Effect of Infiltration-and Pyrolyzation-Treatment on Mechanical Properties of Pressureless Sintered SiC/h-BN Ceramics

Composites of SiC/h-BN ceramic were fabricated by pressureless sintering at 1700℃ for 2 h. The sintered samples were alternately infiltrated with solutions of silica sol and phenolic in vacuum, and then pyrolyzed at 1450℃ for 1 h. The density, flexural strength and Vickers hardness of SiC/h-BN composites before and after infiltration-and pyrolyzation-treatment were investigated, and the strengthening mechanism of the composites was analyzed. The results show that the relative density and mechanical properties of SiC/h-BN composites were improved significantly after infiltration-and pyrolyzation-treatment, as an example, the relative density of increased from 69.7% to 74.9%, and the flexural strength increased near 1.5 times for the composite SiC/20 mass% h-BN; XRD patterns and microstructure of the prepared composite revealed that the SiC particles formed during the pyrolyzation-treatment were nanosized, which precipitated on the inner wall of pores of the sintered composite SiC/h-BN, Therewith, of which the resistance to crack propagation along grain boundaries was obviously increased, i.e., the mechanical properties of SiC/h-BN composite were improved.