In-Situ Coating of High-Silicon Electrical Steel using Laser Powder Bed Fusion

Theorists, experimentalists, and industrialists have all acknowledged that further improvements of electrical steel (ES) magnetic properties using the current chemical composition (< 3.2 wt% Si) and conventional manufacturing routes remains extremely challenging. However, to enable the prevailing vehicle and aircraft electrifications revolution, further developments in materials and electrical machine designs are required. Today, additive manufacturing (AM) unlocks opportunities to produce steels with high Si content (> 6.5 wt% Si) which are otherwise unprocessed through conventional thermomechanical route due to the brittle nature of high-silicon alloys. However, challenges around their inferior magnetic properties remain to be overcome. Here, a novel in-situ coating, i.e., lamination during 3D printing of 6.5%Si steel is demonstrated. The in-situ steel lamination via “Successive Building and Coating” approach was conducted through a combination of powder coating and printing strategies that enabled a production of a near net shape laminated high Si electrical steel. The Ar atomised 6.5 wt% Si steel powder was coated with (Mn,Zn) ferrite via sol-gel auto-combustion method and with SiO2 via sol-gel method for comparison purposes. The coated powder was fused in the ProX300 Laser Powder Bed Fusion to build successive and insulated layer-by-layer structure of high Si steel parts. The in-situ lamination was successfully achieved; however, the coating layers were non-uniform and occasionally discontinuous. It was concluded that the distance between the coating layers varies and cannot be correlated to powder thickness layer. It is demonstrated that a higher powder layer thickness (L) results in a thicker and non-uniform insulating coat layer during in-situ lamination; therefore, a smaller L was recommended. Furthermore, the successive layer-by-layer formation of matrix-coat perpendicular to building direction indicated that Buoyancy effect was affected by other factors that directly influence the-2-metallic-ceramic melt pool dynamics. Finally, it is demonstrated that ferrimagnetic (Mn0.8,Zn0.2)Fe2O4 laminated samples possess superior magnetic properties compared to amorphous SiO2 laminated samples.