Prior particle boundaries and microstructural homogenization of a β-solidifying γ-TiAl alloy fabricated from prealloyed powder

Prior particle boundaries (PPBs), microstructural heterogeneity and hot workability of Ti-44Al-6Nb-1Mo-0.3 (B, Y) (at%) alloy fabricated via SPS of its prealloyed powder were investigated systematically. It was found that, during SPS consolidation below a-transus temperature, the original alpha(2) dendrites and martensites within prealloyed powder decomposed towards an equilibrated alpha(2) + ( )gamma + B2/beta triphase structures. However, at early SPS stage, PPBs and two types of microstructural heterogeneities took place, and PPBs trended to generate at triple junctions of particle contact. The circular network, which was actually alpha(2)/gamma lamellar colonies concentrated structures at interparticle contact positions, was proved to be induced by powder surface oxygen contamination. And the other microstructural heterogeneity, existing between individual domains of former powder particles, was ascribed to non uniform solidification microstructures of initial powder. Besides, PPBs were proved seriously detrimental to both high-temperature strength and ductility. Therefore, SPS with sufficient sintering time at 1240 degrees C was proposed to completely eliminate PPBs and produce uniform fine-grained alpha(2) + ( )gamma + B2/beta microstructure, in order to obtain excellent hot workability.