In situ synthesis of N-containing CoCrFeNi high entropy alloys with enhanced properties fabricated by selective laser melting

Although there have been extensive studies on CoCrFeNi high entropy alloys (HEAs), they are still far from industrial applications due to their inferior strength. Based on the approach of interstitial atom strengthening which has been shown to be one of the effective ways to modify the properties of metallic materials, a series of (CoCrFeNi)_100-xN_x (x = 0, 0.25 and 0.50 at. %) HEAs were prepared in this study by selective laser melting (SLM). It was found that nitrogen addition in CoCrFeNi HEA can slightly refine the microstructure but did not change the preferred orientations after SLM. By increasing the nitrogen content in the matrix, the strength increases while the ductility is reduced. Also, the addition of nitrogen in CoCrFeNi HEA can decrease the stacking fault probability, leading to the increased stacking fault energy (SFE) in N-doped CoCrFeNi HEA. The increased strength in N-doped CoCrFeNi HEA samples mainly attributes to the solid solution strengthening of nitrogen, whereas the ductility loss results from the impediment on the formation of deformed twins induced by increased SFE. These results can provide a new strategy for designing high-strength N-doped HEAs.