Effect of Isothermal Forging Strain Rate in Two Phase Region on Structure and Mechanical Properties of Ti-6.5Al-2Sn-4Zr-4Mo-1W-0.2Si Alloy

In order to determine the optimum isothermal forging process parameters of Ti-6.5Al-2Sn-4Zr-4Mo-1W-0.2Si alloy,the effects of strain rates of 1×10^-1,1×10^-2and 1×10^-3s^-1on the microstructure and properties of the alloy were investigated.The results show that with the decrease of strain rate,the primary equiaxedαphase decreases significantly due to theα→βphase transition,and the secondary lamellarαevolves from short rod-like to long strip.During isothermal forging,theαlamellae are seriously bent,and transformed into necklace or equiaxedαgrains owing to the occurrence of dynamic/static globularization.The tensile tests at room temperature and 550℃show that the alloy achieves good matching of strength and plasticity at medium strain rate of 1×10^-2s^-1with fracture mode of ductile fracture.Fracture toughness is affected by disordered lamellarαin the microstructure,and reaches the maximum value at 1×10^-1s^-1.