$Si_3N_4$-TiN electro-conductive ceramic composites used 7wt% $Al_2O_3$ + 3wt%; $Y_2O_3$ or 5wt%MgO as sintering aids were fabricated by pressureless sintering at 1800℃ for 1h. It was room temperature flexural strength by 3-point bending test, $K_{IC}$ and Vickers hardness that were measured in order to investigate the effects of TiN on the mechanical properties. Oxidation resistance was evaluated by measuring the weight gain after exposure to air at 1100℃ for 100h. and electrical resistivity was measured by the Van der Pauw method and 2-prove method too.
It was found that the reaction of between $Si_3N_4$ and TiN didn't bring to anything product, according to the results of XRD and EDS. Phases identified from XRD in sintered body with 7wt% $Al_2O_3$ + 3wt% $Y_2O_3$ were $\beta-Si_3N_4$, $\alpha-Si_3N_4$, $Si_3N_4 \cdot Y_2O_3$ and TiN. Mechanical properties of the composites were not influenced by the addition of TiN less than 30vol%, but oxidation resistance of the composites was rapidly decreased with the addition of Tin. Relation between the composition of $Si_3N_4$-TiN electro-conductive ceramic composites and their electrical resistivity was investigated. The resistivity of the compoisites was decreased with the volume fraction of TiN increasing.
The relationship between the resistivity and the composition of the $Si_3N_4$-TiN composites containing more than 30 vol% TiN can be successfully explained by the effective medium theory and the percolation theory. Therefore, it is suggested that the mechanism of electronic conduction in $Si_3N_4$-TiN composites should be electronic conduction caused by contact between grains of electro-conductive TiN.
