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

Abstract Silicon nitride (Si 3 N 4 ) as a structural ceramic material, its strength, and toughness are the decisive characteristics of damage tolerance and reliability. In this work, Si 3 N 4 ceramics is enhanced via evolution of grain interface between Si 3 N 4 and ZrO 2 , which bending strength and fracture toughness reached 982.8 MPa and 9.81 MPa·m 1/2 , respectively. The interface evolution of the ZrO 2 and Si 3 N 4 grains were investigated via both first‐principles molecular dynamics simulation and experiment. The Si 3 N 4 /ZrO 2 interface structure was observed by high‐resolution transmission electron microscopy, include: (i) glass phase film, (ii) Zr 3 N 4 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 Si 3 N 4 /ZrO 2 interface bond. Moreover, the embedded‐like composite structure between Si 3 N 4 and ZrO 2 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 Si 3 N 4 and ZrO 2 , cracks tend to propagate through the grains of ZrO 2 and deflects when it encounters the rod‐like Si 3 N 4 grains. In the same time, the ZrO 2 plays a role with respect to refinement of the β‐Si 3 N 4 grain size and decrease of the glass phase content.