The Si-doped BCC-based high-entropy alloy to overcome soft magnetic–mechanical properties trade-off via coherent B2 nanoprecipitates

The trade-off between magnetic property and mechanical property usually occurs in traditional soft magnetic materials (SMMs) because the strengthening strategy (e.g. precipitation hardening) can worsen soft magnetic properties through the hindrance of magnetic domain wall motion. This dilemma is overcome in current work by developing the FeCoNiAlSi_0.01 (Fe_24.94Co_24.94Ni_24.94Al_24.94Si_0.24 in at.%) high-entropy alloy (HEA) (termed as Si0.24 HEA) with excellent soft magnetic performance and attractive mechanical property through coherent B2 nanoprecipitates (6 nm) distributed in body-centered-cubic (BCC) matrix. The atom probe tomography (APT) result shows that the B2 nanoprecipitates have similar composition to the BCC matrix. The Si0.24 HEA shows small width of domain branching and low anisotropy constant leading to the optimum alternating current (AC) soft magnetic properties. The respective total loss (AC P_s), the coercivity (AC H_c), and the eddy current loss (P_e) at 950 Hz of the Si0.24 HEA are 21.20 W/kg, 230 A/m, and 16.25 W/kg, which is reduced by 45 %, 44 %, and 48 % compared with the FeCoNiAl (Si-free HEA). The Si0.24 HEA shows good mechanical property with the yield strength of 987 MPa and engineering strain of 30 %, which is 12 % and 1.3 times higher than that of the Si-free HEA. Moreover, the current studied HEAs exhibit high saturation magnetization (M_s = 108–115 Am²/kg) and Curie temperature (T_C = 1053–1097 K, larger than T_C of Fe (1043 K)), which indicates their perspective high-temperature applications as novel SMMs for the need of modern power electronics and electrical machines.