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

Abstract

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.