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A novel Ti–2Al–1.3V (wt.%) alloy was prepared by thermomechanical consolidation of a composite powder produced by high-energy ball milling of a mixture of TiH2 granules with a low oxygen content (0.1wt.%) and Ti–6Al–4V machining chips with a high oxygen content (0.8wt.%) at a mass ratio of 2:1. The microstructures and mechanical properties of the alloy in as-extruded state and after different heat treatments were investigated. The as-extruded alloy exhibits a martensite microstructure consisting of ultrafine and nanometer sized α' laths and aciculae and domains of layered structure containing δ(TiH) layers. The alloy in this state is brittle and fractures prematurely before yielding due to the ultrafine martensitic microstructure and hydrogen embrittlement associated with the high hydrogen content of the alloy. After vacuum annealing at 700°C for 6 h followed by furnace cooling, the alloy is further dehydrogenated with the hydrogen content being reduced to 0.008wt.%, the microstructure of the alloy changes into a full α/β lamellar microstructure with the continuous and discontinuous β layers being only 80–90 nm thick and the lamellar colony sizes being 10–30μm. The fine structured alloy in this heat treatment condition shows an excellent combination of high tensile yield strength of 996 MPa and ductility of 13.9%. After a further heat treatment of 980°C for 1 h followed by air cooling, the microstructure of the alloy consists of equiaxed α grains and α/βt lamellar structured domains (βt = β transformed structure), and unfortunately, this microstructure leads to a significant decrease of both the tensile yield strength (to 876 MPa) and the tensile ductility (to 7.4%). The fracture behavior of the alloy in different states is also studied, and the correlation between the microstructure and mechanical properties is discussed. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the effects of ZrO 2 types including YSZ and nano-ZrO 2 as well as their contents on the phase compositions, macrostructures, microstructures, physical properties, mechanical properties and biocompatibility of Ti2448-ZrO 2 composites fabricated by spark plasma sintering (SPS). The mechanical properties such as hardness and compressive yield strength of the composites have been systematically investigated. The experimental results demonstrate that the hardness and compressive yield strength of the composites all dramatically increased with increasing the content of YSZ and nano-ZrO 2 . Meanwhile the nano-ZrO 2 could be beneficial to the uniformity of microstructure and improvement in mechanical strength of the composites. The biocompatibility of the composites containing nano-ZrO 2 was found to possess better corrosion resistance. In conclusion, Ti2448-ZrO 2 composites are potentially useful in biomedical applications with their mechanical and biological properties being evaluated in this work. [ABSTRACT FROM AUTHOR]

Powder metallurgy (PM) Ti–6Al–2Sn–4Zr–2Mo–0.1Si–(0, 2, 4)W (wt%) alloys were fabricated by thermomechanical consolidation of TiH 2 -based powder compacts and subsequent heat treatments. Samples of the as-fabricated alloys were also heated at 650 °C for 200 h. The addition of 2 or 4 wt%W to the base alloy changed its microstructure of parallel α/β lamellar colonies and grain boundary α (α GB) to an interwoven α/β t microstructure consisting of α GB and a network of interpenetrating α plates with β transformed structure (β t) domains comprising variants of fine α laths and β matrix. The partition of the β stabilizing W between β and α phases and the low diffusivity of W atoms limited the growth of α plates/laths, decreasing the thickness of α plates/laths and increasing the volume fraction of β. The increased hardening of the β phase and enhanced α/β interface strengthening associated with the 4 wt%W addition led to a significant increase in the tensile strength of the alloy from 1281 ± 10–1411 ± 12 MPa. However, the high flow stress and the very fine microstructure caused significant strain localization in the weak α GB , resulting in premature fracture of the α GB (intergranular fracture) and the low ductility (1.4%). Here, premature fracture meant the fracture occurred prior to the alloy reaching its ultimate tensile strength. The heating caused the β interlaths in the W-free alloy to partially dissolve and become β particles distributed along the original lines of β interlaths accompanied by the precipitation of α 2 -Ti 3 Al in the α plates. The addition of W inhibited the dissolution of β interlaths and caused the precipitation of a higher volume fraction of α 2 precipitates during heating. The microstructural changes caused by heating resulted in a slight decrease in strength and a significant decrease in ductility for the W-free alloy, but a significant increase of the yield strength of the 2 W and 4 W alloys with some sacrifice of the tensile ductility. The microstructural reasons for the effects on mechanical properties were analyzed with the assistance of detailed characterization of the dislocations in the deformed specimens. • Effects of W alloying on a PM Ti–6Al–2Sn–4Zr–2Mo–0.1Si alloy are investigated. • W refines α plates and enhances formation of β transformed structure domains. • W enhances hardening of the β phase and α/β interface strengthening. • W increases the microstructural stability and prevents the strength reduction from heating. • High W content promotes α 2 precipitation strengthening of the alloy after heating. [ABSTRACT FROM AUTHOR]

Two samples of an α + β Ti-4Al-4Mo-4Sn-0.5Si (wt%) alloy, one with fine prior β grains and a heterogeneous microstructure and the other with coarse prior β grains and a homogeneous microstructure were prepared by extrusion of compacts of TiH 2 /Al/Mo/Sn/Si powder blend at 1200 and 1300 °C respectively. The heterogeneous microstructure is manifested by softer Mo-rich regions with a full α/β lamellar structure containing a high number density of parallel and nanometer sized FCC δ (TiH) needles in a harder matrix with a microstructure consisting of interweaved α plates and β transformed structure (β t) domains and grain boundary α (GB α) layers. The matrix also contains a small fraction of Sn-rich regions which have the same microstructure as the matrix. The Mo-rich and Sn-rich regions form due to the limited diffusion of Mo and Sn alloying elements. This heterogeneous microstructure sustains a high tensile yield strength of 1199 MPa, a high strain hardening rate, and an excellent tensile ductility of 12.0%. In contrast, the homogeneous microstructure comprising of interweaved α plates and β t domains together with GB α layers sustains a similar high strength, but a clearly lower strain hardening rate and a significantly lower tensile ductility of 3.5%. Non-homogeneous deformation capacity, the release of energy by forming numerous microcracks and the intermittent growth of microcracks of the heterogeneous microstructure suggest that this microstructure has a high plasticity and high resistance to the growth of microcracks. • The α + β titanium alloy fabricated has a heterogeneous microstructure and fine prior β grains. • The heterogeneous microstructure encompasses softer Mo-rich regions in a matrix of α/β t microstructure. • This alloy exhibits a superior combination of high strength (YS: 1199 MPa and excellent ductility (12.0%). • This is attributed to the compatible deformation and high microcrack growth resistance of the microstructure. [ABSTRACT FROM AUTHOR]

• With an addition of 0.2 wt%Si, the Si atoms are equally in α and β phases. • Si solute atoms retard the growth of α phase, causing refinement of the α/β t lamellar structure. • Si atoms enhance solid solution strengthening and Si atoms enhanced α/β t interface strengthening. • Increasing the Si content to 0.5 wt% cause a further increase of the yield strength by 50 MPa. • With a high strength, the tensile ductility deteriorates, due to the premature fracture of grain boundary α layers. Ti-4Al-4Mo-4Sn-xSi (wt%) (x = 0, 0.2, 0.5) alloys were fabricated by hot extrusion of compacts of blends of TiH 2 , AlMo60 master alloy and other required elemental powders followed by heat treatments involving vacuum annealing, solution treatment, air cooling and aging. The microstructure of the alloys consists of α plates, lamellae of α and transformed β structure (β t), β t blocks as well as grain boundary α layers. With the addition of 0.2 wt%Si, the Si atoms exist in equal concentration in both α and β t regions as solute atoms, and they retard the growth of α phase, causing a decrease of the average thickness of α plates and lamellae and slight increase of the volume fraction of β t lamellae and blocks. The solid solution strengthening and enhanced α/β interface hardening brought by the 0.2 wt%Si cause the yield strength of the Ti-4Al-4Mo-4Sn alloy to increase significantly from 1030 to 1130 MPa with a slight decrease of the tensile ductility (7.4% vs 6.8%) and without changing the fracture behavior. With the addition of 0.5 wt%Si, the extra Si causes nanometer sized silicide (Ti 5 Si 3) precipitates to form in both α and β t regions and further microstructural refinement. The additional α/β interface hardening and precipitation hardening cause the yield strength of the alloy to increase further to 1177 MPa, but the tensile ductility deteriorates clearly with the elongation to fracture decreasing to 4.9%. The main reason for this ductility decrease is the premature fracture of grain boundary α layers caused by the higher flow stress which can induce more strain localization at the grain boundary α layers. [ABSTRACT FROM AUTHOR]