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

摘要

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. phase. Si addition induces an increase in both gamma-lamellar and gamma-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 beta phase is probably very limited because of the high volume fraction of alpha(2) 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. phase through an increase in gamma-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.