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 Al 2 O 3 and LiAlSiO 4 as positive and negative expansion materials. The CTE value, relative density and flexural strength of LiAlSiO 4 -Al 2 O 3 coating were characterized. The effect of LiAlSiO 4 -Al 2 O 3 coating on the oxidation resistance and flexural strength of SiC substrate was systematically studied by cyclic oxidation tests at 1400 °C. Results showed that LiAlSiO 4 -Al 2 O 3 coating with 20 wt% LiAlSiO 4 exhibited optimal properties, featuring the excellent relative density of 93.14 %, appropriate CTE of 5.815 × 10 −6 /°C, and high flexural strength of 56.35 MPa. The weight gain of the SiC with LiAlSiO 4 -Al 2 O 3 coating was 0.49 % after 100 h of oxidation, much lower than 2.25 % of bare SiC substrate, indicating that LiAlSiO 4 -Al 2 O 3 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.