Modifications of partial-dislocation-induced defects and strength/ductility enhancement in metastable high entropy alloys through nitrogen doping

We identified the role of partial-dislocation-induced defects (PDIDs) on the nanostructural evolution and the resultant macroscopic deformation in high entropy alloys (HEAs) with their phase stability modified via nitrogen doping. We found that deformation proceeds by the extension and expansion of partial dislocation induced defects (PDIDs) such as extended stacking faults (ESFs), ε-martensite and deformation twin bands in these alloys. Simultaneous strength/ductility enhancement was achieved through modifications of PDIDs and phase stability in Fe50Mn25Cr15Co10 by nitrogen addition. We suggest that the formation of closely spaced ESFs reduce the stacking irregularity and therefore closely spaced ESFs is the energetically stable deformation nanostructure. The formation of closely spaced ESFs has the advantage of the deformation homogeneity because of the more uniform slip strain distribution by smaller shear vector of partial dislocations and the large strain rate sensitivity, leading to the enhanced ductility. This intrinsic nature of overlapped ESFs on the effective reduction of stacking irregularities induces the development of closely spaced ESFs and their transition to ε-martensite band and then to deformation twin band with increasing strain. The modifications of various PDIDs in high entropy alloys with their phase stability modified by nitrogen doping is in good agreement with the prediction of the partial dislocation induced deformation nanostrucure based on the energy criteria under quasi-static deformation proposed in this study.