Hot Corrosion and Oxidation Behavior of Pt-Aluminide and Pt-Rh-Aluminide Coatings Applied on Nickle-Base and Cobalt-Base Substrates

This case study compared the microstructure, hot corrosion, and isothermal oxidation behavior of two modified diffusion aluminide coatings on two substrates. The first coating was a platinum aluminide (Pt-aluminide) coating on a nickel-base Inconel 738LC alloy, while the second was a platinum-rhodium aluminide (Pt-Rh-aluminide) coating on a cobalt-base FSX-414 alloy. The coatings were created through electroplating with Pt and Rh, followed by diffusion heat treatment and above-pack aluminizing. Using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), the substrate microstructure, coating morphology, and chemical composition were studied. The analysis revealed that both coatings consisted of a dual-phase, with PtAl2 + beta-(Ni-Pt)Al phases on the nickel-base substrate and PtAl2 + CoAl phases on the cobalt-base substrate. Hot corrosion testing was conducted at 900 degrees C for 100 h in the presence of 75%Na2SO4 + 25%NaCl salts, while oxidation behavior was studied at 1050 degrees C for 200 h for both coatings. The study results showed that the Pt-Rh-aluminide coating on the cobalt-based substrate had better resistance to hot corrosion, while the Pt-aluminide coating on the nickel-based substrate had better oxidation resistance. The study also discussed the role of Pt, Rh, and substrate composition on the coatings' hot corrosion and oxidation behavior. The morphology of oxide scales and corroded and oxidized coatings cross-sections were studied using SEM, EDS, and XRD analysis.