Thermal fatigue failure mechanism in the joint of nano Cu/Ti–Si3N4 ceramic substrates after thermal fatigue test

Abstract

Thermal stress fatigue failure caused by mismatch in the coefficients of thermal expansion (CTE) between the metal layer and ceramic sheet during a high and low temperature cycle is considered as the big issue of high-power ceramic substrates. The aim of this study is to explore the thermal fatigue mechanism of nano Cu/Ti–Si3N4 ceramic substrates after thermal fatigue test. Thermal fatigue test has been performed by thermal cycles experiment from −30 °C to 150 °C. After thermal cycles, the microstructure of the interface is observed by SEM and TEM. The results show after 400 thermal cycles, the nano-Cu metal layer oxidizes severely. Various oxides are found in the corrosion zone, such as CuO, CuAlO2 and CuAl2O4. Higher dislocation density and nanoscale-twins are observed in Cu or Cu2O, which indicate that Cu and Cu2O alleviates thermal stress. As the number of thermal cycles increases, CuO CuAlO2, CuAl2O4 as a corrosion layer in the corrosion zone were formed. The corrosion layer is difficult to alleviate interfacial thermal stress, and easy to form cracks in the joint zone.