Low temperature texture development in Nd2Fe14B/α-Fe nanocomposite magnets via equal channel angular pressing

L Besley,A Kato,A Molotnikov,H Kishimoto,C Davies,J S Garitaonandia,K Suzuki

doi:10.1063/1.5006359

Abstract

While suitable texture has been developed in Nd2Fe14B/α-Fe nanocomposites via thermomechanical processing methods such as die upsetting by incorporating low melting point eutectic Nd-Cu additives, significant grain coarsening occurs during this process due to the high temperature and long timescales involved, resulting in a loss of exchange coupling. Equal channel angular pressing (ECAP) is a severe plastic deformation technique which has been successfully used to produce a suitable texture in single-phase Nd2Fe14B at temperatures on the order of 500°C while preserving grain sizes on the order of 20-30nm. We investigate the development of texture in a commercial Nd2Fe14B/α-Fe nanocomposite alloy with added Nd90Cu10 produced via ECAP and then characterise it using texture x-ray diffraction and magnetic measurements. It is found that initial texture can be developed in this nanocomposite system at T = 520°C via ECAP. The average grain size of Nd2Fe14B as measured via X-ray diffraction after ECAP remains below 50nm with a developed texture. The effect of varying the amount of Nd90Cu10 additive is also investigated. It is found that with decreasing Nd90Cu10, the degree of texture is reduced while the volume fraction of α-Fe increases. This work demonstrates the development of texture in nanocomposite Nd2Fe14B/α-Fe with Nd-Cu additives whilst maintaining a grain size of approximately 50nm.

Highlights

Nd2Fe14B/α-Fe nanocomposite magnets promise excellent performance with high theoretical maximum energy products due to the effects of exchange coupling.[1,2,3] In order to realise the full potential of nanocomposites, texture must be developed without losing exchange coupling
While texture can be developed in nanocomposites via thermomechanical processing such as die upsetting and the incorporation of low melting point eutectic Nd-rich additives that help improve the workability and facilitate texture development in these materials,[4,5,6,7,8] the temperature and timescale required for such processing causes grain coarsening, resulting in a final microstructure with grain sizes on the order of 200-1000nm,[8] well above the predicted exchange length for Nd2Fe14B.1
Beyond t=25h, Hc, |BH|Max and Mr begin to I shows the change in grain size with varying annealing time

Summary

Introduction

Nd2Fe14B/α-Fe nanocomposite magnets promise excellent performance with high theoretical maximum energy products due to the effects of exchange coupling.[1,2,3] In order to realise the full potential of nanocomposites, texture must be developed without losing exchange coupling. While texture can be developed in nanocomposites via thermomechanical processing such as die upsetting and the incorporation of low melting point eutectic Nd-rich additives (such as Nd-Cu and Nd-Ga) that help improve the workability and facilitate texture development in these materials,[4,5,6,7,8] the temperature and timescale required for such processing causes grain coarsening, resulting in a final microstructure with grain sizes on the order of 200-1000nm,[8] well above the predicted exchange length for Nd2Fe14B.1. Other works show that exchange coupling may be observed experimentally at grain sizes slightly above this limit, but still on the order of 30-50nm.[9,10] In order to maintain. While texture can be developed in nanocomposites via thermomechanical processing such as die upsetting and the incorporation of low melting point eutectic Nd-rich additives (such as Nd-Cu and Nd-Ga) that help improve the workability and facilitate texture development in these materials,[4,5,6,7,8] the temperature and timescale required for such processing causes grain coarsening, resulting in a final microstructure with grain sizes on the order of 200-1000nm,[8] well above the predicted exchange length for Nd2Fe14B.1 Other works show that exchange coupling may be observed experimentally at grain sizes slightly above this limit, but still on the order of 30-50nm.[9,10] In order to maintain

Methods

Results

Conclusion