Mullite/SiB6 coating for microcrack heal and microwave absorption performance at high temperatures

To address the critical demand for multifunctional coatings in extreme aerospace environments, this study developed a mullite/SiB₆ composite coating via atmospheric plasma spraying. The coating exhibits outstanding microwave absorption at room temperature, with a minimum reflection loss (RLmin) of −34.60 dB and an effective absorption bandwidth (EAB, RL < −10 dB) of 2.09 GHz. After annealing at 800℃, it maintains excellent performance, with RLmin below –20 dB and EAB exceeding 2 GHz, owing to its superior self-healing property. The borosilicate glass with a low oxygen diffusion coefficient produced by SiB₆ oxidation effectively fills cracks and pores, thereby preventing further oxidation of the coating. The coating exhibited excellent self-healing properties, with its porosity decreasing sharply from 9.59 % (as-sprayed) to 0.44 % after heat treatment at 1000℃. These findings highlight the potential of this coating as a high-temperature self-healing microwave absorber for extreme aerospace environments.