Microstructure evolution and corresponding tensile properties of Ti–5Al–5Mo–5V–1Cr–1Fe alloy controlling by multi-heat treatments

Highlights

• Three different heat treatment conditions (solution, single-step and two-step aging) were investigated in this paper.

• An excellent combination of strength and ductility can be obtained via two-step aging treatment.

• Both tensile and compression twins were found near the tensile fracture of the two-step aged alloy.

Abstract

The effects of microstructure morphology on corresponding tensile mechanical properties of Ti–5Al–5Mo–5V–1Cr–1Fe alloy controlling by three different heat treatment conditions (solution, single-step and two-step aging) were investigated in the present paper. The results show that the solution temperature exhibited an important impact on the precipitation behavior of secondary-α phase (α_s) during aging, in which the content of α_s gradually increased with the increase of solution temperature. When the alloy was single-step aged at 500–600 ​°C, the needle-like α_s precipitated from matrix, as well as the content of α_s decreased and coarsened corresponding to the increase of aging temperature. Compared with single-step aging, the α_s slightly increased when the alloy was subjected to two-step aging heat treatment. The tensile results show that the α_s is the main strengthening phase in the alloy. Moreover, its content as well as the intensity of the precipitation mode directly affects the strength, whereas inevitably with an accompanying penalty on ductility. In general, the higher solution temperature and the lower first-step aging temperature result in a more intensive α_s and then lead to the higher strength. Meanwhile, $\left\{10\overline{1}2\right\}$ and $\left\{10\overline{1}1\right\}$ twins were found in two-step aged tensile samples, which may impart twinning-induced plasticity (TWIP). Overall, this study demonstrates that the alloy can be heat treated to achieve an excellent match between strength and ductility and to provide sufficient stress and optional ductility (ultimate strength of 978–1439 ​MPa and elongation of 8.25–18.9%).