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The Influence of Sintering Temperature on Properties and Microstructure of TiN/Si3N4 Composite

Electrical discharge machining can be used easily for the materials which has good conductivity. In order to improve conductivity of Si3N4 based ceramics, TiN/Si3N4 composite was sintered by adding TiN into Si3N4 powder. In the present research, influence of sintering temperature (1535-1925°C, 8 temperatures) on properties and microstructure of the TiN/Si3N4 composite were investigated with La2O3, AlN as sintering additives, liquid phase pressure less sintering used. Densities of the sintered sample were measured. Bending strength, hardness, fracture toughness and electrical resistively of the sample were tested. Phase composition and microstructure of the samples were analyzed by XRD, SEM and EDX. The results showed that the density and fracture toughness of the sintered bodies reached maximum at temperature of 1760°C (relative density of 97.9%; fracture toughness of 8.5 MPa•m1/2) in the sintering temperature range of 1535~1925°C. With increasing of temperature, the bending strength and hardness of the samples kept raising, reached maximum at temperature of 1925°C (bending strength of 634MPa and Vickers hardness of 1869). But the weight lost at the highest temperature was the severe. Microstructure and EDX showed that crystals of the Si3N4 transferred into complete β phase from α + β both phases. The grain of Si3N4 grew up into long columnar from equiaxial fine particles. The fine grain of TiN grew up also. The comprehensive performances of the samples are better at sintering temperature of 1760°C. The long columnar β-Si3N4 grains interweaved with conductive TiN particles, formed conductive nets through sintering. At this sintering temperature, the bending strength of TiN/Si3N4 sintered body was 560MPa，Vickers hardness 1708MPa. The conductivity of the sintered bodies was irregular with the difference of temperature. The minimum of the conductivity is 20Ω.