Directed energy deposition of Fe-5.5Si electrical steel with Ti additions for balanced magnetic and mechanical performance

Abstract

High-silicon electrical steels show excellent soft magnetic properties, but their widespread employment has been limited due to their inherently poor workability. To overcome this limitation, additive manufacturing methods are being explored. In this study, high-silicon electrical steels with Ti additions showing improved core loss and yield strength have been fabricated by directed energy deposition. Increasing the Ti content from 0 to 1.5, 3, and 4.5 wt% led to grain size reduction and columnar-to-equiaxed transition, facilitated by enhanced constitutional supercooling and the presence of TiO inoculant particles. The formation of precipitates due to Ti addition was observed, where increasing Ti contents resulted in coarsening of the precipitates. The reduced grain size and formation of precipitates caused a slight reduction of the total core loss at a frequency of 1000 Hz for 3 wt% Ti, due to a decreased eddy current loss even with an increased hysteresis and anomalous loss. Grain size reduction also significantly increased the yield strength of Ti-added samples via the Hall-Petch effect. However, an increased Ti content coarsened the precipitates, which weakened the precipitation strengthening effect. Overall, Fe-5.5 wt% Si with 3 wt% Ti addition exhibited the lowest total core loss at 1000 Hz and the highest strength, representing an optimized alloy modification for high-frequency applications like high-speed electric motors.