残余应力对涂覆Al2O3涂层的ZrO2陶瓷的强度和裂纹扩展阻力的影响

本研究在ZrO₂基体表面涂覆一薄层Al₂O₃涂层, 利用基体与涂层之间热膨胀系数不匹配, 在Al₂O₃-ZrO₂预应力陶瓷(简称A_CZ_S预应力陶瓷)表层引入压应力。采用维氏压痕法评价残余应力对A_CZ_S预应力陶瓷的表层和基体中裂纹扩展阻力的影响。理论分析结合实验结果表明: 表层的压应力使得A_CZ_S预应力陶瓷的裂纹扩展阻力增大, 最终导致强度和损伤容限提高; 且A_CZ_S预应力陶瓷表层的压应力和裂纹扩展阻力随着基体截面积与涂层截面积比值的增加而增大。当ZrO₂基体表层的Al₂O₃涂层厚度为40 μm时, 表层压应力使A_CZ_S预应力陶瓷的弯曲强度达到(1207±20) MPa, 相比于同种工艺下制备的ZrO₂陶瓷强度提高了32%, 同时也是Al₂O₃强度的3倍。此外, A_CZ_S预应力陶瓷也表现出很好的抗热震性能。

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

By covering a thin Al₂O₃ coating on ZrO₂ substrate, compressive stress caused by the mismatch of thermal expansion coefficients between the coating and substrate was introduced in the surface layer of Al₂O₃-ZrO₂ pre-stressed ceramics (marked as A_CZ_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 ZrO₂ substrate to Al₂O₃ coating. Due to the residual compressive stress existing in Al₂O₃ coating, a high flexural strength of (1207±20) MPa was measured for ZrO₂ specimens coated with 40 μm Al₂O₃. The flexural strength is 32% higher than that of monolithic ZrO₂, and about triple of the value of Al₂O₃. Meanwhile, compared to ZrO₂, the A_CZ_S pre-stressed ceramics exhibit superior thermal shock resistance.