High-Temperature Properties of TC11-(TiB + TiC) Titanium Matrix Composites Fabricated by Hot Isostatic Pressing

To meet the demand for lightweight, high-strength, and high-temperature-resistant structural materials in aerospace applications, TC11-(TiB + TiC) composites with varying B4C contents (0, 2 and 5 wt.%) were fabricated by hot isostatic pressing (HIP), and their microstructures and high-temperature mechanical properties were systematically investigated. Results reveal that in situ TiB whiskers and TiC particles were obtained in all the composites, and the matrix microstructure changed non-monotonically with the B4C content. A fine and uniform basketweave microstructure was obtained at 2 wt.% B4C, whereas at 5 wt.% the reinforcements formed a quasi-continuous network along the prior particle boundaries, and pores developed at the grain boundaries owing to B4C agglomeration and incomplete local reaction. At room temperature, the yield strength rose from 1020 MPa to 1586 MPa with increasing B4C, but the fracture strain dropped from about 37% to 11%. At 650 °C, however, the base alloy softened severely, its peak stress falling from 1998 MPa to 484 MPa. The composites, by contrast, were strengthened, with the peak stresses of TMC2 and TMC5 reaching 603 and 841 MPa, exceeding the base alloy by 24.6% and 73.8%, respectively. This reversal can be attributed to a change in the role of the reinforcements. At room temperature, the reinforcements act primarily as stress-concentration sites. At elevated temperatures, however, they function as a rigid load-bearing skeleton. Load transfer through this skeleton, together with the relaxation of interfacial stresses by matrix plasticity, accounts for the monotonic increase in high-temperature strength with increasing reinforcement content. The moderate CTE mismatch between the reinforcements and the matrix may provide a secondary contribution, as suggested by the increasing apparent microstrain from XRD and the stacking faults within TiB observed by HRTEM. In addition, the B27 crystal structure of TiB, its [010] growth habit, and the well-bonded symbiotic TiB/TiC interfaces may further impede dislocation motion at elevated temperature.