Cold-worked Copper Research Articles

The theory of small angle scattering from dislocations

Abstract The small angle scattering of x-rays or neutrons from crystals containing a random network of dislocations is calculated. Three causes of density changes associated with dislocations are considered : that due to the elastic strain field from edge dislocations, that due to second-order elasticity effects and that due to the dislocation cores. It is found that in the range of angles for which experimental evidence is available, the effect due to the elastic strain field from edge dislocations predominates. The magnitude of the scattering expected from the theory for a dislocation density of about 1011 cm−2 is of the same order as that found recently from small angle neutron scattering experiments on heavily cold-worked copper.

Resistivity due to dislocations in copper

The scattering of electrons by a dislocation with a hollow core is treated. It is found that the effect of such a core upon the electrical resistivity may be many times greater than the effect of the strain field. If the change in volume of the crystal due to dislocations is set equal to the core volume (of the order of one atomic volume per interatomic distance of dislocation), a rough calculation indicates that the change in resistivity for 1 per cent change in volume is about one-half of that observed in annealing experiments on cold-worked copper. It is suggested that the general magnitude of the interaction between conduction electrons and the core may be correct, even if the specific hollow-core model is not valid. Hence it appears that a consideration of the scattering by the core provides order-of-magnitude agreement with experiment for the resistivity due to dislocations.

The internal friction of cold-worked copper at low temperatures

Abstract The internal friction of cold-worked polycrystalline copper has been measured in the temperature range 20° to 300°K, and a study made of the maximum in the curve of internal friction versus temperature first observed by Bordoni. The measurements indicate how the internal friction varies as a function of the amount of cold work, and also the effect of impurities in the metal and of neutron irradiation. The results are discussed with particular reference to recent theoretical treatments by Seeger.

Stress Annealing in Vacuum Deposited Copper Films

An apparatus has been built for the measurement of mechanical stress in vacuum deposited films. A study of the stress changes during pulse annealing has been made with copper films deposited at several substrate temperatures between -150°C and +75°C. The annealing spectrum shows a prominent peak centred near room temperature which matches a resistance annealing peak in similar films and also in cold worked copper. The fall of tensile stress in this region suggests a vacancy mechanism. The theory of Murbach and Wilman for the behaviour of initial stress with temperature is not supported by these results.

Annealing of Cold-Worked Copper by Electron Irradiation

Copper wires were cold worked at room temperature to approximately a 15% reduction in area and were then irradiated at temperatures between 100° and 150°C with 1.25-Mev electrons. The residual resistivity was observed to decrease as a function of exposure at temperatures above 100°C. The higher the temperature at which the irradiation was performed, the greater was the rate of resistivity decrease. From these data, it is concluded that one of the primary defects produced by electron irradiation becomes mobile in the temperature range, 100°–150°C. It is suggested that interstitials and vacancies produced by the irradiation initiate a process which results in the annihilation of dislocations. From an analysis of the temperature dependence of the rate of decrease, a value for the activation energy for vacancy migration in copper has been deduced: 1.28±0.10 ev.

Scattering of Electrons from Clustered Vacancies in Copper

The excess resistivity, $\ensuremath{\rho}$, and resistivity per unit stored energy, $q$, associated with dislocations, vacancies, and interstitials are briefly reviewed, and the same quantities are calculated for clustered vacancies. For clusters of more than one hundred vacancies, which seem to exist at room temperature in cold-worked or bombarded copper, $q$ is larger by factors of about 3, 8, and several hundred than the corresponding ratios for vacancies, interstitials, and dislocations.

XLI. The internal friction of cold worked copper at low temperatures

Abstract Bordoni (1949 and 1954) has reported the existence at low temperatures of a large peak in the values of internal friction plotted against temperature for several cold worked metals, and we are making a more detailed survey of the position. Our work has so far been confined to experiments on 99·999% polycrystalline copper, arid it has been shown (Niblett and Wilks 1955) that the different types of results obtained by Bordoni for different metals can all be induced in copper by subjecting it to varying amounts of cold work. Although measurements are still in progress it seems worth while to give a preliminary report, particularly of those results which appear to be inconsistent with an explanation of the peaks, published recently by Mason (1955).

Resistance and Thermoelectric Measurements of Cold-Worked Copper and the Resistance Minimum at Low Temperatures

Measurements of the change of residual resistance ratio of copper as a function of the percentage reduction in cross-sectional area by cold-working in liquid helium, liquid nitrogen or at room temperature and subsequent ageing treatments show (1) the relative change of the ratio during recovery between 77\ifmmode^\circ\else\textdegree\fi{}K and room temperature to that accompanying recovery and recrystallization at higher temperatures; (2) that there appears to be no recovery process taking place below 77\ifmmode^\circ\else\textdegree\fi{}K; (3) that specimens cold-worked in liquid helium or nitrogen and aged at room temperature have a higher residual resistance ratio than specimens both cold-worked and aged at room temperature.

Distortion of turbo-alternator rotor windings through thermal stress

The theory of copper shortening in turbo-alternator rotor windings is extended to take account of recent research on silver-free and silver-bearing coppers. The interaction of the turns of a slot stack operating within the elastic strength of the material is analysed and the results are applied to determine the stress distribution in a large winding of cold-worked silver-bearing copper under various conditions of practical interest. Deformation rates at given temperatures are estimated for such a winding. The basis of evaluation of the stack interface friction coefficients applied in the estimate is indicated.

Thermoelectric Power of Cold-worked Copper at Low Temperature

THE influence of cold-working on the thermoelectric power has been measured by a number of workers1. At room temperature we carried out measurements on copper and silver wires. For a certain amount of cold-working it is found that the relative increase of the absolute thermoelectric power is greater than the relative increase of the resistivity. These results do not agree with the theoretical prediction of T. Hirone and K. Adachi2.

Internal Friction and Young's Modulus of Cold-Worked Copper Single Crystals

The internal friction and Young's modulus of single crystals of copper were measured as a function of strain amplitude after they were subjected to various amounts of cold work and different annealing treatments. It was found that the position of the peak in the internal friction versus cold-work curve was dependent upon the strain amplitude of the measurement. No minimum in the Young's modulus versus cold-work curve was found as contrasted with Lawson's result for polycrystalline copper. A minimum was found in the internal friction versus annealing time curve, and a maximum was found in the corresponding Young's modulus curve. The results are semiquantitatively explained using a dislocation model.

Conductivity of Cold-Worked Metals

In the vicinity of an edge type dislocation, the density of electrons, and therefore the width of the filled portion of the conduction band is not uniform. To keep the electrons in equilibrium, an electrostatic potential is required. The scattering caused by this potential is used to calculate the increased resistance of isotropically cold-worked copper.

Temperature-Dependence of Magnetic Susceptibility of Annealed and Cold-worked Copper

INVESTIGATIONS recently carried out on the variation with temperature of the magnetic susceptibility of annealed and cold-worked copper have shown a different temperature-dependence in the two cases. A qualitative attempt is made to account for the difference on present theoretical lines.

Magnetic Self-Recovery in Cold-Worked Copper

FROM time to time many investigations have been carried out on the effect of cold-working on the magnetic properties of various metals1, but there are still no very reliable conclusions to be drawn from the work. We have recently been making a comprehensive study of the effect of cold-working on the magnetic properties of pure metals, over a range of temperatures, and in the case of copper have observed evidence of a systematic change of magnetic susceptibility with time. This effect is most easily interpreted as a magnetic self-recovery or self-annealing of the metal, the observed susceptibility gradually approaching a stable value at a rate dependent on the temperature at which the metal is maintained. This effect appears to be related to X-ray observations which have recently shown that a self-recovery of cold-worked copper takes place fairly rapidly, even at room temperature2,3,4.

Structure and Ferromagnetism of Cold-Worked Copper Containing Iron

Structure and Ferromagnetism of Cold-Worked Copper Containing Iron

XLVI.Latent energy due to lattice distortion of cold-worked copper

XLVI.<i>Latent energy due to lattice distortion of cold-worked copper</i>

Societies and Academies

LONDON. Institute of Metals (Annual Autumn Meeting at Dosseldorf), Sept. 11.—W. J. P. Rohn: The reduction of shrinkage cavities and vacuum melting. Shrinkage cavities may be diminished if care is taken that the solidification of an ingot starts from its bottom end and advances gradually to the top end. This control can be approximated with water-cooled copper moulds. Shrinkage cavities may be totally avoided if melting and freezing are performed in an electrically heated melting furnace in a crucible of the shape of a finished ingot, and, after melting and refining is completed, the current is cut off gradually from the bottom with a well-controlled speed.—M. Tama: Progress in dcctric furnaces for non-ferrous metals. New induction furnaces of large capacity are described. They have been developed for high melting-point alloys such as nickel-brass and phosphor-bronze. Thirty-four dcctric annealing furnaces of the resistor type are in successful operation in one large metallurgical plant.—N. F. Budgen: Pinholes in cast aluminium alloys. Gas evolution at solidification is the causation factor of greatest importance, and the means whereby gases may be absorbed by aluminium alloys are discussed. Shrinkage during solidification plays some part in producing pinholes.—O. F. Hudson, T. M. Herbert, F. E. Ball, and E. H. Bucknall: Properties of locomotive firebox stays and plates. Of the two main sections of the paper the first is devoted to a consideration of the conditions existing in a locomotive firebox. The other main section of the paper gives the results of an investigation of the oxidation of arsenical copper in firebox atmospheres. The rate of oxidation of arsenical copper in various atmospheres has been determined within the range of 260°-600° C. Small proportions of chlorine as hydrochloric acid gas and also of sulphur dioxide cause marked increase in the amount of oxidation. There was no evidence that the presence of arsenic in the copper had any influence on the rate of oxidation. The softening and elastic properties of cold-worked copper containing small percentages of other elements has also been investigated, the object being to obtain, by alloying and suitable mechanical and thermal treatment, copper, otherwise suitable for firebox purposes, which will have and retain at service temperature a reasonably high elastic limit, say, of the order of 5 tons/in.2 One of the most promising alloy additions is silver, of which so small a quantity as 0.05 per cent appears to be sufficient.—A. v. Zeerleder and P. Bourgeois: E (fect of temperatures attained in overhead electric transmission cables. Cables made, respectively, of copper, pure aluminium, steel-aluminium, and Aldrey were submitted to temperatures lower than the usual annealing temperatures for periods ranging from several months up to one year, and the effect on the mechanical properties was examined. Aldrey is not affected by temperatures which will seriously diminish the tensile strength of copper. Cables consisting of aluminium alloys having undergone previously an appropriate heat-treatment-such as Aldrey-are thus able, in spite of their lower electrical conductivity, to be loaded with higher current densities than copper cables, without danger of slow annealing.—J. Newton Friend: The relative corrodibilities of ferrous and nonferrous metals and alloys. (2) The results of seven years, exposure to air at Birmingham. The metals examined included tin, lead, nickel, zinc, aluminium, and various coppers and brasses. All resisted corrosion much more efficiently than the wrought iron and carbon steels. Nickel proved less resistant than copper. Aluminium ranked with lead, tin, and stainless steel in offering a very high resistance to corrosion.—C. Blazey: Idiomorphic crystals of cuprous oxide in copper. A description is given of idiomorphic crystals of cuprous oxide in copper, containing 0.43 per cent oxygen, which had been heated for a long time at a temperature above 800° C. The grain size of the copper was large and the cuprous oxide crystals were arranged in groups with uniform orientation, but in any one grain of copper the orientation of the groups varied. Long heating at a high temperature is necessary with, possibly, a favourable relationship to the crystallographic planes of the copper matrix.