Characterisation of the microstructure and thermal properties of Nd ₂Zr ₂O ₇ and Nd ₂Zr ₂O ₇/YSZ thermal barrier coatings

The microstructure of following thermal barrier coatings (TBC) was characterised in this paper: monolayer coatings Nd ₂Zr ₂O ₇ and 8YSZ; a double ceramic layered (DCL) coating. Coatings were characterised by thicknesses that did not exceed 300μm and porosities of approx. 5%. The chemical and phase composition analysis of the DCL layers revealed an external Nd ₂Zr ₂O ₇ ceramic layer approx. 80μm thick, a transitional zone approx. 120μm thick and an internal 8YSZ layer 100μm thick. For the case of the monolayer coating, the Nd ₂Zr ₂O ₇ pyrochlore phase was the only one-phase component. The surface topography of both TBC systems was typical for plasma sprayed coatings, and compressive stress state had a value of approx. 5-10MPa. Measurements of the thermal parameters, i.e., thermal diffusivity, point to considerably better insulative properties for both new types of layers when compared to the standard 8YSZ layers.