STRUCTURE EVOLUTION IN DIRECTIONALLY SOLIDIFIED BICRYSTALS OF NICKEL BASE SUPERALLOYS

Bicrystal samples of Ni base superalloy IN792 were produced to study the structure evolution in directional solidification process. In the case of converging grains, the misaligned dendrites were able to block the better aligned dendrites at the grain boundary. The dendrite blocking leaded to inclination of the grain boundary from the misaligned grain to the better aligned grain. Thus, the better aligned grain was overgrown by the misaligned grain. In the case of diverging grains, dendrite development at the grain boundary leaded to inclination of the grain boundary from the better aligned grain to the misaligned grain. Consequently, the better aligned grain overgrew the misaligned grain.