Microstructure and oxidation behavior of a novel bilayer (c-AlPO4–SiCw–mullite)/SiC coating for carbon fiber reinforced CMCs

Abstract

Abstract A novel cristobalite aluminum phosphate particle (c-AlPO4) modified SiC whisker toughened mullite coating (c-AlPO4-SiCw-mullite) was prepared on SiC coated carbon fiber reinforced SiC composites (C/SiC) by a new sol-gel method combined with air spraying to improve the oxidation resistance of SiCw-mullite coating. Results show that c-AlPO4-SiCw-mullite coatings with 10 and 20\u2009wt.% of c-AlPO4 exhibited obviously improved oxidation resistance at 1773\u2009K in ambient air for 100\u2009h than SiCw-mullite coating. Moreover, the oxidation resistance of c-AlPO4-SiCw-mullite coatings were rapidly declined when the c-AlPO4 in c-AlPO4-SiCw-mullite coating were set to 30 and 40\u2009wt.%. The c-AlPO4-SiCw-mullite coating with 20\u2009wt.% of c-AlPO4 showed most pronounced oxidation resistance, the weight loss rate after the oxidation in ambient air for 210\u2009h was merely 3.00\u2009×\u200910−5 g·cm−2\u2009h−1. The failure of c-AlPO4-SiCw-mullite coating with 20\u2009wt.% of c-AlPO4 was due to the generation of penetrative micro-cracks and micro-holes in the coating, which cannot be self-healed by the silicate glass layer after long time oxidation at 1773\u2009K.