Laser weldability and interface microstructure of CoCrNi-based medium-entropy alloy to Inconel 718 superalloy

CrCoNi medium-entropy alloy (MEA) and Inconel 718 superalloy were welded together using pulsed lasers with different powers of 300 W and 400 W. The specific phase composition and microstructural characteristics of the welded joints were systematically revealed using a combination of XRD, BSEI, EDS, and EBSD methods. The results show that the welded joints are mainly composed of a fusion zone (FZ), and the heat-affected zone is not obvious. FZ is a non-equiatomic medium-entropy alloy with a face-centered cubic structure and a relatively complex composition. FZ has a typical V shape, with equiaxed grains in the center and columnar grains in the area adjacent to the base materials. Nano-sized Laves phases (Cr2Nb) precipitate within FZ adjacent to the interface between FZ and base materials. As the laser power increases from 300 W to 400 W, the particles transform from a needle-rod shape to a spherical shape. The Microhardness of FZ is significantly higher than that of the base materials, owing to the higher critical shear stress required for dislocation slip of FZ with new compositions and precipitation-hardening caused by the Laves phases within FZ.