Mechanical properties of Si3N4-SiC three-layer composite materials

The effects of microstructure and residual stress on the mechanical properties of Si(3)N(4)-based three-layer composite materials were investigated. The microstructure of each layer was controlled by the addition of two differently sized silicon carbides: fine SiC nanoparticles (similar to 200 nm) or relatively large SiC platelets (similar to 20 mu m). When the SiC nanoparticles were added, the average grain size of Si(3)N(4) 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 Si(3)N(4) was not much changed because of the large size of the platelets. Three-layer composites were fabricated by placing the Si(3)N(4)/SiC-nanoparticle layers on the surface of the Si(3)N(4)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.