Phase precipitation behavior and tensile property of a Ti–Al–Sn–Zr–Mo–Nb–W–Si titanium alloy

Abstract

The characteristic of precipitation behavior of α₂ phase and silicide, and the tensile properties at room temperature and 650 °C after heat treatments in a novel Ti–Al–Sn–Zr–Mo–Nb–W–Si titanium alloy (BTi-6431S) were investigated by microstructure analysis and mechanics performance testing. The results show that no second phase precipitates after solution treatment (980 °C/2 h, air cooling (AC)). However, when the solution-treated specimens are aged at 600 °C (600 °C/2 h, AC), α₂ phase precipitates in the primary α phase, and the size of α₂ phase increases with the aging temperature increasing to 750 °C. Meanwhile, 50–100-nm S₂-type silicide particles precipitate along lamellar phase boundaries of transformed β phase after aging at 750 °C. BTi-6431S alloy shows the best 650 °C ultimate tensile strength (UTS) and yield strength (YS) when treated in solution treatment. However, aging treatment results in a decline in 650 °C ultimate tensile strength. This may be attributed to the loss of solution strengthening due to the depletion of Al, Si and Zr of the matrix caused by the precipitation of Ti₃Al and (TiZr)₆Si₃. Silicide is a brittle phase; therefore, its precipitation causes a sharp decrease in the room-temperature ductility of BTi-6431S alloy.