Forging strength-ductility unity in a high entropy steel

Abstract

Fe72.4Co13.9Cr10.4Mn2.7B0.34 high entropy steel was prepared by magnetron sputtering. The alloy exhibits a high yield strength of 2.92 ± 0.36 GPa while achieving appreciable plasticity of 13.7 ± 1.9% at the ultimate compressive strength (3.37 ± 0.36 GPa). The distribution of iron and chromium shows an unusual, characteristic spinodal-like pattern at the nanometer scale, where compositions of Fe and Cr show strong anticorrelation and vary by as much as 20 at.%. The high strength is largely attributable to the compositional modulations, combined with fine grains with body-centered cubic (BCC) crystal structure, as well as grain boundary segregation of interstitial boron. The impressive plasticity is accommodated by the formation and operation of multiplanar, multicharacter dislocation slips, mediated by coherent interfaces, and controlled by shear bandings. The excellent strength–ductility combination is thus enabled by a range of distinctive strengthening mechanisms, rendering the new alloy a potential candidate for safety-critical, load-bearing structural applications.