For high temperature oxidation resistant coating on C/C composites, multi layer system composed of a Y2SiO5 outer layer and a SiC inner layer is proposed. Atmospheric plasma spraying (APS) technology is employed to form Y2SiO5 coating. Influences of two spraying parameters, (1) particle size and (2) plasma secondary gas (H2) flow rate, on microstructure and gas tightness of Y2SiO5 coating are investigated. To improve adhesion between Y2SiO5 layer and SiC layer, forming an interlayer is examined. High temperature oxidation resistance of the coating system is investigated. The results are summarized as follows:
(1) In a condition that median particle size is 14.51 μm and H2 flow rate is 2SLPM, Y2SiO5 coating has low porosity and gas permeability of Y2SiO5 coating is 1.49×10−13 m2/(Pa·s).
(2) Y2SiO5 layer adheres to SiC layer by forming YSix interlayer.
(3) The coating system in this study show high temperature oxidation resistance at 2073 K.
