Effects of Residual Stresses on Strength and Crack Resistance in ZrO2 Ceramics with Alumina Coating

By covering a thin Al 2 O 3 coating on ZrO 2 substrate, compressive stress caused by the mismatch of thermal expansion coefficients between the coating and substrate was introduced in the surface layer of Al 2 O 3 -ZrO 2 pre-stressed ceramics (marked as A C Z S pre-stressed ceramics).Vickers indentation test was carried out to check the crack resistance in the surface layer and substrate influenced by the residual stresses.The enhancement of the crack resistance in surface layer results in a high flexural strength and excellent damage tolerance.Both theoretical analysis and experimental results show that the compressive stress and crack resistance in the surface layer increase with the increasing ratio of the cross-sectional area of ZrO 2 substrate to Al 2 O 3 coating.Due to the residual compressive stress existing in Al 2 O 3 coating, a high flexural strength of (1207±20) MPa was measured for ZrO 2 specimens coated with 40 μm Al 2 O 3 .The flexural strength is 32% higher than that of monolithic ZrO 2 , and about triple of the value of Al 2 O 3 .Meanwhile, compared to ZrO 2 , the A C Z S pre-stressed ceramics exhibit superior thermal shock resistance.