층상조직 TiAl 합금의 열적 안정성에 미치는 Si 첨가효과

Abstract

Thermal stability of Si-doped TiAl alloys with the lamellar microstructure was investigated by partial melting in an optical floating zone(FZ) furnace to ascertain the possibility of usage as a seed material. The lamellar stability of TiAl and TiAl-X(X=Mo, Nb, W) alloys, which proved to be thermally unstable, was improved dramatically by Si addition. In the results of partial melting, it was found that there are two boundaries of Al content(low Al limit and high Al limit) which devide stable and unstable compositions. It is thought that when Al content is lower than low Al limit, recrystallization can be occurred by β-phase formation at high temperature, and when Al content is higher than high Al limit, the lamellar stability will be deteriorated by rapid variation of α/γ phase volume fraction during heating and cooling. The lamellar stability of TiAl-Si alloys can be predicted by drawing above two boundaries at TiAl-Si isothermal section. Moreover, the lamellar stability of TiAl-X-Si alloys can be also predicted by converting the compositions to TiAl-Si compositions. In addition, lamellar orientation control was successfully performed by directional solidification using the Ti-46Al-l.5Mo-1Si alloy as a seed material.