Alumina sol-assisted sintering of SiC-Al2O3 composites

The composite sol-gel (CSG) technology has been utilized to process SiC-Al2 O3 ceramic/ceramic particulate reinforced composites with a high content of SIC (up to 50 vol%). Alumina sol, resulting from hydrolysis of aluminum is opropoxide, has been utilized as a dispersant and sintering additive. Micro structures of the composites (investigated using TEM) show the sol-originat ing phase present at grain boundaries, in particular at triple junctions, i rrespective of the type of grain (i,e,, SiC or Al2O3), It is hypothesized t hat the alumina film originating from the alumina sol reacts with SiO2, fil m on the surface of SiC grains to form mullite or alumina-rich mullite-glas s mixed phase. Effectively, SiC particles interconnect through this phase, facilitating formation of a dense body even at very high SIC content. Compa rative sinterability studies were performed on similar SiC-Al2O3, compositi ons free of alumina sol, It appears that in these systems the large fractio n of directly contacting SiC-SiC grains prevents full densification of the composite. The microhardness of SiC-Al2O3 sol-gel composites has been measu red as a function of the content of SiC and sintering temperature. The high est microhardness of 22.9 GPa has been obtained for the composition 50 vol% SiC-50 vol% Al2O3, sintered at 1850 degrees C.