Abstract

In this work, we investigate the effects of substituting Ni/Al for Cr on the thermomagnetic and magnetocaloric properties of FeCoNiCrAl-type high entropy alloys (HEAs). Ni and Al appear to prefer the BCC phase, and increases in the Al composition appear to stabilize the BCC phase. In contrast to Al, Ni content yields an increase in the FCC phase fraction, resulting in a drop off in magnetization. The phase transformation from BCC to FCC was intensified at annealing temperatures of 800 °C and higher due to increased diffusion rates and the resulting spinodal decomposition. A magnetic phase transition around 150 K was found in the FeCoNi1.5Cr0.5Al annealed alloy potentially corresponding to the FCC phase, and a very broad magnetic phase transition was observed in the annealed FeCoNiCrAl alloy, resulting in a high refrigerant capacity of RCFWHM = 242.6 J⋅kg-1 near room temperature. A peak magnetic entropy change of −ΔSM = 0.674 J⋅kg-1⋅K-1 was also obtained at applied fields of ∼70 kOe at 290 K in the FeCoNiCrAl HEA. These magnetocaloric values are comparable to Fe-based metallic glasses such as Fe-Tm-B-Nb and Fe-Zr-B-Co alloys, with a similar transition near room temperature.

Highlights

  • Magnetocaloric materials have the potential to improve the efficiency of traditional gas compression refrigeration, providing a solid state cooling methodology with no need for environment-harming refrigerants

  • High entropy metallic glasses (HEMG) with rare earth (RE) elements exhibit strong topological and chemical disorder, resulting in an enhanced large magnetocaloric effect (MCE) and refrigerant capacity, which are important for improving the efficiency of the refrigerant

  • The as-cast FeCoNi1+XCr1-XAl high entropy alloys (HEAs) exhibit a dominant BCC phase with a relatively low portion of FCC phase; only the BCC phase was observed at the equiatomic (X=0) and near equiatomic (X=0.1) FeCoNiCrAl HEAs

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Summary

INTRODUCTION

Magnetocaloric materials have the potential to improve the efficiency of traditional gas compression refrigeration, providing a solid state cooling methodology with no need for environment-harming refrigerants. Second order magnetic transitions exhibit a smaller peak value, but over a much wider temperature range This allows them to operate over a larger temperature range, and their overall performance can be captured by the refrigerant capacity (RC). High entropy metallic glasses (HEMG) with rare earth (RE) elements exhibit strong topological and chemical disorder, resulting in an enhanced large magnetocaloric effect (MCE) and refrigerant capacity, which are important for improving the efficiency of the refrigerant.. High entropy metallic glasses (HEMG) with rare earth (RE) elements exhibit strong topological and chemical disorder, resulting in an enhanced large magnetocaloric effect (MCE) and refrigerant capacity, which are important for improving the efficiency of the refrigerant.1–5 Their Curie temperatures (TC) are much below room temperature (RT), which is unsuitable for ambient temperature applications. We systematically investigate the effects of substituting Ni or Al for Cr on the thermomagnetic and magnetocaloric properties of FeCoNi1+XCr1-XAl and FeCoNiCr1-XAl1+X HEAs with X=0-0.5 (both based on an equiatomic FeCoNiCrAl HEA)

EXPERIMENTAL PROCEDURES
RESULTS AND DISCUSSION
CONCLUSIONS

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