Abstract
Air plasma-sprayed (APS) ceramic coatings are being explored as chemical, environmental, electrical, and thermal barrier systems for components employed in sodium-cooled fast-spectrum nuclear reactors. The design and constructional requirements of several components demand the APS coatings be in continuous contact with the aggressive and corrosive liquid-sodium (coolant) environments. Conventional APS coatings were found to be susceptible to liquid-metal corrosion in high-temperature liquid-sodium environments. Towards this, three of the emerging thermal barrier ceramics such as Titania-Stabilized Zirconia (TiSZ), Lanthanum Zirconate (LZ), and Yttrium Aluminum Monoclinic (YAM), are investigated in the current work by exposing APS deposited ceramic coatings in liquid-sodium at 400 °C for 500 h and 1000 h. TiSZ coatings exhibited severe erosion of the topcoat and a complete degradation at the end of 1000 h due to grain boundary dissolution and the weakening of intersplat boundaries. LZ coatings showed partial failure due to the combined effects of erosion of the topcoat and spallation due to the formation of delamination cracks in the bulk of the topcoat. Except for some mild surface attacks, YAM coatings revealed erosion resistance, phase stability, chemical inertness, and structural integrity in liquid-sodium.
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