A STUDY ON COMPOSITE COATINGS OF YTTRIUM ION-PLATING AND PACK ALUMINIZING FOR HIGH-TEMPERATURE APPLICATIONS

Yttrium (Y) was incorporated by an ion-plating method either before or after pack aluminizing to maximize the corrosion resistance of IN 713 C. Various combinations of pack aluminizing and yttrium -ion plating w ere examined with respect to coating sequence, aluminum activity, and corrosive environment. Of all the various coating combinations examine d, the best corrosion resistance was obtained from H/A + Y (high-activ ity aluminizing + Y-ion plating) type composite coatings. Uniformity o f the Y deposition was greatly dependent upon the surface condition of the aluminide-coating layer. The high-activity aluminide coating gave better uniformity of Y deposition than did the low-activity-aluminide coating. Improvement of corrosion resistance by the Y-modified-alumin ide composite coatings of H/A + Y type occur because the presence of Y between the Al2O3 columns improves Al2O3 scale adherence and substant ially prevents depletion of Al in the aluminide-coating layer.