Evolution of the α phase and microhardness for hot isostatic pressed Ti-6Al-4V alloy during multi-pass deformation

Abstract

The microstructural and microhardness evolution, as well as the deformation/phase transformation mechanism in a hot isostatic pressed Ti-6Al-4V alloy during multi-pass deformation at variable temperature parameters of 950-900-850 °C and 950-850-900 °C were investigated. The result shows that dynamic recrystallization of β phase for one-pass deformation, been/kinking, fragmentation and spheroidization of lamellar α phase for two-pass and three-pass deformation occurred during multi-pass deformation. And the evolution process of lamellar α phase included two aspects: rotation and the change in length, thick, spheroidization. The orientation distribution of lamellar α changes from bimodal to single peak, and the angle of single peak is close to 95°with the compression axis. And the spheroidization of lamellar α phase contains the formation of sub-structure, localized shear deformation and fracture of su-bstructure, diffuseness of β phase, separation and spheroidization. The spheroidization fraction of lamellar α phase gradually increases with the increase of strain rates. For different temperature matching (950-900-850 °C and 950-850-900 °C), the significant influence is the variation trend and degree in the length and thickness of lamellar α phase. For the analysis of mechanical properties, it is found that the microhardness value increase with the increase of strain and the main influence of integrated hardness during multi-pass deformation is the lamellar structure and the contribution value of c ɑl is greater at higher deformation temperature. • The multi-pass hot compression features of Ti-6Al-4V alloy prepared by hot isostatic pressing(HIP) were study. • The microstructure evolution of α phase at variable temperature parameters corresponding to complex strain matching was invested. • The influence of integrated hardness and contribution value was revealed.