Stray grain formation in single crystal Ni-base superalloy welds

The effects of processing conditions and crystallographic orientation of growing dendrites on Stray grain formation have been investigated in welds of single crystal Ni-base superalloys. The degree of constitutional supercooling (CS) at the solidification front has been used as a metric to quantify the effects. Numerical calculation results showed an appreciable effect of dendrite orientation on CS. For experimental verification, welds were made on a single crystal but in an asymmetric crystallographic orientation under three different processing conditions. Stray grain formation was observed to increase and become extensive on one side of the weld as power and welding speed increased. This result is in agreement with the calculated predictions and confirms that the degree of CS is a good metric. (C) 2003 American Institute of Physics.