Influence of Jog Concentration on the Conservative Motion of Dislocations in Copper
01 Dec 1966-Journal of Applied Physics (American Institute of Physics)-Vol. 37, Iss: 13, pp 4987-4990
Abstract: In an annealed crystal of low dislocation density, the critical resolved shear stress necessary to move circular prismatic edge‐dislocation loops along their glide cylinders was compared to the range of stresses within which various segments of the three‐dimensional network began to move. Etch‐pit observations showed that the first segments of the network moved at 2 g/mm2 but that only 60% had moved when the maximum resolved shear stress had reached 38 g/mm2.Circular prismatic loops, which because of their shape have a high jog concentration, were found to move at a critical resolved shear stress greater than 50 g/mm2. It was suggested that jog concentration should be expected to vary from one segment to another of the three‐dimensional network in an annealed crystal, and that this is probably one important reason for the widely different stresses at which individual segments begin to move.
Lawrence Berkeley National Laboratory
INFLUENCE OF JOG CONCENTRATION ON THE CONSERVATIVE MOTION OF DISLOCATIONS
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Jourm*1 of Applied Physics
UIflVERSITY OF CALIFORNIA
Lawrence Radiation Laboratory
ARC Contract No. W-71405.-eng-48
INFLUENCE OF JOG CONCENTRATION ON THE CONSERVATIVE
MOTION OF DISLOCATIONS IN COPPER
Pierre Petroff and Jack Washburn
• Inorganic Materials Research Division, Lawrence Radiation Laboratory,
and Department of Mineral Technology, College of Engineering,
University of California, Berkeley, California
In an annealed crystal of low dislocation density the critical
resolved shear stress necessary t'o move circular prismatic edge dislocation
loops along their glide cylinders was ccnpared to the range of stresses
within which various segments of the three dimensional network began to move.
Etch-pit observations showed that the first segments ofthe network moved
but that only 60% had moved when the maximum resolved shear
stress had reached 38g/mm 2
Circular prismatic loops, which because of their shape have a
high log concentration, were found to move at a critical resolved shear
stress greater than
It was suggested that jog concentration
should be expected to vary from one segment to another of the three
dimensional network in an annealed crystal and that this is probabiy
one important reason for the widely differenttresses at which individual
segments begin to move.
01 Aug 1970-Journal of Applied Physics
Abstract: Glide velocity measurements were made on isolated screw and 60° dislocations in silicon for the temperature range 775°–925°C. The x‐ray topographs which were used to reveal dislocation displacements also gave qualitative information concerning the early stages of dislocation multiplication in highly perfect silicon crystals. Freshly generated dislocations were more mobile than aged dislocations. Pinning points which were tentatively attributed to thermal jogs developed along the lines. The pinning point spacing decreased with increasing temperature as would be expected for a jog formation energy of 1.2 eV. Heating to above 1000°C effectively immobilized all the dislocations present in the crystal. On subsequent loading at 825°C, no motion took place until the stress was high enough to cause catastrophic multiplication when a segment of dislocation did break away. This resulted in the formation of heavy bands of slip. For fresh dislocations the temperature dependence of velocity was analyzed on the basis of a kink pair nucleation and kink propagation model. The measured activation energy for motion of both 60° and screw dislocations was 1.8±0.3 eV.
01 Apr 1969-Journal of Applied Physics
Abstract: Preyield dislocation motion and multiplication were studied in large‐grained polycrystalline OFHC copper by the etch‐pit technique. Specimens were loaded in compression and dislocation arrangements were observed in both the stressed and unstressed conditions. The dislocation loops generated by the first few active sources on both primary and secondary slip systems generally traversed the entire cross section of the grain. The observations were consistent with the idea that jog density is an important factor in determining the mobility of a dislocation segment. The external surface was found to be a preferential site for dislocation multiplication even when grown in segments, where they cut the surface, were immobile, and stress concentrations were carefully avoided. It is suggested that the rapid increase in length per unit volume of moving dislocation line that is associated with macroscopic yield requires motion of dislocation segments of high jog density.
01 Jun 1972-Journal of Applied Physics
Abstract: Copper single crystals of extremely low dislocation density have been obtained through a thermal cyclic annealing. Ball indentation in the dislocation‐free area of (111) surface produced large dislocation rosettes, each arm extending in the 〈110〉 cystallographic orientations consisted of a row of prismatic dislocation half‐loops. Half‐loops of a diameter larger than 20 μ were easily produced in regular shape and they seemed much less mobile than independent dislocations under glide shear stress.
15 Mar 1969-Journal of Applied Physics
Abstract: Strain centers with attendant prismatic dislocation loops have been studied in copper crystals of low dislocation density by use of Borrmann x‐ray topograph and etch‐pit techniques. Direct comparison of these defects with the two techniques showed an exact correlation. While the nature of the centers of the strain could not be certainly determined, there was evidence that the loops were of the interstitial type.
01 Jan 1976-Materials Transactions Jim
01 Jun 1960-Journal of Applied Physics
Abstract: A modification of an etch discovered by Lovell and Wernick has been shown to be a reliable means of revealing dislocations as etch pits on (111) faces of copper crystals. The etch has been employed to study dislocation distributions in as‐grown, annealed, and deformed crystals.A high‐temperature anneal is found to lower the dislocation density of melt‐grown crystals. A ``double‐etch'' technique is employed to observe the motion of dislocations, and to show that the dislocations initially present in these crystals are mobile at low stresses. Subboundaries are numerous in these crystals and are found capable of hindering dislocation movement. Observations of the dislocation structure of crystals deformed in bending and in tension are reported, including the appearance of ``glide polygonization'' after room‐temperature deformation.
01 Sep 1960-Philosophical Magazine
Abstract: The stresses round a circular prismatic dislocation loop are determined and used to calculate the spacings between such loops in a row generated from a source of internal stress. The results are consistent with the available experimental observations.
01 Oct 1961-Journal of Applied Physics
Abstract: Copper (99.999%) crystals with a dislocation density of 50/mm2 have been prepared. These crystals were stressed by applying a pure bending moment, and they were etched with a dislocation etch either before and after or while the stress was applied. The motion of dislocations was determined by observing the size and nature of the dislocation etch pits. The resolved stress necessary to move grown‐in dislocations was about 4 g/mm2. Examples of dislocation motion under stress, then return motion when the stress was removed, and of multiple motion under stress were observed. Multiplication of dislocations occurred at a resolved stress of about 18 g/mm2. The observed phenomena are discussed in terms of simple dislocation theory.
01 Apr 1963-Acta Metallurgica
Abstract: Rows of prismatic dislocation loops have been observed in thin films obtained from copper foils which have been water quenched from 1055°C. These rows emanate from precipitates in the copper and lie in the 〈110〉 directions, but only those lying nearly parallel to the surface contain many loops. The spacing of the loops is consistent with the theory of Bullough and Newman( 1 ) which enables a value of the critical resolved shear stress to be estimated. This value indicates that the outside loops in the rows inclined to the surface of the thin film are lost to the surface by slip under the influence of their image forces. The loops, which are thought to be equivalent to platelets of interstitial atoms are too numerous to result merely from the differential expansion of the precipitate and the copper, which suggests growth of the precipitate during quenching.
01 Feb 1964-Acta Metallurgica
Abstract: The continuous shear stress shear strain behavior for tubular polycrystalline specimens of copper and its dilute alloys deformed in torsion at room temperature was studied using a strain resolution of the order of 10−9. Irreversible plastic deformation began at the smallest measureable stresses. The small but measurable apparent elastic regions observed in all specimens very near zero applied stress are thought to be associated with the small unrecoverable prestrains produced during the handling and gripping operations. These apparent elastic regions were completely absent in specimens deformed following the introduction of fresh, mobile dislocations into their gage section surfaces. The addition of solute concentrations up to 0.1 at % aluminum in copper had little effect upon the movement of these freshly introduced dislocations. Polycrystalline copper strain hardens readily at room temperature and exhibits a discontinuous plastic behavior only following prior straining. The anelastic unloading behavior is also demonstrated for annealed copper specimens. It is suggested that plastic deformation starts by the motion of a few favorably oriented dislocation segments that can glide over great enough distances to form strong new interactions with other dislocations.
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