Non-equilibrium solidification of Fe–B eutectic alloys under electric current pulse

Abstract

This paper aims to explore the effects of electric current pulse (ECP) on the formed microstructure in Fe–B eutectic alloys. ECP treatment can change the microstructure morphology and phase composition of the Fe–B eutectic alloys from regular eutectic under conventional solidification conditions to (α-Fe) + interdendritic irregular eutectic structure. The results demonstrate that there is a maximum value of the peak current, when the maximum value is not reached, the peak current increases; the α-Fe refinement effect is obvious, the volume fraction of α-Fe increases. When the maximum value is surpassed, the α-Fe grain size increases, the volume fraction of α-Fe decreases. The phenomenon can be explained by the cluster theory for liquid metals and the non-equilibrium diffusion theory. The solidification path of Fe–B eutectic alloys under different peak ECPs was drawn, and the formation mechanism of irregular eutectic under different conditions was explained. The results of the soft magnetic properties experiments show that the morphology of the Fe₂B phase and its degree of granulation have a great influence on the magnetic properties. As the size of Fe₂B phase increases, the coercivity H_c increases. As the grain size of Fe₂B decreases, the coercivity and residual magnetic field strength decrease.