Preparation of plasma sprayed nanostructured GdPO4 thermal barrier coating and its hot corrosion behavior in molten salts

Nanostructured GdPO4 coatings, designed as the outer layer of double-ceramic-layer thermal barrier coatings (DCL-TBCs), were produced by air plasma spraying (APS). The coatings have close chemical composition to that of the agglomerated particles used for thermal spray. Nanozones with porous structure are embedded in the coating microstructure, having a percentage of ~30%. Hot corrosion tests of the coatings were carried out in V2O5 and Na2SO4+V2O5 salts at 900 °C for 4 h. Results indicate that dense reaction layers, consisting of GdVO4 and Gd4(P2O7)3, form on the coating surfaces, which could suppress further penetration of the molten salts. In the V2O5 molten salt, the reaction layer is thicker and less molten salt trace could be found beneath the layer.