Preparation of UFG-Ti by ECAP at the normal temperature and research of mechanical properties

Based on equal channel angular pressing (ECAP), we designed the extrusion sample and proposed a new ECAP method with titanium rod packaged in copper cover. With this method we prepared UFG-Ti for 1, 2, 4 passes at room temperature. The extrusion force during ECAP could be controlled at low level, which effectively suppressed the fragmentation of the titanium sample and avoided the instability of the extruded bar. The microstructure of the prepared UFG-Ti was observed using the optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). Compression tests were performed on the UFG-Ti at different strain rates by the universal testing machine and the SHPB system. Results show that titanium grains are remarkably refined with the proposed ECAP method, and the improvement of mechanical properties caused by grain refinement is significant. The flow stress of 4-pass UFG-Ti is improved by 71% and 86% under quasi-static and dynamic compression load, respectively. At last, we studied the strain rate dependence of the UFG-Ti and find that the UFG-Ti exhibits low rate sensitivity.