Dynamic interaction between a coherent precipitate and an edge dislocation

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Dynamic interaction between a coherent precipitate and an edge dislocation is analyzed by means of a discrete atom method, which is based on classical statistical mechanics and linear elasticity. Precipitates having a dilatational misfit strain and elastic constants different from those of the matrix phase are treated in anisotropic elastic systems under a plane strain condition. A coherent interface transforms into a semicoherent one by nucleating dipolar dislocations at a stress concentration in a coherent precipitate. One of the dipolar dislocations glides along the precipitate-matrix interface to become a misfit dislocation, and the other slips into the matrix phase to become a lattice dislocation. In accordance with continuum elasticity, a coherent particle with a positive misfit strain migrates to the tension side of an edge dislocation, whereas a particle with a negative misfit diffuses to the region of compression. Morphological change is, however, caused by the dislocation as the particle tries to capitalize on the dislocation stress field, and the particle shape depends on its stiffness and elastic anisotropy. Under an applied shear, a hard coherent particle with a positive misfit strain is sheared along the shear direction, but a soft particle responds in the opposite direction. Elastic interaction between a coherent particle and an edge dislocation can be so strong that the particledislocation complex remains coupled even at a high shear strain applied to the system. Some composite applied stresses can cause an edge dislocation to split into two partials. One of the partials, a glissile component, is found to engage actively in the morphological evolution of a particle during a diffusional relaxation.

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Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science