Additive manufacturing of heavy rare earth free high-coercivity permanent magnets

A.S Volegov,S.V Andreev,N.V Selezneva,I.A Ryzhikhin,N.V Kudrevatykh,L Mädler,I.V Okulov

doi:10.1016/j.actamat.2020.02.058

Abstract

Laser based powder bed fusion is a promising manufacturing method that can be used for the fabrication of hard magnets such as NdFeB with nearly any given geometrical shape. However, the weak performance, e.g., low coercivity, of the 3D-printed magnets currently hinder their application. In this work, we demonstrated a proof-of-concept of powder bed additive manufacturing of heavy rare earth free NdFeB magnets with technologically attractive coercivity values. The 3D-printed NdFeB magnets exhibit the highest (up-to-date for the additively manufactured magnets without heavy rare earth metals) coercivity values reaching μ0Hc = 1.6 T. The magnets were synthesized using a mixture of the NdFeB-based and the low-melting eutectic alloy powders. The essential function of the eutectic alloy, along with binding of the NdFeB-based magnetic particles, is the significant improvement of their coercivity by the in-situ grain boundary (GB) infiltration. The fundamental understanding of the magnetization reversal processes in these 3D-printed magnets leads to the conclusion that the excellent performance of the additively manufactured hard magnets can be achieved through the delicate control of the intergrain exchange interaction between the grains of the Nd2Fe14B phase.

Highlights

The development of energetics and robotics, miniaturization of existing high-tech devices as well as electric and hybrid vehicles require an annual increase in the production volume of permanent magnets and at the same time improvement of their magnetic properties
We aim to prove the concept of one-step additive manufacturing process of permanent magnets with high coercivity
The eutectic alloy performs two functions, namely, (i) a binder function to create a permanent magnet body from the powder and (ii) an effective separation function of nanoscale grains of the main hard magnetic phase that suppresses the exchange interaction between the grains contributing to the increase in coercivity of such a magnet

Summary

Introduction

The development of energetics and robotics, miniaturization of existing high-tech devices as well as electric and hybrid vehicles require an annual increase in the production volume of permanent magnets and at the same time improvement of their magnetic properties. The temperature of permanent magnets used in generators and electric motors, exceeds room temperature and often reaches up to 400 K. In the case of soft magnetic materials, the eddy currents can be decreased by designing their topological structure [1]. This approach is unsuitable for rare earth magnets because of their high brittleness. The high temperature coefficient of coercivity limits the torque and power density of the devices at operating temperatures.

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Conclusion