Search Results (146)

Ti–6Al–4V is the primary titanium alloy for aerospace, biomedical, and additive manufacturing applications; however, the high cost of powders produced by atomization limits their widespread adoption. This study aims to develop a cost-effective method for producing chemically homogeneous pre-alloyed Ti–6Al–4V powders from titanium sponge. A combined process is proposed, involving the hydrogenation of titanium sponge, mechanical alloying of the hydride phase with Al and V powders, and subsequent vacuum dehydrogenation. The formation of the brittle δ-TiH₂ phase facilitated intensive material comminution and effective distribution of the alloying elements. According to laser diffraction data, the median particle size decreased from 450 to 30–35 µm. X-ray diffraction (XRD) analysis confirmed the sequential α-Ti → δ-TiH₂ transition and the formation of a stable α + β two-phase structure characteristic of Ti–6Al–4V following dehydrogenation. SEM observations demonstrated that the final powders predominantly consist of individual fractured particles with limited hard agglomeration, favorable for powder flowability and compaction behavior. EDS analysis indicated a relatively homogeneous microscale distribution of Al and V without observable large-scale segregation. The synthesized powders exhibited low impurity levels, with O < 0.07 wt.% and H < 0.02 wt.%. The developed approach represents a promising and economical alternative to expensive atomization techniques for powder metallurgy and additive manufacturing. Full article

The fatigue performance of titanium alloys is a critical determinant of the service life and structural integrity for aerospace and marine engineering components. But within the framework of damage tolerance design, resistance to fatigue crack propagation is regarded as a key indicator governing the fatigue performance of these engineering structures. In previous work, while the general fatigue performance of Ti–6Al–4V-0.55Fe alloy has received systematic study, targeted research focusing on its resistance to fatigue crack propagation remains limited. Therefore, in this work, compared with Ti–6Al–4V ELI alloy, the fatigue crack propagation behavior and fracture mechanism of Ti–6Al–4V-0.55Fe alloy with a duplex microstructure were systematically investigated. The results show that when ∆K < 12.75 MPa⋅m^1/2, Ti-6Al-4V-0.55Fe alloy demonstrates superior resistance to fatigue crack propagation. Fractographic analysis indicates that the primary difference between the two alloys lies in the stage of crack initiation and early propagation. This behavior is attributed to the addition of trace Fe, which enhances α/β boundary resistance and thereby retards crack growth. Moreover, crack propagation of TC4-F alloy is also slowed by the increased path length from bypassing the α_p phase. Full article

SiC fiber-reinforced aluminum matrix (SiC_f/Al) composites have the potential to replace titanium alloys for fan/compressor blades due to their low density and favorable high-temperature performance. In this study, thermal exposure and thermal cycling tests were conducted to simulate service environments and to clarify their effects on the microstructure and interfacial properties of a SiC_f/AlFe5Si2 composite. Thermal exposure was performed at 260–450 °C for 20–100 h, and thermal cycling was carried out between 300 or 350 °C (1 h dwell) and room temperature for 20–100 cycles. Interfacial shear strength was evaluated by push-out tests, while microstructural evolution was examined using SEM, TEM/EDS, and XRD. Three-dimensional finite element simulations were used to assess mismatch-driven residual-stress distributions during the cooling stage after thermal excursion. The results showed that interfacial shear strength decreased with increasing exposure temperature/time and degraded more severely under thermal cycling than under isothermal exposure at the same temperature. A rapid loss of interfacial strength occurred above ~400 °C, associated with significant interfacial-layer thickening and the formation of brittle Al_xSiO_y phases. The interfacial reaction layer followed parabolic growth kinetics, yielding a preliminary apparent activation energy of Q ≈ 150 kJ/mol estimated from two isothermal temperatures. The simulations indicated large opposing stresses between the matrix and the carbon-rich layer, supporting a mechanical driving force for interfacial debonding; however, heating/dwell time-dependent effects were not explicitly modeled and are discussed as limitations. These findings provide quantitative guidance for defining service-temperature limits and improving interfacial thermal stability in SiC_f/AlFe5Si2 composites. Full article

This study analyzes the joint deformation behavior of low-alloy steel P355GH and commercially pure titanium Grade 1 in thick bimetallic pack assemblies during high-temperature vacuum roll bonding (HTVRB). Rheological properties were determined using a Gleeble 3800 (800–1000 °C, 0.1–10 s⁻¹). A 3D finite element model was developed and validated against laboratory rolling (error < 6% for force, <10% for layer geometry). Four sealed pack configurations were analyzed: nominally symmetrical (A1), asymmetrical with thin cover (A2), asymmetrical with thick cover (A3), and symmetrical (A4). For the first time, the effect of intensive combined titanium redistribution during initial rolling was quantitatively described, identified as the primary cause of longitudinal thickness variation (up to Δ = 125%) and deformation non-uniformity (ϑ = 0.32–0.96). Recommendations for industrial rolling have been established. High single-pass reduction (~20% initial passes) exacerbates titanium redistribution, risking delamination and equipment failure. A two-phase roughing strategy is recommended: a first phase with gradual reductions (5–10%) to suppress titanium flow until bonding initiation (40–50% total reduction); a second phase with higher reductions to ensure bonding and refine brittle intermetallic and carbide phases. The findings support production of geometrically precise large-sized titanium clad steel plates for power engineering and other applications. Full article

To address the issues of high cutting temperatures and severe tool wear during titanium alloy machining, this study proposes a hybrid surface modification strategy combining micro-textures and multicomponent titanium nitride (TiN)-based coatings on cemented carbide tools. Using YG8 cemented carbide as the substrate, micro-dimple textures were fabricated by fiber laser, and three coatings with different architectures (TiAlSiN, TiSiN/TiAlN, and TiSiN/TiAlSiN/TiAlN) were deposited via multi-arc ion plating technology. Based on a two-factor (texture diameter and texture spacing) and three-level orthogonal experiment, the evolution behaviors of surface morphology, phase composition, and mechanical properties of the textured multicomponent TiN-based coatings were systematically characterized and comparatively analyzed. The results reveal that: compared to the monolithic-structured TiAlSiN coating, the TiSiN/TiAlSiN/TiAlN and TiSiN/TiAlN composite coatings with multilayered composite structures can effectively relieve the residual stress inside the film–substrate system, and significantly suppress the phenomena of coating cracking and localized spallation caused by irregular protrusions of the recast layer at the micro-texture edges. X-ray diffraction (XRD) and crystallite size analyses indicate that the amorphous Si₃N₄ phase promoted by the Si element in the composite coatings effectively impedes the growth of TiN columnar crystals, achieving significant grain refinement. Mechanical property tests confirm that the existence of multicomponent composite interfaces effectively hinders dislocation movement. Among them, the textured TiSiN/TiAlSiN/TiAlN composite coating exhibits the optimal comprehensive performance; its microhardness, nanohardness, and H/E ratio (characterizing the resistance to plastic deformation) are increased by 17.94%, 8%, and approximately 45%, respectively, compared to those of the textured TiAlSiN coating. This study deeply elucidates the synergistic strengthening and toughening mechanisms between micro-texture parameters and the internal structures of the coatings, providing important theoretical guidance and experimental data support for the surface design of long-lifespan tools oriented towards the high-efficiency machining of titanium alloys. Full article

This study compares the microstructural evolution and mechanical properties of TC4 (Ti-6Al-4V) titanium alloy joints welded by Tungsten Inert Gas (TIG) and laser processes, following a post-weld annealing treatment at 650 °C for 2 h. Distinct microstructures were obtained: the TIG-welded joint developed a heterogeneous mixture of short-rod α and lamellar β, while the laser-welded joint formed a more homogeneous equiaxed α structure with uniformly distributed β-phase nanoparticles. Electron backscatter diffraction (EBSD) results confirmed that the annealing treatment significantly weakened the strong welding-induced texture and disrupted the epitaxial growth mode of columnar grains. Mechanical testing demonstrated that annealing improved the strength-toughness balance, but the extent and mechanism differed between the two processes. For the TIG-welded joint, the ultimate tensile strength slightly decreased, while elongation and impact toughness increased by 18% and 10.4%, respectively. In contrast, the laser-welded joint maintained its original strength while achieving greater improvements in ductility and toughness, with elongation and impact toughness increasing by 20% and 15.2%, respectively. This divergence is attributed to insufficient recrystallization and the persistence of residual coarse grains, limiting the TIG joint’s performance. However, in the laser-welded joint, the pinning effect of β-phase nanoparticles and associated grain refinement enhanced ductility without compromising strength. Full article

The development of multilayer coatings based on titanium carbides and nitrides remains one of the most active areas in materials science, owing to their ability to markedly enhance wear resistance and extend the service life of machine components. Particular interest is currently focused on tailoring conventional TiN/TiCN architectures through alloying metal additions. In this study, the tribological and mechanical performance of aluminum- and zirconium-doped TiN/TiCN multilayer coatings deposited by direct-current magnetron sputtering onto 41Cr4 steel was investigated. The morphology, elemental distribution, and phase constitution of the multilayer coatings were examined. It is shown that increasing the number of bilayers from two to four in TiN/TiCN–based multilayer coatings leads to improved tribomechanical characteristics. It was determined that zirconium provides a more pronounced beneficial effect than aluminum. The four-bilayer TiZrN/TiZrCN coating simultaneously exhibited the lowest coefficient of friction (0.11) and wear rate (10⁻⁶ mm³ m⁻¹ N⁻¹) at a hardness of 16.4 GPa. 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

This study employed a gradient heat treatment strategy to efficiently acquire microstructure parameters and establish the microstructure–hardness relationship in Ti-6Al-4V-1.5Zr-1.0Nb-0.5Mo alloy, addressing the knowledge gap in rapid optimization of heat treatment windows. Gradient solution treatment in the α + β region (859–928 °C) revealed that hardness reaches a minimum at a Vα_p/Vβ_t ratio of approximately 0.5, a condition to be avoided if aging is not applied. Subsequent aging at 500 °C, a common temperature for such alloys, highlighted the solution-treated sample at 908 °C as possessing high hardening potential, attributed to its high β_t fraction (Vβ_t = 70%) and sufficient retained β phase that promoted fine α_s precipitation. Gradient aging (502–590 °C) of this optimized microstructure further showed that peak hardness (>350 HV1, measured under a 1 kg load) was achieved at 502 °C and 551 °C, where the Vα_p/Vβ_t ratio remained near the optimal 3:7, and the precipitated refined α_s exhibited minimal width. The hardness of the bimodal microstructure is governed by two principal factors: the Vα_p/Vβ_t ratio (optimum near 3:7) and the precipitation efficiency of refined α_s from retained β phase. The gradient approach proves to be an effective high-throughput method for rapidly correlating heat treatment parameters with microstructure and properties, accelerating the design of heat treatments for titanium alloys. Full article

This work investigates the NiTi shape memory alloys fabricated via laser powder-directed energy deposition (LP-DED). The properties of NiTi alloys produced by powder metallurgy or additive manufacturing routes are strongly influenced by the type of feedstock material employed. Two powder feedstocks were used for DED fabrication: a blended mixture of elemental nickel and titanium powders with a nominal chemical composition of Ni56Ti44 (wt.%) and a pre-alloyed NiTi powder containing 55.75 wt.% Ni. Samples fabricated from both types of powders were subjected to microstructural characterization, phase composition analysis, and mechanical and corrosion testing. It was found that DED processing on a non-preheated CP-Ti substrate is prone to warping and that samples deposited from the elemental Ni and Ti powder mixture exhibited pronounced inhomogeneity of microstructure and mechanical properties along the build direction, accompanied by the formation of the Ti₂Ni secondary phase. The absence of a superelastic plateau was observed in the corresponding stress–strain response. On the contrary, the samples deposited from the pre-alloyed NiTi powder exhibited a microstructure composed of B2 and B19′ phases and already demonstrated a clear superelastic response in the as-built condition during tensile loading. Based on the tensile test results, this NiTi material was used only for superelasticity testing. The superelastic behavior was further enhanced by post-deposition heat treatment, which significantly increased the recovery rate from 53% to 89%. Full article

Heterostructure (HS) refers to a class of structural materials composed of two or more different chemical components or crystal structures. Integration of Inconel 625 (IN625) nickel-based superalloy and Ti6Al4V (TC4) titanium alloy to a HS material offers a promising strategy to achieve graded thermo-mechanical properties, extended service temperature ranges, and significant weight reduction, which are highly desirable in aerospace applications. However, obtaining a better metallurgical bonding between the two alloys remains a critical challenge. In this study, laser directed energy deposition (L-DED) technology was employed to fabricate IN625/TC4 HS materials with a nonlinear gradient transition, following systematic investigations into the phase composition and crack sensitivity of IN625/TC4 gradient layers prepared from mixed powders of varying compositions. In addition, microstructure, phase distribution, and mechanical properties of HS materials at room temperature were characterized. The metallurgical defect-free IN625/TC4 HS material was successfully prepared, featuring a smooth transition of microstructure, reduced cracking sensitivity, and reliable metallurgical bonding. Furthermore, a novel design concept and illustrative reference for the L-DED fabrication of N625/TC4 HS material with excellent comprehensive performance was presented, while providing a theoretical metallurgical basis and data support for the potential applications of IN625/TC4 HS materials in the field of aerospace. Full article

In this work, two configurations of Ti/HAp functionally graded coatings were fabricated on Ti–6Al–4V alloy substrates using detonation spraying. The coatings differed in the number and sequence of Ti and hydroxyapatite (HAp) deposition cycles, resulting in distinct gradient architectures: Configuration 1 incorporated a sharper transition from the Ti-rich base to the HAp-rich surface, whereas Configuration 2 featured a smoother and more gradual compositional gradient. The microstructure and elemental distribution were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Both configurations exhibited well-defined gradient layering, with titanium concentrated near the coating–substrate interface and an increased Ca and P content toward the upper bioceramic region. Raman spectroscopy confirmed the preservation of hydroxyapatite as the main phase, showing a characteristic 961 cm⁻¹ band. Adhesion strength measured according to ASTM C633-13 was 45.78 ± 4.4 MPa for Configuration 1 and 52.32 ± 6.7 MPa for Configuration 2, both significantly exceeding the minimum required 15 MPa. The findings demonstrate that detonation-sprayed Ti/HAp gradient coatings provide strong adhesion and stable bioceramic surfaces, making them promising for metal implant applications. Full article

Liquid γ-TiAl alloy was prepared by vacuum induction melting within graphite crucibles, then cast using a centrifugal technique. In this process, the degree of superheat (ΔT)—defined as the temperature above the melting point—was carefully controlled, with experiments conducted at ΔT of 200 K (i.e., 200 Kelvin above the melting temperature). It was observed that carbon content in the alloy increased nonlinearly as the melt was held longer in the graphite crucible; for example, carbon concentration rose from an initial value of approximately 0.21 at% to 0.98 at% after 100 s of holding and to 2.11 at% at 650 s of holding. When the melt was held for over 100 s at ΔT = 200 K, titanium carbide (TiC) and titanium aluminum carbide (Ti₂AlC) particles formed along the crucible wall. This resulted in changes to the phase fractions and a corresponding increase in aluminum concentration in the melt. Two types of Ti₂AlC phases were observed: one consisted of coarse Ti₂AlC particles, which were crystallized through peritectic reaction from the TiC carbide and liquid phase. The other consisted of fine Ti₂AlC particles, which were decomposed from the α₂ (Ti₃Al) phase within the interlamellar regions. After 20 s of holding at ΔT = 200 K, carbon rapidly dissolved into a solid solution. Prolonged holding led to significant grain refinement: the microstructure evolved from columnar to equiaxed grains, primarily due to TiC crystallization. This transition is significant because finer, equiaxed grains can enhance mechanical properties such as strength and toughness. The findings provide valuable insight into the interaction between graphite crucibles and γ-TiAl melts, demonstrating how controlled superheat and holding time influence carbon uptake, carbide formation, and microstructural evolution—factors critical for optimizing the performance and manufacturability of γ-TiAl components. Full article

Lock-in thermography is a widely used nondestructive testing technique for detecting subsurface defects in solid materials. In this study, one-dimensional analytical modeling and three-dimensional finite element simulations were combined to elucidate how lateral heat conduction influences quantitative depth estimation in titanium alloy material using two inversion strategies: the blind frequency method and the phase difference method. Parametric analyses were conducted for defect radius-to-depth ratios ranging from 0.5 to 8 under various excitation frequencies. Results show that the blind frequency method can significantly underestimate defect depth with errors of up to 20.7% when the radius-to-depth ratio is as small as 0.5. To mitigate this bias, an exponential correction model was developed to compensate for lateral conduction effects, reducing the error to within ±5%. The accuracy of the phase difference method is found to depend jointly on defect depth, excitation frequency, and the ratio of defect radius to thermal diffusion length; estimation errors become negligible when this ratio exceeds 3. The novelty of this work lies in identifying lateral conduction as a key bias source and establishing a quantitative correction framework for the depth inversion based on the blind frequency method. The proposed approach is expected to enhance the accuracy of quantitative thermography for engineering applications. Full article

The aim of this work is to investigate the effect of annealing (at temperatures ranging from 260 °C to 530 °C) of thin-walled Al-Mn-Mg-Ti-Zr samples manufactured by selective laser melting (SLM) on their tensile mechanical properties, hardness, and surface roughness. The results of this study may contribute to the development of post-processing modes for thin-walled products made of corrosion-resistant aluminum alloys with increased strength, manufactured using SLM technology. Hierarchical clustering methods allowed us to identify three groups of thin-walled samples with different strain-hardening mechanisms depending on the annealing temperature. The greatest hardening is achieved in the first group of samples annealed at 530 °C. Metallographic analysis showed that at this heat treatment temperature, there are practically no micropores (macrodefects) and microcracks. X-ray phase analysis showed the precipitation of Ti and Zr, as well as the formation of an intermetallic phase with a composition of Mg8Al16. At lower heat treatment temperatures, from 260 °C to 500 °C, the observed hardening is statistically significantly lower than at 530 °C. This phenomenon, combined with the formation of intermetallic phases and the precipitation of titanium/zirconium, contributes to the hardening of thin-walled Al-Mn-Mg-Ti-Zr alloy samples manufactured by SLM. The main results of this study show that the optimal strain hardening of thin-walled Al-Mn-Mg-Ti-Zr alloy samples manufactured by SLM is achieved by heat treatment at 530 °C for 1 h. The strengthening mechanism has two characteristics: (1) dispersion strengthening due to the formation of precipitates and (2) reduction in macrodefects at high temperatures. Full article