Research Progress on Failure Mechanism,Material Selection and Structural Design of Long-life Thermal Barrier Coatings
Thermal barrier coatings(TBCs)are efficient functional insulation coatings applied to power equipment such as aircraft engines and gas turbines.They have advantages such as low thermal conductivity,good high-temperature phase stability,and fracture toughness.With the continuous enhancement of power systems,key components must often be used in extremely high temperature environments,which can easily lead to the cracking,delamination,degradation,and premature failure of a coating.Therefore,the development of thermal barrier coatings high insulation values and long lives is very important.This article summarizes several typical failure mechanisms of thermal barrier coatings,including failure induced by stress,failure caused by sintering,and failure caused by the infiltration of calcium-magnesium-aluminum silicate(CMAS)and thermally grown oxide(TGO).In order to reduce the residual stress,it is necessary to gradually improve the failure prediction models of TBCs with different preparation processes and different materials,which will improve the reliability and accuracy of the prediction model results.On the other hand,the coating strain tolerance can be increased to release the residual stress,such as by increasing the porosity of the coating and prefabricating cracks in it,which will alleviate the coating stress concentration.In view of the problem of high-temperature sintering,methods to adjust the internal pore structure of the coating by doping metal oxides in the matrix require further study.The thermal-mechanical-chemical coupling effect can be considered to delay the erosion of CMAS,and an in-situ autogenous method can be used to prepare a dense layer,but there have been few studies on this aspect.In addition,a TGO layer with large grain size can be prepared on the surface of the adhesive layer in advance,which can slow down the grain boundary diffusion and limit the growth of TGO by increasing the grain size.Methods have been proposed to reduce the internal porosity of the coating,reduce the difference in interlayer thermal expansion coefficients,and reduce the surface roughness to suppress coating failure.Therefore,the progress on thermal barrier coating research is summarized from two aspects:material selection and the structural design of top coatings.From the perspective of material selection,the problems with using zirconia and some yttrium-stabilized zirconia(YSZ)in long-term high-temperature environments are summarized.In recent years,some advanced coating materials have been developed,including oxide-stabilized zirconia,A2B2O7 oxide,rare-earth tantalite,and self-healing materials.In order to reduce the residual stress,it is necessary to gradually improve the failure prediction models of TBCs with different preparation processes and materials,which will improve the reliability and accuracy of the prediction model results.On the other hand,the coating strain tolerance can be increased to release the residual stress,such as by increasing the porosity of the coating and prefabricating cracks in it,which will alleviate the coating stress concentration.In view of the problem of high-temperature sintering,methods to adjust the internal pore structure of the coating by doping metal oxides in the matrix require further study.The thermal-mechanical-chemical coupling effect can be considered to delay the erosion of CMAS,and an in-situ autogenous method can be used to prepare a dense layer,but there have been few studies on this aspect.In addition,a TGO layer with large grain size can be prepared on the surface of the adhesive layer in advance,which can slow down the grain boundary diffusion and limit the growth of TGO by increasing the grain size.From the perspective of structural design,preparation methods for different coating structures have been introduced.Layered structures,columnar structures,nanostructures,and functionally graded structures are reviewed from the perspectives of their microstructures and corrosion resistance,internal thermal stress,and thermal cycle life values.Finally,the future development directions for long-life thermal barrier coatings are outlined.This review not only discusses the shortcomings of the existing research and direction of future research,but also provides a theoretical basis for the development of a new generation of TBCs with higher corrosion resistances,better thermal insulation values,and longer lives.
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维普
