Development of Fe-Ni based Metal Amorphous Nanocomposites for Electric Motor Applications

2018-10-15T17:40:02Z (GMT) by Natan Aronhime
Metal amorphous nanocomposite (MANC) soft magnetic materials (SMMs) offer a transformational technology to increase efficiency and limit rareearth use for high-power, high- torque-density motors. These materials consist<br>of nanocrystals that are usually ~10 nm in diameter embedded in an amorphous matrix. MANC SMMs can have usable peak inductions comparable to Si-steels<br>with resistivities that allow the high switching frequencies required for high torques. High-frequency switching allows motor size reduction, thereby minimizing volume and weight and can enable new high-efficiency motor designs. In this thesis, Fe-Ni based MANCs are developed along with the<br>analysis on their structural composition, crystallization kinetics, and magnetic properties. A broad Fe-Ni composition space is explored, and an<br>(Fe70Ni30)80Nb4Si2B14 alloy is determined as being of primary interest. Crystallization products are determined to be both bcc and fcc for primary crystallization, while secondary crystallization produces an Cr23B6 phase. TTT<br>diagrams for primary and secondary crystallization are determined for (Fe70Ni30)80Nb4Si2B14 as well as for a Cu-containing alloy. Adding Cu was found to increase the crystallization rate for both primary and secondary<br>crystallization. This is accompanied by a lowering of the Avrami exponent from 2.5 to 1.5. Magnetic properties are explored in depth, and strain-annealing is introduced as an effective method of tuning the permeability. In (Fe70Ni30)80Nb4Si2B14, it increases the permeability from 40,000 to 16,000. Adding dilute amounts of other early transition elements is found to effectively increase the resistivity, although permeability is affected as well. The base alloy has a resistivity of about 135 μΩ-cm, while adding early transition elements can increase it to over 200 μΩ-cm while maintaining reasonable magnetic properties.<br>Toroidal losses are measured and compared to other alloys in the literature and/or commercially available. (Fe70Ni30)80Nb4Si2B14 was found to have losses<br>of 2.1 W/kg and 6.0 W/kg at 1 T, 400 Hz, and 1 T, 1 kHz respectively. These losses are fit to the Steinmetz equation with fitting parameters. These fitting parameters are then used in COMSOL modeling of a switched reluctance motor,<br>and are compared to a motor comprised of a 3.5%Si-steel. <br>