Nickel Base Metallic Glass Powders for Application as Plasma Sprayed Coatings
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NICKEL BASE METALLIC GLASS POWDERS FOR APPLICATION AS PLASMA SPRAYED COATINGS V. PANCHANATHAN, Marko Materials, Inc., N. Billerica, MA 01862 and C.L. TSAI and S. WHANG, Institute of Chemical Analysis, Materials Science Division, Northeastern University, Boston, MA 02115, U.S.A. ABSTRACT New nickel rich alloys containing molybdenum and chromium prepared as metallic powders are reported. Using standard plasma spray techniques, these powders (-170 mesh) can be deposited onto metallic substrates as dense, well bonded coatings having predominantly glassy structure. Such coatings exhibit high structural strength, hardness and good corrosion resistance in various corrosive media. INTRODUCTION Metallic glass alloys (also referred to as amorphous metallic alloys having non-crystalline structures) are well known for their outstanding mechanical properties (i.e. high strength and hardness) and excellent corrosion resistance (1,2). Such properties of metallic glasses can be advantageously used if they can be made to form dense, well bonded, hard, wear and/or corrosion resistant coatings on an inexpensive base material having less desirable properties. Marko Materials, Inc. has synthesized a new generation of nickel-base alloys which can be prepared as metallic glass powders by a novel rapid solidification technology. These powders can, then, be deposited as coatings on metallic base materials by standard plasma spray processing technique. Some unique physical characteristics of these powders give rise to their excellent sprayability. The spray parameters can be so chosen that the powders are melted in the plasma flame followed by deposition onto the base metal as a dense homogeneous coating. Note that the metallic glass structure of the powders is destroyed due to melting of the particles in the plasma flame; however, upon impacting the base metal the molten particles once again undergo rapid solidification - a condition which leads to reconstitution of the metallic glass structure in the as-sprayed coating. The alloys have been so formulated with a proper balance in composition that once formed as plasma sprayed coatings, they exhibit high structural strength, high hardness and excellent corrosion resistance in various corrosive and oxidizing media. ALLOY COMPOSITIONS The alloy compositions were formulated which are designated as MARKOMETR 1064 and MARKOMET 1067 (see Table 1 below). TABLE 1 Alloy Designation MARKOMET 1064* MARKOMET 1067*
Ni 51.5 50
Composition, wt% Mo Cr 39 8 26 18
Fe --
4.4
B 1.5 1.6
When subjected to solidification from the melt at a rapid rate of n106 C/second, the above alloys form a single metallic glass phase. Using a rapid *MARKOMET is
a registered trademark of Marko Materials,
Inc.
138 solidification powder processing technique, MARKOMET alloys were produced as metallic glass powders with particle sizes typically under 170 mesh. These powders possess excellent sprayability and form dense, well bonded coatings on metallic substrates by the method of plasma spray processing. The plasma sp
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