Direct observation of the interaction of yttrium and sulfur in oxidized NiAl

摘要

The adhesion of protective oxide scales can be dramatically improved if alloys are doped with reactive elements (e.g. Y, Zr, Ce, Hf). This beneficial effect of reactive elements has been known for over 50 years. Many mechanisms have been proposed, but the effect is still not fully understood in detail. Recently, Strawbridge and Hou published a review of the reactive element effect [1]. Two possible models which emerge for the effect are a change of growth mechanism [2-4] and the so-called sulfur effect [5-l 5]. Concerning the first model it has been proposed that reactive elements alter the growth mechanism of the oxide scale resulting in reduced stress. Such a change in transport mechanism during alumina growth has been shown by 018 /SIMS experiments [16, 17].