Experiments and transient finite element simulation of γ-Y₂Si₂O₇/B₂O₃-Al₂O₃-SiO₂ glass coating on porous Si₃N₄ substrate under thermal shock

A dense γ-Y₂Si₂O₇/B₂O₃-Al₂O₃-SiO₂ glass coating was fabricated by slurry spraying method on porous Si₃N₄ ceramic for water resistance. Thermal shock failure was recognized as one of the key failure modes for porous Si₃N₄ radome materials. In this paper, thermal shock resistance of the coated porous Si₃N₄ ceramics were investigated through rapid quenching thermal shock experiments and transient finite element analysis. Thermal shock resistance of the coating was tested at 700 °C, 800 °C, 900 °C and 1000 °C. Results showed that the cracks initiated within the coating after thermal shock from 800 °C to room temperature, thus leading to the reduction of the water resistance. Based on the finite element simulation results, thermal shock failure tended to occur in the coating layer with increasing temperature gradient, and the critical thermal shock failure temperature was measured as 872.24 °C. The results obtained from finite element analysis agree well with that from the thermal shock tests, indicating accuracy and feasibility of this numerical simulation method. Effects of thermo-physical properties for the coating material on its thermal shock resistance were also discussed. Thermal expansion coefficient of the coating material played a more decisive role in decreasing the tangent tensile stress.