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. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.