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

Si+mullite/BSAS (1–xBaO–xSrO.A12O3–2SiO2, 0≤x≤1)+Er2SiO5 environment barrier coatings (EBCs) were prepared by electron beam physical vapour deposition and plasma spraying for Cf/SiC substrates. The oxidation resistance and failure mechanism of the EBC were investigated by oxidation tests at 1400°C, X-ray diffraction and scanning electron microscopy. The results show that the local EBCs fell off after 133 h oxidation at 1400°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/A12O3 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.