Toshio Miyoshi

Solidification and crystallization behaviors of Fe3B/Nd2Fe14B-based nanocomposite permanent-magnet alloys and influence of micro-alloyed Cu, Nb and Zr

Abstract Rapid solidification process of Nd 2 Fe 14 B-based nanocrystalline permanent-magnet alloys and crystallization processes of the relevant amorphous alloys are investigated. Accumulated experimental results are discussed in terms of temperature–time–transformation diagrams for Nd 4 Fe 77.5 B 18.5 . Solidification and crystallization kinetics is strongly influenced by minor amounts of additives, particularly Cr, Cu, Nb, and Zr, knowledge of which has been applied to design alloy composition. Development of a high coercivity Fe 3 B/Nd 2 Fe 14 B-type nanocomposite magnet based on Nd–Dy–Fe–B–Cr–Co–Cu–Nb/Zr is described as an example.

Structure and magnetic properties of Nd/sub 2/Fe/sub 14/B/Fe/sub x/B-type nanocomposites prepared by strip casting

A series of isotropic nanocomposite permanent magnets composed of Nd/sub 2/Fe/sub 14/B (the majority phase) and Fe/sub 3/B and/or Fe/sub 23/B/sub 6/ are developed by converting phase formation behavior with partial replacement of Fe with Ti and B with C. The glass forming ability of the melt of the new series of alloys is great enough to allow application of the strip casting technique as the means of rapid solidification process. Powders exhibit excellent magnetic properties ranging from (B/sub r/,H/sub cJ/)=(0.88 T, 470 kA/m) to (0.80 T, 1010 kA/m), closely matching to the property range covered by the conventional isotropic Nd-Fe-B hard magnetic powders.

Effects of Nb addition on structural and magnetic properties of Fe-B/Nd/sub 2/Fe/sub 14/B based nanocomposite magnets

Effects of Nb addition on Ti-doped Nd-poor and B-rich composition are investigated. It is found that Nb addition improves the glass-forming ability of rapidly solidified Nd-Fe-B-Ti-based alloys, resulting in significant improvements of magnetic properties in a low cooling-rate regime. Moreover, magnetic properties of the alloys prepared by various surface speeds of Cu wheel, V/sub s/, were almost constant at an excellent level. As a result of transmission electron microscope observation, microstructure was relatively identical and fine regardless of V/sub s/. Therefore, Nb addition is effective to obtain the high performance of magnetic properties within a wide range of cooling rates.

High-coercivity nanocomposite permanent magnet based on Nd-Fe-B-Ti-C with Cr addition for high temperature applications

The effects of Cr addition on structural properties, magnetic properties, and temperature dependence of thermal flux losses of Fe-B/Nd2Fe14B based nanocomposite magnets is reported. By addition of Cr, coercivity increased up to 1470 kA/m.

Effects of Cu-Nb/Zr addition on magnetic properties of Fe/sub 3/B/(Nd-Dy)/sub 2/Fe/sub 14/B nanocomposite magnets

Improving magnetocrystalline anisotropy to create materials with high coercivity by means of partial replacement of Nd with a heavy rare earth element such as Tb and Dy requires considerable refinement of grain size in order to keep the relation between intergranular exchange energy and magnetocrystalline energy unchanged. Addition of small amounts of Cu and Zr is shown to be effective to manipulate crystallization behaviors and hence structure of the Fe/sub 3/B/Nd/sub 2/Fe/sub 14/B-type nanocomposite permanent magnets containing heavy rare earth elements. The impact of the simultaneous addition of Cu-Zr is that improvement of magnetic properties can he achieved with a smaller amount of additives than Cu-Nb addition reported earlier. An example is Nd/sub 3.4/Dy/sub 1.0/Fe/sub 71.7/B/sub 18.5/Cr/sub 2.4/Co/sub 2.4/Cu/sub 0./ /sub 4/Zr/sub 0.2/ with H/sub cJ/=462 kA/m, B/sub r/=0.97 T, and (BH)/sub max/=105 kJ/m/sup 3/.