The Second Phases and Their Effects on Properties in Ti40 Burn Resistant Titanium Alloy Thermally Exposed for Long Time

The second phases in Ti40 alloy after thermal exposure for a long time were found to be Ti₅Si₃ and α phases and their effects on the creeping properties of alloy were studied. It is found that the Ti₅Si₃ precipitates along grain boundary are not continuous, which lead to the decrease of thermal stability after exposure below 540°C for conventional forging. The Ti₅Si₃ precipitates grow greatly after exposure at 700°C for 100 h, which results in great decrease of the thermal stability and its tensile fractograph seems to be brittle intergranular fracture. The coarse Ti₅Si₃ and α phases appear after exposure at 540°C for 100 h for isothermal forging, reducing the thermal stability greatly. The Ti₅Si₃ precipitates along grain boundary are not continuous after creep exposure at 540°C, 250 MPa for 100 h so that the alloy has good creeping property for conventional forging; however, there are many coarse rod-like Ti₅Si₃ and α phase if the heat treatment is unsuitable which reduce the creeping property greatly. Many coarse α phases emerge after creeping for isothermal forging, which lead to the great reduction of creeping resistance.