Wang et al. have synthesized SiBCN ceramic matrix with TaC addition by mechanical alloying plus reactive hot-pressing sintering methods, in which BN, graphite and TaC powders were mixed with ball-milling and sintered at to obtain SiBCN-TaC composites. For the synthesis, the ball-milling process refined the TaC powders down to 5 nm without reacting with other components, allowing to form agglomerates that are composed of spherical clusters with a diameter of 100 nm-200 nm. TEM analysis showed that TaC is distributed either randomly in the form of nanoparticles with sizes of 10-20 nm within the matrix or distributed in BN with smaller size of 3-5 nm. As a result, the composite with 10 wt% addition of TaC improved the fracture toughness of the matrix, reaching 399.5 MPa compared to 127.9 MPa of pristine SiBCN ceramics. This is mainly due to the mismatch of thermal expansion coefficients between TaC and SiBCN ceramic matrix. Since TaC has a larger coefficient of thermal expansion than that of SiBCN matrix, TaC particles endures tensile stress while the matrix endures tensile stress in radial direction and compressive stress in tangential direction. This makes the cracks to bypass the particles and absorbs some energy to achieve toughening. In addition, the uniform distribution of TaC particles contributes to the yield stress explained by Hall-Petch relationship due to a decrease in grain size.Wang, Bingzhu, et al. "Effects of TaC addition on microstructure and mechanical properties of SiBCN composite ceramics." Ceramics International 45.17 (2019): 22138-22147
