STRAY GRAIN FORMATION IN NICKEL-BASE SUPERALLOY SINGLE-CRYSTAL WELDS

摘要

A single-crystal nickel-based superalloy (alloy Rene N5) was welded using laser and electron beam processes. The resultant microstructure was examined by optical microscopy. It was found that extensive stray grain formation took place, and furthermore, the stray grain formation was not symmetrical with respect to the weld centerline. The results were interpreted with the use of the theories of Kurz and co-workers on dendrite tip growth and constitutional supercooling ahead of the advancing dendrite solidification front. It was found that the theories explain the observations quite well, and provide the basis for optimizing the weld conditions in the future so as to yield stray-grain free welds in single crystals.