Processing, microstructure, and mechanical properties of chopped SiC fibers reinforced ZrB2–hBN–based composites

This study selected ZrB₂–hBN ceramics as the matrix for low-cost second-generation SiC fibers, due to their low modulus and ability to be sintered at relatively low temperatures. The resulting composites, which contained up to 30 wt.% short-chopped SiC_f, were consolidated using reactive spark plasma sintering at 1550 and 1700°C under 50 MPa for 5 min. Without needing to prepare interfaces on the SiC_f surfaces, fiber pullout, strengthening, and toughening during the fracture process were realized. By constructing the volatility phase diagram for the fiber, the microstructural changes that occurred on the fiber surfaces during sintering were successfully illustrated. Mechanical properties of ZrB₂–hBN ceramics with 10 wt.% SiC_f sintered at 1550°C still showed considerable improvements, including an elastic modulus of 187 GPa, a flexural strength of 337 ± 16 MPa, and a fracture toughness of 4.12 ± 0.25 MPa m^1/2, increases of 12.6%, 61.2%, and 118%, respectively, compared to the counterparts without adding chopped fibers. Variations in these properties were linked to the matrix porosity and SiC_f pullout behaviors, which were subsequently analyzed using the He–Hutchinson model.