| Thermal Barrier coatings（TBCs）were applied to the hot-ended components of gas turbine,making the substrate alloy could be served in the environment where the higher temperature.The service life of coatings,corrosion resistance to high temperature oxidation and CMAS were the important indicators to measure the functional performance of TBCs.The yttrium aluminum garnet(Y3Al5O12,YAG)of new TBCs material has great phase stability and oxygen barrier properties,low thermal conductivity and good resistance to CMAS,and based its lower coefficient of thermal expansion,the TBCs structure with the YAG/8YSZ double ceramic layer was designed in this paper.The bonding layer of NiCoCrAlY was developed by explosive spraying（D-GUN）,and the YAG and 8YSZ ceramic layers were prepared by atmospheric plasma spraying（APS）.Assisted with SEM and XRD,the cross-section and surface characteristics of the coating before and after oxidation,CMAS corrosion and shock test were analyzed.Then the high temperature oxidation resistance and CMAS corrosion performance of 8YSZ single ceramic TBCs and YAG/8YSZ double ceramic systems were exploited in atmospheric environment,and the reactivity between CMAS and YAG was discussed.Finally,the thermal shock test was used to characterize the cycle life of the two coating systems.High temperature oxidation failure is one of the main failure modes of TBCs.In this paper,the explosion spraying（D-GUN）was used to develop the adhesive NiCoCrAlY layer,then each ceramic TBC of YAG/8YSZ double and 8YSZ single was applied on the adhesive layer by atmospheric plasma spraying（APS）.Assisted with SEM and XRD,The cross-section and surface characteristics of the coating before and after oxidation were analyzed.The oxidative weight gain kinetics of 8YSZ single ceramic and YAG/8YSZ double ceramic TBCs after isothermal oxidation at 1100℃were analyzed.Further,the microstructure and phase of YAG ceramic layer and the growth process and growth kinetics of TGO were also studied.The results showed that no obvious phase structure transformation appeared on the YAG ceramic layer after isothermal oxidation for 300 h,and the porosity was slightly reduced.Compared with the 8YSZ single ceramic layer system,the YAG/8YSZ double ceramic layer system has a lower oxidative weight gain rate and TGO growth rate,which reduced by 1.7and 1.4 times respectively.Simultaneously,the rate ofβ-NiAl phase consumption of the bonding layer and the growth rate of the island oxide became lower than before,indicating better resistance of YAG/8YSZ double ceramic layer to high temperature oxidation.CMAS corrosion has become one of the important factors for the failure of thermal barrier coating（TBCs）on the surface of aero-engine blades.The corrosion tests of YAG/CMAS mixed powder（mass ratio 1:1）and two kinds of TBCs coated with CMAS powder at 1250℃for 12 h and 1 h,4 h and 12 h,respectively.The reaction between YAG powder and CMAS and the CMAS corrosion process and corrosion mechanism of two kinds of TBCs were studied.The results showed that YAG and CMAS powder reacted only at the edge of YAG powder at 1250℃,and YAG showed good CMAS resistance and high temperature stability.After 8YSZ single ceramic TBCs corrosion for 1 hour,the ceramic layer reacted violently with CMAS.The transition from tetrahedral phase to monoclinic phase of 8ysz was initiated by Y ions leaching,and CMAS infiltrated into 8YSZ ceramic layer completely after 12 hours.However,in the process of TBCs corrosion of YAG/8YSZ double ceramics,CMAS can not penetrate the ceramic layer of YAG surface layer,and the ceramic layer of 8YSZ bottom layer is not damaged by erosion.At the same time,the internal structure of YAG ceramic layer remains intact,and only the needle and block high melting point lazy apatite phase is formed at the interface of CMAS/YAG,and its seal blocks the infiltration of CMAS in the pores and cracks of the coating.The corrosion resistance of YAG/8YSZ double ceramic TBCs was improved.Finally,based on the simulation of actual service conditions for TBCs,the thermal shock test was used to characterize the cycle life of the two coating systems.The results show that the thermal shock frequency of YAG/8YSZ double ceramic TBCs system accounted for 41%of the 8YSZ single layer system,showing the poor resistance to thermal shock.That might be due to the factors such as much interfaces and large differences in thermal expansion coefficients between layers existed in YAG/8YSZ double ceramic TBCs system.In summary,the YAG/8YSZ double ceramic TBCs system exhibited good stability and oxidation and CMAS resistance at high temperatures,providing theoretical and experimental references for the application of YAG/8YSZ double ceramic TBCs. |
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