Microstructure and Performance of Laser-Welded GH3128/Mo Dissimilar Joints

Laser beam offset welding of GH3128 and molybdenum (Mo) dissimilar joints was studied with an emphasis on the role of laser beam offset (LBO). It was found that the change of LBO significantly affected the properties of GH3128/Mo dissimilar joints. When the LBO increased from − 0.1 mm (i.e., laser spot was centered on Mo surface) to + 0.3 mm (i.e., laser spot was centered on GH3128 surface) at the step size of 0.1 mm, the amount of melted Mo gradually declined; the welding mode gradually changed from fusion welding to welding–brazing; macro-segregation of Mo-rich phases in fusion zone (FZ) gradually disappeared; the average microhardness of FZ significantly decreased, and therefore, microhardness distribution in FZ became more uniformly; the quantity of grain boundary liquation observed in heat-affected zone (HAZ) of GH3128 side gradually decreased; and recrystallization of grains in the HAZ of Mo was gradually suppressed. Joints with the optimal LBO of + 0.2 mm reached the maximum tensile strength of about 560 MPa. When using a small LBO, i.e., LBOs were + 0.1, 0, − 0.1 mm, the HAZ of Mo was greatly softened and embrittled. When adopting a large LBO, i.e., LBO was + 0.3 mm, the melt near Mo-FZ interface might fail to moisten Mo surface and spread on Mo surface, thus resulting in the reduction in tensile strength.