Creep Properties of Directionally Solidified Ti-46Al-1.5Mo-0.2C Alloys Using a Seeding Technique

摘要

Creep properties of directionally solidified Ti-46Al-1.5Mo-0.2C alloys with well aligned lamellar microstructure have been dramatically improved. The ingots were manufactured by seeding technique directional solidification. Directionally solidified Ti-46Al-1.5Mo-0.2C alloys showed excellent creep properties. However, the creep resistance decreased as the angle between lamellar orientation and loading axis increased. It is found that the control of the lamellar orientation is most important to improve the creep resistance of TiAl alloys. In the results of TEM analysis of creep specimen before and after creep test, it was found that no carbides were formed before creep test. But, after creep test, carbides were formed in gamma lath, gamma / gamma interfaces, gamma / alpha_2 interfaces and dislocations. In the case of creep test at 750 deg C, the quantity of carbides found in dislocations decreased as the load level increased. It was thought that superior thermal stability of Ti-46Al-1.5Mo-0.2C alloy suppressed the dynamic recrystallization and the coarsening of the lamellar microstructure, and the excellent creep resistance was maintained for long time due to this thermal stability.