Soft magnetic alloys are utilized in electromagnetic devices, such as motors, transformers, and switches because they exhibit high magnetic permeability/saturation induction and low coercivity/energy loss. However, they are limited by poor mechanical properties except in the nanocrystalline grain size regime, which is difficult to access via conventional manufacturing processes. An Fe-Si-B-Nb-Cu alloy produced under the tradenames Finemet, Vitroperm, Metglas FT3, etc., is fabricated by melt spinning thin amorphous foils, which are subsequently annealed to produce a nanocrystalline microstructure. With this process, nanocrystalline microstructures are not possible for larger product forms. Additive manufacturing (AM) has emerged as a technique for enabling rapid solidification of these alloys, with the intent of achieving the same amorphous/nanocrystalline microstructures in larger geometries.
In this study, laser directed energy deposition (L-DED) was used to produce bulk forms of an Fe-Si-B-Nb-Cu soft magnetic alloy. Pre-alloyed powder feedstock in the form of micron-scale flakes was ball milled from nanocrystalline ribbons. Compact metallurgical specimens were fabricated in thin wall and cube geometries with several different laser power processing conditions to study the effects of processing conditions on microstructure and properties. Different build plates were used to determine the influence of alloy dilution on the resultant microstructure, mechanical and functional properties. To facilitate the use of a matching composition build plate, which is ideal for preventing undesired alloy dilution, a novel technique of stacking several nanocrystalline foils together was developed. Scanning electron microscopy (SEM) with wavelength dispersive spectroscopy (WDS) and electron backscattered diffraction (EBSD) was used for advanced characterization of the microstructural constituents. The mechanical properties were assessed with micro- and nanoindentation. The magnetic behavior was determined using vibrating-sample magnetometry. The results obtained for alloy microstructure, mechanical properties, and magnetic properties were compared to conventionally processed nanocrystalline ribbons, and the significance of these properties achieved with metal AM will be discussed in the context of achieving higher-efficiency electromagnetic components.
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.