Microstructure evolution and mechanical properties of commercial pure titanium subjected to rotary swaging

Abstract

The wide applications of pure titanium (Ti) are greatly limited by its low strength and hardness. In this paper, we employed an industrial method of rotary swaging (RS) to improve the strength of commercial pure (CP) Ti and uncovered the elementary mechanisms governing microstructural changes under RS. Specifically, the {10-12} extension and {11-22} contraction twins take place in the coarse grains at the early stage of RS deformation, which contributes to the increase of yield strength and moderate ductility. As for the late stage, the twins disappear and are replaced by textured nanostructured grains; meanwhile, there exists a hardness gradient along the radial sample direction. High strain rate RS brings about profuse twins and rapid grain refinement at room temperature in contrast to conventional severe plastic deformation. We rationalize that the high yield strength of CP Ti (up to 955 MPa) is attributed to dislocation, grain boundary and texture strengthening. This result may provide some insights in microstructure-based design of metals with superior mechanical properties subjected to this scalable RS technique.