Dislocation cell formation and work hardening in the unidirectional glide of f.c.c. metals I: Basic theoretical analysis of cell walls parallel to the primary glide plane in early stage II

Abstract

Past research leads to the conclusion that dislocation cell formation in work-hardened crystalline materials occurs when dislocations assemble into low energy configurations. On the assumptions that the dislocation cells formed in f.c.c. metals in early stage II also approach the lowest energy for a given dislocation content in the material and that the initial dislocation arrangement before cell formation consists of linear dipolar mats, i.e. sets of similar edge dislocations in coplanar arrays but alternating sign from one mat to the next, the structure of the resulting cells is investigated. It is found that the initial pile-up-like arrays should transform into tilt walls with or without some twist component, such that the axis of relative misorientation is roughly parallel to the original edge dislocations. By a simple consideration of energies it is found that cell formation should begin at or below about 1.2 τ 0 where τ 0 is the initial critical flow stress. Again if the minimum energy is considered, it is found that for low stacking fault energy materials Lomer-Cottrell locks should form prominently, such that the primary dislocations become rotated roughly normal to the Lomer-Cottrell locks. These results are in good agreement with available experimental evidence.