Influence of B₄C on oxidation resistance of PSN/borosilicate glass-B₄C field-based repair coating of C/C aircraft brake materials at 700–900 °C

PSN/borosilicate glass-B₄C coating was designed for use as field-based repair coating on carbon/carbon (C/C) composites for aircraft brakes. The first PSN layer was transition layer that improved wettability between glass coating and C/C, and the second layer of borosilicate glass-B₄C formed outer glass layer. Effect of B₄C content on oxidation behavior of C/C repair coating was investigated. The coating with 25 wt% B₄C demonstrated excellent oxidation resistance and could effectively protect C/C composites from oxidation. Weight losses of −3.1% at 700 °C and −2.9% at 900 °C were observed after being oxidized for 10 h. Repair coating with smooth, dense, and crack-free structure could be rapidly formed as B₄C content of the coating increased to 25 wt% and 35 wt% with increasing oxidation time. B₄C in repair coating could be oxidized into B₂O₃ glass and it could heal defects in the coating. Residual B₄C dispersed in the coating could dispersion strengthen glass coating and inhibit crack formation in the coating.