Preparation and failure mechanism of LaZrCeO thermal barrier coating by EB-PVD
Thermal barrier coatings,consisting of a metal bonding layer,ceramic surface layer,and thermal growth oxide,are widely utilized in turbine blades for aero engines as protective coatings.The LaZrCeO/YSZ double ceramic thermal barrier coating was prepared on a Ni-based superalloy matrix using EB-PVD technology.The composition,phase structure,and thermal cycle life of the thermal barrier coating were investigated by adjusting the deposition energy of the ingot.Furthermore,the failure mechanism of the thermal barrier coating under 1100℃thermal cycle was analyzed.The results indicate that the Zr content in the LaZrCeO coating increases proportionally with the rise in ingot deposition energy,while maintaining a consistent La/Ce ratio.Additionally,the increase in evaporation electron beam leads to changes in coating phase structure from single fluorite phase to compound pyrochlore and fluorite phase structure,and finally to single pyrochlore structure.Thermal cycling tests at 1100℃demonstrate that the average thermal cycle life of LaZrCeO/YSZ ceramic thermal barrier coating with composite pyrochlore and fluorite phase structure reaches 1518 cycles,indicating excellent thermal physical properties.As the thermal cycle progresses,the Al element in the bond coat diffuses outward to form a thermally grown oxide(TGO)layer,while the Cr element reacts with LaZrCeO and oxygen to generate LaCrO3 and ZrO2.At elevated temperatures,Ni and Co elements diffuse and react with oxygen to produce(Ni,Co)(Cl,Al)2)O4 compounds.The chemical reactions induce cracks in either the TGO layer or the interface layer,reducing the toughness between the metal bond layer and ceramic layer,and leading to thermal barrier coating failure.
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