HOT DEFORMATION BEHAVIOR AND MICROSTRUCTURE EVOLUTION OF A HIGH-Nb-CONTAINING TiAl BASED ALLOY

The hot deformation behavior of a high-Nb-containing TiAl based alloy has been studied using the processing map approach. Compression tests were conducted in the temperature range of 950-1300 degrees C and the strain rate range of 0.001 s(-1) to 10 s(-1) on a Gleeble-3800 testing system. The flow stress was found to be strongly dependent on the temperature and the strain rate. The regimes of flow instability have been delineated in the temperature range of 950-1200 degrees C and the strain rate ranges from 1 s(-1) to 10 s(-1), as well as in the temperature of 1250-1300 degrees C and the strain rate of 10 s(-1). The optimal hot-working conditions for the investigated TiAl alloy are in two regimes: (i) in the temperature range 950-1100 degrees C and at the strain rate of 0.001 s(-1) to 0.1 s(-1), and (ii) in the temperature range 1250-1300 degrees C and at the strain rate of 0.001 s(-1) to 1 s(-1). The material exhibited dynamic recrystallization to produce a fine-grained microstructure in these conditions. In the temperature range 1150-1200 degrees C with the strain rate 0.001 s(-1), the alloy exhibited superplasticity.