Search Results (895)

Laser powder bed fusion (LPBF), one of the most established metal additive manufacturing technologies, depends strongly on the physical, morphological, and rheological characteristics of the powder feedstock to ensure process stability, layer uniformity, and final part quality. This study compared three AlSi10Mg powders intended for LPBF: one ultrasonic-atomized powder and two gas-atomized powders from different suppliers. The powders were evaluated in the as-received condition and after exposure to high-temperature/high-humidity and high-temperature/low-humidity environments. Particle size distribution, SEM/EDS, helium pycnometry, Karl Fischer moisture analysis, apparent density, Carney funnel flow, FT4 powder rheometry, and a LAMMPS-based Carney funnel simulation were used. The ultrasonic-atomized powder showed the lowest moisture uptake (77.74 ppm after humid conditioning, compared with 386.9 and 495.7 ppm for the gas-atomized powders), fewer satellite particles, lower agglomeration, and higher apparent density. Its Carney funnel flow time remained nearly constant (8.0–8.6 s), whereas one gas-atomized powder increased from 12.2 to 15.2 s after humid exposure. FT4 measurements also indicated lower effective internal friction and wall-friction angles for the ultrasonic-atomized powder, while the gas-atomized powders exhibited greater resistance to motion and stronger sensitivity to the applied stress state. Although the powders showed broadly similar chemical composition, differences in particle size distribution, morphology, moisture sensitivity, and frictional behavior led to clear differences in flow performance. Because the powders also differed substantially in particle-size distribution, the effects attributed to atomization route are interpreted together with particle size and supplier effects rather than as route effects alone. The LAMMPS simulation remained qualitative because the modeled mass was limited to 10% of the estimated powder mass; nevertheless, it reproduced the same discharge ranking observed experimentally in the Carney funnel tests. Full article

This study investigates the effects of laser power and scanning rate on the surface morphology, relative density, microhardness and microstructure of pure tungsten fabricated by laser powder bed fusion (LPBF). Increasing the laser power or decreasing the scanning rate effectively suppresses spheroidisation and enhances densification, achieving a maximum relative density of ~98%. However, excessive laser power intensifies Marangoni convection, leading to surface protrusions that reduce density. Microstructural analysis reveals that the laser-scanned surface is dominated by fine columnar grains (390–480 HV), whereas the side surface comprises coarser columnar grains with lower hardness (~390 HV). Electron backscatter diffraction analysis confirms that the side surface contains a high proportion of grains exceeding 100 μm and reveals a significant peak (~41.8%) at ~3.5° for low-angle grain boundaries, indicating substantial internal stress and microstrain. Pole figures show a weak preferred orientation (maximum texture intensity of 3.161). Phase analysis shows no significant phase transformation after LPBF, while internal stress and microstrain increase notably. Full article

Laser powder bed fusion (LPBF) induces pronounced microstructural anisotropy in NiTi alloys, which strongly governs their corrosion behavior in physiological environments. Here, the orientation-dependent microstructure and corrosion performance of LPBF NiTi alloys were systematically investigated on the XY (perpendicular to build direction) and XZ (parallel to build direction) planes. The XY plane is dominated by polygonal B2 grains, whereas semi-quantitative XRD analysis and TEM observations indicate a relatively larger contribution of lamellar B19′ martensite on the XZ plane. Electrochemical tests in Hank’s solution (pH 3–7) reveal pronounced corrosion anisotropy. At pH 7, the XZ plane exhibits a higher charge transfer resistance (143.9 vs. 109.1 kΩ cm²) and a lower corrosion current density (0.231 vs. 0.599 μA cm⁻²) than the XY plane. After 72 h immersion, the $R_{ct}$ of the XZ plane remains approximately 31% higher than that of the XY plane at pH 7, while its apparent donor density is lower than that of the XY plane at pH 3 (7.38 × 10²⁹ vs. 12.33 × 10²⁹ cm⁻³). The superior electrochemical response of the XZ plane correlates with its denser lamellar B19′ morphology and lower passive-film donor density. Competition between interface-assisted passivation and interface-related electrochemical heterogeneity is proposed as a possible contributor to the anisotropic corrosion response. Full article

Low-melting-point impurities in powder feedstock can trigger local melting phenomena in laser powder bed fusion (LPBF) parts and may initiate defects in printed components. Here, we combine bulk chemistry with automated, high-throughput particle-by-particle SEM/EDS to identify and quantify Sn-containing impurity particles in two gas-atomized Al–Mg–Zr powder batches with different bulk Sn levels. The aim was not to establish a direct batch-to-batch performance comparison, but to clarify whether Sn was uniformly distributed among the powder particles or concentrated in rare impurity particles. Although ICP analysis indicated only 0.07 ± 0.02 wt.% Sn in the Sn-higher batch and <0.01 wt.% Sn in the Sn-lower batch, automated SEM/EDS screening of 20,001 particles per batch revealed that Sn was present as a very small number of highly enriched particles with Sn > 45 wt.% (eight particles in the Sn-higher batch and three particles in the Sn-lower batch). In the Sn-higher batch, Sn-rich particles were predominantly spherical and fell within the LPBF feedstock size window (Dmax ≈ 25–40 μm), implying that standard sieving would not remove them. BSE imaging and EDS mapping of polished sections and fracture surfaces of LPBF specimens built from the Sn-higher batch revealed spatially localized Sn-rich features associated with pores and Sn-rich phases on the fracture surface, supporting a direct powder-to-part transfer. These results demonstrate that low bulk impurity levels can mask highly localized, particle-scale contamination and highlight the need for particle-level compositional screening to support robust powder qualification and reuse decisions in LPBF. Full article

Metal additive manufacturing (AM) enables components with high geometric complexity and functional integration; however, these advantages are realized only when topology optimization (TO) aligns with AM-specific constraints. This review examines TO strategies for metal AM, with emphasis on laser powder bed fusion (LPBF) as the most established industrial route. It categorizes and assesses density-based methods, level-set approaches, and lattice or architected-material optimization, focusing on how each captures manufacturability (overhang limits, minimum feature size, surface roughness), physics (residual stress, thermal distortion), and AM-induced anisotropy. It further distinguishes algorithms that embed constraints directly into the TO loop from workflows that rely on post-optimization repair. It discusses implications for robustness and transferability across machines and alloys. Experimental and numerical evidence for titanium alloys, aluminum alloys, nickel-based superalloys, and stainless steels is synthesized to relate design decisions and processing conditions to reported gains in stiffness-to-weight ratio, strength, fatigue performance, and buy-to-fly efficiency. Persistent gaps include validation under realistic load spectra, uncertainty quantification, standardized benchmarks, microstructure-informed objectives, and sustainability metrics. Beyond synthesizing existing TO formulations and constraints, this review contributes a criteria-based decision structure linking TO method selection, constraint strategy, and process-physics coupling and identifies four inherent paradoxes defining the field’s open challenges. Full article

Fe-Cr-B alloys are recognized as candidate wear- and corrosion-resistant materials strengthened by high-hardness boride phases. Conventional casting produces coarse continuous network borides and severe elemental segregation under near-equilibrium slow solidification (10⁻¹–10² K/s), resulting in high brittleness and limited service reliability. Laser processing includes laser cladding (10³–10⁶ K/s), LPBF/DED (10⁶–10⁸ K/s) and laser remelting, which feature extreme non-equilibrium rapid solidification but differ significantly in thermal gradient G, solidification rate R, and phase evolution behavior. To avoid over-extrapolation, this review strictly classifies evidence into direct LPBF evidence, direct DED evidence, laser cladding evidence, casting evidence, and indirect inference. Quantitative comparisons reveal that laser cladding refines borides from 150 to 300 μm to 10.8–20 μm, while DED further achieves 1–5 μm equiaxed grains and relative density > 98%. Meanwhile, laser-cladding Fe-Cr-B coatings achieve a maximum hardness of ~1052 HV_0.5, and ~18% higher wear resistance and ~70% lower cavitation mass loss compared with cast counterparts. Non-equilibrium mechanisms including solute trapping, interface absolute stability, constitutional undercooling, and columnar-to-equiaxed transition (CET) controlled by the Gⁿ/R ratio are systematically analyzed. Thermal–solutal coupling, grain nucleation, and boride precipitation kinetics under rapid cooling are emphasized. Current limitations include incomplete non-equilibrium thermodynamic databases, insufficient standardization, limited post-processing (heat treatment, HIP) studies, and missing unified performance datasets. Future directions are proposed toward quantitative phase-field modeling, standardized tribocorrosion characterization, high-throughput experiments, and machine learning-assisted optimization. This review provides a rigorous analytical framework for the composition–process–microstructure–performance design of laser-processed Fe-Cr-B alloys. Full article

TA15 titanium alloy fabricated by Laser Powder Bed Fusion (L-PBF) exhibits high strength but poor ductility due to its fine acicular α′ martensitic microstructure. This study systematically investigates the effects of post-annealing treatments (800–950 °C for 0.5–4 h) on the microstructural evolution and mechanical performance of L-PBF-built TA15. Results show that with increasing temperature and time, the metastable α′ martensite decomposes into a progressively coarser lamellar (α + β) structure. This transformation leads to a decrease in strength and hardness but a significant improvement in ductility, with elongation increasing from (8.5 ± 0.5)% (as-built) to (19.4 ± 1.1)% (900 °C/2 h) as the ultimate tensile strength (UTS) decreased from (1100 ± 29) to (895 ± 37) MPa. However, annealing at 950 °C, which approaches the β-transus temperature, induces a coarse Widmanstätten structure in the alloy. Although this structure yields a relatively high elongation (23.8 ± 3)%, it also leads to excessive strength loss, with an ultimate tensile strength of only (833 ± 23) MPa, rendering it less desirable for structural applications requiring high load-bearing capacity. Moreover, such coarse lamellar structures are generally associated with poor fatigue resistance, as cracks tend to propagate along prior β grain boundaries. An optimal strength-ductility synergy is achieved by annealing at 900 °C for 0.5 h, yielding an ultimate tensile strength of (951 ± 13) MPa and an elongation of (18.8 ± 1.7)%. These findings provide crucial guidance for tailoring the mechanical properties of L-PBF-fabricated TA15 alloy through post-processing heat treatments. Full article

Titanium alloys are irreplaceable in aerospace, biomedical and marine industries due to their low density, high specific strength and excellent biocompatibility. Conventional manufacturing methods suffer from low material utilization and difficulty in fabricating complex components, while additive manufacturing (AM) realizes near-net-shape forming of customized structures but introduces unique non-equilibrium microstructures and defects, which significantly alter the corrosion behavior and limit the long-term service reliability of additively manufactured (AMed) titanium alloys. This work systematically analyzes the corrosion behavior of titanium alloys fabricated by four mainstream AM processes: LPBF (laser powder bed fusion)/SLM (selective laser melting), EBM (electron beam melting), DED (directed energy deposition) and WAAM (wire arc additive manufacturing). It quantitatively summarizes the key electrochemical parameters and discusses the regulatory effects of matrix composition, post-treatment and service environment on their corrosion behaviors. The universal corrosion mechanisms—namely, passive film breakdown, micro-galvanic corrosion, and defect-induced localized corrosion—as well as process-specific corrosion mechanisms inherent to AMed titanium alloys are systematically elucidated. This study offers theoretical foundations for optimizing corrosion resistance and ensuring the reliable engineering implementation of AMed titanium alloys. Full article

Laser powder bed fusion (LPBF) is a widely utilized metal additive manufacturing (AM) process for fabricating intricate geometries with high mechanical strength. However, achieving defect-free parts remains challenging due to complex thermodynamics and process variability. Component quality is primarily determined by mel-pool morphology, which depends on key process parameters such as laser power, scan speed, and layer thickness. Improper parameter selection causes defects like porosity (keyhole and lack of fusion), balling, and residual stresses, compromising structural integrity. Optimizing these parameters is crucial but difficult due to the multi-scale, multi-physics nature of the process, which traditionally relies on costly, time-intensive experimental trials. We present results from a data-driven approach using machine learning (ML) models to predict and optimize LPBF melt-pool characteristics, reducing reliance on trial-and-error experimentation. We find that laser power and scan speed predominantly influence the melt-pool formation. Higher scan speeds produce more favorable melt pools, whereas excessive laser power at low scan speeds leads to deep keyhole defects. To predict and classify melt pools efficiently, several ML models are deployed, including logistic regression, decision trees, ensemble learning, and fully connected neural networks. The standard neural network achieved the highest cross-validated macro-F1 score of 0.978 ± 0.014, while the weighted neural network achieved the highest recall for the rare optimal melt-pool class, 0.967 ± 0.050. These findings show that class-weighted learning provides a recall-oriented strategy for identifying suitable LPBF process windows, while avoiding overreliance on single train-test split performance. The findings underscore the effectiveness of ML in accurately classifying LPBF melt pools to rapidly identify optimal process parameters. Full article

Additive manufacturing (AM) of metallic lattice structures, particularly those made of Ti-6Al-4V, has significant potential for biomedical applications due to their lightweight nature and favorable mechanical properties. However, laser powder bed fusion (LPBF) processes often introduce residual stresses and distortions, which compromise dimensional accuracy and part performance. This study presents a simulation-based approach for optimizing process parameters and post-processing strategies to minimize these issues. Using the Simufact Additive 1.0 ink, 2023 software, voxel sensitivity analysis was conducted to identify an optimal mesh size of 0.35 mm. A Design of Experiments (DoE) approach in MINITAB was applied to optimize key LPBF parameters, including laser power, scanning speed, and scan width. Simulations incorporating stress relief and hot isostatic pressing (HIP) were conducted to assess their impact on residual stresses and distortions. The results show that stress relief effectively reduces maximum distortion by up to 50% in the X direction and 17% in the Z direction for an FCC lattice structure with a 0.75 mm strut thickness. HIP further decreases deflection angles by 77%. The simulation predictions correlate well with the experimental measurements, supporting the use of simulation-driven process optimization to enhance the dimensional stability and mechanical reliability of Ti-6Al-4V lattice structures for biomedical implants. Full article

The microstructural characteristics and precipitate features of titanium matrix composites (TMCs) are critical to tribological performance. In this study, TiCp/TA15 composites were fabricated via laser powder bed fusion (LPBF). The as-built composite was then heat-treated at 750 °C for 2 h to obtain a uniform duplex (α + β) microstructure with enhanced TiC precipitation, which was labeled as HT-750. The influence of the microstructural evolution on the tribological performance was systematically investigated. Compared to the as-built composite, the HT-750 composite exhibited a microhardness increase from 360.2 ± 6.4 HV to 459.2 ± 3.1 HV, a reduction in the friction coefficient from 0.649 ± 0.167 to 0.581 ± 0.111, and a decrease in the wear rate from 8.24 ± 0.44 × 10⁻⁴ mm³/(N·m) to 4.81 ± 0.39 × 10⁻⁴ mm³/(N·m), indicating a significant enhancement in wear resistance. This improvement is primarily attributed to the synergistic strengthening effect of the duplex matrix and TiC particles, which enhanced the load-bearing capability and suppressed surface plastic deformation. During the friction process, the dominant wear mechanisms of as-built and HT-750 composites evolved over time but exhibited distinct differences. The as-built composites were prone to continuous plastic deformation and damage accumulation, resulting in severe delamination, oxidative, and abrasive wear. Conversely, the HT-750 composites demonstrated higher resistance to plastic deformation and crack propagation, effectively mitigating interfacial shear and inhibiting damage evolution, with the wear mechanism being dominated by oxidative wear accompanied by abrasive wear and minor delamination. This work provides deep insights into the wear mechanisms of additively manufactured TMCs. Full article

GH4141 + 0.2 wt.% Y₂O₃ superalloy was fabricated using laser powder bed fusion (LPBF) technology and subjected to solution and ageing heat treatments. The effects of laser power (1100, 1300, 1500 W) on the microstructure and mechanical properties of the ODS nickel-based superalloy were investigated. The results indicate that as the laser power increased from 1100 W to 1300 W, defects such as cracks and pores in the specimens decreased, the grains were refined, and the microstructure became more uniform; when the laser power was further increased to 1500 W, the grain size coarsened significantly, precipitation phases at the grain boundaries became coarser or locally aggregated, and crack sensitivity increased. EDS analysis revealed enrichment of C, Cr, Mo and Ti in the dark phases at the grain boundaries, which may be associated with MC-type and M₂₃C₆-type carbides; no significant agglomeration of Y₂O₃ particles was observed in the matrix. Room-temperature tensile properties exhibited a pattern of initially increasing and then decreasing with increasing laser power. The tensile strength and elongation after fracture of the specimens were relatively similar under 1100 W and 1500 W conditions, whilst the specimen tested at 1300 W achieved the optimal balance of strength and toughness, with a tensile strength of 1460 MPa and an elongation after fracture of 14.3%, representing increases of approximately 9.8% and 54% compared to the 1100 W and 1500 W conditions, respectively. At 760 °C, the 1300 W specimens still maintained excellent high-temperature strength. Full article

Laser powder bed fusion (LPBF) of high-strength aluminum alloy 7075 (AA7075) is severely limited by hot cracking. However, the underlying mechanisms, particularly the coupling between thermal fields, solidification microstructure, and cracking behavior, remain insufficiently clarified. This study elucidates these mechanisms by integrating experimental characterization with thermal simulation to investigate the temperature field, microstructure, and cracking relationships in both AA7075 and a crack-resistant 7075-Er-Zr alloy. Results show that coarse hot crack morphology is highly dependent on linear energy density E_L. In AA7075, E_L < 450 J/m promotes laterally inclined cracks (short, narrow cracks extending from the melt pool boundary toward the track center), whereas E_L higher than that value leads to the continuous centerline cracks (long, wide cracks along the track center). Fine microcracks are also observed at melt pool boundaries. The 7075-Er-Zr alloy demonstrates superior crack resistance. At E_L = 600 J/m, longitudinal centerline cracks still penetrate along the track, but the alloy achieves crack-free tracks at 200 W with scanning speeds above 1000 mm/s, otherwise exhibiting only short discontinuous cracks. Microcracks at melt pool boundaries are markedly suppressed in the modified alloy. The enhanced crack resistance is attributed to Er/Zr-induced grain refinement and a transition to an equiaxed grain structure, which disrupts intergranular gaps. Critically, thermal simulations identify an annular region with a peak temperature gradient. In AA7075, this region develops aligned columnar grains that facilitate both microcracks and centerline cracks. In the 7075-Er-Zr alloy, microcracks are fully eliminated within this region. However, a residual crystallographic texture persists in the annular region, which promotes the continued occurrence of centerline cracks under high energy density (e.g., E_L = 600 J/m). The annular region remains a critical weak link, and its microstructural control determines the prevailing crack type. This work provides a fundamental understanding of the thermal-microstructural origins of cracking and offers a theoretical foundation for developing crack-resistant aluminum alloys via LPBF. Full article

This study investigates the effect of laser powder bed fusion (L-PBF) parameters and T7 heat treatment on the defect formation, microstructure, and mechanical properties of a high-strength Al-Cu 224 aluminum alloy. The laser power (200–370 W), scanning speed (130–1900 mm/s), and hatch spacing (90–130 μm) were varied to evaluate their influence on hot cracking and porosity. Microstructural characterization using optical microscopy, scanning electron microscopy, and electron backscatter diffraction revealed that an energy density of 400 J/mm³ substantially reduced visible hot cracking in the examined microscopic regions by reducing the thermal gradients. However, this resulted in increased keyhole porosity, thereby limiting the relative density to 95%. The as-built samples exhibited a yield strength of 152 MPa and an elongation of 9.2%, and the T7 heat treatment improved the yield strength to 233 MPa, whereas the elongation remained unchanged. Keyhole pores served as primary crack initiation/propagation sites during tensile loading, reducing ductility. Lower energy densities increased the geometrically necessary dislocation density and promoted cracking because of higher residual stresses due to greater accumulated plastic strain and lattice curvature. These results clarify process–structure–property relationships, emphasize the trade-offs between defect types and performance, and provide a robust framework for optimizing L-PBF processing of high-strength Al alloys through parameter tuning and post-heat treatment. Full article

Poor consolidations and the strength–conductivity trade-off limit the performance of copper alloys fabricated by laser powder bed fusion (LPBF). To address this, this study developed a strategy combining the response surface methodology (RSM) with direct ageing treatment (DAT) to achieve a favorable strength–conductivity synergy. The results showed that under the optimal process parameters, a high relative density of 99.25% (8.95 g/cm³ for theoretical density) was obtained. After direct ageing treatment at 490 °C for 60 min, the CuCrZr exhibited an ultimate tensile strength of 399.31 MPa and a thermal conductivity of 326.53 W/(m·K). To reveal the underlying mechanisms, this study employed a combination of systematic characterization via high-resolution transmission electron microscopy (HRTEM) and quantitative modeling. HRTEM characterized the uniformly dispersed nanoscale body-centered cubic (BCC) Cr precipitates that form semi-coherent interfaces with the face-centered cubic (FCC) Cu matrix, showing a crystallographic misorientation of approximately 10.5° intermediate between the classic Nishiyama–Wassermann and Kurdjumov–Sachs orientation relationships. Quantitative modeling indicates that the high strength arises from a synergistic effect: coherent strain fields exerted by the precipitates effectively pin retained dislocations, coupling Orowan and dislocation strengthening. Meanwhile, solute precipitation reduces lattice distortion, restoring notable thermal conductivity. Full article