Effect of high-temperature long-term aging/annealing treatment on the microstructure and mechanical properties of bimodal heterogeneous TiB_w/TC4 composites

High temperature service stability is a key index to measure the performance of materials in extreme environments. In this work, TiB_w/TC4 titanium-matrix composites (TMCs) with a unique bimodal heterostructure were prepared by two-step low-energy ball milling and vacuum hot-pressing sintering (HPS). The as-HPSed composite with 10 wt% coarse-grained TC4 (CG) has the best comprehensive mechanical properties at room temperature. After 650 °C/25 h aging/annealing, the elongation of the material is 6.4 %, and the K_IC is 40.3 MPa·m, which is 48.8 % and 6.3 % higher than that of untreated composite, respectively. Compared with TC4 matrix alloy prepared by the same route, the elongation increased by 106.5 %. The results demonstrate that the bimodal heterostructure has excellent high temperature stability. The fracture mechanism analysis indicates that the coarsening of α grains, the increase of β phase content and the plastic deformation of CG zones are the main factors to improve the plasticity of the composite after aging/annealing.