Study on the Repair of Irregular and Deep Cracks Induced by Thermal Shock Using Al-Cu-O Reactions in Al2O3 Ceramics

The irregular and deep cracks induced by thermal shock in Al2O3 ceramics were repaired by applying Cu powder layer on their surface and heating at 1200 °C under an atmosphere of air. The Al-Cu-O liquid phase formed at 1200 °C by the reaction of molten Cu, oxygen, and Al2O3 phases penetrate deep into the narrow cracks, and the precipitation phases of Cu2O and CuAlO2 densely fill the crack interior. Our observation and analysis of the filled cracks and the surrounding areas of the repaired cracks, as well as the microstructural analysis results obtained through SEM-EDS and TEM observation, suggested the aforementioned crack repair mechanism. The bending strength of the coated surface after repairing the cracks is 301.8 MPa (ΔT = 300 °C), which is twice as strong as the specimen after thermal shock and 10% higher than the original strength of the base material.