Abstract
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 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 (>6.5wt.%Si) which are otherwise unprocessed through conventional thermo-mechanical 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-lamination during 3D printing of 6.5wt.%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 6.5wt.%Si steel powder was coated with (Mn0.8,Zn0.2)Fe2O4 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 results in a thicker and non-uniform insulating coating layer during in-situ lamination; therefore, thinner layer thickness was recommended. Finally, it is demonstrated that (Mn0.8,Zn0.2)Fe2O4 laminated samples possess superior magnetic properties compared to SiO2 laminated samples.
Due to increasing levels of residual stress in the structure during LPBF 3D printing; and considering that these stresses can deteriorate the magnetic performance parts in the form of increased hysteresis losses, Neutron Diffraction experiment was conducted on the manufactured parts printed with bidirectional and island scan strategies. The results proved that bidirectional scan strategy leads to lower residual stress compared to island. It was evident from the results
that majority of the stress in the structure was rooted in each cell in the form of lattice parameter-related strain and not in the inter-plane distance known as the Dspacing-related residual strain. Through this project, the results pointed us to the optimum 3D printing conditions for the Fe-6.5Si for normal conditions (30 µm layer thickness and 250 J/m laser energy input) operated with bidirectional scan strategy to the max. relative density of 99.15%. By conducting the in situ-lamination, it was concluded that while this process, in general, lead to a drop in relative density, magnetic saturation, and permeability of the sample in comparison with pure Fe-6.5wt%Si printing, but on the other hand, the iron-ceramic layers orderly lamination happened successfully and due to this effect, the magnetic loss of the samples dropped to results even below to that of conventionally manufactured Fe-3.5wt.%Si NOES sheets magnetic loss values. While, the silica-lamination process produced parts with better layered structure, the magnetic loss component of the ferrite-laminated samples was lower and it yielded better magnetic loss result (0.95 W/kg for best ferrite-laminated against1.08 W/kg for the best silica-laminated sample).
Finally, by envisioning the idea of metal-ceramic phase separation and investigating LPBF 3D printing of the coated Fe-6.5wt.%Si powders, in situ-laminated parts were manufactured. By subsequent evaluation of the influencing parameters, the optimum printing conditions for this new method are presented. It was concluded in this project that this method is worth further investigation and in situ-lamination of ceramic layers in Fe-6.5wt%Si structure is possible.
The residual strain results demonstrated that the Island scan strategy introduces much less residual stress in to the structure of the 3D printed part compared to bidirectional scan strategy. Furthermore, the analysis of our work presented new insights on additive manufacturing of near-net shaped NOES parts. We measured and analyzed the evolution of residual stress that builds up in the microstructure during annealing of the 3D printed part and explained the stress relief and recovery stages of heat treatment of the 3D printed Fe-6.5wt.%Si Electric steel.
On the significance of this feasibility study, designing new competitive alloys with a focus on 6.5wt% Si steels was demonstrated. Here, the correlations between AM processing parameters with microstructure and crystallographic texture (local and global) evolution in NOES variants were established. Importantly, an alternative fabrication method for optimization of NOES
components via metal selective laser melting (SLM) 3D printing using in situ lamination was developed. Finally, fully laminated layer-by-layer high-silicon steel parts with optimized microstructures and magnetic properties via SLM AM technology using a novel “in situ building and coating” technique were successfully produced. This novel 3D printing strategy presented here, may be up-scaled to full-scale e-machine components. Ultimately, through extensive alloy design and in situ alloying trials, the optimum chemical composition of NOES can be recommended for the AM routes with benchmarking obtained characteristics compared to conventional electrical steel processing routes.
| Date of Award | 16 Mar 2026 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | Soran Birosca (Supervisor) & Jurgita Zekonyte (Supervisor) |
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