Microstructural evolution and strain-hardening behavior of multi-pass caliber-rolled Ti–13Nb–13Zr

The multi-pass caliber-rolling (MPCR) process is a rod-manufacturing process that has recently proven capable of fabricating ultrafine-grained bulk rods with superior mechanical performance for biomedical uses. There have rarely been studies which focused on MPCR-processed nonferrous alloys in spite of the great potential of doing so. The present work elucidates the metallurgical phenomena which occur during the MPCR process of Ti–13Nb–13Zr alloy, such as strain accumulation, microstructural evolution, and strain-hardening behavior. These factors were discussed in light of dislocation storage and annihilation. A FEM analysis revealed a significant amount of plastic strain applied by the MPCR process, most of which was considered as redundant strain. The heavy deformation induced a fragmentation of lamellar structure and strong grain refinement as the rolling passes increased in number. Both dynamic globularization and continuous dynamic recrystallization played key roles in such a microstructural change. In addition, a dislocation-based analysis provided further insight into the microstructural evolution and strain-hardening behavior of MPCR-processed titanium alloys.