Effects of applied stress on coherent precipitates via a discrete atom method

Morphological evolution of coherent precipitates under an applied stress is analyzed by means of a discrete atom method, which is predicated upon Hookean atomic interactions and Monte Carlo diffusion, and mates no assumption of a specific shape. Precipitates having elastic constants different from those of the matrix phase art treated in dislocation-free, anisotropic elastic systems under a plane strain condition with a purely dilatational misfit. Under an applied tensile stress, soft particles with a positive misfit strain tend to become plates perpendicular to the applied stress axis, while hard particles elongate along the stress direction. If the elastic interaction between the applied stress and the coherency strain is strong enough, precipitates often split into smaller particles and then follow coarsening. Even in the absence of a coherency strain, particles are shown to undergo morphological evolution through Eshelby’s inhomogeneity effects. A particle shape depends on the following variables: the sign and magnitude of the coherency strain, the sense and magnitude of the applied stress, its stiffness relative to the matrix phase, and the magnitude of the interfacial energy.