Constructing tri-modal microstructure via new three-step heat treatments for improved tensile strength and creep resistance in (TiB+TiC+Y₂O₃)/α-Ti composite

In this study, new three-step heat treatments were carried out on the (TiB + TiC + Y₂O₃)/α-Ti composite to improve the high-temperature performance. The microstructure characterization, tensile properties and creep behaviors of titanium matrix composites before and after heat treatments were systematically studied. Results indicate that the microstructures changed from the basket-weave structure to the tri-mol structure after heat treatments. The cooling process mainly affects the morphology of the secondary α-Ti phases. TiC and Y₂O₃ undergo extensive spheroidization, while TiB tends to merge and grow. The heat-treated composite exhibited a great improvement in tensile and creep properties, the ultimate tensile strength at 650 °C was increased to 906 MPa with an increase of 10 %, and the creep life 650 °C/230 MPa was improved to 151.7 h with an increase of 91 %. During creep, there are obvious dynamic recrystallization and limited dislocation movement. The three-step heat treatment enhanced the stability of the α/β interface and improved the interface relationship between silicides and titanium matrix. The stable α/β interfaces in transformed β-Ti matrix, fine silicides and spheroidized TiC and Y₂O₃ particles contributed to the high strengthening efficiency.