Consolidation of SiC/BN composite through MA-SPS method

Hexagonal-BN has been selected as a second phase for SiC/BN composite to improve SiC's machinability and thermal shock resistance. In this research, nano-metric SiC/BN was prepared through mechanical alloying (MA) from Si + C + BN powder and then consolidated by SPS without any sintering aids. XRD results after MA revealed the absence of sharp peaks corresponding to SiC and BN. The density and the intensity of the SiC and BN peaks on XRD increased with temperature during SPS. The final density of the composite reached approximately 90-99% with 50/50 of SiC/BN to 100/0. During the consolidation process, crystallization, phase separation, and ordering were observed simultaneously. This phenomenon could accelerate the mass transfer for the consolidation and the preparation of bulk SiC/BN composite without any sintering aids. In a 50/50 SiC/BN ratio, the Vickers hardness of the nano-structured reference sample prepared by the conventional method with sintering aids could not be measured due to high porosity. However, the well-consolidated sample prepared in our research showed a hardness of approximately 3 GPa.