Enhancement of Si3N4 ceramics via evolution of grain interface between ZrO2 and Si3N4 under pressureless sintering

Silicon nitride (Si3N4) as a structural ceramic material, its strength, and toughness are the decisive characteristics of damage tolerance and reliability. In this work, Si3N4 ceramics is enhanced via evolution of grain interface between Si3N4 and ZrO2, which bending strength and fracture toughness reached 982.8 MPa and 9.81 MPa & BULL;m(1/2), respectively. The interface evolution of the ZrO2 and Si3N4 grains were investigated via both first-principles molecular dynamics simulation and experiment. The Si3N4/ZrO2 interface structure was observed by high-resolution transmission electron microscopy, include: (i) glass phase film, (ii) Zr3N4 film. First-principles molecular dynamics simulation reported here provide an atomic-level description of the formation mechanisms of the interface structure. The Si-O bond and Zr-N bond was formed to provide the Si3N4/ZrO2 interface bond. Moreover, the embedded-like composite structure between Si3N4 and ZrO2 was formed during the sintering process, which can deflect cracks and result in an increase in the fracture energy. Due to the strength difference of Si3N4 and ZrO2, cracks tend to propagate through the grains of ZrO2 and deflects when it encounters the rod-like Si3N4 grains. In the same time, the ZrO2 plays a role with respect to refinement of the & beta;-Si3N4 grain size and decrease of the glass phase content.