Modeling analysis of hybrid laser-arc welding of single-crystal nickel-base superalloys

Heat transfer and dynamic fluid flow have been calculated to predict hybrid laser-arc weld pool geometry by establishing a three-dimensional numerical model. Based on previous analytical methods, a mathematical model and a general procedure are extended for calculating the fraction of misoriented stray grains in hybrid laser-arc welds. Solidification microstructures in hybrid welds in single-crystal materials are evaluated by combining the crystallographic orientation of growing dendrites with the solidification front orientation that is derived from a geometric model of the dendritic growth pattern. It is shown that finer dendrite arm spacing is always found near the solid-liquid boundary of the top side of the weld or weld root, and the coarsest dendritic microstructure occurs in the center of the weld crown. It is also found that a higher welding speed and a lower arc current or laser power are beneficial to the minimization of stray-grain formation. Calculated weld geometries are compared to previous experimental work, and calculated dendrite arm spacing agrees reasonably well with the experimental result.