Magnetic Properties of High Permeability Alloys Hardperm in the Ni–Fe–Nb System

Abstract

Ni–Fe–Nb alloys were vacuum melted, annealed in hydrogen atmosphere over the temperature range 950 to 1350°C and then cooled at various rates from a temperature above their order-disorder transformation points. Measurements of magnetic properties, electrical resistivity and hardness for the alloys showed that the values of initial and maximum permeabilities were highest at approximately 9% Nb and decreased sharply with a further increase in Nb content. In the Ni–Fe–Nb alloy system, the highest initial permeability of 125000 was obtained for the alloy of 79.27% Ni, 11.76% Fe and 8.97% Nb when cooled at 300°C/hr after annealing at 1150°C for 2 hr, and the highest maximum permeability of 580000 for the alloy of 79.19% Ni, 12.16% Fe and 8.65% Nb when cooled at 400°C/hr after annealing at 1250°C for 1.5 hr. The alloy with the highest initial permeability exhibited a coercive force of 2.3 mOe, a hysteresis loss of 2.7 erg/cm³/cycle for a maximum magnetic induction of 5 kG, an electrical resistivity of 74.8 μΩ-cm, and Vickers hardness 207. These alloys have been named Hardperm. The high permeability of Ni–Fe–Nb alloys appears to be due to the removal of impurities, homogenization and grain growth by high-temperature heat treatment and also to the low value of magnetostriction constant in the proper ordering state.