Effects of Welding Speeds on Microstructures and Properties of a CoCrNiSi0.2 Medium Entropy Alloy in Electron Beam Weld Joints

As an excellent welding technique, the electron beam welding technology may easily melt certain refractory metals by the high energy generated during the electron beam welding process, thus obtaining well-formed joints with a large depth of fusion and small deformation. The technology has been applied to weld high- or medium-entropy alloys, and obviously improved performances of joints. In this study, the electron beam welding technology was used to weld a medium-entropy CoCrNiSi0.2 alloy. Microstructures of the weld joints and its quasi-static mechanical properties affected by changing the welding speeds were also studied. The research showed no obvious HAZ in the CoCrNiSi0.2 medium entropy alloy, and the weld zone and base metal present a single FCC phase. Furthermore, grain refinement occurs in the weld zone, and the hardness test shows that the hardness of weld zones are generally higher than that of the base metals correspondingly. In contrast to specimens at other welding speeds, the weld joints possess a higher hardness and a maximum tensile strength at 360 mm·min−1, a higher yield strength of the weld joints occured at 720 mm·min−1, and the fracture presents a form of ductile fracture.