Analyses of the role of grain boundaries in mesoscale dynamic fracture resistance of SiC–Si 3N 4 intergranular nanocomposites

Abstract

Silicon carbide (SiC)–silicon nitride (Si 3N 4) nanocomposites with SiC dispersions as well as Si 3N 4 matrix of mesoscale dimensions (∼1 μm) are considered to have exceptional strength attributed to interactions of SiC dispersions with Si 3N 4 grain boundaries (GBs). However, an account of GBs on the strength of these nanocomposites is not available. In order to analyze this issue, cohesive finite element method (CFEM) based mesoscale dynamic fracture analyses of SiC–Si 3N 4 nanocomposites with an explicit account of length scales associated with Si 3N 4 GBs, SiC particles, and Si 3N 4 grains are performed. Analyses indicate that primary mechanism of fracture in the nanocomposite microstructures is intergranular Si 3N 4 matrix cracking. GBs are responsible for crack deflection and accordingly damage is limited to a smaller geometric region in microstructures with GBs. On an average, a microstructure with GBs present is stronger than the corresponding microstructure with GBs removed. However, in cases where the second phase SiC particles are in the wake of microcracks the microstructure without GB becomes stronger against fracture in comparison to the corresponding one with GBs owing to the crack bridging effect caused by the second phase SiC particles.