Materials Performance

MAR 2017

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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42 MARCH 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 3 COATINGS & LININGS Other alloys displayed intermediate performance, with higher levels of molyb- denum and/or chromium generally leading to increased resistance, but this was quali- tative only. Conclusions In 90% CO-2.5% H 2 -7.5% Ar at 1,100 °C with TiO 2 powder present (a suitable simu- lant for the proprietar y industrial cell), attack was attributed to a complex mixture of oxidation and carburization resulting in the formation of chromium oxides, alumi- num oxides, and multiple carbides. Corro- sion attack was either general/uniform (with void formation) or intergranular with associated precipitation along grain bound- aries depending on alloy composition. No quantitative correlation between alloy composition and resistance to attack was observed, but qualitative trends were present. UNS N06230 and N06625 showed reasonable resistance to this environment and UNS N06600 showed good but slightly lesser performance. UNS N07214 showed the poorest performance. Beta-aluminide coatings were partially protective, but any local failure led to extremely heavy local- ized attack. Material lifetime could poten- tially be improved by preventing the metal oxide powder from directly contacting the substrate by means of a coating or tiling. Acknowledgments The author gratefully acknowledges the Core Research Program of TWI for support- ing this and subsequent research. References 1 P.A. Schweitzer, Corrosion Resistance Tables: Metals, Plastics, Nonmetallics and Rubbers, 2nd ed. (New York, NY: Marcel Dekker, Inc., 1986), p. 1,166. 2 L. Coudurier, D.W. Hopkins, I. Wilkomirsky, "Fundamentals of Metallurgical Processes," International Series on Materials Science and Technolog y, 2nd ed, Vol. 27 (Oxford, U.K.: Pergamon Press, 1985), p. 74. Editor's note: This article is based on information previously published by TWI (Cambridgeshire, United Kingdom). Copyright © TWI, Ltd., 2017. Reprinted with permission. ROGER BARNETT, CEng, CChem, and CSci, is a senior project leader with TWI, Granta Park, Great Abington, Cambridgeshire, CB21 6AL, U.K., email: roger.barnett@twi. co.uk. An experienced researcher, he has worked on projects at TWI for eight years, including molten salts, high-temperature degradation, coating/material selection, failure analyses, and microstructural characterization. He holds M.A. and M.Sci. degrees in natural sciences and a Ph.D. in materials science and metallurgy from Cambridge University.

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