Low Temperature Pressureless Sintering of SiC-Mullite Composites

6H-SiC and α-Al2O3powders were mixed as raw materials(in mass ratio of 7:3) with BaO and TiO2as sintering additives.The SiC-mullite composites were prepared via pressureless sintering in hydrogen atmosphere for 1 h after the green body was pre-oxidated at 1 200 ℃ for 1 h.The effects of sintering temperature and BaO–TiO2 content on the sintering properties and phase composition were investigated.The results show that the compactness improves obviously with the increase of sintering additives at sintering temperature of 1 500 ℃.The apparent porosity of the sample was 0.17% at BaO–TiO2 additive of 8%(mass fraction).BaAl2Si2O8 was generated via the reaction of BaO,α-Al2O3 and SiO2when the green body was pre-oxidated.During the sintering process,BaAl2Si2O8 formed a liquid glass phase,which could promote sintering and the formation of mullite.The main crystal phase of the sample was 6H-SiC and mullite,and the minor phase was glass phase and Al2SiO5.