High Magnetic Permeability Alloys “Hardperm” in the Ni–Fe–Nb–W and Ni–Fe–Ta–W Systems

Abstract

Ni–Fe–Nb–W and Ni–Fe–Ta–W alloys were heated in pure hydrogen atmosphere at 1150°C for 3 hr and then cooled at various rates from a temperature above their order-disorder transformation points. In the Ni–Fe–Nb–W system, an alloy of 79.4% Ni, 11.54% Fe, 8.51% Nb and 0.50% W cooled at the rates of 240 and 300°C/hr showed the highest initial permeability of 109000 and the highest maximum permeability of 463000. In the Ni–Fe–Ta–W system, the highest initial permeability of 101000 is obtained with an alloy of 73.40% Ni, 10.96% Fe, 14.11% Ta and 1.53% W cooled at the rate of 200°C/hr, and the highest maximum permeability of 557000 with an alloy of 73.50% Ni, 10.96% Fe, 14.99% Ta and 0.55% W cooled at 300°C/hr. The hardness and electrical resistivity of these alloys are considerably higher than those of Permalloy-type alloys. The high permeability of these alloys is largely due to the major contribution of high-temperature heat treatment in hydrogen atmosphere to the homogenization, removal of impurities, and the very low saturation magnetostriction and crystal magnetic anisotropy in a proper state of ordering.