Investigation on the microstructure homogenization in a TiAl based alloy prepared by elemental powder metallurgy

A Ti-48Al (at. pet) alloy prepared by elemental powder metallurgy (EPM) has been heat treated under various conditions. Through optical and scanning e lectronic microscopy, EDAX, XRD analysis, and DTA, it was shown that the ho t pressed microstructure consisted of alpha(2)-Ti3Al and TiAl phases. The a lpha(2)-Ti3Al phase was island-like, and had a high stability and heredity in subsequent heat treatments. The supersaturation of Al in the island-like alpha-Ti3Al phase strongly influenced the transformation of alpha(or alpha (2)) to alpha(2)/gamma lamellar colonies. After a heat treatment at 1380 de grees C for 0.5 h and 1000 degrees C for 8 h, a fully lamellar microstructu re with a colony size of 50 mu m was obtained. This result indicates that a homogeneous composition and an equilibrium microstructure in EPM TiAl-base alloys can only be obtained after heat treatment at temperatures above alp ha transus temperature (T-alpha).