The influence of nickel on the magnetic and mechanical properties of Co-Fe-V alloy

The magnetic and mechanical properties of a new Co-Fe-V-Ni alloy have been determined over a range of heat treating temperatures and compared with those of conventional Co-Fe-V alloy. To simulate operating conditions within an aircraft generator, properties were measured under varying degrees of stress (±300 MPa) and temperature (-50 to +350°C). The material displayed excellent mechanical properties, maximum yield strength (600°C anneal) and elongation (800°C anneal) being 1550 MPa and 20 percent, respectively. In the stress-free condition the material possesses high coercivity and power loss (minimum value 12 A/cm and 205 W/kg at 1.8 T, 400 Hz) low resistivity (30 μΩcm maximum), and a lower saturation magnetization (2.23 T) compared to Co-Fe-V alloy (2.35 T). A 730°C anneal induces optimum magnetic properties. Variations in properties with heat-treating temperature are gradual, the addition of nickel having eliminated the sharp change in properties seen in Co-Fe-V alloy at 700°C. Magnetic properties are influenced by externally applied mechanical stress. Tensile stress improved the dc characteristic, and the material requires 67 percent less field to magnetize to 2 T than 650°C treated Co-Fe-V, but 133 percent more than the latter treated at 750°C while under the same stress conditions. Optimum ambient temperature is approximately 200°C with both the dc and ac magnetic properties deteriorating above and below this temperature. Provided the dc magnetic properties of this alloy are acceptable to generator designers, its superior mechanical properties over conventional Co-Fe-V alloy make it a strong contender for rotor application.