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The wide applicability of titanium (Ti) has prompted the analysis to improve its mechanical strength through the addition of different alloying elements. Among these, Ti materials with pre-mixed pure Ti and titanium nitride (TiN) powders as the starting materials have exhibited improved mechanical properties and tribological performance. In this study, the tribological properties of Ti matrix composites with ring-shaped TiN dispersoids were evaluated. The materials were fabricated from pre-mixed pure Ti powder and core–shell structured Ti–(N) powder, which were prepared by heat treatment at 1273 K under N2 gas. The tribological behavior of the Ti–TiN composites was studied by varying the applied load using a ball-on-disk wear test under oil lubrication conditions. The initial familiarity period of the Ti–TiN composites decreased. Subsequently, compared to the pure Ti specimen employed as a reference material, the friction coefficient was significantly lower and more stable. This is attributed to the ring-shaped, hard TiN dispersoids, which prevented the adhesion phenomenon and improved the oil film formability owing to the increase in microhardness and abrasive wear resistance of the nitrogen solid solution in the core region. [ABSTRACT FROM AUTHOR]

The decomposition behavior of ZrO2 particles and uniform distribution of Zr and O solutes were investigated by employing in situ scanning electron microscope-electron backscatter diffraction (SEM-EBSD) analysis and thermogravimetric-differential thermal analysis (TG-DTA) to optimize the process conditions in preparing Ti-Zr-O alloys from the pre-mixed pure Ti powder and ZrO2 particles. The extruded Ti-Zr-O alloys via homogenization and water-quenching treatment were found to have a uniform distribution of Zr and O solutes in the matrix and also showed a remarkable improvement in the mechanical properties, for example, the yield stress of Ti-3 wt.% ZrO2 sample (1144.5 MPa) is about 2.5 times more than the amount of yield stress of pure Ti (471.4 MPa). Furthermore, the oxygen solid-solution was dominant in the yield stress increment, and the experimental data agreed well with the calculation results estimated using the Hall-Petch equation and Labusch model. [ABSTRACT FROM AUTHOR]

• Heat treatment was vital for complete dissolution of W in Ti-4Fe matrix after sintering. • Ultrafine-gains formed in extruded Ti-4Fe-(1–3)W alloys compared to coarse grains in Ti-4Fe. • Ti-4Fe-(0–3)W alloys exhibited excellent mechanical properties during tensile test. • Tensile yield strength of Ti-4Fe-(0–3)W increased as W content increased. Thermomechanical processing and solid-solution strengthening are effective ways to improve the mechanical properties of Ti alloys with elements such as W and Fe. In this study, we present a novel extruded Ti-Fe-W alloys with improved mechanical properties. To analyze the effect of W on the mechanical properties and microstructure of the alloys, Ti-4Fe-xW (x = 0–3 wt%) alloys were prepared by spark plasma sintering followed by homogenization heat treatment and hot extrusion. The microstructure of the as-sintered specimens included undissolved W particles distributed in the acicular α + β matrix. However, heat treatment at 1300 °C for 1 h led to the complete dissolution of W. After hot extrusion at 850 °C, an ultrafine equiaxed (globular) microstructure was observed, in which Fe and W preferentially diffused into the β phase. The main effect of W on the microstructure was a remarkable grain refinement by activation of dynamic recrystallization and impediment of the grain boundary mobility in Ti-4Fe-(1–3)W (~1 µm) when compared to Ti-4Fe (~3 µm). Additionally, W increment resulted in a gradual decrease of the average size of α grains. The tensile yield strength increased as W content increased so that the Ti-4Fe-3W alloy exhibited a remarkably high tensile strength, yielding at ~1123 MPa with an elongation of ~26%. Finally, theoretical and experimental analyses suggested that grain refinement and solid-solution strengthening were the main mechanisms contributing to the strengthening phenomenon in W-containing alloys. [ABSTRACT FROM AUTHOR]

Two types of Ti-based materials with (1) N solutes and (2) TiN particles, as used in powder metallurgy (PM), were prepared from the same pre-mixed pure Ti and TiN powders. An optimized post heat treatment (HT) was applied to the forged samples to completely dissolve the N, originating from TiN particles existing as solid-solution atoms, into the Ti matrix. XRD analysis clearly indicated that only the (0002) α-Ti peak shifted to a lower diffraction angle after HT due to lattice expansion on the c-axis caused by N atoms in solution. Ti-based materials with N solutes showed a large increment in their tensile and compression strengths. Ti composites with TiN dispersoids, however, showed only a very small stress increment. For example, 20 MPa should be the incremental strength rather than the final tensile strength with the addition of 2-mass% TiN particles. Quantitative evaluation of the strengthening mechanism of the Ti-based materials with N solutes using the Hall-Petch equation and the Labusch model revealed that the N solid solution strengthening factor was 90–95% of the total increment in the tensile yield stress. The N solid-solution is thus highly effective in improving the strength of PM Ti materials, relative to Ti composites reinforced with TiN particles. • Ti materials and Ti composites with TiN particles fabricated by powder metallurgy. • 1273 K heat treatment used to completely dissolve nitrogen solutes in matrix. • (0002) α-Ti peak shifts to lower diffraction angle with increasing TiN content. • Nitrogen solution gives larger yield stress increment than TiN dispersoids. • Solid solution strengthening equal to 90–95% of total YS increment. [ABSTRACT FROM AUTHOR]

TiNi shape memory alloys (SMAs) are one of the significantly important materials group, which serve in the advanced applications requiring unique characteristics. Although their wide use is well established, further improvement of mechanical properties is still needed. The conventional TiNi SMA is usually manufactured by casting, hot forging and heat treatment processes. In this study, Ti-x at.%Ni alloys, with x equals 50, 51, and 52, were fabricated by powder metallurgy (PM) process through spark plasma sintering, followed by hot extrusion, homogenization, solution, aging and cryogenic quenching treatment. The effects of the compositions, processing conditions, and quenching media on the microstructural and mechanical properties of the alloys were evaluated by XRD, SEM, TEM analyses and tensile hysteresis test. The results showed that hot extrusion could lead to a considerable grain refinement, while the cryogenic quenching lead to a shift in the transformation temperatures and to an improvement of the tensile properties of the alloys such as the tensile strength increment and marginally improved ductility. • TiNi alloys have been synthesized using SPS, hot extrusion and heat treatment. • Conventional water quenching vs cryogenic quenching were compared. • Hot extrusion refined the microstructure and improved transformation. • Cryogenic quenching enhanced tensile properties. • Ni content improved tensile properties and strain recovery. [ABSTRACT FROM AUTHOR]

• Interfacial β-phase of AZ31B/Al layered material grew more easily than γ-phase. • Maximum Charpy impact toughness obtained with a 2 μm intermetallic compound layer • Cracks in intermetallic layer did not propagate into AZ31B/pure Al layers. [ABSTRACT FROM AUTHOR]

Abstract: AZ61B alloy powder composite with Al2Ca fine dispersoids was developed by using CaO additive particles as raw materials. For synthesis of Al2Ca in the matrix, CaO particles were elementally and uniformly mixed with AZ61B alloy chips via ECABMA process. The mechanism in formation of Al2Ca intermetallics was investigated by XRD and SEM–EDS analysis when AZ61B alloy green compacts containing CaO additives were heat treated at 380–625°C in argon gas atmosphere. A change in a standard free energy in formation of Al2Ca via reaction between CaO and Mg–Al alloy was calculated by using a standard Gibbs free energy of each element contained in the green compact. Both of the theoretical analysis by thermo-dynamic and experimental investigation clarified that Al2Ca and MgO were synthesized by employing Mg–Al alloy, not pure Mg as the matrix material. Microstructural analysis indicated that needle-like intermetallic of (Mg,Al)2Ca or Al3Ca4Mg were formed as intermediately created compounds in the solid-state reaction between CaO particles and Mg–Al alloy to synthesize Al2Ca and MgO dispersoids. [Copyright &y& Elsevier]

Oxygen solid solutions are well known to impose a strong hardening effect on Ti and its alloys, but induce the undesirable embrittlement behavior. In order to improve the ductility of Ti materials with high oxygen content, Ti(O), herein, a heteromicrostructure consisting of two phases with different oxygen contents was synthesized by redistributing the oxygen solutes through heat treatment over the dual (α + β) phase temperature range, followed by water quenching. The heteromicrostructure formation and plastic deformation mechanisms were investigated by erectron backscattered diffraction (EBSD) analysis of the quenched Ti(O) material under tensile deformation coupled with SEM. It was found that the elongation at break of the sintered Ti-0.94 mass% O alloy remarkably recovered from 6% to 19% owing to the above-mentioned heat treatment and water quenching process. The quenched Ti(O) material consisted of equiaxed grains with high oxygen content, fine α' phase grains, and misorientation regions in the equiaxed grains with low oxygen content. The high and low oxygen content phases were derived from the α and β phases, respectively. The β phase was responsible for plastic deformation, which improved the tensile elongation of the Ti(O) material. [ABSTRACT FROM AUTHOR]

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 (α p) 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. [Display omitted] [ABSTRACT FROM AUTHOR]

Titanium is well-known for its high strength, good corrosion resistance, and biocompatibility. For further improvement of its mechanical properties, it is alloyed with other elements, such as zirconium. In this study, pre-mixed pure Ti powder and ZrH 2 particles were employed to prepare extruded Ti–Zr alloys with a low hydrogen content via dehydrogenation after sintering. The Zr solutes were uniformly dissolved in the α-Ti matrix by applying the optimal conditions for homogenization and water-quenching heat treatment. The synthesized Ti–Zr alloys consisted of the equiaxed fine α-Ti grains via dynamic recrystallization during extrusion. When the ZrH 2 particle content was less than 10 wt%, the extruded Ti–Zr alloys showed a large tensile elongation of more than 25% at room temperature with a yield stress of approximately 850 MPa. In the case of Ti–10% ZrH 2 powder, the mean α-Ti grain size was 2.7 μm, which was smaller than that of extruded pure Ti (3.5 μm). By applying the Hall–Petch equation for grain refinement and Labusch model for Zr solid solution to quantitatively estimate the increase in the yield stress, it was clarified that both factors had an equal effect for Ti–5 and –10 wt% ZrH 2 powder even with the dominance of solid-solution strengthening by Zr solutes for alloys with small Zr content. • Ti–Zr sintered alloys fabricated from pre-mixed Ti and ZrH 2 powders. • Uniform solution of Zr in α-Ti matrix by homogenization and water-quenching. • Ti–Zr alloys consisted of the equiaxed fine α-Ti grains. • Zr solid solution and α-Ti grain refinement were main strengthening factors. [ABSTRACT FROM AUTHOR]

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. • Nitrogen atoms were homogenized in the α-Ti materials by applying the heat treatment. • The materials revealed an α microstructure with various grain morphologies. • Homogenized heat treatment caused the microstructure evolution of Ti-(N) materials. • Increasing nitrogen content enhanced tensile strength. • The yield strength improvement was attributed to grain refinement and solid solution strengthening. [ABSTRACT FROM AUTHOR]

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 N 2 gas atmosphere. Ti 2 N 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 Ti 2 N 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. [ABSTRACT FROM AUTHOR]