Room-temperature ferromagnetic transitions and the temperature dependence of magnetic behaviors in FeCoNiCr-based high-entropy alloys

Suok-Min Na,Jin-Hyeong Yoo,Paul K Lambert,Nicholas J Jones

doi:10.1063/1.5007073

Abstract

High-entropy alloys (HEAs) containing multiple principle alloying elements exhibit unique properties so they are currently receiving great attention for developing innovative alloy designs. In FeCoNi-based HEAs, magnetic behaviors strongly depend on the addition of alloying elements, usually accompanied by structural changes. In this work, the effect of non-magnetic components on the ferromagnetic transition and magnetic behaviors in equiatomic FeCoNiCrX (X=Al, Ga, Mn and Sn) HEAs was investigated. Alloy ingots of nominal compositions of HEAs were prepared by arc melting and the button ingots were cut into discs for magnetic measurements as functions of magnetic field and temperature. The HEAs of FeCoNiCrMn and FeCoNiCrSn show typical paramagnetic behaviors, composed of solid solution FCC matrix, while the additions of Ga and Al in FeCoNiCr exhibit ferromagnetic behaviors, along with the coexistence of FCC and BCC phases due to spinodal decomposition. The partial phase transition in both HEAs with the additions of Ga and Al would enhance ferromagnetic properties due to the addition of the BCC phase. The saturation magnetization for the base alloy FeCoNiCr is 0.5 emu/g at the applied field of 20 kOe (TC = 104 K). For the HEAs of FeCoNiCrGa and FeCoNiCrAl, the saturation magnetization significantly increased to 38 emu/g (TC = 703 K) and 25 emu/g (TC = 277 K), respectively. To evaluate the possibility of solid solution FCC and BCC phases in FeCoNiCr-type HEAs, we introduced a parameter of valence electron concentration (VEC). The proposed rule for solid solution formation by the VEC was matched with FeCoNiCr-type HEAs.

Highlights

High-entropy alloys (HEAs) contain multiple principle alloying elements with nearly equiatomic composition, unlike conventional alloys which are based on one major element and several minor elements such as iron in steels.[1]
Those maps reveal a typical dendrite microstructure composed of body-centered cubic (BCC) and facecentered cubic (FCC) phases in the matrix[9,10] and an Fe-rich BCC phase corresponding to the island
To evaluate the possibility of solid solution FCC and BCC phases in FeCoNiCrX HEAs, we introduced a parameter of valence electron concentration (VEC) which is the number of total electrons accommodated in the valence band including s, p- and d-electrons.[13]

Summary

INTRODUCTION

Structure leads to the significant enhancement of ferromagnetic properties by adding non-magnetic alloying elements such as Al, Ga and Sn to FeCoNiMn alloy.[5,6] In contrast to the addition of Mn, ferromagnetic FeCoNi alloys can become paramagnetic at RT by adding Cr or CrMn in an equiatomic composition, resulting in a significant reduction of the Curie temperatures (TC) from 868 K to 156 K for the Cr addition and 23 K for the CrMn addition in simulation.[7] It was observed that the TC increased to 355 K and 640 K when Al and Ge, respectively, were added to the FeCoNiCr alloy.[8]. We present the results of the FeCoNi and FeCoNiCr alloys as the base composition response

EXPERIMENTAL PROCEDURES

RESULTS AND DISCUSSION

CONCLUSIONS