Microstructure and mechanical properties evolution of Ti–5Al–5Mo–5V–1Cr–1Fe alloy under rapid heat treatment
Fucheng Qiu, Tuo Cheng, O. M. Іvasishin, Dmytro G. Savvakin, Guangyu Ma, Yuchao Song, Huiyan Xu
Abstract
Starting microstructure with nonuniform micro-scale grains is designed for the study of microstructure and mechanical properties after rapid heat treatment (RHT) and subsequent aging. RHT was used to retard β grain growth in single-phase β region, while RHT and aging parameters affected size of secondary α and, hence, tensile strength and ductile characteristics. Heating rate for aging is important parameter affecting ω phase precipitation, which, in turn, affects the size of secondary α. Fast heating for aging avoided formation of ω phase, while ω phase formed at slow heating and duplex aging conditions results in refined α precipitations. After single-step aging with fast heating rate, proved by the calculation of strength based on the strengthening mechanism, the RHT temperature for the highest strength is at the bottom of single-phase β region. However, the nonuniformity of starting grain size results in the nonuniform β grain size after RHT, which affects the strengthening and elongation negatively. Proper selection of RHT parameters and fast heating for subsequent aging leads to refined secondary α and high balance of tensile properties (1415 MPa, 5.2%). Formation of ω phase at slow heating and at duplex aging resulted in marked drop in ductility with some variation of strength level (1344 MPa, 2.2%, and 1433 MPa, 0.7% correspondingly). Homogenising of the starting grain size by decreasing the β solution treatment temperature leads to achievement of the best tensile properties (1480 ± 12.5 MPa, 8.2% ± 0.99%).