The Extension of Jogs on Dissociated Dislocations in F.C.C. Metals

Abstract

Experimental observations of jogs on dissociated dislocations are discussed. It is shown that using the weak-beam technique of electron microscopy both extended and apparently cont,racted jogs can exist on the same dislocation: the extension of jogs depends on several factors including the height of the jog and the character of the dislocation. It is found that complex jogs which may be combinations of (110) and (112j jog lines, also exist, and the occurrence of these may be relat,ed to the mechanism of the dislocation int,ersection process.Es werden experimentelle Beobachtungen von Versetznngssprungen an aufgespaltenen Versetzungen diskutiert. Mit Hilfe der elektronenmikroskopischen "weak-beam"-Technik wird gezeigt, daB sowohl aufgespaltene als anscheinend auch zusammengezogene Spriinge an derselben Versetzung existieren kijnnen. Die Aufspaltung der Versetzungssprunge hangt von mehreren Faktoren ab, u. a. von der Hohe des Sprunges und dem Charakter der Versetzung. Es wurden komplexe Versetzungssprunge gefunden, welche eine Kombination von (1 10)-und (1 12)-Sprunglinien sein konnen. Ihr Auftret'en kann mit den .Uberschneidnngsprozessen von Versetzungen in Zusammenhang gebracht werden.

A dissociated dislocation in an ultrathin silicon plate

“…On the other hand, previous measurements of the separation distance S of the dissociated screw dislocation reveals a large spread in the values in the range 2.3 nm [25] to 5.8 nm [12]. High internal stresses can doubtless contribute to the cause of this large spread of S, among which free surface effects are very difficult to handle on a rigorous basis, despite some qualitative or quantitative observations of elastic relaxation due to these surfaces [27][28][29][30][31]. It will be shown in section 3 that S can depend drastically, in an ultrathin plate, on the position and orientation of the fault plane.…”

A review of the determination of dislocation parameters using strong‐ and weak‐beam electron microscopy

“…This method allows the resolution of single partials with a separation of 2 2 n m in dissociated configurations, the measurement of these distances rather accurately (5 1 nm) as well as the study of the geometry of dislocation loops (Hausserman et al, 1973; Wilkens et al, 1973), and precipitates and clusters of point defects (Jenkins, 1974). It has also become possible to observe jogs on dislocations and to study their structure (Carter & Ray, 1974;Carter & Hirsh, 1977;Carter, 1979Carter, , 1980.…”

The effect of solute interaction and anisotropic elasticity on Shockley partial dislocations in an F.C.C. alloy

“…materials. I n particular it has been found that the concept of a dislocation line tension [2, 31 can be used to explain the shape of constrictions caused by jogs in dissociated dislocations [4 to 61, the extension of jogs on such dislocations [7], and the effect which jogs can have on the ext,ension of P-type nodes in low stacking-fault energy (SFE) materials [8, 91. When anisotropic, rather than isotropic, elasticity theory is used to calculate the line energy and line tension of the Shockley partial dislocations in low SFE copper alloys, it is predicted that the partial dislocations will be unstable within = 10" of the edge orientation [lo to 121 and that the line tension will actually be negative within ; r 5" of this orientation. The line tension, T, in these calculations is given be [3] where E (= E(O)), the energy factor, is the prelogarithinic term in the self energy of an infinitely long straight dislocation with character 8.…”

“…Experimental studies of the properties of Shockley partial dislocations were previously limited by the resolvable detail in strong-beam images and the initial observations [lo] of this predicted instability may have been influenced by the inclination of the dislocations to the foil surface [13] and to the presence of jogs on the dislocations [7]. More recent observations using the weak-beam technique [5, 13, 141 have confirmed that Shockley partial dislocations close to the edge orientation are very much more flexible than those close to the screw orientation; the maximum value of T in these materials is predicted to occur close to the 25" orientation due to anisotropic elasticity.…”