Role of dendrite branching and growth kinetics in the formation of low angle boundaries in Ni-base superalloys

An experimental study coupled with a local thermal undercooling model has been used to discriminate between possible contributions to the evolution of misorientation producing low angle grain boundaries during solidification in the Ni-base superalloys, CMSX4 and CMSX10N; these include: (a) successive dendrite branching, (b) dendrite bending during steady state growth and (c) thermal-undercooling driven transient dendrite growth kinetics. While extensive dendrite branching/steady state growth led to an average spread of misorientation ≈2.3° and was random in nature, enhanced growth kinetics accompanying non-steady state conditions produced an accumulated misorientation up to 6°; the latter was suggested to potentially include plastic deformation of the dendrite stems within the mushy zone.