Soft Magnetic Properties of Agglomerates of Fe Nanoparticles Fabricated by Cold Spray Technique

The development of soft magnetic devices requires high-performance soft magnetic materials and high degree of design freedom. We aim to obtain high soft magnetic properties and high degree of design freedom in molding by molding high-performance soft magnetic powders using additive manufacturing. Fe nanoparticles are attracting attention as a soft magnetic material because of their high saturation magnetization and low coercivity. Achieving high packing density without lowering soft magnetic properties is a challenge when nanoparticles are used as the starting material. A bulk-like structure with high packing density, comprising pure Fe nanoparticles were sucessfully fabricated by the cold spray deposition technique. The packing density of the particles was estimated to be 96%, which was 31% larger than that of conventional compression molded samples at room temperature. Although the size of the Fe nanoparticles slightly increased in the post annealing process, the grain growth was limited after cold spraying. The coercivity of the cold sprayed sample was lower than that of the compression molded samples because of the higher packing density of the nanoparticles. These results indicate that the cold spray technique is suitable for fabricating bulk-like structures using nanoparticle materials.