Dense Al-Y-Si-O-N ceramic coating on the surface of porous Si3N4 was fabricated with oxides of
Al2O3 -Y2O3 -SiO2 sol and Si3N4 of porous substrate using sol鄄gel method. Microstructure and properties of ceramic
coating at the different temperatures were studied mainly. Phase composition and element component was analysed by
XRD pattern and EDS,respectively, and microscopic morphology of surface and cross鄄section of coating was observed
by the SEM. The ceramic coating is densified when the coating is sintered at 1 400益, and phase compositions of
coating are consisted of 茁鄄sialon, Si2ON, SiO2 and amorphous phase. The results show that the water absorption of
porous Si3N4 is decreased from 32. 8% to 90%, and the flexural strength of porous Si3N4 is increased from 2. 1% to
25. 9%.