Research On The Mitigation Of EB-PVD Prepared Gd-Doped Thermal Barrier Coatings Against High Temperature Volcanic Ash Induced Degradation

In order to further improve the aero-engine thrust-to-weight ratio,thermal barrier coatings are widely applied to the surface of high-temperature components of turbine engines for thermal insulation.However,as the temperature of the front section of the turbine engine continues to increase,high temperature degradation of the thermal barrier coating is becoming more and more serious.Both volcanic ash and calciummagnesium-alumino-silicate(CMAS)can adhere to the surface of coated turbine blades under working conditions.CMAS can cause obvious erosion on the coating,which leads to degradation and failure involving premature peeling of the coating.This poses a threat to the materials integrity of turbine components.In this study,real volcanic ash from Sakurajima,Japan,was used for the investigation of high temperature corrosion.7YSZ(7 wt.% yttrium stabilized zirconia,7YSZ)and 0.5 wt.% Gd-7YSZ thermal barrier coatings were prepared.The resistance of 7YSZ and Gd-doped 7YSZ coatings against high temperature corrosion by volcanic ash was studied.The main contents are as follows:(1)The phase composition and elemental composition of volcanic ash powder and CMAS powder were measured in this study.Compared with artificial CMAS,volcanic ash is more complex in both elemental and phase compositions,as well as showing stronger crystallinity.Perhaps for thermal barrier coatings,the biggest threat posed by volcanic ash exposure is that the melting point of volcanic ash is much lower than CMAS.(2)7YSZ and 0.5Gd-7YSZ coating samples were prepared by electron beam physical vapor deposition technology,and their properties were compared.The porosity,microstructure and surface phase structure of the prepared coatings were analyzed.The hardness and elastic modulus of 7YSZ coatings were 8.03 GPa and 102.01 GPa,respectively.In comparison,the hardness and elastic modulus of 0.5Gd-7YSZ coatings were 11.64 GPa and 132.29.GPa.These measured values are within the range of acceptable mechanical properties of typical thermal barrier coatings.(3)The volcanic ash was covered on the prepared coating specimens before the thermal cycling evaluation of their resistance to volcanic ash corrosion.Post heattreated samples were subsequently characterized by SEM,EDX,and PLPS.It was found that after 5 thermal cycles,the volcanic ash completely penetrated the 7YSZ ceramic layer and reached the TGO.In contrast,the Gd-doped 7YSZ coating can indeed mitigate the molten volcanic ash from penetrating through the coating,thereby protecting the entire thermal barrier coating system.