Additive Manufacturing of layered metal composites with soft magnetic properties

Abstract

There is a great demand for more efficient electric motors, with less energy consumption and lower cost. Generally, the core of the electric motor is composed of thin sheets of Fe-Si alloy stacked alternately with layers of electrically insulating material, which is a strategy that aims the reduction of eddy current losses. The addition of 6.5%wt. of silicon in this alloy promotes optimized electrical and magnetic properties, but it is not produced through conventional techniques, once this Si content allows the formation of B2 and D03 phases, which promotes a brittle behavior of the material. Thus, the Laser Powder Bed Fusion (L-PBF), an Additive Manufacturing (MA) technique, emerges as an alternative route for processing these alloys, because it involves high cooling rates, which makes it difficult to form these brittle phases. However, even though these brittle phases are formed, they will not be a restriction for L-PBF. Furthermore, this process allows to obtain a structure with alternated layers of the Fe-6.5Si (%wt.) and material with high electrical resistivity, similar to the layered structure of transformers, which reduces eddy current losses, but through the L-PBF technique, thinner layers could be processed, which will further reduce these losses. Previous studies in processing Fe-Si alloy with high Si content by L-PBF showed promising results, although only simple geometries were fabricated. However, further studies are still needed for a better understanding of the relationship between process/microstructure/properties, to improve the quality of processed parts, to investigate microstructure in more detail, and to suggest new processing strategies, for example, obtaining layered composites, using remelting and heating the substrate. Therefore, this project aims to process the Fe-6.5Si (%wt.) individually and also in layered composites of Fe-6.5Si (%wt.) and insulating electric material (or low electric conductivity) (e.g., silicon, silica, and ferrosilicon) both conditions by L-PBF. Then, evaluate the microstructure and phase formation using x-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy, the mechanical properties through Vickers hardness and compression tests and magnetic properties through obtaining the B-H curve and measurements of magnetostriction and magnetoresistance. Finally, a correlation between processing/microstructure/properties will be investigated and the feasibility of this alternative route will be discussed.