Nanostructured plasma sprayed thermal barrier and wear resistant coatings

Ceramic oxides are widely used as thin and thick coatings in most high-end applications in order to protect metallic components, such as turbine blades and high-performance bearings, operating in severe tribological and thermal conditions. These demanding technological applications are characterized by constantly increasing requirements: nanostructuration is one of the most promising approaches for enhancing the mechanical properties of ceramic coatings. The present work investigates the influence of nanostructuring on properties and performance of wear resistant Al2O3–TiO2 coatings and ZrO2–Y2O3 thermal barrier coatings deposited by plasma spray from nanostructured precursors. According to the principles of design of experiment (DoE), an experimental campaign was designed and carried out in order to identify the optimal set of deposition parameters maximizing wear (Al2O3–TiO2) and thermal shock (ZrO2–Y2O3) resistance of the coatings and interfacial adhesion to the substrate. To evaluate the morphology and the residual relative amount of nanostructure within the sprayed coatings, samples were characterized by optical and electronic microscopy; hardness, porosity and thermal diffusivity were also measured, and phase composition was analyzed by Xray diffraction. Wear resistance of Al2O3 – TiO2 coatings was assessed by tribological tests (block on ring configuration in the absence of lubrication) measuring friction coefficient, weight loss and worn out volume and estimating the Archard’s coefficient. Adhesion between the ZrO2 – Y2O3 coatings and the substrate (Inconel® alloy) was evaluated by tensile tests, according to ASTM C633 procedure. Finally, thermal shock resistance of TBCs was estimated performing cyclic water quenching tests.