Comparison in microstructure and mechanical properties of porous Si3N4 ceramics with SiC and Si3N4 coatings

Porous Si3N4 ceramic is gaining interest for its wide applications, but the low surface hardness decreases the mechanical erosion resistance, and many surface open pores decrease the moisture resistance seriously. Using chemical vapor deposition (CVD) of SiC and Si3N4, respectively, the surface of porous Si3N4 ceramic was densified. During CVD, the SiC and Si3N4 particulates deposited on the inner and on the outer surface of the porous Si3N4 ceramic leading to an obvious improvement of mechanical properties, especially for surface hardness. As the deposition content of SiC and Si3N4 increased, the mechanical properties of porous Si3N4 ceramic increased gradually with the total porosity decreasing slowly. After CVD, the pore size of porous Si3N4 ceramic decreased obviously, and the inner part of the porous Si3N4 ceramic was still porous.