Complete-joint-penetration vacuum laser beam welding of nickel-based superalloy 718Plus

Deep-penetration welding of nickel-based superalloys is an indispensable manufacturing technique for aircraft engines, aerospace engines, and nuclear containers. In this study, a newly developed vacuum laser beam welding method was used to weld a 9 mm thick superalloy 718Plus. A defect-free complete joint penetration weld with a high depth-to-width ratio was fabricated. The macro/microstructures, microhardness, tensile properties, and fatigue properties of weld joints under both as-welded and heat-treated conditions were systematically examined. The weld joint showed a microstructure of planar, cellular, columnar, and equiaxed crystals from the fusion line to the center line. The post-weld heat treatment had an insignificant effect on the grain structure but changed the precipitated phase in the weld. The newly formed γ′ and η phases were observed in the heat-treated sample. The mechanical properties showed microhardness, tensile strength, elongation, and fatigue strength of 488.6 HV, 1347.0 MPa, 13.7%, and 399 MPa, respectively, which were 104.6%, 93.2%, 77.8%, and 74.2% of those of the base metal, respectively. Both as-welded and heat-treated samples exhibited ductile ruptures. The excellent mechanical properties of the heat-treated joints were attributed to the formation of precipitated phases.