High-Temperature Thermal Protective Performance of High-Entropy Rare-Earth Tantalate (Nd0.2Dy0.2Ho0.2Y0.2Er0.2)TaO4 Coating Deposited By Atmospheric Plasma Spraying

High-entropy rare-earth tantalates have potential for use in thermal barrier coatings, but current research has focused mostly on powder or bulk materials instead of coatings. In this work, atmospheric plasma spraying technology was employed to prepare novel high-entropy rare-earth tantalate (Nd_0.2Dy_0.2Ho_0.2Y_0.2Er_0.2)TaO₄ (HE-RETaO₄) coatings on the surface of nickel-based alloys. The as-sprayed HE-RETaO₄ powders undergo a ferroelastic phase transition from the monoclinic (m) phase to the metastable tetragonal (t′) phase during the spraying process. Owing to the influence the cationic radii of multispecies HE-RETaO₄, its phase transition temperature is lower than that of YTaO₄, leading to the formation of a ferroelastic domain toughened structure at lower temperatures. Under the plasma flame assessment at 1200 and 1300 °C, the insulation temperatures of the HE-RETaO₄ coatings are 220 and 200 °C, respectively. The sluggish diffusion of HE-RETaO₄ hinders diffusion of elements, ultimately engendering a profusion of equiaxed grains with comparable aspect ratios and a substantial divergence in energy between intragranular regions and boundaries. In addition, the microcracks generated within the HE-RETaO₄ coatings rapidly expand along the high-energy grain boundaries of the equiaxed grains, eventually leading to mechanical delamination and coating failure. This work provides a powerful theoretical basis for the application of HE-RETaO₄ as a high-temperature protective material.