Computational Design and Development of Low Cost, High Strength, Low Loss Soft Magnetic Materials for Traction Drive Motor Applications

QuesTek proposes to apply its Materials By Design approach to design a high performance, low cost soft magnetic material capable of achieving significant cost savings to approach the DOE motor cost target of $4.7/kW in 2020. In order to meet the ambitious motor targets, traction motors in electric vehicles (EV) must become even more compact, light-weight, and highly efficient. For a compact design, EV motors must operate at high speed, which in turn places the rotor under high mechanical stresses. Materials used for rotor cores thus require high strength in order to withstand the centrifugal forces generated during high speed revolution. Additionally, motors operating at high frequencies must demonstrate low core losses as well as high strength because core losses increase exponentially with increasing frequency. The conflicting microstructures required for high strength and low electrical losses makes the simultaneous achievement of high strength, low loss soft magnetic materials very difficult. The idea of this Phase I is to design and develop a high strength, low cost soft magnetic Fe-Si alloy by utilizing strengthening precipitates that are designed to be small enough not to significantly impede the motion of the domain walls, but of the desired length scale to impede dislocation motion to increase mechanical strength. A material that could satisfy both the high yield strength requirements for the rotor of higher speed EV motors and the low core losses, which are important for the stator during high frequency operation of the motor, would lead to significant cost savings to help achieve the DOE motor cost targets. One of the critical limitations in the design of the high speed interior permanent magnet (IPM) motors used in current hybrid electric vehicles is the mechanical strength of the rotor. Thus, there is a pressing need for a high strength, low cost, low core loss, and easily processable soft magnetic alloy for use in the rotor core of EV electric motors. The design of a high performance electrical steel sheet for the core of the motor plays a large role in the traction performance and fuel efficiency of an EV. Electrical steels used in rotor cores require high strength without sacrificing magnetic properties to contribute significant cost savings to meet the DOE motor cost targets. QuesTek will utilize its systematic and integrated computational materials engineering (ICME) approach to design and develop a low cost, high strength, low core loss soft magnetic alloy that will enable a more compact, lighter motor for significant cost savings. QuesTeks proposed Fe-Si soft magnetic alloy material development efforts will leverage our previous development efforts on Fe-Co soft magnetic alloys. Our previous experience designing precipitation strengthened Fe-Co soft magnetic materials and mapping out the processing steps to form thin-rolled sheets, which are assembled and stacked into laminates will be extremely valuable in the development of high strength, low loss Fe-Si alloys. With this background, QuesTek will explore alloy design concepts that may focus on incorporating nano-scale precipitates ( & lt;10 nm diameter), maximizing resistivity, controlling grain size, and controlling grain texture. QuesTek will utilize its expertise in computational materials design and in-house models to design both the alloy composition and processing steps to create the structure that delivers the desired mechanical and magnetic properties. Utilizing a computational materials design approach, QuesTek is prepared to design and develop low cost, high strength, low core loss soft magnetic core materials at the prototype scale that show promise to provide cost savings in traction drive motor applications.