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.