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0985-NN03-14

Salt Fog Testing Iron-Based Amorphous Alloys Raul B. Rebak1, Louis F. Aprigliano2, S. Daniel Day3, and Joseph C. Farmer3 1 Chemistry and Materials Science, Lawrence Livermore National Laboratory, 7000 East Ave, L- 631, Livermore, CA, 94550 2 Consultant, Berlin, MD, 21811 3 LLNL, Livermore, CA, 94550 ABSTRACT Iron-based amorphous alloys are hard and highly corrosion resistant, which make them desirable for salt water and other applications. These alloys can be produced as powder and can be deposited as coatings on any surface that needs to be protected from the environment. It was of interest to examine the behavior of these amorphous alloys in the standard salt-fog testing ASTM B 117. Three different amorphous coating compositions were deposited on 316L SS coupons and exposed for many cycles of the salt fog test. Other common engineering alloys such as 1018 carbon steel, 316L SS and Hastelloy C-22 were also tested together with the amorphous coatings. Results show that amorphous coatings are resistant to rusting in salt fog. Partial devitrification may be responsible for isolated rust spots in one of the coatings.

INTRODUCTION Metallic amorphous alloys or metallic glasses have been studied extensively for the last three decades due to their unique characteristics, including superior mechanical properties and corrosion resistance [1]. To produce an amorphous alloy from a liquid state, cooling rates in the order of 106 to 1 degrees K per second are required, depending on the glass forming ability of the melt [1]. The amorphous alloys are chemically and structurally homogeneous since they do not contain grain boundaries, dislocations and secondary phases, which are common in the crystalline materials [1]. The corrosion resistance of amorphous alloys depends on the alloy composition [2-4]. Moreover, amorphous alloys are more corrosion resistant than their polycrystalline cousins of equivalent composition. Amorphous alloys are also hard and can be used in areas where both resistance to wear and corrosion are simultaneously needed. When amorphous alloys partially or fully re-crystallize, they lose their characteristic corrosion resistance. This process is called devitrification [5]. The fact that amorphous materials are highly corrosion resistant is generally attributed to the absence of crystalline defects in the alloy; however the actual mechanism of this resistance is still not fully understood [1]. Iron (Fe) based alloys such as austenitic stainless steels containing approximately 18% chromium (Cr) are widely used in the industry due to their corrosion resistance characteristics. However, polycrystalline Types 304 and 316 stainless steels are not as corrosion resistant as other polycrystalline alloys such as the nickel (Ni)-based Hastelloy C-22 alloy (Table I) [6]. On the other hand, it has been recently shown that Fe-based amorphous alloys have higher localized corrosion resistance than even alloy C-22 [7]. Recently Fe-based amorphous alloys have been produced in bulk compositions so they can be applie