Effect of Heat Treatment on the Microstructure and Mechanical Properties of High-Strength Ti-6Al-4V-5Fe Alloy

The effect of heat treatment on the microstructure characteristics and mechanical properties of the high-strength and low-cost Ti-6Al-4V-5Fe alloy was investigated. Two-phase (alpha + beta) and single-phase (beta) solution treatments and aging were applied to determine the relationship between microstructures and properties. The size of the grain after treatment of the solution in the beta single phase was only dozens of micron for the primary alpha(alpha(p)), which exhibited an obvious pinning effect on grain growth. The morphology and volume fraction of alpha(p) phase were highly sensitive to the heat treatment temperature and remarkably influenced the properties of the alloy. When the solution temperature was 780 degrees C and the aging temperature was 550 degrees C, the largest proportion (40%) of the globular alpha(p) phase and small secondary alpha(alpha(s)) phases resulted in the best performance of the alloy, with an ultimate strength of up to 1300 MPa and 9.57% elongation. The fracture surface of tensile specimens was systematically studied, showing a ductile mode of tensile failure after the sample was treated below 800 degrees C and then aged. However, it exhibited a brittle mode when the alloy is treated above 800 degrees C.