Probing the structural evolution and its impact on magnetic properties of FeCoNi(AlMn)x high-entropy alloy at the nanoscale

We report the first nanoscale investigation of FeCoNi(AlMn)x high-entropy alloys (HEAs) processed by laser metal deposition. The structural evolution alloy upon chemical composition variation (0.2 ? x 1.5) was investigated combining imaging and spectroscopies in (scanning) transmission electron microscopy (S)TEM with density functional theory (DFT). A gradual change from a face-centered cubic (FCC) towards an ordered full-Heusler (L21) phase increasing Al Mn contents observed. Direct atomic-scale calculations revealed interplay between B2 L21 structures for = 1.5, wherein latter, occupy two different Wyckoff sites. By decreasing x, FCC dominates exhibiting intense separation tendency, ordering phenomena, nano-precipitation. Although not chemically discriminated, plasmon-peak splitting low-loss energy loss spectra presence valence densities within phase. Lorentz TEM showed that nano-precipitates nano-sized grains structure based on tripled unit cell are pinning-sites magnetic domain walls dislocations. All compositions exhibited soft-magnetic behavior coercivity (Hc) values< 1000 A/m. FeCoNi(AlMn)1.5 L21/B2 nanostructure highest magnetization (Ms) relatively low Hc, attributed to large moment synergistic effect Mn-Al according DFT, whilst does impose negative effect. Phase trends seem decrease Ms however, overall impact is intense, opening up new avenues tuning FeCoNiAlMn properties through chemically-designed decomposition regimes.