Microstructural evolution during high temperature deformation of Ti-47Al-2Cr-4Nb

The microstructural changes during high temperature deformation behavior of Ti-47Al-2Cr-4Nb intermetallic compound have been investigated by isothermal compression tests at temperatures ranged 1000-1200 degrees C with strain rates ranged 10(-3)-10(-1)s(-1). The stress-strain curve exhibited a peak stress, then the flow stress decreased gradually into a steady state stress with increasing the strain. The flow softening behavior during high temperature deformation is attributed to the dynamic recrystallization. The dependence of flow stress on temperature and strain rate was formulated well using the Zener-Hollomon parameter. The activation energy was measured as 295kJ/mol and the stress exponent was measured as 3.1 for Ti-47Al-2Cr-4Nb. The dynamically recrystallized microstructures were investigated and the relationship between recrystallized grain size and temperature compensated strain rate was discussed. The dynamically recrystallized grain size decreased with decreasing the temperature and increasing the strain rate, while the recrystallization rate increased with increasing the temperature and decreasing the strain rate. The dynamic recrystallization started at the initial grain boundaries and it is suggested that the nucleation of dynamic recrystallization is controlled by the grain boundary migration.