Effect of sintering additive composition on microstructure, thermal and mechanical property of multi-step spark plasma sintered silicon nitride

Dense silicon nitride composites were fabricated by multi-step spark plasma sintering (SPS). As the induced phase, 6 wt% Mo was added and related with the unadulterated & beta;-Si3N4 seeds produced by the in-situ reaction during the sintering process. Si3N4 samples sintered with 7 mol% CeO2 and Yb2O3 by multi-step SPS exhibited a higher mechanical property, namely, a bending strength of 981 MPa and a fracture toughness of 8.85 MPa m1/2, while the thermal diffusivity was lower than that for Si3N4 samples sintered with 7 mol% CeO2 (27.77 mm2/s). The result was attributed primarily to the fully phase transformation and the abnormal growth of large & beta;-Si3N4 grains, resulted from a longer time of solution-reprecipitation process during SPS.