributed to the strengthening of the fine cellular sub-grains and the twinning-induce plasticity (TWIP) effect. After deformation, dynamic recrystallization (DRX) was observed and its presence is closely related to the unique microstructure of the single crystalline struts.