From Vernier Defects and Verhakungen to Solitons and Kinks

Abstract

The paper retraces, from a personal viewpoint, the development of atomistic models of dislocations in crystals from the model of Prandtl, Dehlinger, Frenkel, and Kontorova (PDFK), first conceived in 1912, to recent work on kinks in dislocations. Among the topics discussed in some detail are the emergence of what has become the theory of solitons, the rate theory of kink-pair generation, and the interplay of experiment and theory in the quantitative investigation of kinks. An outcome of this interplay, the determination of the planes of the elementary slip steps of screw dislocations in body-centred cubic metals, has proved to be the ‘open sesame!’ of quite a number of puzzling phenomena in the plastic deformation of bee metals. These include non-uniformities in the flow-stress-temperature relationship, anomalous slip, alloy softening, tension-compression asymmetry in uniaxial straining tests, and the enigma of ‘reversible’ vs. ‘irreversible’ y-relaxation. The key for the understanding of these phenomena is a transformation of the screw-dislocation cores in bee metals from a configuration capable of slipping on {110} planes at low temperatures to one with a {112} slip plane at elevated temperatures.