An assessment of the mechanically alloyed equiatomic FeCoNiMnSi high entropy amorphous alloy for non-isothermal crystallization kinetics and magnetocaloric refrigeration application

Abstract

We studied an equiatomic FeCoNiMnSi high entropy amorphous alloy successfully processed via mechanical alloying technique. The structural, magnetic, and magnetocaloric characteristics of the resulting materials were examined using X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and a vibrating sample magnetometer. The structural analysis showed a prominent amorphous phase formation as the milling time increases from t = 0–35h of mechanical alloying. The differential scanning calorimetry was employed to investigate the non-isothermal crystallization kinetics of the 35-h milled sample. The results revealed that the milled powder consists of a single exothermic peak with its apparent activation energy (Eg, Ex, Ep) being determined using the Kissinger, Ozawa, and Augis-Bennett equations. The findings exhibit Ex > Ep > Eg, representing that nucleation is more complicated than the growth mechanism during the crystallization process. Meanwhile, under non-isothermal conditions, the Kissinger-Akahira-Sunose, Friedman, and Flynn-Wall-Ozawa models were calculated using the local activation energies that agree with the apparent activation energy. Furthermore, the Johson-Mehl-Avrami-Kolmogorov exponent (n) and Avrami-Ozawa combined [F(T)] models exhibit high-dimensional nucleation and growth with an increasing nucleation rate enabled by lowering the local activation energies as a function of degree of conversion with respect to temperature. In magnetic measurements, a feasible mathematical model was proposed as a novel strategy for predicting the value of saturation magnetization as a milling time function. The model has an exceptional predictive capability, confirmed by fitting other research outcomes. Finally, the proposed system also delivers the best magnetocaloric properties with a maximum magnetic entropy change of 3.70 Jkg−1 K−1 at 150 K curie temperature and a refrigeration capacity of 252.86 J/kg with 1000 Oe applied magnetic field.