Superplastic Behavior and Deformation Mechanism of TC18 Titanium Alloy

Superplastic tensile behavior and deformation mechanism of TC18 titanium alloy were investigated by high temperature tensile test at 720-950℃ with initial strain rates of 6.7×10-5s-1-3.3×10-1s-1.The results show that under the optimal superplastic deformation condition (890℃ and 3.3×10-4s-1),the maximum elongation is 470%, the peak stress is 17.93MPa and with uniform grain size.Below the phase transus Tβ,the elongation firstly increases and then decreases.A maximum elongation of 373% is obtained at 830℃ and with initial strain rate of 3.3×10-4s-1 and the peak stress is 31.45MPa.The superplastic deformation mechanism of the TC18 titanium alloy in two-phase region is mainly grain rotation and boundary sliding,and the deformation coordination mechanism is dislocation slipping and climbing; the superplastic deformation mechanism in single phase region is intragranular dislocation motion and the deformation coordination mechanism is dynamic recovery and dynamic recrystallization.