Study On Oxidation Resistance Strategy And Interfacial Oxidation Behavior Of Thermal Barrier Coatings

As an essential protective material for aero-engine turbine blades,TBCs has become the most feasible method to significantly increase engine service temperature in the face of the limited development potential of single crystal casting and air-film cooling technology.However,TBCs is faced with extremely harsh conditions,such as long-term near Mach number,high-temperature gas impact,high-speed centrifugal force,Volcanic ash corrosion,solid particle erosion and interface oxidation,resulting in extremely complex failure mechanism.Especially,coating oxidation caused by TGO excessive growth is not only a complex thermodynamic coupling physical nonlinear problem,but also the primary factor causing TBCs spalling failure.Therefore,exploring reasonable oxygen resistance strategies,controlling the interface oxidation behaviors and inhibiting the TGO excessive growth,have become the primary task for prolonging TBCs service life.The purpose of this paper is to reduce the TBCs oxidation rate,and prolong the high temperature oxidation resistance life.Aiming at the traditional APS coating,oxygen resistance and interfacial oxidation behavior were studied from the oxygen transport mechanism in TBCs.Firstly,the oxygen transport resistance of YSZ TBCs was studied.Then,YAG/YSZ double ceramic layer structure TBCs with the function of reducing oxygen ion diffusion was designed.Based on the above TBCs,the gas permeation rate of oxygen in the remelting area is further reduced by laser remelting the YAG top ceramic layer,thus the high temperature oxidation resistance life of TBCs with laser remelting YAG/YSZ double ceramic layer structure was improved.Moreover,the evolution rules of TGO growth,structure and morphology during high temperature oxidation were also studied.Finally,the integrated protection scheme of TBCs with coating structure design-micromorphology control-oxidation resistance performance improve was established in this paper.The main conclusions are summarized as follows:（1）The addition YAG ceramic layer and laser remelting ceramic layer are both effective strategies for YSZ TBCs oxidation resistance.The ionic diffuse rate of oxygen in ceramic layer was significantly reduced by double ceramic layer TBCs,which composed of YSZ and YAG ceramic top layer with low oxygen permeability.And the gas permeation rate of oxygen in ceramic layer was efficiently decreased by reducing gas permeation channels of oxygen,resulted from obtain the relatively dense remelting zone with a certain stain tolerance by laser remelting ceramic layer.（2）By researching oxygen resistance of YSZ TBCs,the influence rules of pre-oxidation layer and remelting layer on oxygen transport and TGO growth behavior were investigated.The results showed that,the TBCs with pre-oxidation and laser remelting treatment had better oxygen resistance,although all TGO thickness and oxidation weight gain per unit area increased with oxidation time increasing for both APS TBCs,pre-oxidation TBCs and laser remelting treatment TBCs.Since the TGO structure of TBCs with pre-oxidation and laser remelting treatment only showed a single Al₂O₃layer,and compared with APS TBCs,the parabolic oxidation rate were reduced by 14.80%and 9.00%,respectively.By designing the YAG/YSZ double ceramic layer TBCs,the effect of additional YAG ceramic top layer on TBCs oxidation rate was studied,the mechanisms of structure and growth in the multilayer mixed oxides were analyzed,and the TGO composition and thickness evolution rules were also clarified.The results showed that,TGO evolved from single Al₂O₃layer to double layer morphology with Al₂O₃near the bonding coating and mixed oxides near the ceramic coating after long-term high temperature oxidation.Simultaneously,the mixed oxides exhibited multi-layer structures,NiCr₂O₄and NiO located at the interface of ceramic coating/mixed oxides,（Ni,Co）Al₂O₄located at the interface of Al₂O₃/mixed oxides,and CoCr₂O₄between them.Due to the oxygen ion diffusion inhibition of YAG ceramic top layer,the growth of（Ni,Co）Al₂O₄in the mixed oxide was significantly inhibited,thus reduced the consumption of Al₂O₃layer.As a result,the thickness proportion of the Al₂O₃protective layer in the total TGO of YAG/YSZ TBCs was always greater than or equal to that of YSZ TBCs after oxidation for the same period,the TGO growth rate was also smaller than YSZ TBCs.At last,compared with YSZ TBCs,the parabolic oxidation rate were reduced by 35.09%.（3）By laser remelting modified the ceramic top layer of YAG/YSZ double ceramic layer TBCs,the influence rules of the remelted YAG layer on TBCs microstructure and gas permeation channels of oxygen were studied,the relationship between TGO growth and oxidation interface fluctuation was analyzed,and the mechanisms of remelted layer on inhibiting oxygen penetration and reducing TGO growth rate were clarified.The results showed that,the closed cracks in remelted area contributed to reduce the oxygen permeation rate,inhibit the TGO excessive growth,and remelted area relaxed part thermal stress of laser modified YAG/YSZ TBCs by providing larger strain tolerance.Compared with unmodifed YAG/YSZ TBCs,the TGO growth rate of the laser remelted coating was larger in the initial oxidation stage and smaller in the middle and final oxidation stages.At last,the parabolic oxidation rates of the laser remelted coating,compared with unmodifed YAG/YSZ TBCs and origial YSZ TBCs,were reduced by 18.42%and 43.91%,respectively.Therefore,YAG/YSZ double ceramic layer TBCs has longer service life and better high temperature oxidation resistance.