Research On Microstructure And Properties Of BN-SiC Ceramic Was Prepared By Pressureless Sintering And Based On Network

Boron nitride ceramic material has good properties such as high temperature resistant, corrosion resistant, etc. Because between atomic layer of the boron nitride was connected only on van der Waals force, so usually boron nitride presented layer crystal structure and easy to peel, the existence of this structure and the covalent bond make boron nitride ceramics are hard to dense, so it usually needs high sintering temperature.To reduce the sintering temperature, BN-SiC compound ceramic prepared by the pressureless liquid phase sintering in this paper, and studied the effects sintering temperature, holding time and the content of sintering additives and second phase of silicon carbide on sintering properties, mechanical properties and microstructure of BN-SiC duplex ceramic, also studied the effects the mechanical mixing method and the network on sintering properties, mechanical properties and microstructure of BN-SiC ceramic.This studies have shown that BN- SiC powder were prepared by network method BN-SiC after molding by 200 MPa cold isostatic pressing were sintering at 1650℃,1700℃, 1750℃, 1800℃ and 1800℃, respectively under the certain time of heat preservation, and the best sintering temperature, 1700 ℃, was got. Under this sintering temperature( 1700℃), in order to determine the optimal time of heat preservation,ceramic material sintering properties were studied for 10 min, 30 min, 60 min and 90 min. Results show that the optimal heat preservation time was 30 min, at this time the density and the high bending strength of ceramic materials was highest, 69.55%, 59 MPa, respectively.In order to obtain sintered body which have high densification degree, sintering additives of this experiment was a certain proportion of Al2O3 and Y2O3. When the content of added sintering additives below 8wt%, relative density and bending strength of BN-SiC ceramic material was increased with the increase of the content of added sintering additives, and achieved the maximum value when added content of sintering additives was 8wt%; When adding content was higher than that of 8wt%, with the increase of adding content relative density and bending strength showed a trend of decline, the best added content of sintering additives was 8wt%. In addition, under the optimum process conditions, the sintering temperature, holding time and content of sintering additives was 1700 ℃, 30 min and 8wt%, respectively. Effects of Second phase Si C on the sintering properties of BN-SiC ceramic material was studied, the performance was highest when added content of SiC was 30wt%, relative density,bending strength and hardness were respectively 74%, 74 MPa and 635 MPa.This paper also has studied the effects the mechanical mixing method and the network on sintering properties, mechanical properties and microstructure of BN-SiC ceramic. It shown that sintering densification degree of network powder along with the change of sintering temperature the same as mechanical powder, but no matter how sintering temperature was changed, sintering densification degree of the former is much higher than the latter, namely sintering powder performance of network powder was better than the mechanical mixing method. Grains of BN-SiC ceramic was prepared with network powders was fine, uniform distribution, contact closely; Grains of BN-SiC ceramic was prepared with mechanical powders was coarse, reunion, pore was bigger between grain.