Highly Dense Amorphous Si 2 BC 3 N Monoliths with Excellent Mechanical Properties Prepared by High Pressure Sintering

The fabrication of dense amorphous Si–B–C–N monoliths is a processing challenge given that it is hard to avoid crystallization at the sintering temperatures needed to attain full density up to 1900°C for conventional hot pressing and SPS methods. We report here successful densification of amorphous Si 2 BC 3 N monoliths achieved by heating at 1100°C and 5 GPa. The relationships between microstructure, types of chemical bonding, and mechanical properties were investigated. The strong amorphous 3‐D networks of Si–C, C–B, C‐N ( sp 3 ), N‐B ( sp 3 ), and C–B–N bonds provide high densities at high applied pressure and thus amorphous Si 2 BC 3 N monoliths show high hardness of 29.4 GPa and elastic modulus of 291 GPa. The amorphous structure is lost with crystallization of β‐SiC and BN (C) reducing contributions from Si–C, C‐N ( sp 3 ), and C–B–N bond networks thereby decreasing mechanical properties.