Study on the microstructure stability of (TiB + TiC + Y₂O₃)/α-Ti composite during thermal exposure and high-temperature tensile creep

This study investigates the microstructure stability of a (TiB+TiC+Y₂O₃)/α-Ti composite and its matrix alloy (Ti-6Al-4Sn-8Zr-0.8Mo-1W- 1Nb-0.25Si) during thermal exposure and tensile creep at 650 ℃. Both materials were prepared by induction skull melting and were subsequently subjected to two different tests: a 200 h thermal exposure at 650 ℃ and a 200 h high-temperature tensile creep at 650 ℃ under 150 MPa. The results demonstrate that the primary phase composition of both materials remains predominantly α-Ti phase before and after the experiments, with no significant changes observed. However, the β-Ti phase underwent varying degrees of dissolution, among which the matrix alloy exhibited the highest degree of dissolution after the creep. The precipitation of silicide is observed during both thermal exposure and creep, predominantly forming short rod-shaped S1 type silicides (Ti, Zr)₅Si₃. Both the dissolved β-phase and reinforcements demonstrate catalytic effects on silicide precipitation. These silicides exhibit significant dislocation pinning effects, thereby enhancing the creep resistance of the materials. Dynamic recrystallization (DRX) occurred throughout thermal exposure and creep processes, with discontinuous dynamic recrystallization (DDRX) identified as the predominant mechanism. While the reinforcements facilitate DRX initiation, the resultant DRX effectively refine grain structures. Importantly, both reinforcements and silicides contribute to maintaining microstructure stability during thermal exposure and high-temperature tensile creep.