Enhanced mechanical properties and thermal shock resistance of Si₂BC₃N ceramics with SiC coated MWCNTs

Bulk Si₂BC₃N ceramics were reinforced with SiC coated multi-walled carbon nanotubes (MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the designed Si₂BC₃N ceramics were comparatively investigated. The results show that nano SiC coating can be formed on MWCNTs through pyrolyzing polysilazane, which improves the oxidation resistance of MWCNTs. A stronger chemical bonding is formed between the SiC coated MWCNTs and SiC particles, contributing to improved flexural strength (532.1 MPa) and fracture toughness (6.66 MPa·m^1/2). Besides, the 2 vol% SiC coated MWCNTs reinforced Si₂BC₃N ceramics maintains much higher residual strength (193.0 MPa) after thermal shock test at 1000 °C. The enhanced properties should be attributed to: (1) the breaking of MWCNTs and the debonding between MWCNTs and SiC interfaces, which leads to more energy dissipation; (2) the rough surfaces of SiC coated MWCNTs increase the adhesion strength during the “pull out” of MWCNTs.