Effect of Severe Deformation on the Indentation of Titanium

Severe plastic deformation (SPD) is a type of deformation processes to obtain utrafine-grained microstructure to enhance mechanical properties of materials. Equal channel angular pressing (ECAP) is one of the effective SPD processes. Commercially pure titanium rods were extruded for 2 passes by the ECAP extrusion at 623 K using three dies of 90°, 120°, and 150° in bending angle. For the extrusions using the 90° die, the titanium rods were extruded for 2, 4, and 8 passes. The microstructure of the extruded specimens was evaluated using transmission electron microscope technique. The bending angle had strong effect on the grain refinement, while the number of the extrusion passes had little effect on the evolution of microstructure. Microindentations were conducted over the extruded Ti rods. The indentation hardness decreased slightly with the increase in the indentation load. The titanium processed by the 90° die had the highest indentation hardness. No significant difference in the indentation hardness was observed with different passes using the 90° die.