Design and preparation of LiAlSiO4-Al2O3 coating for the oxidation resistance improvement of SiC ceramics

The low coefficient of thermal expansion (CTE) coating was designed for SiC oxidation-resistant applications by using Al2O3 and LiAlSiO4 as positive and negative expansion materials. The CTE value, relative density and flexural strength of LiAlSiO4-Al2O3 coating were characterized. The effect of LiAlSiO4-Al2O3 coating on the oxidation resistance and flexural strength of SiC substrate was systematically studied by cyclic oxidation tests at 1400 degrees C. Results showed that LiAlSiO4-Al2O3 coating with 20 wt% LiAlSiO4 exhibited optimal properties, featuring the excellent relative density of 93.14 %, appropriate CTE of 5.815 x 10-6 /degrees C, and high flexural strength of 56.35 MPa. The weight gain of the SiC with LiAlSiO4-Al2O3 coating was 0.49 % after 100 h of oxidation, much lower than 2.25 % of bare SiC substrate, indicating that LiAlSiO4-Al2O3 coating effectively hindered the diffusion of oxygen and improved the oxidation resistance of SiC substrate. Moreover, the dense coating blunted defects on the SiC substrate surface, which maintained the high strength of the coated SiC after long periods of oxidation.

Automated summary

A low coefficient of thermal expansion (CTE) coating was developed to improve the oxidation resistance of SiC. The coating, composed of LiAlSiO4 and Al2O3, exhibited favorable hydrophobicity, appropriate CTE, and high flexural strength. The experimental results demonstrated that the coating not only enhanced the oxidation resistance of SiC, but also maintained the high strength of the coated SiC.