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.