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NANO2021-Nanoteknologi og nye materiale

Additively manufactured magnetic high entropy alloys for renewable electricity

Alternative title: Magnetiske høyentropilegeringer for fornybar elektrisitet produsert ved additive metoder

Awarded: NOK 10.0 mill.

Soft magnets are standard components in electromagnetic generators (such as wind turbines) and electric motors (such as those in electric cars) as well as intelligent systems consisting of sensors and actuators. These are important for the digitalisation of our society and industry as well as the development of smart cities. They are expected to be transformation drivers towards a more sustainable circular economy and a globally renewable energy system that supports economic and social development. However, their functional and mechanical properties can be significantly improved. In "Magnificent" we produced new soft magnetic materials, based on high entropy alloys (HEAs), with improved magnetic properties. HEAs consisting of at least 5 different elements coexisting in atomically disordered structures are little explored. Variable elemental compositions can lead to unexpected and promising properties and functionalities as compared to existing soft magnets. We used digitized and high throughput approaches in material selection, synthesis, and characterisation as well as Additive Manufacturing. Samples with various compositions based on the FeCoNiMnAl, FeCoNiMnGe and FeCrNiMnGe systems have been produced with Laser Metal Deposition (LMD). Characterization methods at the micro and nano level are critical for the material development. These methods have provided a quick assessment for the selection of the most suitable materials with respect to their magnetic and structural performance. We started with the FeCoNiMnAl material system and used magneto-optical imaging as well as scanning electron microscopy with X-ray analysis for a quick assessment of the magnetic behaviour and microstructure. More detailed analysis has been performed using high-resolution electron microscopy, electron and X-ray diffraction methods and magnetic force microscopy (MFM). We have focus on correlated methods where local structure and chemistry are linked to the magnetic properties. In parallel with the experimental activities, we have performed theoretical modelling to connect the measured magnetic properties with the composition and microstructure of the samples. Three representative compositions of the FeCoNiMnAl system in the as-printed and heat-treated state have been extensively studied. We focused on the FeCoNiMnAl system produced with both LMD and a Melt Spinning process performed by our international partners in Slovak Academy of Sciences. In addition, Kerr Microscopy was conducted by our international partners at the Manchester University in order to measure the magnetic hysteresis loops in selected areas of the LMD samples, allowing estimates of the local coercivity to be made. Lorentz Microscopy is used to investigate the magnetic performance in selected samples and establish a correlation between magnetic domain walls movements and defects in the alloys. We achieved relatively early in the project (in 2021) our goal to produce HEAs with soft magnetic properties equal or better to the state of the art and we confirmed reliability in 2022. We devoted most of 2023 in assessing mechanical stability of the developed materials via combining tensile testing with µ-CT and SEM. The material structure is very complex and further basic research is needed for a deeper insight and understanding. This will delay the project outcomes reaching higher TRL (5-6), but the recent outstanding results make it worth it. In 2023 SINTEF utilised the methodology developed in Magnificent to offer industrial services on soft magnet development (SOFTMAGNETICS) to one of the projects industrial advisors (Elkem). Utilising the competence and methodology developed in Magnificent, SINTEF (and Elkem) also participated in an MERANET proposal (HEAMAG) whilst SINTEF coordinated an EU Horizon Europe proposal (MagNEO), with UiO being amongst the partners. In line with RRI principles, we establish health and safety protocols for raw materials and products in accordance with life cycle considerations in existing national and European directives. We also assessed the biocompatibility/cytotoxicity of the developed materials. Although further research will be more conclusive, it seems that elemental powders may represent higher hazard for human health than the alloyed materials. This suggests that health and safety measures should be stricter when elementary powders are used in feedstock preparation and/or additive manufacturing than when alloyed powders are utilized in AM processing (e.g. LPBF) or HEA recycling. "Magnificent" held an open dialogue with various stakeholders through seminars, conferences, workshops and interviews in national media. During 2022-23, six oral presentations were given at conferences (2 digital and 4 physical), 3 interviews (NRK P2) and 2 peer reviewed articles were published. Two additional manuscripts are in preparation. A workshop on HEAs is scheduled for December 2023

Within Magnificent, soft magnetic materials based on HEAs were successfully produced via additive manufacturing. The results are significant in scientific and societal terms. It is the first time that FeCoNi(AlMn)x HEAs produced via LMD, have been studied in terms of their magnetic properties. A detailed nanoscale investigation of the produced alloys, by combining atomic scale imaging and spectroscopies along with DFT calculations, was introduced also for the first time to the scientific society. This investigation revealed the coexistence of two ordered structures, which was never reported before for FeCoNi(AlMn)x HEAs. Thorough investigations of the magnetic properties of the aforementioned systems, (e.g., saturation magnetization and coercivity) associated with topography and magnetic domain structures, are also valuable technical insights to the research field. The favourable soft magnetic properties of the FeCoNiAlMn HEAs, is already a good technological basis. Further compositional and microstructural tuning of these HEAs will make them as suitable materials for electromechanical devices important for the green transition and sustainable growth. Additive manufacturing processing via LMD proved to be an attractive high throughput method for material screening. The preliminary cytotoxity assessment suggested that increased focus on HSE should be given in feedstock production and/or additive manufacturing practices when handling elemental powders. The HSE risk associated with pulverized HEAs is reduced and this is significant for the recycling of HEA-based magnets considering the criticality issues of metals like Co which necessitate material reuse/recycling. The magnetic material development methodology established in Magnificent is based on material screening via quantum mechanical modelling, high throughput synthesis and high throughput characterization. This can be further enriched with machine learning assisting quantum mechanical modelling for screening hundreds of thousands candidate alloy compositions, micromagnetic, microstructural and thermodynamic modelling coupled with various high throughput synthesis, characterization and testing. Variations of this approach have been already employed in a direct industrial project between SINTEF and Elkem (one of project's industrial advisors) where soft magnetic materials were selected via DFT computation of magnetic anisotropy energy and total magnetization, magnetometry characterization, arc-plasma synthesis, CALPHAD computations, and microstructural characterization. It was also utilised in two international proposals (M-ERANET, Horizon Europe) with consortia consisting of magnet producers, magnet end-users from the renewable energy and automotive sectors, additive manufacturing and material research specialists.

Conversion between movement and electricity has become a critical part of the global renewable energy system, with wind mills and electric vehicles as prominent examples. Soft magnetic materials are in the heart of electromagnetic generators and electric motors, but there is still much to desire from their functional and mechanical properties. Non-ideal magnetic properties may lead to fatigue and loss of generation efficiency or even mechanical failure. The present project aims to introduce a new generation of materials for soft magnets: high entropy alloys (HEA) generated with additive manufacturing (AM). HEA have demonstrated surprising combinations of properties in various fields, and a few recent works have indicated that this may also be the case for soft magnetic materials. Furthermore, the rich compositional freedom in these materials implies huge possibilities of tailoring functional and mechanical properties to specific applications. The goal of Magnificent is to identify novel HEA-based soft magnets with superior magnetic properties that exhibit significantly reduced losses and fatigue compared to the current state-of-the-art. At the same time, processing by AM facilitates net shape construction of complex geometries and potentially low-emission, distributed production. The project constitutes a complete suite of synthesis and characterization tools, facilitating screening of a large number of potential candidate materials in the search of optimal compositions. In addition, modelling efforts will contribute to the screening by suggesting new materials as well as rationalizing experimental results. But first and foremost, the project partners have endorsed the principles of responsible research and innovation, with specific actions on health, environment, and safety, proactive ethical principles, and a comprehensive risk assessment.

Publications from Cristin

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NANO2021-Nanoteknologi og nye materiale