Magnetostrictive Loss Reduction Through Stress Relief Annealing in an FeNi-based Metal Amorphous Nanocomposite

FeNi-based metal amorphous nanocomposite alloys are emerging soft magnetic materials with promise for high-speed motor applications. Here we demonstrate a technique to optimize magnetic properties in toroidal cores wound from strain annealed (Fe70Ni30)80Nb4Si2B14 amorphous metal ribbon (AMR). In-line strain annealing (SA) of the AMR yields a strip permeability that monotonically decreases with increasing SA tensions. After winding into toroidal cores, dramatic changes in magnetic properties are observed and determined to be of magnetostrictive origin. A procedure to re-anneal wound toroidal cores to reduce hysteresis and reverse magnetostrictive effects is developed inclusive of casting curvature effects. We investigate re-annealing temperatures between 300 – 470 °C for cores produced from each SA condition. Magnetic core loss, WL, coercivity, Hc, squareness ratio, Kr, and permeability, µr are measured as a function of (stress relief) re-annealing temperature to optimally achieve W1T,400 Hz = 0.51 W/kg, Hc = 2.42 A/m, Kr = 0.22, and µr = 35,300.