Abstract: High-temperature titanium alloys' thermal stability and creep resistance are significant during service in high temperatures. This study systematically investigated the thermal stability and mechanical properties of Ti-6.5A1-2.5Sn-9Zr-0.5Mo-1Nb-1W-0.3Si-xSc (x, 0-0.5 wt.%) at 650 °C. The lamellar secondary α phase is refined and the formation of Sc₂O₃ is increased with the increasing scandium (Sc) additions, which improves the strength of the alloy, while excessive Sc₂O₃ becomes the crack source and deteriorates the plasticity. The oxygen content in the matrix is reduced by the interaction between Sc and oxygen, inhibiting the growth of the Ti₃Al phase and improving the thermal stability of the alloy. Meanwhile, Sc accelerates the dissolution of the residual β phase and precipitation of fine, diffusely distributed ellipsoidal silicides, which strongly prevents dislocation movement. The enhancement of creep resistance for the Sc-containing alloy is attributed to the refined lamellar secondary α phases, Sc₂O₃ particles, Ti₃Al phase, and silicides, especially the precipitated silicides. Eventually, the 0.3Sc alloy shows optimal thermal stability (the plasticity loss rate 17.3%) and creep resistance (steady-state creep rate 4.4 × 10^-7 s^-1). The investigation results provide new insights into the mechanism and thermal stability improvement in high-temperature titanium alloys modified by rare earth (RE).

Key words: Titanium alloy, Creep, Microstructure, Silicide, Scandium