Grouping of pinning points on dislocation lines

Abstract

Mobile pinning points on or near dislocation lines tend to group together. The driving force is the entropy of the dislocation lines. External oscillating stresses, which exceed a certain critical amplitude, increase this grouping tendency. These phenomena are first considered in detail for the model of one mobile pinner between two immobile ones. Equations for the equilibrium distributions without and with external stress and for the entropy force are derived. A partly quantitative partly qualitative extension to many pinners on the line is given. Consequences for the distribution of pinning points, created by radiation damage, quenching or cold work, and for the interpretation of internal friction and modulus defect measurements are discussed. It is suggested that external oscillating stresses be used to enhance the precipitation of point defects, such as vacancies, interstitials, or impurities, on dislocation lines.