Microstructure and thermal stabilities in various atmospheres of SiB0.5C1.5N0.5 nano-sized powders fabricated by mechanical alloying technique

Abstract

SiB0.5C1.5N0.5 powders were fabricated by two routes of mechanical alloying using c-Si, h-BN and graphite powders as starting materials. For the SiB0.5C1.5N0.5 powder prepared by one-step milling (simultaneously milling of three starting materials) for 20 h, nano-crystalline SiC (4–5 nm) and amorphous SiBCN were formed with a little amount of free Si remained. For the SiB0.5C1.5N0.5 powder prepared by two-step milling, during which Si and graphite powders (with a mole ratio of 1:1) were milled for 15 h, and then milled with BN and the residual graphite for 5 h, free Si could be no longer observed due to the complete milling. These results showed that nano-crystalline SiC, which has two polytypes (3C-SiC and 6H-SiC), distributed in the amorphous SiBCN matrix. The thermal stabilities of SiB0.5C1.5N0.5 powders in Ar, N2 and air were investigated. The SiB0.5C1.5N0.5 powders show a very good oxidation resistance particularly above 920–1400 °C despite that few percent of mass loss happened below 920 °C.