Hot corrosion and thermal shock behaviour of plasma sprayed GNP reinforced Samarium niobate coating for high temperature applications

Abstract

Advancements in high-temperature ceramics have positioned rare earth niobates (RENbO₄) as strong contenders for next-generation thermal barrier coating (TBC) applications. Compared to yttria-stabilized zirconia (YSZ), Samarium niobate (SmNbO₄; SN) with a monoclinic structure has garnered significant interest as a TBC material owing to their remarkable ultra-high temperature phase stability (>1200 °C), coupled with intrinsically low thermal conductivity, higher fracture toughness and exceptional resistance to high-temperature corrosion phenomena. This study examines the hot-corrosion and thermal shock behavior of three distinct TBC systems: conventional YSZ, SN, and graphene nanoplatelet (GNP) reinforced SN (SN-1GNP) coatings under a Na₂SO₄ –V₂O₅ molten salt environment at 950°C for different exposure time (3 and 6 h) and thermal cycles (0, 40, 80, 120, and 160 cycles). These ceramic topcoats were applied to Ni-Al bond-coated In718 substrates using atmospheric plasma spray (APS) technique. Hot corroded and thermally cycled coatings were comprehensively characterized using Scanning Electron Microscope (SEM), EDS, XRD, and image analysis. The GNP-reinforced SN composite coating exhibited superior hot-corrosion and thermal cyclic performance compared to YSZ and SN coatings. SEM micrographs revealed unique characteristics with strong adhesion between top surface and the intermediate layers with GNP flakes embedded on the SN matrix effectively resisting the coating from salt penetration. The findings emphasize the high-temperature performance of SN-1GNP coatings, making them ideal for protecting and insulating alloy components in gas turbines, aircraft engines and various other IC engine components operating in hot corrosive environments.