Radial Dependences of the Phase Composition, Nanohardness, and Young's Modulus for Ti-2 wt % Fe Alloy after High-Pressure Torsion

The specimens of Ti-2 wt % Fe alloy were annealed at three different temperatures, in the beta-Ti, alpha-Ti + beta-Ti and alpha-Ti + TiFe fields of the Ti-Fe phase diagram, then water quenched and subjected to high-pressure torsion (HPT). The X-ray diffraction analysis showed that the main phase in all annealed specimens was the alpha phase (more than 90%), while the main phase after HPT was the omega phase. Hardness H and Young's modulus E were determined by nanoindentation at the center, in the middle of the radius, and near the edge of each specimen. It was found that the H and E values were different for specimens annealed at different temperatures and depended on the radial coordinate of the indentation region. The maximum H values were obtained in the middle of the radius of the specimens. The E values of all specimens decreased from the center to the edge, reaching very low values. The paper discusses structure transformations during HPT, the behavior of the radial dependences of H and E, and probable causes of a strong decrease in E values.