The pressureless sintering of Sialon ceramics

During the pressureless sintering of Si 3N 4, Al 2O 3, AlN and Y 2O 3 mixed powder, as SiO, CO and N gas are produced in the process reaction and since raw powder Si 3N 4 has a higher decomposition pressure at the sintering temperature and pressure, there is a sintering weight loss anti densification process accompanying the sintering densification process. In order to solve this problem the effect of packing powder compositions, sintering temperature and sintering time on the densities of pressureless sintered Sialon ceramics were studied. The physical and chemical mechanisms of sintering process were discussed. Four kinds of packing powder constitution are A(Si 3N 4), B(Si 3N 4+SiO 2), C(Si 3N 4+Al 2O 3+AlN) and D(Si 3N 4+Al 2O 3+AlN+BN) respectively. The typical composition of feeding powder was Si 3N 4 65%～70%, Al 2O 3 20%～25%, AlN about 10 %, adding Y 2O 3 6%. Sialon ceramic, whose packing powder constitution was 70%Si 3N 4+24%Al 2O 3+3%AlN+3%BN, with relative density of more than 99% and bending strength of 612.2 MPa was prepared. When Z =2 in the molecular formula of Si 6- Z Al Z O Z N 8- Z , the favorite sintering condition was at temperature 1 750 ℃ and sintering time 40 min. The process of the Sialon sintering was transitional liquid phase sintering, which was controlled by several factors.