Formation of Protective Aluminum-Oxide Layer on the Surface of Fe-Cr-Al Sintered-Metal-Fibers via Multi-Stage Thermal Oxidation

Authors: Loai Ben Naji, Osama M. Ibrahim, Khaled J. Al-Fadhalah

Abstract:

The objective of this paper is to investigate the formation and adhesion of a protective aluminum-oxide (Al₂O₃, alumina) layer on the surface of Iron-Chromium-Aluminum Alloy (Fe-Cr-Al) sintered-metal-fibers. The oxide-scale layer was developed via multi-stage thermal oxidation at 930 ^oC for 1 hour, followed by 1 hour at 960 ^oC, and finally at 990 ^oC for 2 hours. Scanning Electron Microscope (SEM) images show that the multi-stage thermal oxidation resulted in the formation of predominantly Al₂O₃ platelets-like and whiskers. SEM images also reveal non-uniform oxide-scale growth on the surface of the fibers. Furthermore, peeling/spalling of the alumina protective layer occurred after minimum handling, which indicates weak adhesion forces between the protective layer and the base metal alloy.  Energy Dispersive Spectroscopy (EDS) analysis of the heat-treated Fe-Cr-Al sintered-metal-fibers confirmed the high aluminum content on the surface of the protective layer, and the low aluminum content on the exposed base metal alloy surface. In conclusion, the failure of the oxide-scale protective layer exposes the base metal alloy to further oxidation, and the fragile non-uniform oxide-scale is not suitable as a support for catalysts.

Keywords: High-temperature oxidation, alumina protective layer, iron-chromium-aluminum alloy, sintered-metal-fibers.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.2021607

References:

[1] D. Whittle, and J. Stringer, “Dispersions resistance by additions of reactive elements or oxide improvements in high-temperature oxidation,” Philosophical Transactions of the Royal Society A, 295, 1980, doi: 10.1098/rsta.1980.0124.
[2] R. Prescott, and M. Graham, “The formation of aluminum oxide scales on high-temperature alloys,” Oxidation of Metals, Vol. 38, Nos. 3/4, 1992.
[3] J. Herbelin, and M. Mantel, “Effects of Al Addition and Minor Elements on Oxidation Behaviour of FeCr Alloys,” Journal de Physique IV Colloque, 05 (C7), pp.C7-365-C7-374, 1995.
[4] A. Strawbridge and P. Hou, “The role of reactive elements in oxide scale adhesion,” Materials at High Temperatures, 12:2-3, 177-181, 1994, doi: 10.1080/09603409.1994.11689484.
[5] K. Ishii, M. Kohno, S. Ishikawa, and S. Satoh, “Effect of rare-earth elements on high-oxidation resistance of Fe-20Cr-5Al alloy foils,” Materials Transactions, JIM, Vol. 38, No. 9, pp 787-792, 1997.
[6] C. Badini, and F. Laurella, “Oxidation of FeCrAl alloy: influence of temperature and atmosphere on scale growth rate and mechanism,” Surface and Coatings Technology, 135 291–298, 2001.
[7] H. Kadiri, H. Molins, Y. Bienvenu, and M. Horstemeyer, “Abnormal high growth rates of metastable aluminas on FeCrAl alloys, “ Oxidation of Metals, 64: 63-97, 2005 doi: 10.1007/s11085-005-5715-0.
[8] J. Samad, J. Nychka, and N. Semagina, “Structured catalysts via multiple stage thermal oxidation synthesis of FeCrAlly alloy sintered microfibers,” Chemical Engineering Journal, 168 470–476, 2011.
[9] R. Zhou, and R. Snyder, “Structures and transformation mechanisms of the Eta. Gamma and Theta transition aluminas,” Acta Crystallographica Section B, 47 617–630, 1991.
[10] W. Fei, S. Kuiry, and S. Seal, “Inhibition of metastable alumina formation on Fe–Cr–Al–Y alloy fibers at high temperature using titania coating,” Oxidation of Metals, 62 29–44, 2004.
[11] B. Pint, J. Martin, and L. Hobbs,” The oxidation mechanism of θ-Al2O3 scales,” Solid State Ionics, 78, 99-107, 1995.
[12] G. Vaneman, and D. Sigler, "Accelerated whisker growth on iron–chromium–aluminum alloy foil,” Patent US 4915751, 1990.
[13] R. Molins, A. Germidis, and E. Andrieu, in Microscopy of Oxidation 3: Proceedings of the Third International Conference on the Microscopy of Oxidation. S. B. Newcomb and J. A. Little, eds., p. 3, Institute of Materials, London, 1997.
[14] C. Badini, and F. Laurella, “Oxidation of FeCrAl alloy: influence of temperature and atmosphere on scale growth rate and mechanism,” Surface and Coatings Technology, 135, 291-298, 2001.