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 MPam(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 degrees 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.