Creep behavior and microstructural properties of a cast low-Ta-containing Ti-48Al-3Nb-1.5Ta alloy

This study investigated the creep behaviors and properties of a cast low-Ta-containing Ti-48Al-3Nb-1.5Ta (at.%) alloy with fine-grained nearly-lamellar (FGNL) microstructure in the condition of 800∼900 °C and 150–250 MPa. The stress exponent and creep activation energy were 2.0 and 395 kJ mol⁻¹, respectively. The Ti-48Al-3Nb-1.5Ta alloy exhibited superior creep resistance, reaching the level of advanced TNM+ and TNB alloys. It was attributed to the high-temperature strengthening effect of Nb and Ta alloying, which impeded diffusion-dependent creep and reduced the stacking fault energy to suppress dislocation climb. Ta alloying elevated the brittle-ductile transition temperature (BDTT) to ∼850 °C under creep conditions. In addition, the Ti-48Al-3Nb-1.5Ta alloy showed good microstructural stability with no detectable precipitation of β(β_o) and ω/τ phases during prolonged creep exposure. Compared to Nb, Ta alloying had a better high-temperature strengthening effect and a lower tendency to form ω/τ phases. Replacing some Nb with Ta can improve the microstructure stability while maintaining the creep resistance of the current TiAl-Nb alloy at 800–900 °C.