Plastic flow behavior of a Ti-Al-Nb-Mn alloy at high temperatures

High-temperature deformation of a gamma TiAl-based alloy containing 49.5 pct Al, 2.5 pct Nb and 1.1 pct Mn is studied using the constant-strain-rate isothermal compression-test technique. Axisymmetric tests were conducted in the strain rate range 0.001 to 10.0/s and at temperatures ranging from 1000 to 1400 C. The flow curves obtained at temperatures below 1250 C exhibit significant flow softening. This is correlated with the occurrence of shear localization, dynamic recrystallization, and wedge cracking. The flow-stress data are analyzed in terms of the strain-rate and temperature sensitivity. Strain-rate sensitivity decreases continuously with an increase in the strain rate and a decrease in the test temperature. In contrast, temperature sensitivity decreases with an increase in strain rate at all temperatures above 1050 C. A constitutive relationship between flow stress and the temperature-compensated strain rate is found to be valid in the temperature range 1000-1250 C. 20 refs