Investigation of the slip geometry of high-purity potassium by in situ X-ray diffraction

摘要

Plastic deformation of bcc metals at intermediate and low temperatures is dominated by [111] screw dislocations which macroscopically seem to glide on planes of high or irrational Miller indices. It is now well established that this non-crystallographic glide is composed of elementary steps of kink-pair formation on three symmetry-equivalent low-index planes. In the present investigation, the slip geometry of high-purity potassium single crystals was investigated by in situ X-ray measurements of the lattice rotation in uniaxial compression in the temperature range from 6 to 70 K. The different alternatives for the elementary glide planes, e.g., {110},{211} or {321}, can be uniquely distinguished from changes of the primary slip direction within the unit triangle. The results showed that the elementary glide step in potassium occurs on {211} planes in the investigated temperature range. In addition, glide of [100] dislocations (obviously products from interactions between mobile and sessile [111] dislocations) becomes dominating in many samples at increasing plastic strain. Numerical simulations of the orientation change in < 111 > {211} glide, based on the model of thermally activated kink-pair formation, were in good agreement with the experimental results.