Nano-scale solute heterogeneities in the ultrastrong selectively laser melted carbon-doped CoCrFeMnNi alloy

Rapid melting and solidification cycle during additive manufacturing provides a non-equilibrium environment that generates a large amount of internal defects, including dislocations, precipitations, and solute heterogeneity. These internal defects not only enhance the strength of materials by interacting with mobile dislocations but also reduce ductility due to coherency loss. To minimize the coherency loss from internal defects, defect size control in the additively manufactured products becomes an important issue. In this work, the high strength-ductility combination of additively manufactured carbon-doped CoCrFeMnNi is achieved by designing nano-scale solute heterogeneities in the matrix. The CoCrFe-MnNi solid-liquid two-phase region and interstitial carbon promote Mn and Ni segregation at cell networks and nano-sized precipitations, respectively. Laser scan speed during additive manufacturing determines the solidification rate that controls the solute cell network size. The MnNi co-segregated solute network not only interacts with dislocations but also induces strong back-stress hardening that contributes to achieving similar to 900 MPa yield strength with similar to 30% elongation which combination is significantly larger than the recent additively manufactured high-entropy alloys. This work demonstrates the importance of heterogeneity control in the additively manufactured materials to gain outstanding mechanical properties.