Microstructure evolution and magnetic shielding effect of permalloy deposition on molybdenum substrate by electron beam freeform fabrication

In view of the excellent soft magnetic properties, 1J85 permalloy was deposited on molybdenum substrate by electron beam freeform fabrication to achieve magnetic shielding effect for molybdenum substrate. The magnetization of molybdenum substrate was increased from 0.04 emu/g to 8.96 emu/g after depositing permalloy layer, corresponding to the decrease in coercivity from 169.44 Oe to 7.33 Oe. The saturation magnetization was increased with the increased heat input. The cellular grain boundaries were demonstrated to be element segregation instead of the conventional dislocation-walls. A reaction layer consisting of numerous Mo-Ni binary phases was located at the interface between permalloy deposition and molybdenum substrate, indicating the maximum microhardness value. The shear strength of the interface between permalloy deposition and Mo substrate was firstly increased and then decreased with the increased heat input. The residual stress in permalloy deposition corresponded to local misorientation and dislocation, which was detrimental to soft magnetic properties. The decrease in residual stress was the main reason for the increased saturation magnetization with the increased heat input.