$Si_3N_4$-based electro-conductive composites were fabricated by hot pressing under the condition of 1750℃, 35MPa for 1 hr. In these composites 20 vol% SiC whisker as a reinforcing material, variable content of TiN(up to 30 vol%) as a conducting particle, and 5wt% MgO as a sintering additive were added to the $Si_3N_4$ matrix. Thereafter the electrical and mechanical properties were tested. In addition, electrical discharge machining experiment has been done by using die-sinking electrical discharge machine.
The relative densities were more than 95% of TD up to 30vol% TiN in spite of slight decreasing with TiN addition. Then microstructures were homogeneous in consequence of sedimentation treatment for $Si_3N_4$ powders and SiC whiskers. According to X-ray analysis there were not crystalline phases by the reaction of starting materials.
In the mechanical properties, flexural strength and Vickers hardness was slightly decreased with the addition of TiN up to 30 vol%, but fracture toughness was not changed. Electrical conductivity was increased with TiN. Specially, SiC whisker added to improve fracture toughness contributed greatly to the conductivity.
By the test of electrical discharge machining, EDM was impossible for $Si_3N_4$-20vol% SiCw material but possible by addition of 10vol% TiN. In addition, machining rate increased with TiN addition. EDM can produce a better surface finish and the reaction product was not found. The maximum machining rate was 2.04㎣/min.
