A variety of coatings have been designed to protect turbine components from corrosion due to the combined effects of environmental contaminants, fuel impurities and elevated temperatures. The most effective of these systems rely upon formation of a protective alumina scale to act as a barrier between the gas path environment and the component.
Protection offered by these alumina-forming high temperature coatings is increased by a number of additive elements, including platinum and chromium, but silicon (Si) is found to be especially beneficial in coatings exposed to high concentrations of sulfur in marine environments. Silicon-modified slurry aluminides are shown to resist to both high temperature and low temperature hot corrosion on both nickel and cobalt alloys in marine service.
Laboratory tests show this corrosion resistance can be further enhanced by redistributing critical elements (particularly silicon) within the microstructure of the silicon-modified aluminide. The benefits of these changes are demonstrated in field engine trials.
