Preparation and mechanical behavior of Si₃N₄ composite ceramics with brick-and-mortar structure

The nacre with brick-and-mortar structure enables multiple toughening and strengthening mechanisms, and bioinspired ceramics with brick-and-mortar structure have been attracting much attention from many researchers. However, the process of constructing precise and uniform microstructure is quite complicated. Herein, we propose a novel and facial method to fabricate composite ceramics with brick-and-mortar structure. Si3N4 microspheres prepared by particle-stabilized foaming and centrifugal spray drying were directly hot pressed after being immersed in suspension and evenly wrapped with ZrO2. The mechanical properties of composite ceramics were optimized by adjusting the pressure during sintering and ZrO2 content. When ZrO2 content was 10 wt% and sintering pressure was 5 MPa, the fracture toughness of ZrO2/Si3N4 brick-and-mortar composite ceramics reached 9.02 MPam(1/2), and the flexural strength was 784 MPa, which were increased by 46.9% and 26.5%, respectively, compared with the control group. While retaining excellent flexural strength, the strong interface also induces crack to deflect and branch along the two-phase interface of the brick-and-mortar structure caused by the residual stress, which was derived from the mismatch of the thermal expansion coefficient of ZrO2 and Si3N4, consuming more fracture energy to achieve the toughening effect.