Influence of Si and C additions on microstructure and mechanical properties of the Ti-43.5Al-1Mo-4Nb-0.1B alloy

Abstract

Separate effects of 0.3 at% Si and 0.2 at% C additions have been investigated on the Ti–43.5Al–1Mo–4Nb–0.1B alloy. Both elements appear to stabilise the γ phase. Si addition induces an increase in both γ-lamellar and γ-grain volume fractions. A heterogeneous distribution of primary and secondary silicides is observed in Al-rich regions of the microstructure, but silicon appears to be mainly in solid solution in the lamellar structure. The solid solution effect of silicon in the more plastically deformable β phase is probably very limited because of the high volume fraction of α2 in this alloy. This may explain the lack of beneficial effect of 0.3 at% of silicon on both tensile and creep properties. Carbon appears to stabilise the γ phase through an increase in γ-grain volume fraction and is found to be in solid solution in the lamellar structure. Our results suggest a very strong solid solution effect of carbon, since addition as low as 0.16 at% leads to an increase in yield strength at room and high temperature, a reduction in the secondary creep rate and a longer creep life.