Rapidly Quenched Nd-Fe-B Magnets

Abstract

Over-quenched Nd-Fe-B flakes for isotropic bonded magnets show high coercivity (iHc) by post-heat treatment. This flake has the lowest temperature coefficient of iHc around -0.45/°C and the smallest grain size in the Nd-Fe-B materials. Enough thermal stability and magnetizability are obtained for isotropic bonded magnets with these characteristics of the flake. The Nd₁₄Fe₈₀B₆ ternary composition has the best hot workability (die upsetting) from stress-strain curves for the initial stage of die upsetting at hot working temperatures. Alignment of c-axis along die upsetting direction is obtained, but decrease in iHc due to grain coarsening is resulted. Ga is the best for enhancing iHc without deterioration in hot workability. Typical magnetic properties of Nd₁₄Fe_79.25B₆Ga_0.75 die-upset magnets are (BH)max=36 MGOe and iHc=19 kOe. The iHc of powders made by pulverizing the die-upset magnet is nearly independent of particle size. Anisotropic bonded magnets are developed using this powder. Typical magnetic properties of Nd-Fe-B-Ga compression moulded magnets are (BH)max=15 MGOe and iHc=19 kOe.