The use of ion implantation techniques to study protective oxide scale adherence effects

Abstract

Data supporting a new mechanism to account for the beneficial effects of active elements such as yttrium on the adherence of protective alumina scales is presented. Previous work involving cast alloys had shown that, in the absence of yttrium, indigenous sulfur at tramp levels segregated to and weakened the bond between the scale and the underlying metal. Yttrium interacted with sulfur to form refractory compounds, thereby reducing the amount of sulfur available for segregation. In this study, the ion implantation of 27Al+ and 32S+ was used to modify alloy chemistries of Ni–Cr–Al–Y alloys. Results of oxidation tests on implanted alloys confirmed the role of yttrium in inhibiting interface segregation of sulfur. Al+ ion implantation did not modify the adherence of alumina scales on Ni–Cr–Al–Y alloys, thereby ruling out radiation damage effects. However, S+ implantation caused scale exfoliation.