Developing Microstructure and Enhancing Strength of Ti-6Al-7Nb Alloy with Heat Treatment Processed by High-Pressure Torsion

Ti-6Al-7Nb alloy with and without heat treatment was processed by high-pressure torsion (HPT), and subsequently its microstructures and mechanical properties were investigated. Herein, the development of the microstructure by HPT processing significantly depended on the initial microstructures even though their minimum grain size was approximately equal and less than 100 nm. The needle-like structure was fragmented into several grains by HPT processing with a small number of revolutions, and grain refinement was more easily achieved than the equiaxed structure. The Ti-6Al-7Nb alloy with a duplex microstructure comprising equiaxed and needle-like structures was obtained with an adequate balance of tensile strength (1280 MPa) and elongation to fracture (22%). The results show that the combination of the initial duplex microstructure of equiaxed α grain, needle-like structure of the α′ phase, and the resultant inhomogeneous microstructure obtained by HPT processing through a moderate number of revolutions is effective in achieving a better balance of mechanical properties in the Ti-6Al-7Nb alloy.