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.