Effect of Mo particle size on microstructure and mechanical properties of spark plasma sintered silicon nitride

Silicon nitride ceramic composites were densified by spark plasma sintering with different-sized Mo particles. In-situ synthesis of Mo-Si compound can accelerate the nucleation of β-Si₃N₄ grain, and the number of β-Si₃N₄ grain nucleation increases with decrease of Mo particle size during spark plasma sintering. The effect of Mo particle size on the grain growth of β-Si₃N₄ is significant, while that for the phase composition of Si₃N₄ samples is negligible. Si₃N₄ ceramic composites with 6 wt% nano-sized Mo addition are shown to have the highest bending strength (922.56 MPa) and fracture toughness (8.94 MPa m^0.5), which is attributed primarily to more elongated β-Si₃N₄ grains obtained by more β-Si₃N₄ grain nucleation.