Oxidation resistance and failure behaviour of environment barrier coatings for Cf/SiC ceramic

Si+mullite/BSAS (1-xBaO-xSrO.A1(2)O(3)-2SiO(2), 0 <= x <= 1) + Er2SiO5 environment barrier coatings (EBCs) were prepared by electron beam physical vapour deposition and plasma spraying for C-f/SiC substrates. The oxidation resistance and failure mechanism of the EBC were investigated by oxidation tests at 1400 degrees C, X-ray diffraction and scanning electron microscopy. The results show that the local EBCs fell off after 133 h oxidation at 1400 degrees C. The main cause of EBC failure is the formation of a glass phase and pores in the interface and intermediate layer of EBCs due to the reaction of Er2SiO5 in the top layer with Si/SiO2 and Al/A1(2)O(3) in the intermediate layer. In addition, the increased stress in the EBCs because of phase transformation and coefficient of thermal expansion mismatch of coating materials accelerated the EBC failure.