High temperature corrosion study on yttrium modified aluminide coatings on IN 713C

Abstract
The addition of active elements in high temperature materials may improve corrosion resistance extensively. In general, the active elements are incorporated in the form of an alloying element either in the bulk or in overlay coatings, as an oxide dispersion, or by ion implantation. In this experiment, yttrium was incorporated by an ion plating method either before or after pack aluminizing to maximise the corrosion resistance of IN 713C. Various combinations of pack aluminizing and yttrium ion plating were examined with respect to coating sequence, aluminium activity, and corrosion environment. From all the various coating combinations examined, the best corrosion resistance was obtained from the H/A + Y (high activity aluminizing + Y-ion plating) type multilayer coatings. Uniformity of 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 aluminide multilayer coatings of H/A + Y type may occur because Y present between the A1₂O₃ columns improves the A1₂O₃ scale adherence and substantially prohibits depletion of Al in the aluminide coating layer.