MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF SELF-COMPOSED SI3N4-TIN CERAMICS PREPARED FROM SI, TIC AND TIO2 MIXED POWDER

Microstructure and mechanical properties of the self-composed Si3N4-Ti N ceramics prepared from Si, TiC and TiO2 mixed powder compacts were s tudied. Si3N4 matrix and TiN particles were formed during the sinterin g process of the ceramics. The results were compared with the reaction bonded Si3N4-TiN ceramics prepared from Si and TiN mixed powder compa cts. The TiN particles in the self-composed Si3N4-TiN ceramics were fi nely and homogeneously distributed in comparison with those in the rea ction bonded Si3N4-TiN ceramics. The fracture toughness was 5.0 MPa.m( 1/2) in Si3N4 ceramics, which incresed with addition of TiN particles. Fracture toughness of 6.3 and 5.9 MPa.m(1/2) were obtained at 20 vol% TiN for the self-composed Si3N4-TiN ceramics and the reaction bonded S i3N4-TiN ceramics, respectively. The incresed fracture toughness is pr obably due to the thermal expansion coefficient difference between the Si3N4 and TiN. The fracture strength was 930 MPa in Si3N4 ceramics an d it was retained up to 20 vol%TiN in the self-composed Si3N4-TiN cera mics, whereas in the reaction bonded Si3N4-TiN ceramics the fracture s trength was 350 MPa at 20 vol%TiN, only 40% of the initial value. This is possibly attributed to the difference in the distribution of TiN p articles between two-ceramics.