Effects of residual stress on the flexural strength and microstructure of Al2O3-ZrO2 composites fabricated by different methods

Due to the mismatch of coefficients of thermal expansion between ZrO₂ and Al₂O₃, thermal residual stress would be induced to the Al₂O₃-ZrO₂ composites during the cooling process. However, Al₂O₃-ZrO₂ composites fabricated by different methods have various stress distribution and stress states, which result in different mechanical properties. In this work, the prestressed coating reinforcement method and the particle enhancement method have been carried out to fabricate Al₂O₃-reinforced ZrO₂ composites (the corresponding specimens marked as AcZs pre-stressed ceramics and Al₂O_3,P/ZrO₂ composites), respectively. The effects of residual stress on flexural strength and microstructure were investigated. Results show that, in the AcZs pre-stressed ceramics, the residual compressive stress exists in the coating, while the tensile stress exists in the substrate. However, the residual stress in Al₂O_3,P/ZrO₂ composites is hydrostatic stress because of the isostatic presses on Al₂O₃ particle in all directions. Furthermore, owing to the residual compressive stress in the surface layer could prevent crack propagation, the flexural strength of AcZs pre-stressed ceramics is higher than that of Al₂O_3,P/ZrO₂ composites with different content of Al₂O₃ particle additions. Generally, the prestressed coating reinforcement method is an effective and low-cost way to improve the mechanical strength of brittle materials, which is more suitable for the preparation of ZrO₂ based ceramics with high strength in this work.