FeCoNiCr_0.4Cu_X High-Entropy Alloys with Strong Intergranular Magnetic Coupling for Stable Megahertz Electromagnetic Absorption in a Wide Temperature Spectrum

Abstract

Electromagnetic (EM) absorbers serving in the megahertz (MHz) band and a wide temperature range (from −50 to 150 °C) require high and temperature-stable permeability for outstanding EM absorption performance. Herein, FeCoNiCr0.4Cu X high-entropy alloy (HEA) powders with a unique nanocrystalline structure separated by a thin amorphous layer (NTA) are designed to improve permeability and enhance intergranular coupling. Simultaneously, the long-range anisotropy is introduced via devising the preparation process and tuning the chemical composition, such that the intergranular exchange interaction is further strengthened for stable permeability and EM wave absorption in a wide temperature range. FeCoNiCr0.4Cu0.2 HEAs exhibit a near-zero permeability temperature coefficient (5.7 × 10–7 °C–1) a in wide temperature range. The maximum reflection loss (RL) of FeCoNiCr0.4Cu0.2 HEAs is higher than −7 dB with 5 mm thickness at −50–150 °C, and the absorption bandwidth (RL < −7 dB) can almost cover 400–1000 MHz. Furthermore, FeCoNiCr0.4Cu0.2 HEAs also have a high Curie temperature (770 °C) and distinguished oxidation resistance. The permeability temperature dependence of FeCoNiCr0.4Cu X HEAs is investigated in-depth in light of the microstructural change induced by tuning the chemical composition, and a new inspiration is provided for the design of magnetic applications serving in wide temperature, such as transformers, sensors, and EM absorbers.

Microstructure Design of High-Entropy Alloys Through a Multistage Mechanical Alloying Strategy for Temperature-Stable Megahertz Electromagnetic Absorption

“…Facing longer wavelengths than gigahertz EMW, absorbers demand larger and more matched complex permittivity and complex permeability to achieve broadband EMW absorption in the MHz band [ 12 – 16 ]. In addition, the harsh service environments bring challenges to the multi-temperature adaptability (at − 50–150 °C) and corrosion resistance of EMW absorbers [ 13 , 17 – 22 ]. Excellent permeability and its temperature stability are of a paramount significance for achieving broadband and temperature-stable EMW absorption in the MHz frequency range [ 13 , 23 ].…”

“…In addition, the harsh service environments bring challenges to the multi-temperature adaptability (at − 50–150 °C) and corrosion resistance of EMW absorbers [ 13 , 17 – 22 ]. Excellent permeability and its temperature stability are of a paramount significance for achieving broadband and temperature-stable EMW absorption in the MHz frequency range [ 13 , 23 ]. Iron–cobalt–nickel-based high-entropy alloy powders (HEAs) prepared by mechanical alloying method (or high-energy ball milling method) are suitable candidates for EMW absorption materials serving in the MHz band and a wide temperature spectrum, which exhibit several advantages.…”

“…Iron–cobalt–nickel-based high-entropy alloy powders (HEAs) prepared by mechanical alloying method (or high-energy ball milling method) are suitable candidates for EMW absorption materials serving in the MHz band and a wide temperature spectrum, which exhibit several advantages. (1) Excellent magnetic properties with high saturation magnetization, low coercivity, high complex permeability, and high Curie temperature [ 13 , 24 ]. (2) High resistivity due to severe lattice distortion effects [ 24 , 25 ].…”

“…The high resistivity can help to reduce the complex permittivity to improve impedance matching and EMW absorption performance. (3) Superior manufacturability of the HEAs with large aspect ratios and nanocrystalline structure at the same time [ 13 , 26 ]. The nanocrystalline structure and large aspect ratios facilitate the averaging of magnetocrystalline anisotropy and the breaking of the Snoek’s limit [ 23 , 27 , 28 ], respectively.…”

“…In the past, our group has successfully prepared flake-shaped FeCoNiCr 0.4 Cu 0.2 HEAs with nanocrystalline and thin amorphous layers nanostructure by mechanical alloying method to break the Snoek’s limit and enhance intergranular magnetic coupling. FeCoNiCr 0.4 Cu 0.2 HEAs with this special structure exhibit excellent and temperature-stable permeability and EMW absorption performance in the MHz frequency range at − 50–150 °C [ 13 , 23 ]. To obtain flake-shaped HEAs to enhance planar anisotropy and break the Snoek’s limit, anhydrous ethanol is usually added as a process control agent [ 25 , 35 ].…”