Microstructural evolution in a powder metallurgical Ti-7Mo alloy with continuous oxygen gradient

Abstract

A titanium alloy containing continuous oxygen gradient was prepared by powder metallurgy (P/M) and the composition–property relationship was studied on a single sample. The alloy was sintered with layered powder of different oxygen contents via vacuum sintering and spark plasma sintering (SPS), respectively. After subsequent heat treatments, high-throughput characterizations of the microstructures and mechanical properties by localized measurements were conducted. The Ti-7% Mo (molar fraction) alloy with an oxygen content ranging from 1.3×10⁻³ to 6.2×10⁻⁵ (mass fraction) was obtained, and the effects of oxygen on the microstructural evolution and mechanical properties were studied. The results show that SPS is an effective way for fabricating fully dense Ti alloy with a compositional gradient. The average width of α′ phase coarsens with the increase of the content of oxygen. The content of α″ martensitic phase also increases with the content of oxygen. At oxygen contents of 3×10⁻³ and 4×10⁻³ (mass fraction), the Ti alloys present the lowest microhardness and the lowest elastic modulus, respectively. The results also indicate that the martensitic phases actually decrease the hardness of Ti-7Mo alloy, and oxygen effectively hardens the alloy by solid solution strengthening. Therefore, the high-throughput characterization on a microstructure with a gradient content of oxygen is an effective method for rapidly evaluating the composition–property relationship of titanium alloys.

Keywords

titanium alloys / oxygen / martensitic transformation / high-throughput method / powder metallurgy (P/M) / mechanical properties

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