On the β-transus and order/disorder transition temperature in superplastic super α2 Ti3Al base alloy

Abstract

Abstract In previous studies on the superplastic deformation mechanisms in regular α 2 and super α 2 Ti 3 Al base alloys at temperature ranges of 900–1050°C, the β grains were considered to be a disordered phase. The ordered α 2 grains were thought to act as the rigid species, and slide and rotate more freely within the disordered β matrix, and the disordered β grains are more likely to be the ones that carry accommodation through dislocation slip plus climb. In this study, it was found that the β grains over the temperature range of 900–1050°C were actually present as an ordered phase since there was no antiphase boundaries and the whole grain was of the same ordered domain. The order–disorder transition temperature for the β phase was determined to be around 1100°C. Since the β grains were in an ordered form at the superplastic temperature regime (900–1050°C), the accommodation process via dislocation glide+climb might have an equal chance in proceeding in the ordered β grains as well as in ordered α 2 grains. Meanwhile, the β transus temperature was determined to be around 1120°C, based on phase characterization and volume fraction extrapolation.