Effect of Si addition on the microstructure and creep properties of the forged titanium alloy

Creep experiments were carried out on pure Ti after annealed (720 °C/2 h, AC), Ti-0.4Si alloy after annealed (720 °C/2 h, AC) and thermal exposed (720 °C/2 h, AC+600 °C/500 h, AC) respectively. The presence mode of Si in Ti-0.4Si alloy after two heat treatments is partial precipitation and complete precipitation respectively. Combined with SEM and TEM characterization, the effects of Si addition on the creep properties and creep mechanism and the dominant roles of solid solution Si and silicide in improving the creep resistance of titanium alloys were investigated. The results show that the annealed Ti-0.4Si alloy has the best creep resistance, indicating that the addition of Si significantly improves the creep resistance of titanium alloys, and the Si has a creep strengthening effect whether it exists in solid solution state or in precipitated state. The high creep activation energy (Q = 253 kJ/mol) of the annealed Ti-0.4Si alloy is due to the strong inhibition of solid solution Si and dynamically precipitated silicide on matrix diffusion, indicating that the precipitation strengthening effect of dynamically precipitated silicide during creep is significantly stronger than that of precipitated silicide before creep, and obviously compensates the diffusion effect of dynamic precipitates during the precipitation process.