Microstructure, oxidation and thermal shock resistance of graphene reinforced SiBCN ceramics

SiBCN ceramics were prepared using various volumes of graphene platelets (GPLs) as nanofiller. The effects of the nanofiller on microstructure, and oxidation and thermal shock resistance of as-sintered ceramics were investigated. The phase composition and microstructures were very similar for all investigated ceramics consisting primarily of beta-SiC, BNC and small amounts of a-SiC with relatively homogeneously distributed 5-10 nm thick GPLs in the matrix. For SiBCN ceramics incorporating graphene as nanofiller, a porous oxide layer forms at 1500 degrees C and the oxidation behavior shows a linear kinetics by thickness measurement method. Gas evolution during heating lead to a passive oxidation behavior and weight loss. Graphene reinforced SiBCN ceramics exhibit thermal shock resistance superior to monoliths of the same material. The graphene distributed in SiBCN matrix can dissipate the energy of crack growth and acts as a stopper to cracks. The toughening mechanisms offered by graphene, including pull-out and bridging appear to aid in ameliorating thermal shock effects. Furthermore, the existence of a dense oxide surface layer retards oxygen diffusion into the inner matrix and heals surface pores and cracks, which also contributes to thermal shock resistance. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.