Interplay between microstructure and deformation behavior of a laser-welded CoCrFeNi high entropy alloy

The emergence of high entropy alloys (HEAs) has drawn extensive attention due to their special alloy design concept and excellent properties. To pave the way for their engineering applications, a prototype CoCrFeNi HEA was processed through laser welding. Sound welds without cracking, pores, lack of penetration, or precipitates were obtained. The microstructure and the deformation behavior of the weld were investigated. The fusion zone (FZ) of the weld exhibits coarse columnar grains and a relatively higher hardness than that of the base metal (BM) due to the residual stress. Although the anisotropic columnar grains in the FZ lead to the loss of ductility, the weld shows a high joint efficiency and a comparable ductility relative to the BM. The deformation during tension is facilitated by both the mechanical twins and dislocation motion. The mechanical twins play a more significant role in the FZ while the dislocation motion dominates the deformation in the BM.