A novel microwave absorber of FeCoNiCuAl high-entropy alloy powders: Adjusting electromagnetic performance by ball milling time and annealing

The FeCoNiCuAl high-entropy alloy powders are prepared in equimolar ratio by mechanical alloying in different milling time and then annealing at 773K. The microstructure, morphology, particle size, magnetic and electromagnetic performance of powders were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), laser scattering particle size distribution analyzer, vibrating sample magnetometer (VSM) and vector network analyzer. The results indicate that flaky particles, which formed in the process of ball milling, show a soft magnetic character, as well as, the ranges of coercivity (H-c) are 67.6-105.1 O-e and the values of saturation magnetization (M-s) range from 69.1 emu/g to 94.2 emu/g. As the increasing of the milling time, the real parts of complex permittivity (epsilon') increase firstly and then decrease, however, the imaginary parts of complex permittivity (epsilon '') close to zero for all the samples. Meanwhile, the real parts of complex permeability (mu') are 1.26-1.56 and the imaginary parts of complex permeability (mu '') are 0.28-0.36 with change of milling time. The reflection loss (RL) of powders can reach -10 dB or less and 30 h-milling sample shows the maximum RL is -19.17 dB at 7.84 GHz with the thickness of 2 mm. After annealing, there appear two new phases, CoFe2O4 and AlFe3, that improve the values of Ms. The increased particles sizes and the enhanced values of Ms of powders all can promote complex permittivity and complex permeability. In addition, the RL also can get increased. These encouraging findings provide the potential advantages of high-entropy alloys for microwave absorption application. (C) 2018 Elsevier B.V. All rights reserved.