Influence of chemistry and microstructure on the activation volume of TiAl alloys

Abstract

Repeated stress-relaxation experiments are conducted from RT to 1073 K on three different γ + α2 TiAl alloys (Ti–46Al with 8Ta, 8Nb or 7Nb). One is a conventional duplex alloy, the two other are novel “convoluted” cast titanium aluminides developed for turbine applications. The data include measurements of the flow stress and activation volume of these alloys at 293, 673, 873, 923, 1023 and 1073 K. Despite differences in composition, processing and microstructure, the values and evolution with temperature or with stress of these parameters are relatively similar for the three alloys. This observation, coupled with the agreement of present results with data in the literature for similar alloys, leads to conclude that the strain-rate dependence of plastic flow in alloys of this class is governed by features of the γ-phase that are relatively insensitive to the α2 phase morphology. The convoluted alloys furthermore feature a yield stress anomaly.