Influence of NiCoCrAlY and diffusion aluminide coating on oxidation and hot corrosion of a Ni-based superalloy

The most common metallic coatings used in today's gas turbine engines are MCrAIX (where M is Ni and/or Co and X is one or more reactive elements such as Y, Hf, etc.) type overlay coatings. However, overlay coating techniques (plasma and flame spraying or physical vapor deposition) are line-of-site processes, and so, it is possible not to deposit coating on some surface of the complex turbine components. The diffusion aluminide coatings can solve this problem. A NiCoCrAlY and diffusion aluminide coating were prepared on K38G cast alloy by multi-arc ion plating and low pressure chemical vapor deposition (LP-CVD) techniques, respectively. The isothermal oxidation behavior of K38G and the coatings was studied in air at 900 and 1000 degrees C. Their hot corrosion behaviors in the presence of 75 wt.% Na2SO4+K2SO4 and 75wt.%Na2SO4+NaCl film at 900 degrees C were studied. The results showed that the two kinds coatings exhibited low oxidation rate at 900 and 1000 degrees C and the presence of salt accelerated the oxidation rate. The NiCoCrAlY coating showed the better hot corrosion resistance than the aluminide coating.