Electron beam offset welding to ameliorate metallurgical compatibility and mechanical performance of refractory metal/Ni-base superalloy dissimilar alloys: Nb/GH3128

Electron beam welding of Nb/GH3128 dissimilar alloys was conducted to obtain crack-free joints. The beam offset process contributed to the improvement of microstructure, and segregation behavior of alloying elements, as well as the elevation of mechanical properties of joints. Cracked joints were obtained as electron beam shift to GH3128 superalloy with 0.5 mm. Brittle Ni₆Nb₇/Laves reaction layer combined with a great number of brittle Laves phase and γ/Laves eutectic in fusion zone acted as the intrinsic factors for cracking. Relative low segregation propensity of alloying elements helped to the promotion of generation of γ/Laves eutectic. As the beam offset value increased from 0.5 mm to 0.9 mm, the tendency of alloying elements to segregate was intensified, promoting the Laves phase and γ/Laves eutectic to be replaced by γ phase, and the hardness of the joints was gradually decreased from 594 HV to 340 HV correspondingly. High hardness is detected in the reaction layer between Nb and the fusion zone, which triggered the brittle fracture of all joints. The joint obtained with a beam offset value of 0.8 mm possess the highest tensile strength 163 MPa, 65% of Nb base metal.