Microstructure and Mechanical Properties of Fiber Laser Welded Joints of CoCrFeNiCu High-Entropy Alloy and 304 Stainless Steel

To expand the engineering application of high-entropy alloys, the CoCrFeNiCu high-entropy alloy and 304 stainless steel were joined by fiber laser welding, and the microstructure and mechanical properties were investigated. An "hourglass-shaped" welded joint without any visible defects was successfully obtained, and four distinct zones were formed in the welded joint: the fusion zone, partial melting zone, the heat-affected zone and base metal. The fusion zone exhibits a refine equiaxed grains and columnar grains with the same crystalline structure to that of the CoCrFeNiCu high-entropy alloy base metal. The content of Cu element was significant decreased and uniform distribution in the fusion zone. Furthermore, the fraction of the low-angle grain boundaries increased in the fusion zone. The hardness in the fusion zone is significant increase compared with CoCrFeNiCu high-entropy alloy, while is lower than that of stainless steel. The welded joint fractured at the CoCrFeNiCu high-entropy alloy base metal, and the fracture mechanism is ductile fracture. The ultimate tensile strength and ductility were 425 MPa and 32.5%, respectively. The result shown that the strength in the fusion zone is higher than that of CoCrFeNiCu high-entropy alloy base metal. The distributed homogeneously of Cu element, grain refinement and changes in misorientation angles are the origin of this joint obtained high strength.