Quantitative analysis on microstructure characteristic of pre-strained β-solidified TiAl alloy during post-heat treatment

The beta/beta o phase in beta-solidified TiAl alloys plays a contradictory role in improving processability at high temperatures but deteriorating performance at service temperature due to its ordering transformation. After exerting its positive role during thermomechanical processing, it must be eliminated or reduced to a minimum through post-heat treatment. In this study, the microstructural evolution of the pre-strained Ti-43.24Al-8.42Nb-0.20W-0.21B-0.24Y alloy on post-heat treatment is investigated, and a quantitative relationship between beta(o) phase content and the pre-strain is established. Due to the difference in driving force of phase transformation, with decreasing pre-strain the microstructure displays varied characteristics from a mixed structure comprising (alpha(2)+gamma) lamellar colonies, gamma blocks, and beta o phase, to a nearly-lamellar structure after post-heat treatment at 1270 degrees C/4h/FC. Only if the pre-strain is less than 0.78, a refined nearly-lamellar structure can be achieved. This work provides important theoretical guidance for practical forging processing of beta-solidified TiAl alloys.