Effect of dendrite arm spacing on castability of a directionally solidified nickel alloy

The effect of dendrite arm spacing on hot tearing susceptibility during directional solidification was explored by casting bi-crystal samples with the same grain boundary misorientation but different dendrite arm spacing. It was found that smaller dendrite arm spacing does reduce the hot tearing tendency. The eutectic melt is more finely dispersed and increasingly discontinuous as the dendrite arm spacing is reduced. The better castability is attributed to the stronger grain boundary cohesion.