Study of Microstructure and mechanical properties of pure commercial titanium via combination of Equal channel angular pressing and Extrusion

There has been much interest in recent years in improving material properties by grain refinements using severe plastic deformation (SPD). With applying severe plastic deformation to metals, the structure changes and nanostructure produce. In this study, ultra-fine grained pure titanium fabricate by combination of Equal channel angular pressing and Extrusion process in different passes (1, 2, 4 and 6 pass). ECAP and Extrusion processes were carried out at 400°C. Then, mechanical and microstructural properties of UFG pure titanium billets produced b combination process of ECAP and extrusion process were examined and the effect of passes on mechanical and microstructural properties was investigated. The results showed that mechanical properties were improved significantly. Ultimate strength increased up to 941MPa, in the best state, while for initial sample was 505MPa, in other word ultimate stress increased about 86.3%. With this combinational method, ultimate stress increased about 60.8% for 1 pass sample, 78.8% for 2 pass sample, 86.3% for 4 pass sample and 80.8% for 6 pass sample rather than initial state. In higher passes the rate of increase are reduced due to the grains size saturation. Hardness increased from 81.85 Hv to 216.65 Hv; In other words, hardness increased 164% from initial value. Further passes of the process only have a minor effect on increasing of billet hardness. Scanning Electron Microscope also revealed that brittle fracture were takeplaced in all sample with shallow dimples.