Shape evolution and splitting of coherent particles under applied stresses

Morphological evolution and splitting of coherent precipitate particles under applied stresses were investigated using a diffuse-interface field kinetic approach. A particular example, γ′ precipitates in Ni-based superalloys, was studied. In the absence of externally applied stress, a coherent γ′ particle exhibits a cuboidal shape, as a result of the competition between anisotropic coherency strain energy and nearly isotropic specific interfacial energy. It was demonstrated that under a uniaxial applied constraint strain, growth of the γ′ particle became tetragonal, resulting in a shape transformation from being cuboidal to tetragonal. As the magnitude of the applied strain was further increased, it is interesting to observe that the γ′ particle became unstable and split into two or more parallel plates. The influences of stress magnitude, precipitate volume fraction, and interfacial energy on the splitting process are discussed.