High temperature deformation behavior and optimization of hot compression process parameters in TC11 titanium alloy with coarse lamellar original microstructure

The high temperature deformation behaviors of α+β type titanium alloy TC11 (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) with coarse lamellar starting microstructure were investigated based on the hot compression tests in the temperature range of 950-1100 °C and the strain rate range of 0.001-10 s−1. The processing maps at different strains were then constructed based on the dynamic materials model, and the hot compression process parameters and deformation mechanism were optimized and analyzed, respectively. The results show that the processing maps exhibit two domains with a high efficiency of power dissipation and a flow instability domain with a less efficiency of power dissipation. The types of domains were characterized by convergence and divergence of the efficiency of power dissipation, respectively. The convergent domain in α+β phase field is at the temperature of 950-990 °C and the strain rate of 0.001-0.01s-1, which correspond to a better hot compression process window of α+β phase field. The peak of efficiency of power dissipation in α+β phase field is at 950 °C and 0.001 s-1, which correspond to the best hot compression process parameters of α+β phase field. The convergent domain in β phase field is at the temperature of 1020-1080 °C and the strain rate of 0.001-0.1 s-1, which correspond to a better hot compression process window of β phase field. The peak of efficiency of power dissipation in β phase field occurs at 1050 °C over the strain rates from 0.001 s-1 to 0.01 s-1, which correspond to the best hot compression process parameters of β phase field. The divergence domain occurs at the strain rates above 0.5 s-1 and in all the tested temperature range, which correspond to flow instability that is manifested as flow localization and indicated by the flow softening phenomenon in stress-strain curves. The deformation mechanisms of the optimized hot compression process windows in α+β and β phase fields are identified to be spheroidizing and dynamic recrystallizing controlled by self-diffusion mechanism, respectively. The microstructure observation of the deformed specimens in different domains matches very well with the optimized results.