High strength-ductility synergy in a laser welded dissimilar joint of CrCoNi medium-entropy alloy and stainless steel

CrCoNi medium-entropy alloy (MEA) and its welded joints has great potential applications in engineering structures since they present superior ultimate tensile strength (UTS) and ductility. However, the mechanical performance of the welded joints of CrCoNi and traditional metal alloys remains mysterious. Here, we applied laser welding to join CrCoNi and stainless steel (SS) 301L to achieve a dissimilar MEA-SS301L joint and investigated its microstructure evolution and mechanical properties. The fusion zone becomes a face-centered cubic single-phase non-equiatomic FeCrCoNi high-entropy alloy (HEA). Its UTS and ductility is 482 MPa and 46% at 300K, respectively; and is respectively enhanced to 791 MPa and 59% at 77K. Our dissimilar joint displays a strength-ductility synergy that exceeds that of all other dissimilar HEA joints and most similar HEA joints. Electron backscattered diffraction, transmission electron microscopy and molecular dynamics simulation uncover that extensive dislocation activities, stacking fault networks, deformation twins, and interactivity between dislocations and twin boundaries are the origin of this high strength-ductility synergy in our joint.