Modulation of microstructure and improvement in the mechanical properties of TiBw/Ti65 composites by rolling at different temperatures

Abstract

The effect of rolling temperature on microstructure evolution and mechanical properties of as-sintered TiBw/Ti65 composites was systematically investigated. The results showed that at 900 °C (in the low α + β phase region), the matrix microstructure primarily exhibited a deformation structure. At 1000 °C (in the high α + β phase region), a bimodal structure was observed, and at 1100 °C (in the β phase region), a basket-weave structure emerged. Additionally, silicides precipitated at 900 °C were fine but grew and coarsened at 1000 °C, eventually dissolving almost completely into the matrix at 1100 °C. This behavior is attributed to the varying solubility of silicides in the α and β phases. With increasing rolling temperature, the dynamic recrystallization (DRX) mechanism within the TiBw/Ti65 composites transitioned from continuous dynamic recrystallization (CDRX) to discontinuous dynamic recrystallization (DDRX). Rolling significantly enhanced the mechanical properties of the composites. The HR-900 composite exhibited the optimal strength-plasticity combination at room temperature, achieving an ultimate tensile strength (UTS) of 1415 ± 21 MPa and elongation (EL) of 6.2 ± 2.7%, mainly due to grain refinement and work hardening. Conversely, the HR-1100 composite demonstrated superior high-temperature mechanical performance, showing improvements of 37.18%, 27.05%, and 9.59% at 963 MPa (650 °C), 789 MPa (700 °C), and 560 MPa (750 °C), respectively, compared to those of the as-sintered materials. The strengthening mechanisms were fine-grain strengthening, dislocation strengthening, and load transfer strengthening of the as-rolled composites, and the primary strengthening mechanism shifts from dislocation to fine-grain strengthening as the rolling temperature increases.