The effect of impurities on the alumina scale growth: An alternative view
- Univ. of California, Santa Barbara, CA (United States). Materials Dept.
- Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany)
High temperature oxidation of Fe-Cr-Al and Fe-Cr-Al-Y alloys is usually accompanied by the formation of a protective scale of {alpha}-Al{sub 2}O{sub 3}. Good oxidation resistance of an alloy requires the slow growth rate of the oxide and the ability of the scale to withstand temperature changes without spalling or cracking. Small alloying additions of reactive elements such as yttrium are well known to improve oxide adherence and change the morphology of the oxide layer. While the scale formed on yttrium-free alloy is typically convoluted or wrinkled and poorly adherent, the yttrium-containing alloy produces a flat and adherent oxide. Improvements in the scale adhesion are now widely considered to be a result of sulfur gettering by yttrium additions. The major point of this sulfur effect is in the assumption that without reactive elements sulfur segregation from the bulk alloy to the scale-alloy interface causes a weakening of the oxide-metal bond. In discussing the reactive element-sulfur interaction, surprisingly not much attention has been given to the fact that yttrium additions not only improve adherence, but they also substantially change oxide morphology. The widely reported effect of yttrium in eliminating oxide wrinkling is though to be of secondary importance. On the other hand, it is known that the flat alumina layer is usually adherent, while the wrinkled scale typically fails in cyclic oxidation conditions. From various results it can be concluded that sulfur in the alloy is not responsible for the structural differences between adherent and non-adherent oxide. If so, there might be other species causing the scale wrinkling and/or affecting adherence. In performing the work described here the authors were searching for an alternative explanation of the reactive element effect and the possible role of impurities other than sulfur.
- OSTI ID:
- 585985
- Journal Information:
- Scripta Materialia, Vol. 38, Issue 1; Other Information: PBD: 18 Dec 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
The influence of sulfur on adherence of Al sub 2 O sub 3 grown on Fe-Cr-Al alloys
Wrinkling of {alpha}-alumina films grown by thermal oxidation. 1: Quantitative studies on single crystals of Fe-Cr-Al alloy