Innovative Coating Technologies for Synthesis of Interface-Exchange-Coupled Permanent Magnets

Worldwide efforts to synthesize Nd-Fe-B or Sm-Co nanoparticles have been unsuccessful because of oxygen pickup. An alternative approach to synthesizing interface-exchange-coupled magnets with uncharted superior properties is to create a microstructure with highly dispersed soft phase (Fe or Fe-Co) embedded in the nanograin hard phase (Nd-Fe-B or Sm-Co). Coating micron-sized Nd-Fe-B particles with Fe or Fe-Co layers has proved to be practical for making such magnets in our previous efforts. Technologies including sputtering, pulsed laser deposition, and electroless and electrolytic coating were used followed by rapid inductive hot compaction and hot deformation. Such exchange-coupled magnets can have (BH)max greater than 45 MGOe. Coating Fe-based Nd-Fe-B particles with Fe or Fe-Co layers is a great challenge since the chemical potential difference between them is small. To accomplish (BH)max > 60 MGOe, in the proposed SBIR-II project innovative coating technologies will to be studied and developed to solve problems such as low deposition rate, non-uniform coating (due to loose bridging of particles), oxidation, and high cost. Applying the proposed innovative approach, the advantage of nanostructure is fully utilized, while the problems associated with synthesizing and handling nanoparticles, such as oxidation and agglomeration, are readily avoided.