Corrosion, Wear, and Galling Tests of IC218, a Chromium-Bearing Alloy of Ni 3 Al
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CORROSION,
WEAR, AND GALLING TESTS OF IC218, A CHROMIUM-BEARING ALLOY OF NI 3AL
BRADFORD A. DULMAINE Carpenter Technology Corporation, Box 14662, Reading, Pennsylvania 19612-4662 ABSTRACT IC218 contains about 8.4% aluminum and about 7.8% chromium by weight and forms a tenacious alumina scale. In this work the ability of the scale to protect against aqueous corrosion and abrasive and adhesive wear was evaluated. Wrought IC218 was heat treated at 1150*C, yielding a microstructure of ordered FCC islands in a disordered FCC matrix. This material was more resistant to corrosion than common stainless steels in 96% or 98% sulfuric acid and in 5% hydrochloric acid. It was approximately equivalent to stainless steels in 10% sulfuric acid, 50% acetic acid, 50% sodium hydroxide, 5% sodium chloride, and in a sodium chloride + ferric sulfate + hydrochloric acid mixture used to test for pitting resistance. The IC218 performed poorly in 45% sulfuric acid, 20% or 65% nitric acid, 20% phosphoric acid, and in electrolytic 10% oxalic acid. It did not exhibit sensitivity to intergranular corrosion. It resisted stress corrosion cracking at a stress level equal to its yield strength, 645 MPa, in 45% magnesium chloride and in NACE TMO177, a test that simulates an oil well environment. IC218 wore more quickly than austenitic stainless steels do in a dry-sand-rubber-wheel test, but resisted galling as well as or better than most of them do. INTRODUCTION The intermetallic compound Ni3 Al has been receiving a great deal of attention recently, primarily because its properties are attractive for high temperature service. Its high aluminum content allows the formation of a very protective scale. In addition to protecting against oxidation at high temperatures, such a scale has the potential to prevent corrosion in aqueous media and to inhibit galling or seizing between mating parts. Most existing alloys that resist corrosion or galling form chromium oxide scales, and the aluminum oxide scale on Ni3Al could have different properties that would make it superior in some applications. Prior to the commencement of the work reported here, the only information available on the aqueous corrosion of nickel aluminides came from limited studies done at Oak Ridge National Laboratory (ORNL)[l] and Rennselaer Polytechnic Institute[2,3]. Recently the results of two larger projects, at the University of Tennessee[4] and at the National Bureau of Standards (now the National Institute of Standards and Technology)[5], have been reported. Also recently, measurements of wear rates in sliding friction and in cavitation have been made at ORNL[6] and the Tennessee Valley Authority[7], respectively. The alloy used in this work, IC218, was developed at ORNL. It contains a substantial amount of chromium (see Table I), which was originally added to increase resistance to embrittlement by oxygen at temperatures between 600*C and 850*C. The chromium may also contribute to aqueous corrosion resistance through the formation of a transient barrier film, although little, if a
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