Effect of CaF2 on thermal shock resistance of Yb2Si2O7-based high-temperature abradable sealing coatings: Simulation and experiment

Yb2Si2O7 is a candidate high-temperature abradable sealing coatings (ASCs) for ceramics matrix composites (CMCs), and the introduction of CaF2 lubrication phase can improve abradable properties of the coatings and prevent damage of blades. However, the CaF2 results in a thermophysical parameter mismatch between the substrate and coating, which might have negative effects on the thermal shock resistance of the ASCs. In this paper, a model of the ASCs with Yb2Si2O7-(0/10/20/30/40/50 vol%) CaF2 as the top-coat layer and Si as the bond-coat layer was simulated by finite element simulation method, and the residual stresses after high temperature thermal shock test at 1100 degrees C were calculated. The simulation results showed that with the introduction of CaF2, the radial tensile stress concentration area changed from the bond-coat layer to the top-coat layer, and the edge effect of the coating was more serious. As CaF2 content increased, the radial tensile stress on the surface as well as the top-coat/bond-coat (TC/BC) interface, and the axial tensile stress at the TC/BC interface, exhibited a remarkable increasing trend. Moreover, the stress gradients at all the interface edges also increased. This could result in the worse thermal shock resistance of the ASCs. The experiment results revealed that more penetrating cracks in the top-coat layer and interface cracks between the Si bond-coat layer and the top-coat layer appeared with the increase of CaF2, and the ASCs showed worse thermal shock resistance, which was consistent with the simulation results. The model established in this study can provide a theoretical basis for the design and optimization of Yb2Si2O7-CaF2 coating.