Effect of Thermal Cycling on Microstructure and Fatigue Properties of Ti-6Al-4V Alloy

Consecutive thermal cycling at 920, 800, 850, 900 degrees C were performed on the Ti-6Al-4V alloy to investigate microstructure, texture evolution, tensile and rotating bending fatigue properties. Results show that after four cycles, the elongated grains in the as-received alloy disappeared due to recrystallization and the microstructure is homogenized. Equiaxed grains grow from similar to 12 to similar to 16 mu m, while the volume fraction remains stable. The as-received Ti-6Al-4V alloy exhibits a transverse texture, and forms microzones parallel to the rolling direction. The rotating bending fatigue limit in the rolling direction 497 MPa is higher than that of the transverse direction 474 MPa. The intensity of the transverse texture is weakened after each thermal cycle and (0001) basal texture appears. Both the tensile strength and yield strength decrease after four thermal cycles due to alpha grain coarsening. The fatigue limit in the transverse and longitudinal directions decrease to 441 MPa and 441 MPa, respectively.