Evaporation of Al and microstructural variation in TiAl alloy during heat treatment

Abstract

A TiAl alloy of Ti-47Al-2Cr-2Nb at.- was used to study phase transformation and microstructure control by heat treatment and a glow discharge spectrometer was applied to analyse the compositional variation from the specimen surface to the interior. It was found that Al tended to evaporate at elevated temperatures. As a result, Al was significantly depleted and a quite different microstructure developed in the outer layer compared with that in the interior. Results also showed that the outer layer appeared thicker with increasing heating temperature, time, and cooling rate, and with changing the environment from vacuum to air. Since the evaporation of Al leads to microstructure variation and perhaps property deterioration as well, it is suggested that this effect should be considered for alloy design and processing.