Corrosion resistance of thermally sprayed high-boron iron-based amorphous-metal coatings: Fe 49.7 Cr 17.7 Mn 1.9 Mo 7.4
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N. Yang Sandia National Laboratory, Livermore, California 94551
J.H. Payer Case Western Reserve University, Cleveland, Ohio 44106-7204
J.H. Perepezko and K. Hildal University of Wisconsin, Madison, Wisconsin 53706
E.J. Lavernia and L. Ajdelsztajn University of California, Davis, California 95616
D.J. Branagan and E.J. Buffa The NanoSteel Company, Idaho Falls, Idaho 83402
L.F. Aprigliano Strategic Analysis, Arlington, Virginia 21811 (Received 22 January 2007; accepted 2 May 2007)
An iron-based amorphous metal, Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 (SAM2X5), with very good corrosion resistance has been developed. This material was prepared as a melt-spun ribbon, as well as gas atomized powder and a thermal-spray coating. During electrochemical testing in several environments, including seawater at 90 °C, the passive film stability was found to be comparable to that of high-performance nickel-based alloys and superior to that of stainless steels, based on electrochemical measurements of the passive film breakdown potential and general corrosion rates. This material also performed very well in standard salt fog tests. Chromium (Cr), molybdenum (Mo), and tungsten (W) provided corrosion resistance, and boron (B) enabled glass formation. The high boron content of this particular amorphous metal made it an effective neutron absorber and suitable for criticality control applications. This material and its parent alloy maintained corrosion resistance up to the glass transition temperature and remained in the amorphous state during exposure to relatively high neutron doses.
I. INTRODUCTION
The outstanding corrosion resistance that may be possible with amorphous metals was recognized several years ago.1–3 Compositions of several iron-based amorphous metals were published, including several with very good corrosion resistance. Examples include thermally sprayed coatings of Fe–10Cr–10–Mo–(C,B), bulk Fe– Cr–Mo–C–B, and Fe–Cr–Mo–C–B–P.4–6 The corrosion resistance of an iron-based amorphous alloy with yttrium, Fe48Mo14Cr15Y2C15B6, was also established.7–11 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0291 J. Mater. Res., Vol. 22, No. 8, Aug 2007
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Yttrium was added to this alloy to lower the critical cooling rate. In addition to iron-based materials, nickelbased amorphous metals have been developed that exhibit exceptional corrosion performance in acids. Very good nickel-based crystalline coatings were deposited with thermal spray but appeared to have less corrosion resistance than amorphous-metal coatings.12 Several iron-based amorphous alloys have been developed with very good corrosion resistance. Most of these alloys are based upon a common parent alloy and can be applied as thermal spray coatings.13,14 One of the most promising formulations is Fe49.7Cr17.7Mn1.9Mo7.4W1.6 B15.2C3.8Si2.4 (SAM2X5), which includes chromium (Cr), molybdenum (Mo), and tungsten (W) for enhanced corrosion resistance, and boron (B) to enabl
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