Crack generation mechanism and control method of electron beam welded Nb/GH3128 joint

Electron beam welding of Nb/GH3128 dissimilar alloys was conducted in this research. Microstructure characterization and finite element simulation were utilized to uncover the cracking mechanism of the joint. The obtained results revealed that a brittle reaction layer, composed of Ni₆Nb₇/Laves phase beside the Nb substrate, was a critical cracking factor triggering the cracking along the reaction layer. The generation of cracks was affected by a certain thermal-mechanical effect. The longitudinal residual stress fluctuated dramatically in the Nb/FZ interface region, resulting in different welding deformation. High transverse residual stress was also detected in the vicinity of Nb/FZ interface, increasing the cracking propensity of Nb/GH3128 joint. This high residual stress combined with the brittle reaction layer illustrated the intrinsic cause of welding crack. Crack-free welding of Nb/GH3128 dissimilar alloys was realized via adopting the beam offset process. The thickness of the brittle reaction layer was dramatically decreased and the brittle Laves phase within FZ was replaced by the γ phase.