Relationship between microstructures and mechanical properties in Ti4.5Al2Mo1.6V0.5Fe0.3Si0.03C for next-generation aircraft applications

The effects of various heat treatments on the microstructure and mechanical properties of an (α + β)-type titanium alloy, Ti4.5Al2Mo1.6V0.5Fe0. 3Si0.03C (KS Ti-9), were investigated systematically for possible use in next-generation aircraft applications. The as-received KS Ti-9 shows strong anisotropy of mechanical strength derived from the intense texture (T-texture) of the primary α phase. This anisotropy continues to be observed in KS Ti-9 annealed at a temperature below β transus followed by air cooling, but the anisotropy drastically decreases in KS Ti-9 when subjected to a duplex heat treatment, that is, when the as-received material of KS Ti-9 is sequentially heated to a temperature slightly below β transus followed by water quenching and then annealed followed by air cooling. It is considered that the reduction in the anisotropy in KS Ti-9 subjected to this duplex heat treatment is associated with the difference in the orientation of the precipitated acicular α phase.