Microstructure and mechanical properties of electron beam welded joints of GH3128 and CoCrFeNi high-entropy alloy

This study addresses the research gap in the field of fusion welding for high-entropy alloys and high-temperature alloys. The microstructure and mechanical properties of CoCrFeNi/GH3128 electron beam welded joints were investigated. Influenced by solidification rate and elemental composition, differences in grain crystallization modes and morphologies were observed on both sides of the weld, accompanied by a columnar-to-equiaxed transition in the weld center. Significant fluctuations in elemental concentrations across the weld indicated elemental segregation, with distinct segregation behaviors observed for Fe, Co, Cr, Ti, Al, W, and Mo elements between columnar and dendritic grains. XRD results revealed the presence of gamma, gamma', FeCrNi solid solution, and various intermetallic compounds such as Ni17W3, Cr4Ni15W, and Fe3Ni2 in the weld zone. Hardness testing showed a gradual increase in microhardness from CoCrFeNi to GH3128 within the weld. Tensile testing indicated a tensile strength of 532.5 MPa and an elongation of 40.4 %, suggesting a ductile fracture mechanism for the joint. Post-tensile testing, noticeable work hardening, tensile deformation in the weld zone, grain refinement, and increased hardness were observed, highlighting the joint's enhanced strain-hardening ability. However, the corrosion resistance of the CoCrFeNi base material decreased.