Rare Earth/Metal Composite Formation by Cold Spray
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Peter C. King, Saden H. Zahiri, and Mahnaz Z. Jahedi (Submitted April 20, 2007; in revised form July 31, 2007) Nd2Fe14B permanent magnet/aluminum composite coatings were produced by cold spray deposition. Isotropic Nd2Fe14B powder was blended with aluminum powder to make mixtures of 20-80 vol.% Nd2Fe14B, and these mixtures were sprayed at temperatures of 200-480 °C. The hard Nd2Fe14B particles tended to fracture and fragment upon impact, while aluminum underwent severe plastic deformation, eliminating pores, and trapping Nd2Fe14B within the coating. It was found that higher spray temperatures and finer Nd2Fe14B particle sizes improved the retention rate of Nd2Fe14B within the composite structure. This was explained from a contact mechanics viewpoint by calculating the effect of process parameters on the rebound momentum of Nd2Fe14B particles. The magnetic properties of Nd2Fe14B remained unaffected by the cold spray process.
Keywords
cold gas dynamic spray, composite, magnetic properties, rare earth, rebound
1. Introduction Cold gas dynamic spray, or simply cold spray, has emerged as a useful technology for the production of high-density metallic coatings without the problems associated with thermal spray techniques such as oxidation and thermal stresses. Cold spray of magnetic materials is one of the more intriguing possibilities. Iron itself is readily cold-sprayable (Ref 1). The idea of using spray technology to produce magnetic components for electronics applications, electric motors and the like, has been mentioned previously (Ref 2). Complex geometries can be built up directly on the substrate, with minimal post-machining operations. Other potential devices include sensors, magnetic couplings, and actuators. High-energy rare earth permanent magnets, such as samarium-cobalt and neodymium-iron-boron alloys, have been the subject of considerable attention in recent years. These materials can be plasma-sprayed, but the resulting coating exhibits porosity, oxidation, and degradation of magnetic properties (Ref 3, 4). Rare earth permanent magnets are hard and brittle, so cold spray requires the magnetic powder to be mixed with a ductile metallic powder and the two sprayed together to form a metal matrix composite. Upon impact with the substrate, the metal matrix particles plastically deform extensively, eliminating pores and trapping the rare earth particles Peter C. King, Saden H. Zahiri, and Mahnaz Z. Jahedi, CSIRO Materials Science and Engineering, Gate 5, Normanby Road, Clayton, VIC 3168, Australia. Contact e-mail: Peter.King@ csiro.au.
Journal of Thermal Spray Technology
before they rebound. Van Steenkiste (Ref 5) has demonstrated the potential of the kinetic spray process for depositing composite coatings employing the rare earth magnetostrictive material, Terfenol-D. Rare earth permanent magnet composites have been produced using cold spray by McCune. The matrix material was a soft ferromagnetic metal such as iron or nickel (Ref 6). By contrast, in the current study, a non-magnetic matrix was chosen so tha
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