Corrosion Behavior of AlNbO_4/Mullite Composite as Environmental Barrier Coating in Water Vapor Environment

AlNbO4/mullite composite environmental barrier coating(EBC) with 5mol% AlNbO4 content was prepared on Si3N4 substrate by atmospheric plasma spraying(APS).There was evidence that the weight loss rate of Si3N4 substrate coated by AlNbO4/mullite composite was less than that of Si3N4 substrate coated by mullite during the first 50h corrosion test.The improved protective capacity of AlNbO4/mullite composite coating was ascribed to the formation of glassy AlNbO4 top surface.After 100h corrosion test,the AlNbO4/mullite coating was still stable and no further corroded cavities were observed.However,slight delamination of the coating and a faster weight loss rate was observed after long time corrosion due to the coefficient of thermal expansion(CTE) mismatch between AlNbO4/mullite composite and Si3N4 substrate.