Abstract

The metallic coatings used to protect the hot-section turbine blades of marine gas turbines are often a mixture of cobalt, chromium, aluminum, and yttrium (CoCrAlY). Using the surface sensitive technique of x-ray photoelectron spectroscopy, the protective oxide scales on CoCrAlY coatings containing nominal levels of 20, 29, and 35 wt% chromium were found to be essentially the same and were predominantly alumina and a yttrium rich phase that is tentatively identified as yttrium aluminum garnet. As increasing levels of chromium in this coating system are known to improve the coating's hot corrosion resistance, the similarity of the initial scales on all these coatings leads to the conclusion that chromium provides its hot corrosion benefit by slowing the propagation phase of the bulk coating attack.

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