Theory of diffraction from D019 ordered c.p.h structures containing complex stacking faults on basal planes

Antiphase boundaries and stacking faults affect the deformation behaviour of intermetallics. In an ordered c.p.h. (close-packed hexagonal) structure of D0(19) type (e.g. Mg(3)Cd, Ti(3)Al-based alloys), stable planar faults of two types are possible on the basal plane. These are antiphase boundaries (APBs) and complex stacking faults (CSFs), which are a combination of an APB and a stacking fault. The latter can be either of shear or of climb type. If the bounding partial dislocations of a CSF lie in its plane, then it is designated as a shear CSF, otherwise it is called a climb CSF. A mathematical formulation of the theory of diffraction from a D0(19) structure having a shear or climb type of CSF has been carried out. The diffraction effects owing to the presence of these CSFs have been found. Integrated intensities and widths of the reflections are affected. These have been evaluated in terms of the probability of the occurrence of these faults.