Microstructural evolution and high-temperature oxidation behavior of plasma sprayed SiC-YSZ TBCs

In this work, the effect of SiC addition on the microstructure, porosity, phase composition, weight gain, and thickness of TGO of the coatings after repeated oxidation at 1300 degrees C for various time of APS SiC-YSZ TBCs have been investigated. The phase of the as-sprayed coatings is consisted of t'-ZrO2, SiC and very little SiO2. With the increase of SiC addition, the diffraction peak intensity of SiC and SiO2 are both increased. SiC and SiO2 can fill into the pores in YSZ effectively. However, the porosity in the coatings has little changed with the increased of SiC addition. The addition of SiC during repeated oxidation at 1300 degrees C can limit the development of the m-ZrO2 phase while causing no ZrO2 lattice deformation. Increasing the SiC addition can impede the growth of TGO between the bonding layer and the ceramic layer, lowering the thermal weight gain rate of the SiC-YSZ coating. The lowest thermal weight gain rate occurs when the SiC composite concentration is 15 wt%. When the composite content of SiC is increased by 10 wt%, the percentage of O element at the interface between the bonding layer and the ceramic layer decreases by approximately 6.56 wt%. Increasing the SiC concentration will improve the compactness of the interface between the bonding and ceramic layers, and limit grain formation in the bonding layer. However, the SiC composite composition must match the ceramic coating's porosity. When the SiC percentage is too low, the ceramic layer's porosity increases and TGO development accelerates. When the SiC concentration is too high, it agglomerates and connects within the coating, causing the coating to fail off during high temperature service.