Effect of Al Content on Microstructure/Phase Distribution and Strength/Ductility in a PM Gamma Alloy (Preprint)

摘要

The strength and ductility variation of TiAl alloys with variations of microstructure and composition are quite complicated and, possible interactions between these effects exist. For example, Al is known to affect strength and the variation in volume fraction of gamma and alpha-2 phases have been credited with the effect. However, the impact of composition versus phase fraction and microconstitutent fraction has not been satisfactorily quantified, especially for multi-element compositions. In an effort to understand such effects, four billets of gamma alloy 03K, nominal composition of Ti-45.5Al-3Nb- 1Cr-0.2W-0.2B-0.4C-0.2Si (at%), were produced from gas-atomized powder. The actual Al content varied between 44.8 and 47.4 at%. The forgings were heat treated to develop three microstructural variants: fully lamellar, nearly lamellar and duplex. The microstructure and Rockwell C hardness were analyzed on all samples, and room-temperature tensile testing was conducted on the fully- lamellar materials. The resulting strength and ductility as a function of Al content and microstructure will be discussed.