Ultrastrong and Ductile Soft Magnetic High-Entropy Alloys via Coherent Ordered Nanoprecipitates

In this project, we aim to realize an optimal balance among the strength, ductility and soft magnetic properties in soft-magnetic high-entropy alloys. To this end, we introduce a high-volume fraction of coherent and ordered nanoprecipitates into the high-entropy alloy matrix. The good combination of strength and ductility derives from massive solid solution, nanoprecipitation and dynamic microband strengthening, yielding mechanical features beyond those reported before for soft magnetic materials. The full coherency of the ordered nanoprecipitates and the matrix contributes significantly to the strength with only a slight increase in coercivity.

Soft magnetic behavior of the HEAs and associated Bloch wall pinning mechanisms. a, Hysteresis loops acquired up to ± 10000 Oe at room temperature. b, Hysteresis loops measured at a fine step size of 2 Oe per second, showing the coercivity of the alloys. c, Growth of the magnetic domain structure in the 3Al-HEA and 7Al-HEA, imaged by Kerr-microscopy, under external magnetic fields. d, Yield tensile strength–coercivity profiles of the investigated soft magnetic HEAs compared to those of other soft magnetic materials, such as NiFe, CoFe, SiFe, Fe and established HEAs. e, Plot of the temperature dependence of the saturation magnetization of the investigated HEAs. — **Soft magnetic behavior of the HEAs and associated Bloch wall pinning mechanisms. a,** Hysteresis loops acquired up to ± 10000 Oe at room temperature. b, Hysteresis loops measured at a fine step size of 2 Oe per second, showing the coercivity of the alloys. c, Growth of the magnetic domain structure in the 3Al-HEA and 7Al-HEA, imaged by Kerr-microscopy, under external magnetic fields. d, Yield tensile strength–coercivity profiles of the investigated soft magnetic HEAs compared to those of other soft magnetic materials, such as NiFe, CoFe, SiFe, Fe and established HEAs. e, Plot of the temperature dependence of the saturation magnetization of the investigated HEAs.

© Max-Planck-Institut für Eisenforschung GmbH

**Soft magnetic behavior of the HEAs and associated Bloch wall pinning mechanisms. a,** Hysteresis loops acquired up to ± 10000 Oe at room temperature. b, Hysteresis loops measured at a fine step size of 2 Oe per second, showing the coercivity of the alloys. c, Growth of the magnetic domain structure in the 3Al-HEA and 7Al-HEA, imaged by Kerr-microscopy, under external magnetic fields. d, Yield tensile strength–coercivity profiles of the investigated soft magnetic HEAs compared to those of other soft magnetic materials, such as NiFe, CoFe, SiFe, Fe and established HEAs. e, Plot of the temperature dependence of the saturation magnetization of the investigated HEAs.

© Max-Planck-Institut für Eisenforschung GmbH

The lack of strength and damage tolerance can limit the applications of conventional soft magnetic materials (SMMs), particularly in mechanically loaded functional devices. Therefore, strengthening and toughening of SMMs is critically important. However, conventional strengthening concepts usually significantly deteriorate soft magnetic properties, due to Bloch wall interactions with the defects used for hardening. Here a novel concept to overcome this dilemma is proposed, by developing bulk SMMs with excellent mechanical and attractive soft magnetic properties through coherent and ordered nanoprecipitates (<15 nm) dispersed homogeneously within a face-centered cubic matrix of a non-equiatomic CoFeNiTaAl high-entropy alloy (HEA). Compared to the alloy in precipitate-free state, the alloy variant with a large volume fraction (>42%) of nanoprecipitates achieves significantly enhanced strength (≈1526 MPa) at good ductility (≈15%), while the coercivity is only marginally increased (<10.7 Oe). The ordered nanoprecipitates and the resulting dynamic microband refinement in the matrix significantly strengthen the HEAs, while full coherency between the nanoprecipitates and the matrix leads at the same time to the desired insignificant pinning of the magnetic domain walls. The findings provide guidance for developing new high-performance materials with an excellent combination of mechanical and soft magnetic properties as needed for the electrification of transport and industry.

Ultrastrong and Ductile Soft Magnetic High-Entropy Alloys via Coherent Ordered Nanoprecipitates

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