Welding of single crystal and directionally solidified nickel base superalloys is gaining increasing importance because of the need for repair welding and rebuilding of failed and eroded components. The microstructure in the weld fusion zone and heat-affected-zone (HAZ) that result from rapid temperature excursions control the weldability and the service performance of the welded components. Therefore, recent work has concentrated on the weldability issues and microstructure development in single-crystal welds. These studies have shown complex interactions between weld pool shape, crystallographic parameters, solidification features, solid-state phase transformations and microstructure evolution. In general, the weld microstructure evolution sequence involves formation of #gamma# dendrite from liquid and epitaxial solidification of #gamma# grains in the HAZ adjacent to fusion line, formation of eutectics along the dendritic boundaries, and precipitation of #gamma# phases within the #gamma# dendrites. The present study pertains to the precipitation of the #gamma# phase and elemental partitioning between #gamma# and #gamma# phase.
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