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.