Tuning the number density of αs precipitates in Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-0.1Si alloys for achieving high strength

Abstract In the present study, the strength of TC21 titanium alloy was tuned by systematically controlling the density of αs precipitations via a two-step heat treatment. The first step consists of hot rolling at 940 °C to form precursor metastable β phase and precipitate a small number of second α phases (αs), followed by subsequent ageing treatment in the second step at a range from 500° to 600°C/4H resulting in more αs precipitations. The obtained results showed that the ageing temperature greatly affects the number density of αs, and thus this factor can be applied to control the ultimate tensile strength to 1.4 Gpa, while retaining a reasonable ductility. It is found that combination of the hindrance of more αs/β phase interfaces to dislocation motion and the smaller deformation of β transus (βtrans) microstructure led to higher strengths.