Deformation mode dependent mechanism and kinetics of dynamic recrystallization in hot working of titanium alloy

Abstract

Dynamic recrystallization (DRX) plays great roles in the microstructure refinement and property improvement during hot working of titanium alloys. Various deformation modes in hot working may greatly affect the DRX mechanism and kinetics, but which has not attracted enough attention. In this work, the DRX mechanism and kinetics of titanium alloy in hot compression deformation (CD) and shear deformation (SD) were comparatively investigated by combining the electron backscatter diffraction technique and crystal plastic finite element models. The results show that discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) coexist in both of CD and SD, while their dominant mechanism and kinetics of DRX are quite different. These differences are found to be strongly dependent on the slip behavior and resulting misorientation development in each deformation mode. In CD, the smaller contribution ratios of basal <a> and pyram <a+c> as well as the gradual formation of {0002} basal texture suppress the lattice rotation and reduce the long-range misorientation gradient (MOG). As a result, the dominant DRX mechanism changes from CDRX to DDRX with strain in CD. However, SD presents much higher contribution ratios of basal <a> and pyram <a+c> compared with CD, and the c-axes of most grains are perpendicular to the direction of shear stress. These greatly improve the lattice rotation and long-range MOG, which makes CDRX always prevail and present larger driving force in SD. Moreover, higher contribution ratio of pyram slip in SD also improves the kernel average misorientation, and thus provides larger driving force for DDRX in SD than in CD. These factors make SD present faster DRX kinetics and thus raising the DRX fraction by 10% and grain size homogeneity by 32% compared with CD. These results suggest that the deformation condition and mode should be well designed for obtaining more refined and homogeneous microstructure in the hot working of titanium alloy components.