Predicting the onset of rafting of γ′ precipitates by channel deformation in a Ni superalloy

The growth or shrinkage, normal to {001}, of the interfaces between the matrix and cuboidal γ′ precipitates is examined for a Ni-base superalloy, by considering the force acting on the interfaces. The force is produced by the precipitate coherency misfit and the stress produced by plastic deformation in channels of the γ′ matrix. A simple expression, which directly addresses the origin of the surface force, is given. The plastic deformation within the initially active γ′ matrix channels exerts the force to cause rafting. The subsequent activation of other types of channels also promotes the rafting in the same direction as the first active channels, when the plastic strain of the former channels increases. These issues are also discussed in terms of analysis based on those dislocations caused by the precipitate misfit and those produced by the plastic deformation.