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 α-transus temperature, the original α2 dendrites and martensites within prealloyed powder decomposed towards an equilibrated α2 + γ + B2/β 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 α2/γ 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 °C was proposed to completely eliminate PPBs and produce uniform fine-grained α2 + γ + B2/β microstructure, in order to obtain excellent hot workability.