Evaluation of the hot corrosion protection of coatings for turbine hot section components

Abstract

A program was conducted to evaluate the relative corrosion resistance of commercially available coatings in laboratory furnace testing. Three turbine section superalloys were selected, MAR-421, IN-738LC and FS-414, and coating types ranged from simple diffusion aluminides to modified aluminides and a CoCrAlY overlay. Results indicate that the coatings were more protective to IN-738LC than to MAR-M421, with a silicon aluminide and platinum-chromium aluminide affording the best protection overall. The simple aluminide was surprisingly quite resistant in the temperature regimes studied, relative to the more complex aluminides, particularly with IN-738LC. The recommendations for corrosion-resistant coatings (for low temperature and high temperature hot corrosion environments) are as follows: silicon aluminide and platinum-chromium aluminide for MAR-M421; simple aluminide, platinum-chromium aluminide and silicon aluminide for IN-738LC; and platinum-chromium aluminide and silicon aluminide for FS-414.