Hot corrosion behaviour of Cr/CoAlHf/YSZ coatings under different temperatures

Abstract

This work examines the effect of substrate temperature on the surface condition and hot-corrosion performance of Superni-718 alloy with Cr/CoAlHf metallic interlayers and 8 wt.% Y₂O₃-ZrO₂ (YSZ) as the ceramic topcoat, using DC and RF magnetron sputtering. This study synthesised the multilayer coating system at substrate temperatures of 200, 250, and 300°C to assess the impact of deposition conditions on coating cohesion, interface stability, and service performance. The coated specimens were hot-corroded in molten salt of Na₂SO₄ (40 wt%) + V₂O₅ (60 wt%) at 900°C for 100 corrosion cycles. Field-emission scanning electron microscopy to characterise the surface and cross-section with energy-dispersive X-ray spectroscopy to determine microstructural changes, oxide-scale integrity, and degradation mechanisms. The coating obtained at 300°C showed enhanced corrosion resistance, attributed to the formation of a compact, well-adhered, and continuous oxide scale that effectively prevented salt-induced degradation. In contrast, the coatings prepared at 250°C provided some protection, whereas those prepared at 200°C showed severe interfacial delamination and oxide spallation under cyclic thermal loading. The results show that the substrate temperature is a critical process parameter for controlling the densification of the coating, the stability of the oxide scale, and long-term corrosion performance. These results provide practical recommendations for the design of systems and the optimisation of the sputter-deposition process for multilayer surface engineering to provide high-temperature protection of nickel-based superalloy components.