Research On The Fabrication And Mechanical Properties Of Nanosized Si₃N₄-based Composite Ceramics

Silicon nitride ceramic has been regarded as one of the promising engineering ceramic materials because of its high strength, high hardness, high corrosion and wear resistance. The nanosized Si₃N₄-based composite ceramics with different amount of TiC and WC were fabricated by hot press sintering. The microstructures were analysed by means of XRD, SEM, EDX and so on. The mechanical properties of nanosized Si₃N₄ ceramics with different amount of TiC and WC were discussed.This thesis is composed of five chapters. In the first chapter, the microstructure, mechanical properties, toughening mechanisms as well as its development tendency are introduced. Based on above work, the purpose and significance of this thesis are pointed out. In chapter two, experimental raw materials, fabrication techniques, the testing method of mechanical properties and token method of microstructure of nanosized Si₃N₄-based composite ceramics are introduced.In chapter three, the effect of TiC on microstructure and mechanical properties of nanosized Si₃N₄ ceramics is discussed. The result show that the crystalline phases of nanosized Si₃N₄-TiC composite ceramics consist ofα-Si₃N₄,β-Si₃N₄,Si₂N₂O and TiC_0.7N_0.3. The TiC reacted with Si₃N₄ during the hot press sintering, with the formation of TiC_0.7N_0.3. Adding proper amount of TiC increases the flexural strength and fracture toughness of nanosized Si₃N₄ ceramics. The Vickers hardness of nanosized Si₃N₄ ceramics increases with the addition of TiC.In chapter four, the effect of WC on microstructure and mechanical properties of nanosized Si₃N₄ ceramics is discussed. The result show that the crystalline phases of nanosized Si₃N₄-WC composite ceramics consist ofα-Si₃N₄,β-Si₃N₄,Si₂N₂O and WC. The Vickers hardness of nanosized Si₃N₄-WC composite ceramics increases with the addition of WC but is lower than monolithic nano-Si₃N₄ ceramic. Adding proper amount of WC particles increases the fracture toughness, but has little effect on the flexural strength.Chapter five summarizes the whole thesis and gives some advice on future works.