Fe–Co–V alloy with improved magnetic properties and high-temperature creep resistance

Abstract

Advanced power systems require soft magnetic materials with a combination of high saturation magnetization and high creep resistance. When the Fe–Co–V alloy laminate is used in a rotor at high temperatures (500–600 °C) coupled with very high rpm, significant creep occurs, which destroys the device integrity. Since grain boundary slide is predominantly responsible for creep deformation in the Fe–Co–V alloy at temperature higher than ∼430 °C, the approach in this study was to reduce the volume fraction of the grain boundaries by making a Fe–Co–V alloy with very large grains. Very large grains, up to mm range, were readily obtained after small cold deformation of ∼3% followed by a normal recrystallization anneal. Fe–Co–V alloy with large grains displays lower coercivity and higher permeability than the commercial Fe–Co–V alloy. Even though its yield strength at 600 °C is lower than the commercial Fe–Co–V, the creep strains of the Fe–Co–V alloy with large grains are only 1/10–1/2 of that for the commercial alloy in the initial and middle periods of the creep test performed at 600 °C under 150 MPa. At the end of the test before the specimens were broken, the Fe–Co–V alloy with large grains showed an accelerated creep strain rate. Better balancing the high-temperature yield strength and creep resistance by creating the optimum grain size would further improve the high-temperature creep resistance of the Fe–Co–V alloy.