Alumina-based ceramics have high melting point, high strength, wear resistance, corrosion resistance and other properties. They are widely used in metallurgy, machinery, aviation, aerospace and other fields. However, the thermal shock resistance of Al2O3 ceramics is poor. The strength retention rate of the material after a single thermal shock of 300℃ temperature difference is only about 22%, which limits its application field. In practical applications, the thermal shock resistance of Al2O3 ceramics plays a decisive role.
Factors affecting the thermal shock resistance of Al2O3 ceramics
The factors affecting the thermal shock resistance of Al2O3 ceramics are mainly microstructure characteristics, surface conditions and geometric dimensions of ceramics.
1. Influence of Al2O3 ceramic microstructure
The microstructure characteristics of Al2O3 ceramics, such as grain size, microcracks, porosity and pore distribution, will have an important influence on its thermal shock resistance. Taking grain size as an example, for Al2O3 ceramics with high density, fine-grained Al2O3 ceramics within a small grain range have better thermal shock resistance; coarse-grained Al2O3 ceramics within a large grain range have better thermal shock resistance. At present, researchers believe that 10μm is the boundary between coarse and fine grains of Al2O3.
In addition, the non-uniform distribution of pores in alumina ceramics has a greater reduction in the strength and Young's modulus of ceramics than the effect caused by the uniform distribution of pores in ceramics. The microcracks in the ceramics themselves do not always immediately cause material fracture in a thermal shock environment, which is often caused by the suppression of the thermal shock crack nucleus by pores. The presence of an appropriate amount of microcracks can improve the toughness of the ceramics through the microcrack toughening mechanism, thereby improving the thermal shock resistance of Al2O3 ceramics.
2. Influence of surface conditions
Al2O3 ceramics usually need to be treated with some mechanical processing methods before use, such as grinding, polishing, milling, etc., which causes changes in surface roughness. The thermal shock resistance of Al2O3 ceramics after grinding and polishing was investigated. The results showed that the Al2O3 ceramics after grinding had better thermal shock resistance. The critical thermal shock temperature difference of Al2O3 ceramics after grinding and polishing was 235℃ and 185℃ respectively. This is because the higher initial defect density on the grinding surface allows the elastic energy generated by thermal shock to be distributed on more cracks, and the extension of each crack is relatively small.
3. Effect of geometric dimensions
The thermal shock resistance of Al2O3 ceramics is also affected by the geometric dimensions of the ceramics. Generally, reducing the thickness of the ceramic can increase the critical thermal shock temperature difference of the ceramic, which is mainly due to the internal bending impulse generated by the bending stress.