Mechanical behavior and microstructural evolution of commercially pure titanium in enhanced multi-pass equal channel angular pressing and cold extrusion

Microstructures together with mechanical properties of commercially pure titanium (CP-Ti) developed by a newly designed multi-pass equal channel angular pressing (ECAP) process and cold extrusion were investigated. A T-type ECAP apparatus was developed to improve the efficiency of common ECAP and the performance of finished products. A much stronger CP-Ti billet was produced by using the proposed processes. As shown in the results, a severe plastic deformation occurred in the material by means of continuous shear deformation during the radical bending process through a repeated route. The resulting mechanical properties such as yield and tensile strength were improved according to the grain refinement that is connected with the Hall–Petch theory. Additively, cold extrusion was conducted to produce a cylindrical type bulk material by using the ECAP. Microstructural refinement with improvement of mechanical properties was attributed to this additional plastic forming process. Finished products developed by the T-type multi-pass ECAP and cold extrusion processes therefore have been shown to be remarkably hardened, such as the ultimate tensile strength of CP-Ti 292.5 initially to 791.9 MPa with significant refinement of the microstructure.