Interphase-boundary dislocations and the concept of coherency

The discrete-lattice concept of coherency applied to interphase boundaries and the elasticcontinuum concept applied to enclosed particles are shown to be mutually consistent. In line with these concepts, a general discrete dislocation description of interphase-boundary structure is developed. It is shown that a coherent interface can contain partial dislocations which we call transformation or 'coherency' dislocations. These dislocations accomplish the transformation lattice deformation between the two phases and maintain continuity of the lattice. They are capable of conservative climb and/or glide during the transformation, but their motion is restricted to the plane of the dislocation loop. Strain energy associated with the coherency dislocations can be reduced by misfit or 'anticoherency' dislocations, generally having lattice Burgers vectors and producing a lattice-invariant deformation which disrupts the uniformity of the lattice correspondence across the interface and thereby reduces coherency. The anticoherency dislocations move as conventional dislocations.