Compositionally complex and high-entropy alloys offer the advantage of access to practically infinite composition ranges for tuning thermodynamic and kinetic features, and with that, novel mechanisms and material properties [1]. Research has so far focused mainly on microstructures and mechanical properties, but attention shifts recently towards functional properties, opening opportunities for discovering new mechanisms and properties [2,3]. This trend is driven by the fact that the massive solid solution state of these materials allows to mix multiple elements in high fractions, thereby creating complex electronic and magnetic structures and to break the crystalline symmetry at atomic scale at enhanced interstitial solubility. These inherent features of high entropy alloys facilitate the design of materials with interesting magnetic, electronic, catalytic, resistive, corrosion, hydrogen storage and invar features.

In this presentation we focus on soft magnetic and invar high entropy materials, but some other applications are also discussed. Soft magnetic materials serve in electrical applications and sustainable energy supply, allowing magnetic flux variation in response to changes in applied magnetic field, at low energy loss. The electrification of transport and manufacturing leads to an increase in energy consumption due to hysteresis losses. Therefore, minimizing coercivity, which scales these losses, is crucial. Yet, meeting this target alone is not enough: soft magnetic alloys in electrical engines must also withstand mechanical loads, i.e., they need high strength and ductility. This is a fundamental design challenge, as most methods that enhance strength introduce stress fields that can pin magnetic domains, thus increasing coercivity and hysteretic losses. We present an approach to overcome this dilemma. We have designed a Fe-Co-Ni-Ta-Al multicomponent alloy with ferromagnetic matrix and paramagnetic coherent nanoparticles. They impede dislocation motion, enhancing strength and ductility. Their small size, low coherency stress and small magnetostatic energy create an interaction volume below the magnetic domain wall width, leading to minimal domain wall pinning, thus maintaining the soft magnetic properties. The alloy has a tensile strength of 1336 MPa at 54% tensile elongation, extremely low coercivity of 78 A/m (<1 Oe), moderate saturation magnetization of 100 A·m2/kg, and high electrical resistivity of 103 μΩ·cm. A related alloy design approach will be presented for invar materials.

1. George, E. P., Raabe, D. & Ritchie, R. O. High-entropy alloys. Nature Reviews Materials 4, 515–534 (2019).

2. Han, L. et al. A mechanically strong and ductile soft magnet with extremely low coercivity. Nature 608, (2022).

3. Rao, Z. et al. Machine learning-enabled high-entropy alloy discovery. Science (80). 85, 78–85 (2022).