The Influence of Cu-Additions on the Microstructure, Mechanical and Magnetic Properties of MnAl-C Alloys

Florian Jürries,Thomas George Woodcock,Kornelius Nielsch,Jens Freudenberger

doi:10.1038/s41598-020-64697-8

Florian Jürries, Thomas George Woodcock + Show 2 more

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https://doi.org/10.1038/s41598-020-64697-8

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Abstract

Alloys of the form (Mn54Al44C2)100-xCux (with x = 0, 1, 2, 4 and 6) were produced by induction melting. After homogenisation and quenching, most of the alloys consist entirely of the retained ε-phase, except for x = 6, in which the κ-phase was additionally present. After subsequent annealing, the alloys with x ≤ 2 consist entirely of a Cu-doped, ferromagnetic τ-phase, whereas the alloys with x > 2 additionally contain the κ-phase. The polarisation of the alloys at an applied field of 14 T decreases with increasing Cu-content, which is attributed i) to the dilution of the magnetic moment of the τ-phase unit cell by the Cu atoms, which do not carry a magnetic moment, and ii) at higher Cu-contents, to the formation of the κ-phase, which has a much lower polarisation than the τ-phase and therefore dilutes the net polarisation of the alloys. The Curie temperature was not affected by the Cu-additions. The stress needed to die-upset the alloys with x ≤ 2 was similar to that of the undoped alloy, whereas it was much lower for x = 4 and 6, due to the presence of intergranular layers of the κ-phase. The extrinsic magnetic properties of alloys with x ≤ 2 were improved by die-upsetting, whereas decomposition of the τ-phase during processing had a deleterious effect on the magnetic properties for higher Cu-additions.

Highlights

The growth of environmentally-friendly technologies such as wind power and electromobility has led to an increasing demand for high-performance permanent magnets such as those based on Nd2Fe14B1,2
All samples, except for x = 6, only showed X-ray diffraction (XRD) peaks corresponding to the ε-phase (P63/mmc, Mg-type) (Fig. 1)
As the ε grains in the homogenised materials are rather coarse and do not have a preferred orientation, the varied intensities of the ε peaks in the XRD patterns (Fig. 1) can be explained by different crystallographic orientations being sampled during the measurement of each alloy

Summary

Introduction

The growth of environmentally-friendly technologies such as wind power and electromobility has led to an increasing demand for high-performance permanent magnets such as those based on Nd2Fe14B1,2. Since such magnets contain significant amounts of rare-earth (RE) elements, the supply of which is described as being critical[3,4], the question of developing sustainable, RE-free alternatives is becoming increasingly important[5]. The aim of this work is to investigate the impact of Cu-additions on the microstructure, mechanical and magnetic properties of MnAl-C alloys. A series of MnAl-C-Cu alloys has been prepared, processed using die upsetting and characterised using a variety of techniques

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