Study of the effect of reactive-element addition by implanting metal ions in a preformed oxide layer

The influence of ion-implanted Y, Hf, Zr and Cr on the oxidation behavior of a Ni-25 wt.% Cr alloy at 1000degC has been investigated. The implantation dose was 5x1016 ions/cm2. Two methods of implantation have been used. One was to implant ions directly into a clean alloy surface; the other was to implant into an approximately 0.6 μm thick Cr2O3 layer formed at 1000degC on the alloy. In neither case did the Cr implantation show any beneficial effects. Implantations of Y, Hf and Zr produced all the reactive element effects, i.e. reduction in oxidation rate, elimination of base-metal oxide formation and improvement in scale adhesion, only if the ions were initially implanted in the alloy. When the ions were implanted into a preformed oxide, the subsequent oxidation process was altered to the same degree as before, but the scale adhesion was not affected. Implications of these results to the mechanism of the reactive-element effect are discussed. (orig.)