Processing Pure Ti by High-Pressure Torsion in Wide Ranges of Pressures and Strain

Abstract

Pure Ti (99.4 pct) is processed by high-pressure torsion (HPT) at applied pressures in a wide range of 1.2 to 40 giga-pascals (GPa) for equivalent strain up to ~200. X-ray diffraction (XRD) analysis clearly reveals that a pressure-induced phase transformation occurs from α phase to ω phase during HPT processing when the applied pressure is more than ~4 GPa and the straining facilitates this phase transformation. The hardness and the tensile strength increase, but the ductility decreases by the phase transformation. Hardness measurements demonstrate that all values obtained at each pressure fall on a single curve when they are plotted as a function of equivalent strain. The hardness increases with an increase in the equivalent strain at an early stage of straining and saturates to a constant level, where the hardness remains unchanged with further straining. It is shown that the saturation level as well as the onset of the saturation depends on the applied pressure.