Thermal shock fatigue strength of ceramics by laser irradiation

Structural ceramics have excellent wear- and heat-resistant characteristics. However, in some applications, they are exposed to very high temperatures and high heat-flux environments, and are also subjected to repeated thermal loadings that change rapidly with time. Such repeated thermal loadings are causes of material fracture. Therefore, it is important to investigate the thermal shock fatigue characteristics of these ceramics. We present results of thermal shock fatigue strength tests for a machinable structural ceramic called MACOR, composed of SiO2-MgO-Al2O3. The thermal shock fatigue experiments were done using a CO2 laser, and the crack generation of the specimens was measured from AE (acoustic emission) signals. Consequently, the thermal shock fatigue strength of MACOR was estimated from the critical power density, and it was proposed that the thermal shock strength of ceramics should be estimated using a minimum value PLF [W/mm2] of the critical power density below which ceramic fracture is independent of the spot diameter. Finally, the PLF of 0.2 W/mm2 was obtained from thermal shock fatigue experiments using MACOR.