Influences of Annealing Treatment on Soft Magnetic Properties, Mechanical Properties and Microstructure of Fe24.94Co24.94Ni24.94Al24.94Si0.24 High-Entropy Alloy

TL;DR

This paper studies how annealing affects the magnetic and mechanical properties of a high-entropy alloy, showing improved hardness and magnetic behavior.

Contribution

The study reveals that annealing preserves the alloy's microstructure while enhancing its mechanical and magnetic properties through dislocation and precipitation strengthening.

Findings

Annealing at 873 K preserves the BCC and B2 phases in the alloy with a coherent relationship.

Annealing increases the hardness of the alloy by 25% due to dislocation and nanoprecipitate strengthening.

The coercivity of the alloy increases after annealing due to inhomogeneous grain distribution and lattice misfit.

Abstract

In order to meet the ever-growing demand in modern power electronics, the advanced soft magnetic materials (SMMs) are required to exhibit both excellent soft magnetic performance and mechanical properties. In this work, the effects of an annealing treatment on the soft magnetic properties, mechanical properties and microstructure of the Fe24.94Co24.94Ni24.94Al24.94Si0.24 high-entropy alloy (HEA) are investigated. The as-cast HEA consists of a body-centered cubic (BCC) matrix phase and spherical B2 nanoprecipitates with a diameter of approximately 5 nm, where a coherent relationship is established between the B2 phase and the BCC matrix. After annealing at 873 K, the alloy retains both the BCC and B2 phases, with their coherent relationship preserved; besides the spherical B2 nanoprecipitates, rod-shaped B2 nanoprecipitates are also observed. After the annealing treatment, the saturation magnetization (Ms) of the alloy varies slightly within the range of 103–113 Am2/kg, which may be induced by the precipitation of this rod-shaped nanoprecipitate phase in the alloy. The increase in the coercivity (Hc) of annealed HEA is due to the inhomogeneous grain distribution, increased lattice misfit and high dislocation density induced by the annealing. The nanoindentation result reveals that the hardness after annealing at 873 K exhibits a 25% improvement compared with the hardness of as-cast HEA, which is mainly due to dislocation strengthening and precipitation strengthening. This research finding can provide guidance for the development of novel ferromagnetic HEAs, so as to meet the demands for materials with excellent soft magnetic properties and superior mechanical properties in the field of sustainable electrical energy.

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