COATING OF NONOXIDE CERAMICS BY INTERACTION WITH METAL POWDERS

Non-oxide ceramics, such as Si3N4, SiC, BN and B4C, interact at elevated temperatures with powders of metals having a high affinity for carbon and nitrogen with the formation of reaction product coatings on the ceramic surface. The diffusion of metal atoms along the ceramic surface plays an important role in the process of coating; starting temperatures for reactions with the formation of coatings correlate with surface self-diffusion rates of the corresponding metals. The coatings obtained on Si3N4 and SiC have a layered structure and their growth is diffusion controlled. The composition of the inner layer of the coatings is in agreement with the presented thermodynamic calculations for the corresponding Si3N4- and SiC-metal interfaces. The composition and morphology of the surface layer depend on the environment and can be modified by changing the treatment conditions. Based on the experimental observations and thermodynamic calculations, a model for the described powder immersion reaction assisted coating (PIRAC) is proposed.