Investigation on Hot Deformation and Processing Parameter Optimization of Ti48Al2Cr2Nb Alloy with Bimodal Grain Size Distribution Fabricated by Powder Metallurgy

The deformation behavior of Ti-48Al-2Cr-2Nb alloy with bimodal grain structure was studied using isothermal compression tests in the temperature range of 950-1100 °C and strain rate range of 0.001-0.1 s −1 . The results show that the flow stress is greatly affected by the deformation temperature and strain rate, and decreases with decreasing strain rate and increasing temperature. All flow stress curves exhibit single peak characteristics, indicating that DRX is the main softening mechanism. The Arrhenius constitutive equation is established according to the relationship among flow stress data, strain rate and temperature. The activation energy for hot deformation and stress index are determined as 390.543 kJ·mol −1 and 2.573, respectively. According to the theory of dynamic material model, the hot processing maps are constructed and the stability and instability regions are identified. The peak power dissipation occurs in the regions of 960-1025 °C/0.001-0.005 s −1 and 1085-1100 °C/0.001-0.006 s −1 , which suggests that these two regions can be regarded as the optimum processing window for the alloy.