Mechanical properties of Si₃N₄-SiC three-layer composite materials

The effects of microstructure and residual stress on the mechanical properties of Si₃N₄-based three-layer composite materials were investigated. The microstructure of each laver was controlled by the addition of two differently sized silicon carbides: fine SiC nanoparticles (∼200 nm) or relatively large SiC platelets (∼20 μm). When the SiC nanoparticles were added, the average grain size of Si₃N₄ was reduced because of the inhibition of grain growth by the particles. On the other hand, when the SiC platelets were added, the microstructure of Si₃N₄ was not much changed because of the large size of the platelets. Three-layer composites were fabricated by placing the Si₃N₄/SiC-nanoparticle layers on the surface of the Si₃N₄/SiC-platelet layer. The residual stress was controlled by varying the amount of SiC added. The mechanical properties of three-layer composites with various combinations of microstructure and residual stress level were investigated.