Dislocation Movements in Metals

Abstract

Defects in crystals are responsible for the differences that exist between the properties of any given real crystal, or crystal aggregate, and those calculated for the corresponding "ideal" crystal; that is, calculated from the mathematical model of an ideally regular array of infinitely many atoms. With respect to a number of properties, such as density, elastic constants, specific heat, and melting point, the differences between real crystals and ideal crystals of the same type are minor. For example, if we calculate the temperature dependence of the specific heat of, say, rocksalt, by considering an ideal array of sodium and chlorine ions in a cubic arrangement, we find a satisfactory agreement between theory and experimental fact. However, besides such "structure-insensitive" properties, there are many "structure-sensitive" properties which reveal enormous differences between ideal and real crystals. In particular, this is true for the whole range of plastic properties of crystals and crystal aggregates. Included are all metals and alloys since these, as is well known from x-ray evidence, are crystalline even though their external shape rarely gives any

Surface-controlled dislocation multiplication in metal micropillars

“…mechanical strength ͉ plasticity P lastic deformation of crystalline materials is mostly carried out by the motion of dislocations, which self-organize into complex structures at the micrometer scale (1)(2)(3)(4). Hence, the yield strength of a crystal can be modified by the interaction between dislocations and other microscopic features with comparable length scales, such as the grain size in the Hall-Petch effect (5-7) or the specimen size itself in the micro tensile and compression experiments (8)(9)(10)(11)(12).…”

Geometrically necessary dislocations and strain-gradient plasticity: a few critical issues

“…In a way, this is reminiscent of the low energy dislocation structure models [3], or of the models developed to explain the formation of arrays of misfit dislocations in epitaxial layers.…”

Effect of external stress on microstructural change during electron-irradiation in nickel.

“…In the specimen of [114] foil normal with external load of 60 g in direction close to [432], radiation-produced loops with diameter larger than 10 nm were observed to rotate and grew into rhombus shaped perfect loops on {11 0} planes under irradiation at 723 K. The rotation of the loop has been observed with a/3(111) Frank loop unfaulting into a/2<11 0) perfect loop' 7 ).…”