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3D printing technology has the potential to allow for the development of customized lightweight porous materials with superior mechanical performances that are difficult to produce by conventional methods. In this study, Ti–Zr gyroid scaffolds with high compressive strength were produced via a selective laser melting (SLM) process using a pre-mixed Ti–ZrH2 powder. The effect of lattice geometries and the addition of ZrH2 on compressive performance were investigated. The results indicated that there was a homogeneous distribution of Zr in α-Ti. By increasing the concentration of ZrH2 to 7 wt.%, the yield strength and ultimate compressive strength increased by 35–55% compared to those of the Zr-free alloy. Young’s modulus was found to be in the range of 1–5 GPa. The high compressive strength and low Young’s modulus of the Ti–Zr gyroid scaffolds obtained in this study showcase the strong potential of this material for implant applications.

In this study, Ti-(N) powders with a core–shell structure were prepared via a nitriding process of titanium (Ti) powders for metal additive manufacturing (AM). Nitriding of spherical Ti powders (D50 = 130 µm and D50 = 63 µm) was carried out at different temperatures from 873 K to 1373 K for 10 min. The nitriding process enabled the manufacture of a core–shell-structured Ti-(N) powder, where an N-enriched shell surrounds a lower N core. The thickness of the N-rich Ti shell increases exponentially with increasing nitriding temperature. Depending on nitriding temperature, a shell layer consisting of Ti2N and TiN compounds can form. Based on X-ray diffraction (XRD) results, it was identified that the N-rich shell is composed of (i) only Ti(N) solid solution when nitrided below 1023 K; and (ii) Ti(N) solid solution, Ti2N and TiN compounds if nitrided at or above 1023 K. The core–shell-structured Ti-(N) powders were subsequently used to manufacture bulk samples by spark plasma sintering (SPS) and laser metal deposition (LMD) processes for comparison. The microstructure was characterized and discussed. LMD-fabricated Ti-N alloy samples exhibited high tensile strength (965 MPa) with good tensile ductility (7.6%) due to the homogeneous distribution of N and fine grain size. In contrast, SPS-fabricated Ti-N alloy samples using the same nitrided Ti-N powder showed much lower tensile strength (708 MPa) with essentially no tensile ductility (0.3%) due to the inhomogeneous distribution of N. LMD can allow the fabrication of strong and ductile Ti-N alloys while it is not possible by SPS.

This study aims to improve the mechanical properties of a Ti–2Fe base alloy by adding W solute and performing hot extrusion at a high temperature (1000 °C). W was added at 0, 1, 2, and 3 wt% using the powder metallurgy route and homogenization heat treatment. The as-extruded materials predominantly consisted of α phase with different microstructure morphologies; Ti–2Fe and Ti–2Fe–1W contained equiaxed α grains, while Ti–2Fe–2W and Ti–2Fe–3W showed equiaxed + acicular and acicular shape, respectively. Effective grain refinement was obtained in Ti–2Fe–2W (average grain size: ~1.64 μm), which greatly contributed to the strengthening. The solid solution of W was studied with X-ray powder diffraction, where a proportional increment of β lattice constant occurred as the W solute increased in the matrix (Ti–Fe). Additionally, electron backscatter diffraction analysis revealed that the W solution reduced the intensity of the prismatic texture along the extrusion direction. Based on the experimental evaluations, extruded Ti–2Fe–2W alloy exhibited a maximum yield strength of 925 MPa with excellent elongation 30% at room temperature, indicating a remarkable trade-off in strength and ductility.

Light elements such as oxygen (O) and nitrogen (N) significantly impact the microstructure and mechanical properties of Ti-based materials through solid solution strengthening. The microstructures of Ti-based materials processed via selective laser melting (SLM) have also been observed to contain a martensitic phase that improves the tensile strength. However, this improvement is achieved at the cost of reduced ductility. This study considered the use of post-heat treatment N dissolution to enhance the ductility of SLM-processed α-Ti materials. Tensile testing of the as-fabricated SLM Ti-(N) revealed a significantly increased strength of ~1200 MPa and a low ductility of 5% for N content of 0.5 wt%. However, the quenched samples exhibited increased ductility by up to 20%, with the microstructure, including primary α (αp) and transformed β structures. Further examination via electron probe micro-analysis (EPMA), transmission electron microscopy (TEM), in-situ high-temperature SEM observation and in-situ EBSD observation during tensile testing revealed that the enhancement in ductility of the quenched SLM-processed Ti-(N) samples was significantly due to alteration of the grain morphology, dislocations and N distribution. The findings of this study further clarify the microstructural evolution and deformation response of SLM-processed Ti-(N) materials under water quenching.

Research related to the substitution of ubiquitous elements for high-cost rare elements during the fabrication of high-performance Ti alloys has attracted significant attention. The microstructure evolution is, however, challenging when several elements with different properties are used. This research aims to study the effect of Si addition on the microstructure formation of the dual-phase Ti alloys in the presence of solid solution-forming elements such as Fe and Cu, and a high oxygen concentration. Ti–4Fe–0.5O–3Cu (TFOC) alloys with different Si contents (0.2, 0.4, and 0.6 wt%) were fabricated from the elemental powders using spark plasma sintering, followed by hot extrusion. The TFOC sintered alloys with 0.2 and 0.4% Si showed very similar microstructures in the lamellae α+β dual-phase. The coarsening of α colonies and primary β grains was remarkable when Si content increased to 0.6%. The obtained primary β grains were, however, significantly smaller than those in previous studies. In contrast, the refined globular α grains (respective grain sizes = 2.6 and 2.2 μm) embedded in the β matrix were observed in the hot extruded TFOC–0.2Si and TFOC–0.4Si alloys due to dynamic globularization. Additionally, EBSD analysis clarified that the hot extruded alloys had the strong fiber textures of (10 1 ¯ 0) and (101) for α and β phases respectively, which were consistent with the XRD results. High-resolution TEM examination demonstrated that Ti2Cu and Ti3Cu intermetallics of a length of 100–400 nm could form preferentially at α/β interfaces. The experimental results showed that 0.4 wt% Si added to TFOC alloys formed fine globular microstructures in the presence of hot plastic deformation.

The demand for using high-performance Cu matrix composites in the electronic industry has recently increased rapidly owing to the low strength and tribological properties of pure copper. Accordingly, research and development of composite processing and related properties have increased. In this study, the Cu matrix was reinforced with different amounts of TiB2 particles by mechanical alloying of elemental powders followed by consolidation employing spark plasma sintering (SPS) whereby high relative density (∼99%) and electric conductivity (∼83–88% IACS) were obtained. Tensile properties and deformation mechanisms of the composites were studied utilizing conventional and in-situ tensile tests with simultaneous FESEM and EBSD observations. In comparison with the reference pure copper, it was found that adding 0.5 wt%TiB2 results in significant ductility increment, which was consistent with the longer strain-softening behavior observed after necking. In addition, using in-situ microstructure characterization, twinning with slip bands were confirmed as deformation mechanisms. By increasing the amount of reinforcement to 5 wt%TiB2, strengthening was remarkable while sustaining a considerable elongation. The Hall-Petch and dislocation strengthening mechanisms were the key models of strengthening based on the calculations and microstructure characterizations since by increasing the TiB2 particles, significant grain refinement and dislocation density were shown.

Customized titanium 3D parts with good mechanical performance have attracted considerable attention for application in structural industries. In this study, α-Ti materials with superior tensile strength and good ductility were fabricated via additive manufacturing (AM). To improve the mechanical properties, core-shell structured Ti-(N) powder was used to introduce nitrogen atoms into selective laser melting (SLM) fabricated Ti materials. The microstructural analysis of as-fabricated Ti materials revealed an α microstructure with various grain morphologies such as irregular/massive grains, equiaxed grains, and refined acicular martensite grains (α՛) when different energy densities (E) from 83 J/mm3 to 278 J/mm3 were applied. Furthermore, we observed that grain refinement occurred with increasing solute nitrogen atoms. The mechanical properties were evaluated based on interrelated aspects, including nitrogen content and energy density, by changing the scanning parameters. Our results showed that as the nitrogen content in the as-fabricated Ti materials increased, a significant improvement in tensile strength and hardness was observed. The yield strength (σys) and ultimate tensile strength (σUTS) increased up to 1072 MPa and 1126 MPa, respectively, when the nitrogen content was approximately 0.5 wt.%, which was approximately three times that of SLM-processed pure Ti (∼0.01 mass% N). The increment in yield strength was further discussed mainly in terms of solid solution strengthening using the Labusch model and grain refinement strengthening using the Hall-Petch equation. This calculation raises the ability to quickly predict the yield strength of Ti materials with nitrogen solid solution produced by selective laser melting.

In this study, interstitial solid solution behavior of nitrogen atoms dissolved in commercially pure Ti fabricated by spark plasma sintering (SPS) followed by the extrusion process was investigated. Microstructural observations of the extruded Ti-(N) samples before homogenization, ExTi-(N), revealed the nitrogen element's segregated regions as a result of a short time of the SPS process. Because of the inadequate sintering time, nitrogen atoms were unable to dissolve in the α-Ti matrix homogeneously, which caused a material degradation through brittle failure initiating at high nitrogen absorbed regions. Applying homogenization heat treatment at 1123 K for 180 min followed by hot extrusion, improved microstructural homogeneity without the nitrogen segregation. Furthermore, grain morphology was transformed from coarse elongated grains with substructures into refined equiaxed α-Ti grains. The yield strength and ultimate tensile strength of the Ti-(N) sample with 0.69 wt%N reached maximum 957 MPa and 1117 MPa, respectively, which represented 148% and 214% increments over as-extruded pure Ti sample. In addition, a 50% enhancement of elongation of homogenized Ti-(N) alloys compared to the non-homogenizing condition was achieved. The improvement of strength and elongation was primarily attributed to grain refinement and solid solution strengthening. The quantitative evaluation of strengthening and mechanisms was discussed in detail by the Hall-Petch formula and Labusch model.

Ti-based materials with high oxygen solute contents were fabricated from mixtures of Ti powder and TiO2 particles by selective laser melting (SLM). Uniformly dissolved oxygen (O) from the TiO2 particles caused c lattice expansion in α-Ti crystals, which effectively increased the strengths of as-built SLM Ti–O materials. The as-built SLM Ti–O material using 1.5 wt% TiO2 showed a yield stress of 962 MPa and 15.3% elongation. The yield stress increases calculated by the Hall–Petch equation and Labusch model were equivalent to those observed experimentally, and O solid-solution strengthening was dominant in increasing yield stress.

This investigation presents a selective laser melting strategy for fabricating high nitrogen-content Ti (Ti-N) materials. Unlike conventional cast Ti materials, Ti-N materials produced in this study exhibited a good balance of mechanical properties with an ultimate tensile strength of 976 MPa and 21.7% elongation due to solid-solution strengthening by N atoms originating in the Ti2N layers covering pure Ti spherical particles.

Titanium powder metallurgy materials with solid solution nitrogen elements were developed by using pure Ti powder with high nitrogen contents (Ti-(N)), which were prepared via heat treatment from 640 °C to 800 °C in a N2 gas atmosphere. Ti2N compound layers were formed at the Ti-(N) powder surface as a shell, and solid solution nitrogen elements were also detected in the matrix of this powder. Ti-(N) powder was consolidated by spark plasma sintering (SPS), where Ti2N compounds were completely decomposed, and hot extrusion was then used to fabricate fully dense titanium with solid solution nitrogen elements. X-ray diffraction analysis showed that the lattice constant of α-Ti along the c-axis clearly increased in proportion to the nitrogen content due to the nitrogen solid solution behavior. Tensile test results revealed that the powder metallurgy titanium with 0.52 mass% nitrogen exhibited a 0.2% yield stress of 813 MPa and 31% elongation, which were remarkably superior to the strength-ductility balance of pure titanium with a 0.2% yield stress of 305 MPa and 25% elongation. In this study, the Hall-Petch equation and Labusch model were used to quantitatively evaluate the mechanism for the α-Ti grain refinement and solid solution strengthening effects of Ti-(N) powder metallurgy materials.

Nickel(Ni) layer was applied to the surface of pure aluminum(Al) by electrodeposition for 15 minutes using a direct current (DC) condition at 0.13 Acm-2. Heat treatment was employed subsequently for 1, 2.25 and 4 hours at the temperatures of 600 and 650oC, which are below and above the eutectic temperature of Al-NiAl3, respectively. All samples were characterized by OM, SEM, EDS and GIXD. DTA was also performed to study heat release in the reactions. After heat treatment at 600oC, the specimens exhibit the non-uniform formation of Ni2Al3 and NiAl3, even after 4 hours of heat treatment where local melting possibly occurs due to the exothermic heat of formation. In contrast, owing to fast interdiffusion of Al and Ni as assisted by a liquid phase formation, multi-layer of Ni2Al3 and NiAl3 was uniformly formed along the interface of the specimens heat treated at 650oC.