Search Results (513)

Reliable property prediction and process selection in laser powder bed fusion are hindered by small, set-level datasets in which key morphology descriptors are intermittently missing, limiting both generalization and actionable co-design. A hybrid multimodal surrogate strategy is introduced that couples engineered process physics features with morphology proxies through a deployable two-stage embedding module and gradient-boosted tree regressors. Set-resolved inputs are assembled from L-PBF parameters, linear energy density and related energy-density variants, pore and prior-β grain summary statistics, and stress–strain-derived descriptors, followed by missingness-aware feature filtering, median imputation, and 5-fold GroupKFold evaluation grouped by set_id, with morphology embeddings learned on training folds and predicted when absent. Across six targets, the final deployable models achieve an RMSE/R² of 11.07 MPa/0.895 (yield), 13.88 MPa/0.873 (UTS), 0.677%/0.861 (elongation), and 2.38 GPa/0.663 (modulus), while roughness and hardness remain challenging (RMSE 2.31 μm and 16.54 HV; R² about 0.12 and 0.11). These surrogates enable constraint-aware candidate generation that identifies a concise set of manufacturing recipes balancing strength and surface objectives under uncertainty-aware screening. The resulting framework provides a practical blueprint for multimodal, small-data additive manufacturing studies and can be extended to richer microstructure measurements and prospective validation to accelerate functional and biomedical alloy development. Full article

As part of a NASA University Leadership Initiative (ULI) program, this work supports the continued development and evaluation of a fatigue-based process window for stress-relieved Ti-6Al-4V specimens produced via laser powder bed fusion (PBF-LB/M). Four-point bend and axial fatigue specimens were fabricated by NASA ULI collaborators across a range of scan velocities (800–2000 mm/s) at a constant power of 370 W using an EOS M290 system. All fatigue specimens were low-stress-ground by a commercial vendor and tested at Case Western Reserve University (CWRU) under load-controlled cyclic loading at a stress ratio of R = 0.1. This paper presents a curated dataset linking PBF-LB/M process parameters to fatigue outcomes across 175 specimens. Of these, 136 fractured and this study includes fatigue crack initiation site identification and defect morphology metrics derived from post mortem SEM analysis. Specimens that reached runout (10⁷ cycles) and did not fracture under subsequent fatigue testing are retained in the dataset, with fractographic fields marked as ‘NA’ to indicate non-applicability. The dataset includes specimen metadata, processing parameters, fatigue life data, fatigue initiation site classification (e.g., keyhole, gas-entrapped pore (GeP), lack-of-fusion (LoF), contamination), defect size and shape descriptors, and spatial location relative to the free surface. These data are intended to support defect-based fatigue life prediction, probabilistic modeling, process–structure–property studies, and machine learning frameworks linking process parameters to fatigue performance in PBF-LB/M Ti-6Al-4V. Full article

In the realm of computational biomechanics, quantifying the reliability of surface-engineered implants is critical yet challenging due to material anisotropy and experimental limitations. Standard deterministic approaches often fail to capture the failure probability of brittle coatings, compromising the accuracy of lifespan predictions. This study’s originality lies in a stochastic framework that addresses titanium boride data scarcity using a geometric decision node (GDN). By autonomously switching between Palmqvist and Radial-Median regimes, the GDN eliminates deterministic bias and provides a failure-probability-based reliability assessment, thereby surpassing the limitations of conventional models. The evaluation was carried out on powder-pack borided Ti6Al4V layers produced at 1000 °C (10, 15, and 20 h). By combining instrumented Berkovich nanoindentation (N = 14, hardness scatter 17.6–34.8 GPa) with a Monte Carlo simulation algorithm (n = 10,000), we successfully modeled the stochastic brittle failure of the coating. The computational model, governed by a multivariate joint probability density function (JPDF), revealed a mixed-mode fracture mechanism where 77.9% of the virtual population developed radial cracks while 22.1% re mained in the Palmqvist regime. Weibull statistical analysis yielded a characteristic toughness of 2.25 MPa·m^1/2 and a low modulus of m = 1.58. This low modulus mathematically quantifies the coating’s sensitivity to microstructural defects, demonstrating that probabilistic algorithms—rather than mean-value deterministic calculations—are essential for ensuring the structural integrity of borided components in biomechanical design applications. Full article

Laser Powder Bed Fusion (LPBF) enables the fabrication of complex titanium alloy components with high geometric freedom; however, surface integrity and tribological performance remain critical limitations for sliding-contact applications in biomedical and aerospace systems. In this study, the influence of in-layer laser remelting on the microstructure, surface topography, and dry sliding tribological behavior of LPBF-fabricated Ti-6Al-4V ELI (Grade 23) is systematically investigated. Disc-shaped specimens were produced using single-scan (SS) and double-scan (DS, in-layer remelting) strategies and tested in ball-on-disc configuration against AISI 52100 steel at a constant normal load of 10 N and three sliding speeds of 0.10, 0.15, and 0.20 m·s⁻¹. Microstructural and phase-related characteristics were analyzed by X-ray diffraction combined with Rietveld refinement and Warren–Averbach analysis, revealing that the DS strategy increases retained β-phase fraction (up to 5.2%) and promotes crystallite coarsening relative to the SS condition, without significantly altering bulk hardness. Surface morphology examined by SEM/EDS and AFM revealed a more homogeneous near-surface topography in the DS condition. Tribological results indicate that sliding speed governs steady-state friction and wear, with specific wear rates increasing progressively from 5.13 to 5.44 × 10⁻⁴ mm³·N⁻¹·m⁻¹ for SS and from 6.47 to 7.52 × 10⁻⁴ mm³·N⁻¹·m⁻¹ for DS across the investigated speed range. The DS specimens exhibited higher wear rates than the SS condition across all tested speeds, while steady-state COF values remained comparable between strategies, indicating that remelting-induced microstructural modifications affect material removal mechanisms without proportionally destabilizing the frictional regime. These findings suggest that in-layer laser remelting represents a process-integrated parameter with measurable consequences for surface integrity and tribological performance, though the generalizability of these results warrants validation across broader experimental conditions. Full article

This work focuses on obtaining a titanium nitride coating on the surfaces of titanium and its alloy powders using a novel method, self-shearing reactive milling, under a nitrogen pressure of 50 bar. The Ti, Ti6Al4V, and Ti-5553 spherical powders were milled for up to 10 h at ambient temperature without grinding balls. As a result of the experiments, a thin, brittle TiN coating formed on the powders’ surfaces. The cross-sections of the milled powders reveal that the TiN layer thickness is in the nanometer range (about 500 nm). By analyzing the sequence of X-ray diffraction patterns, it is evident that only for the Ti6Al4V powder milled for 10 h, two peaks are observed that can be attributed to a TiN phase. On the other hand, Raman spectroscopy revealed characteristic TiN spectra even for samples collected at the initial stage of self-shearing reactive milling. An important aspect of the experiment was the preservation of the spherical shape of the milled powders, which makes them a potential feedstock for additive manufacturing of functionally graded biomaterials. Full article

Additive manufacturing (AM) of Ti-6Al-4V alloy is widely used in aerospace and medical fields due to its excellent strength and corrosion resistance. However, the microstructural heterogeneity induced by the AM process often results in fatigue properties inferior to those of their forged counterparts. Synchrotron Radiation Computed Tomography (SR-CT) was employed to conduct an in situ three-dimensional investigation of fatigue damage evolution in Ti-6Al-4V alloy fabricated via laser powder bed fusion (LPBF). Experimental results revealed phenomena of crack bridging and deflection, accompanied by the consistent presence of local high-density zones (LHDZs) throughout the fatigue damage progression. Combined with quantitative analysis of crack propagation rates, the influence of LHDZs on fatigue damage evolution was analyzed, and the relationship between AM processes, LHDZs, and fatigue damage was discussed. The results indicate that the basket-weave α-phase microstructure in Ti-6Al-4V prepared by LPBF exhibits a high correlation with the distribution of LHDZs, and the orientation of LHDZs aligns with the crack propagation direction. By adjusting process parameters such as cooling rate and temperature gradient, the formation of LHDZs can be modified, thereby influencing the fatigue properties of the material. This provides theoretical support for achieving process optimization of the fatigue properties of Ti-6Al-4V alloy prepared via LPBF. Full article

This study examines the effect of vanadium addition on the microstructure and mechanical properties of low-cost powder metallurgy Ti-4Al-2Fe-3Cu alloys. Alloys with and without 6 wt.% V were fabricated by hot extrusion of blended elemental powders followed by vacuum heat treatment. Microstructural analysis revealed that the base alloy exhibits a coarse lamellar α/β structure, while vanadium addition promotes a refined basketweave morphology with a significantly higher β-phase fraction, increasing from 28.1% to 46.2%. Energy-dispersive spectroscopy confirmed preferential partitioning of Fe, Cu, and V into the β phase. Mechanical testing showed that the addition of 6 wt.% V markedly enhances strength, increasing yield strength and ultimate tensile strength from 1122 MPa and 1214 MPa to 1291 MPa and 1349 MPa, respectively, while maintaining comparable tensile ductility (~3.5%). The strength improvement is attributed to α-plate refinement, increased β-phase fraction, and solid-solution strengthening of the β phase. These results demonstrate that vanadium addition is an effective approach for improving the strength of low-cost PM titanium alloys without compromising ductility. Full article

Although processing windows have been widely reported for LPBF Ti-6Al-4V, the distinct roles of laser power, scanning speed, and hatch distance remain unclear beyond VED-based comparisons. In this work, the distinct effects of laser power, scanning speed, and hatch distance on the microstructural evolution and mechanical response of laser powder bed fusion (LPBF) Ti-6Al-4V (Ti64) are investigated within a stable processing window with comparisons among different parameter combinations at a comparable VED. A total of 56 processing conditions were designed, and microstructure/texture and properties were characterized by OM/SEM, EBSD, microhardness (HV0.5), and hole-drilling residual stress measurements. Within the selected processing window, prior-β grain morphology, α’ martensite thickness, texture, microhardness, and residual stress exhibit distinct sensitivities to different processing parameters. Specifically, lower scanning speeds and smaller hatch distances promote more continuous <001>β epitaxial growth, whereas higher scanning speeds or larger hatch distances produce fragmented prior-β grains. The α’ lath thickness shows the strongest dependence on scanning speed with a secondary influence from hatch distance, while laser power mainly provides an overall thermal modulation. Furthermore, the macroscopic α (0002) texture is mainly governed by the β solidification texture, with α-variant selection playing a secondary, amplifying role. In addition, microhardness correlates with α’ martensite thickness following a Hall–Petch equation. The peak residual stress is more sensitive to scanning speed, while bulk residual stress varies more significantly with hatch distance. These findings demonstrate that process parameters, in addition to VED, can guide microstructural control and mechanical optimization in LPBF Ti64 alloy. Full article

Multi-material structures based on titanium alloys represent a promising approach for the fabrication of functionally graded orthopedic implants capable of combining high mechanical strength with reduced stiffness to minimize the stress-shielding effect. In the present work, multi-material Ti15Ta/Ti6Al4V specimens were fabricated by laser powder bed fusion (L-PBF) for the first time, and the processing parameters of the transition zone were systematically optimized. Three regimes were investigated: baseline (93 J/mm³), double scanning (186 J/mm³), and reduced speed (116 J/mm³). The microstructure and elemental distribution were examined by SEM and EDS; mechanical properties were evaluated through tensile testing and microhardness measurements; biocompatibility was assessed using osteoblasts and gingival fibroblasts. The double scanning regime provided the highest density of the transition zone (99.49%). Tensile failure of the specimens occurred in the Ti15Ta region, confirming the quality of the metallurgical bond. The ultimate tensile strength ranged from 534 to 543 MPa with an elongation at break of 15.7–16.4%. Heat treatment at 875 °C led to the formation of an equilibrium lamellar microstructure and smoothing of the interface. Cell viability on both alloys exceeded 88% as confirmed by flow cytometry and remained above the 70% non-cytotoxicity threshold defined by ISO 10993-5. The obtained results demonstrate the technological feasibility of fabricating multi-material Ti15Ta/Ti6Al4V structures and achieving high-quality metallurgical bonding, which constitutes a necessary first step toward the development of functionally graded orthopedic implants. Full article

Aiming at the contradiction between forming quality and efficiency in the existing research on thick-layer laser powder bed fusion (LPBF) manufacturing of Ti6Al4V, this study focused on the influence of near-circular keyhole defects caused by scanning speed on the short-term mechanical properties of Ti6Al4V alloy manufactured by high-efficiency LPBF with a 100 μm layer thickness, the build rate of which reached 14 mm³/s. When the scanning speed decreased to 800 mm/s, the relative density decreased from 99.87% to 99.27%, and the maximum pore size increased from 19.6 μm to 87.2 μm. Under the conditions of high relative density (above 99.8%) and maximum pore size less than 20 μm, the annealed Ti6Al4V samples could achieve a tensile strength of 1009.7 MPa, a yield strength of 914.0 MPa, an elongation of 15.2%, and an impact toughness of 41.71 J/cm². With the increase in porosity and a maximum pore size exceeding 50 μm, the tensile strength became more unstable and exhibited a declining trend, while the impact toughness decreased by more than 5%. This is mainly attributed to the stress concentration around large-sized pores, leading to the easy generation of long and deep cracks at the edges and reducing the material’s ability to resist crack initiation and propagation. Full article

A Ti6Al4V alloy fabrication via laser powder bed fusion (L-PBF) leads to the formation of coarse columnar β grains that give rise to anisotropic mechanical properties and inadequate strength. Incorporating the rare-earth oxide, yttrium oxide (Y₂O₃), has proven an effective strategy in enhancing the mechanical performance of Ti6Al4V alloys. Nevertheless, the critical Y₂O₃ content required to achieve an optimal strength–ductility balance in L-PBF Ti6Al4V has not been systematically determined. To address these critical gaps, this study, for the first time, systematically investigates the effect of various Y₂O₃ contents on the microstructural evolution and mechanical properties of Ti6Al4V alloys fabricated via L-PBF. The results demonstrate that a Y₂O₃ addition of 0.2 wt.% produces β grains and α phases with average sizes of 61.6 and 7.6 μm, respectively. Transmission electron microscopy observations reveal that Y₂O₃ nanoparticles, together with elemental Y nanoparticles formed by reduction, are distributed both within the α-Ti matrix and along phase boundaries. This distribution effectively reinforces grain boundaries and promotes heterogeneous nucleation, thereby refining the microstructure. Mechanical property tests indicate that the alloy strength significantly improves as the Y₂O₃ content increases. Specifically, the alloy with 0.2 wt.%Y₂O₃ exhibits a tensile strength of 1106 MPa, a yield strength of 1074 MPa, and an elongation of 10.7%. This study proposes an innovative rare-earth strengthening method for refining the microstructure of L-PBF-fabricated titanium alloys and comprehensively enhancing their mechanical properties. Full article

Laser Powder Bed Fusion (L-PBF) can enable in situ microstructural tailoring of metallic components by precisely controlling the layer-wise processing parameters. Layer rescanning is one such strategy used to induce localized microstructural modification. In this study, we investigated the effect of a lattice-based selective rescanning approach applied to different base scan strategies for Ti-6Al-4V samples. The lattice regions were selectively rescanned at 50% reduced laser power relative to the initial scan along the same laser path. Relative density, porosity, martensitic α′ morphology, phase fraction, and Vickers microhardness were compared with those of non-rescanned reference counterparts. Different scan strategies, including unidirectional, stripes, and chess, exhibited distinct responses to selective rescanning, resulting in localized variations in martensitic phase formation and hardness values. The extent of localized microstructural modification and hardness enhancement was strongly governed by the underlying scan strategy. Selective rescanning using the stripes strategy yielded the largest contrast between non-rescanned and rescanned regions. The unidirectional strategy showed strong effects of rescanning, but the heat-affected zones extended to the non-rescanned regions. In contrast, the chess strategy exhibited comparatively moderate changes owing to its inherent thermal-management characteristics. These findings demonstrate that selective rescanning can provide an effective, localized approach for tailoring microstructure and hardness enhancement in L-PBF Ti-6Al-4V, with its effectiveness strongly dependent on the underlying scan strategy. Full article

Cr-Al composite coatings were fabricated on Ti-6Al-4V alloy substrates via mechanical alloying using a high-energy planetary ball mill. The coatings exhibited a distinctive bilayer architecture comprising an inner layer with coarse reinforcing particles and an outer layer featuring a refined, homogenized microstructure. Systematic investigations were conducted to elucidate the influence of rotational speed on coating formation, microstructural evolution, phase composition, and high-temperature oxidation performance. The findings revealed that insufficient milling speeds failed to facilitate adequate powder deposition, resulting in poor interfacial adhesion and the formation of porous or thin coatings. Conversely, excessive rotational speeds induced surface roughening and coating delamination. Optimization studies identified 250 r/min as the optimal milling speed, yielding dense, well-adherent coatings with superior oxidation resistance. Cyclic oxidation testing at 850 °C demonstrated that coated specimens exhibited significantly reduced mass gain compared to uncoated substrates. Post-oxidation characterization confirmed the formation of a protective corundum-type oxide scale (α-Al₂O₃ and Cr₂O₃) and revealed a four-layered structure in the oxidized coating: (I) a dense oxide film serving as an oxygen barrier, (II) a dense alloyed layer, (III) a porous alloyed layer, and (IV) an inner diffusion zone. These results demonstrate that the mechanically alloyed Cr-Al coatings provide effective protection against high-temperature oxidation for Ti-6Al-4V alloy substrates. Full article

Laser metal deposition operates on the principle of layer-by-layer material addition, wherein each layer is formed by overlapping individual single tracks. Consequently, clads formed serve as the fundamental building blocks for this technology. Their quality directly affects the overall build quality, particularly the geometric characteristics, which are also critical to process productivity. In the present work, geometric characteristics of TiC/Ti6Al4V single tracks fabricated via laser metal deposition are optimised. An artificial neural network model was developed to predict the clad width, height, and dilution using processing parameters, laser power, scan speed, and powder feed rate, as model inputs. The Particle Swarm Optimisation algorithm was employed for hyperparameter selection. The hyperparameter-optimised model achieved a mean squared error of 0.00183 and an R² score of 0.979 during training, and a mean squared error of 0.00709 and an R² score of 0.887 during testing. Although the small discrepancy between training and testing metrics suggests slight overfitting, likely due to the size of the dataset, the model achieved a mean absolute percentage error of less than 10% during testing. Subsequently, process plots generated by the model predictions were used to identify suitable parameters, and a processing map was developed to highlight the window that achieves suitable dilution (14–24%), defect-free sound bonding, and thick and dense clads. Full article

The dynamic development of laser therapy in dentistry is associated, among other factors, with the bactericidal effect of the energy emitted by laser devices. Therefore, they are also helpful for decontamination. They are increasingly used in the treatment of peri-implantitis, a bacterial inflammation of peri-implant tissues that is the most severe late complication of implantation and a potential cause of implant loss. Therefore, this study aimed to assess the safety of laser decontamination of the implant surface with respect to its effect on the integrity of the implant structure. In the present study, blocks of the titanium alloys Ti-6Al4V and Ti6Al7Nb were fabricated using electron-beam powder bed fusion and laser powder bed fusion, respectively. These alloys, commonly used in implantology, here in the form of Ti block scaffolds, have been exposed to an Er³⁺:YAG laser under various parameters (energy range of 50–320 mJ, exposure times of 20 or 30 s), and their effects have been further observed. To determine the changes induced by the laser, the following techniques were used: X-ray diffraction (XRD), Rietveld refinement method, scanning electron microscopy (SEM) with EDS (Energy-dispersive X-ray Spectroscopy), and thermography. The results show that the proposed Ti6Al4V and Ti6Al7Nb scaffolds can be exposed to an Er³⁺:YAG laser without damage when the power is limited to 0.5 W. Full article