A. Z. Macknojia, J. V. Tran, M. P. McKinstry, J. Galindo, Y. Jin, S. Dowden, S. M. Patil, M. V. Pantawane, K.V. Mani Krishna, R. Banerjee, S. S. Joshi, N.B. Dahotre
University of North Texas,
United States
Keywords: Additive Manufacturing, Electrical Steels, Toroidal Cores, Laser Powder Bed Fusion
Summary:
In this work, we report additive manufacturing of Fe-6.5wt% Si electrical steel with greater than 99% relative density. The higher Si content compared to conventional ~3.5 wt% results in superior soft magnetic performance yet imposes multiple hurdles during manufacturing due to cracking tendency. Laser additive manufacturing provides a feasible way of fabrication along with possibilities of implementing disruptive design methodologies. In the current work, after careful optimization of the laser powder bed fusion process, we printed 3 design varieties of toroidal transformer cores with varying cross-sectional area. The as printed material exhibited single phase columnar microstructure. The printed cores were subjected to stress relief heat treatment at 1150oC for 1h in Ar atmosphere. The heat treatment resulted in massive grain growth with sizes in the millimeter regime. Concurrently, ordered B2/DO3 evolved in the α-Fe matrix on a nanometer length scale. The magnetic performance of the printed material was evaluated using vibrating sample magnetometer, whereas the printed cores were examined using in-house built AC testing setup. Heat treated soft magnetic toroidal core with the least cross-sectional area performed better compared to other designs exhibiting the lowest core losses and coercivity. As a note, a part of this work was performed as a senior design project in Department of Materials Science and Engineering, University of North Texas in Fall 2021 and Spring 2022. The work was published in the journal Materials & Design in 2024 (Paper DOI: https://doi.org/10.1016/j.matdes.2024.112883).