Wet-oxygen corrosion resistance and mechanism of bi-layer Mullite/SiC coating for Cf/SiC composites

A bi-layer oxidation-resistant coating consisting of a mullite outer coating, and a SiC inner coating on the surface of C-f/SiC composites was prepared by the chemical vapour deposition and an air spray sol-gel process, and its corrosion behavior was evaluated in a wet-oxygen coupling environment. Results show that the formation of SiO2 glass layer and its reaction with mullite particles to form aluminosilicate glass layer, leading to an increase in the density of the mullite outer coating, so that the weight loss of bi-layer Mullite/SiC coating coated C/SiC sample was only 1.11 x 10(-3) g.cm(-2) in the first 100 h of oxidation. However, the weight loss of the coated sample reached 26.82 x 10(-3) g.cm(-2) after 200 h of oxidation due to a part of the mullite outer coating was detached. The SiO2 glass phase reacted with water vapour to generate gaseous Si(OH)(x), which created distinct holes on the surface of the SiO2 glass layer or inside the molten aluminosilicate glass layer. Eventually, the mullite outer coating was blistered and detached from the surface of the sample due to the combination and growth of holes.

Automated summary

A bi-layer oxidation-resistant coating composed of mullite and SiC was prepared and evaluated for its corrosion behavior on C-f/SiC composites. The coating showed good oxidation resistance initially, but detached after prolonged exposure to wet-oxygen environment.