A Model of “Lattice” Hardening in Irradiated Copper Crystals with the External Characteristics of “Source” Hardening

Abstract

A model is proposed to explain the formation of slip lines in irradiated copper crystals during the propagation of the Lüders front. In this model it is shown that, due to the sweeping up of the irradiation produced defect clusters by deformation, the critical stress to produce a slip line is that required to operate the source in producing the first dislocation loop in the environment of the defect clusters. As the slipped area expands a pile‐up forms and the stress required to expand this pile‐up falls. Since on this scale a normal tensile machine is soft, i.e. the load is constant, the pile‐up rapidly increases in size and velocity and hence slip lines should form very quickly. This has been verified by high‐speed photography. The sweeping up of the damage by deformation has also been verified experimentally. The model has important consequences for “source” and “lattice” hardening. It is shown that the lattice hardening of the dispersed defects produces all the characteristics of the deformation which have formerly been used as evidence of “source” hardening.

Deformation microstructure of neutron-irradiated pure polycrystalline metals

“…Early studies of radiation hardening produced competing models for the hardening mechanism, based on either dislocation source locking or lattice friction. Several researchers have proposed that both mechanisms operate, with source hardening responsible for the upper yield point and lattice hardening responsible for the lower yield stress observed in metals irradiated at low temperatures [19,20]. The loss of work hardening capacity produces sharp decreases in uniform elongation.…”

Mapping Flow Localization Processes in Deformation of Irradiated Reactor Structural Alloys

“…It is also well known that the velocity of glide dislocations increases exponentially with stress [25], which invokes high strain rates in channels. Indeed, high speed photography of the surface slip lines resulting from DCD has shown that they develop very rapidly, in less than a millisecond [28,29]. Details of the barrier clearing process(es) are specific to particular types of barriers and are still very much debatable.…”

Deformation mode maps for tensile deformation of neutron-irradiated structural alloys

“…It is also well known that the velocity of glide dislocations increases exponentially with stress [31], which invokes high strain rates in channels. Indeed, high speed photography of the surface slip lines resulting from DCD has shown that they develop very rapidly, in less than a millisecond [18,35]. Details of the barrier clearing process(es) are specific to particular types of barriers and are still very much debatable.…”