Competitive grain growth in directional solidification of a nickel-base superalloy

The structure evolution of bi-crystal samples during directional solidification was explored. It was found that in the case of diverging dendrites the better aligned grains overgrew the misaligned grains by means of the dendrite development from the better aligned grains, However, in the case of converging dendrites the result differs in two ways from the prediction of the generally accepted model for competitive grain growth. First, the misaligned dendrites are able to overgrow the better aligned dendrites. Second, the misaligned grains are able to overgrow the better aligned grain by blocking the dendrites of the better aligned grains at the grain boundary. The results can explain the potential sources of misorientation defects in seeded single crystal components and can be used to optimize process design to eliminate the stray grain defects in seeded single crystal casting.