Enhanced mechanical properties and thermal shock resistance of Si_2BC_3N ceramics with SiC coated MWCNTs

Bulk Si_2 BC_3 N 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 Si_2 BC_3 N 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 m1/2). Besides, the 2 vol% SiC coated MWCNTs reinforced Si_2 BC_3 N ceramics maintains much higher residual strength(193.0 MPa) after thermal shock test at 1000 ℃.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.

Enhanced thermal shock and oxidation resistance of Si_2BC_3N ceramics through MWCNTs incorporation

Multi-walled carbon nanotubes(MWCNTs)reinforced Si_2BC_3N ceramics were prepared through mechanical alloying(MA)and following spark plasma sintering(SPS).The thermal shock resistance of Si_2BC_3N ceramics was evaluated comparatively through ice water quenching test and theoretical prediction.Furthermore,the oxidation resistance of MWCNTs incorporated Si_2BC_3N ceramics was evaluated under high temperature.The results show that the calculated parameters such as the critical thermal shock temperature(R)and the thermal stresses resistance(R_(st)),as well as the toughness(R"")are improved with addition of 1 vol%MWCNTs.In addition,the crack propagation resistance of 1 vol%MWCNTs incorporated Si_2BC_3N ceramics is obviously improved through generating more tortuous crack propagation paths attributing to the"crack bridging","pull-out",and"crack deflection"mechanisms of MWCNTs.Therefore,the residual strengths of 1 vol%MWCNTs containing specimens remained the highest after the thermal shock tests.Besides,the present work also reveals that the oxidation resistance is more sensitive to relative density than MWCNTs addition.