Experimental investigation on the indentation hardness of precursor derived Si–B–C–N ceramics

The elasto-plastic response of the precursor derived Si–B–C–N ceramics upon contact loading was determined by depth sensing nanoindentation technique. The indentation response of as-thermolyzed Si–B–C–N ceramic was compared with the heat-treated counterpart. The as-thermolyzed ceramic was X-ray amorphous and the heat-treated ceramic was phase separated and crystallized. The hardness and reduced elastic modulus values of the as-thermolyzed ceramic were ～16 GPa and ～172 GPa, respectively. The reduction in hardness to ～9 GPa in the heat-treated ceramic was attributed to phase separation and crystallization of SiC and Si₃N₄. Furthermore, high elastic recovery with a plastic work ratio of ～0.3 was observed and ascribed to volume controlled deformation mechanism.