Characteristics of the evolution of defect structure during phase transformations in the Pd-H system

The pattern of evolution of the defect structure in the Pd-H system during phase transformations is formulated on the basis of x-ray data. It is shown that once the random dislocations formed during phase transformations in the a phase reach their critical density, they assemble into dislocation walls. This process results in the formation of a cellular dislocation substructure in the α phase. After the formation of the cellular substructure in the α phase the random dislocations created during phase transformations climb into the hydride phase, thereby curtailing the evolution of defect structure in the α phase. The subsequent influx of dislocations into the β phase maintains continued evolution of the defect structure (from cellular to block dislocation substructure). Not until that time is it possible for the evolution of the defect structure in the α phase to terminate, culminating in the formation of a block substructure. The nature of the observed phenomenon is discussed.