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

Abstract

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 (α + β) and single-phase (β) 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 β single phase was only dozens of micron for the primary α(α_p), which exhibited an obvious pinning effect on grain growth. The morphology and volume fraction of α_p phase were highly sensitive to the heat treatment temperature and remarkably influenced the properties of the alloy. When the solution temperature was 780°C and the aging temperature was 550°C, the largest proportion (40%) of the globular α_p phase and small secondary α(α_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°C and then aged. However, it exhibited a brittle mode when the alloy is treated above 800°C.

Fig. 8 Results of the elemental mapping of the surface of alloy samples that were heated at different temperatures. (a) (e) and (i) was solution treated at 700°C, 780°C and 820°C, respectively, then aged at 500°C. (a) (e) and (i) SEM images. (b)–(d), (f)–(h) and (j)–(l) EPMA elemental maps of Fe, V and Al, respectively.