Fine-grained Copper Research Articles

Dislocation microstructures and surface morphology in fatigued fine-grained copper polycrystals

Transmission electron microscopy observations of the dislocation substructure in fine-grained copper polycrystals fatigued at room temperature were carried out to investigate the correlation between surface morphology and the underlying dislocation substructure. The results indicate that samples fatigued under constant plastic strain amplitude well into the saturation region develop a small-scale surface roughness. The volume fraction of persistent slip band (PSB)-type structures is extremely low. PSB structures formed by the dominant slip system are observed only within narrow twin grains and are associated with an extrusion-like surface profile. The results are interpreted in terms of the size effect that allows one dominant slip system to operate in the plane parallel to a coherent twin boundary.

Microstructure and Hardness of Copper Powders Consolidated by Plasma Pressure Compaction

Bulk fine-grained copper samples were prepared by consolidating copper powders using the technique of plasma pressure compaction (P 2 C). The specimens were obtained by consolidating the powder particles under conditions of electrical pulse and no-electrical pulse and at two different temperatures. Results reveal that pulsing of the powders prior to consolidation led to higher microhardness values than the samples that were obtained by consolidating the powder particles under no-pulse. Both nanohardness and microhardness increased with an increase in the temperature of consolidation. Samples consolidated at the higher temperature revealed evidence of grain coarsening. The influence of processing variables on microstructure development and hardness is presented and discussed.

Microporous fine-grained copper: Structure and properties

Abstract Powder metallurgy processing has been used to produce copper compacts with fine grain sizes (1-10 μm) that are pinned by submicron-size to micron-size gas-filled voids in the volume fraction range 0.05-0.2. The effect of subsequent heat treatment on the grain size and void size and shape was quantified. These changes strongly depended on whether the powder was consolidated using a coldpressing-and-sintering route, or hot pressing; thus the pressed and sintered compacts densified further whereas the hot-pressed compacts exhibited swelling during subsequent thermal exposure. Such materials were mechanically tested in compression and tension at room temperature, and high yield strength, attributed to grain-size strengthening, was recognized. Tensile ductility in excess of 20% was simultaneously obtained although some unusual features, atypical of fcc metals, including upper and lower yield points and a low work-hardening rate were noted. Approximate calculations examining the interaction of dislocat...

Microporous fine-grained copper: structure and properties

Microporous fine-grained copper: structure and properties

Investigation of possibility to get superplastic state of nanostructured copper

The possibility of realisation of superplastic state of nanostructured (NS) copper (grain size 0.1–0.3 μm) produced by equal-channel angular pressing has been studied during creep and tensile tests in vacuum and under the influence of aluminium grain boundary diffusion fluxes from external source (coating). The creep acceleration effect for NS copper under the influence of aluminium grain boundary diffusion fluxes is found. The effect takes place in a lower temperature range as compared with fine-grained copper. It has been established that at 473K strong increase of strain rate sensitivity (m = ∂ lgσ ∂ lg ϵ) takes place during deformation of copper under influence of aluminium diffusion fluxes (m = 0.5) in comparison with pure copper (m = 0.19)

Rebuttal to “In defense of diffusional creep”

Rebuttals to the recent criticisms of Burton and Reynolds and of Greenwood to our papers challenging the existence of diffusional creep are presented and responses by us to the following specific areas are discussed. (1) Denuded zones, universally to be considered direct evidence for diffusional creep, are seen only under conditions where a high stress exponent (as opposed to a value of unity) is observed, indicating that diffusion-controlled dislocation creep is the operative deformation process. (2) The creep rate of fine-grained superplastic materials is invariably orders of magnitude greater than predicted by diffusional creep; in these cases, the deformation process has been established to be grain-boundary sliding accommodated by slip (GBS) rather than diffusional creep. (3) The creep behavior of fine-grained copper measured by Burton and Greenwood can be described by a diffusion-controlled dislocation creep mechanism at high stresses, by GBS at intermediate stresses, and by Harper-Dorn creep at low stresses, with no clear evidence for diffusional creep.

Localization of deformation in collapse of a thick walled cylinder

The thick walled cylinder method is used to study the character of plastic deformation localization (PDL) in materials with various crystalline lattice structures, defect packing energy, and grain size. It is shown that the development of the localization process leads to restructuring of the medium during collapse. The character of this restructuring, determined by the type of PDL bands and crack formation, depends to a large degree upon grain size. It is shown that the restructuring of fine-grained copper and Teflon is similar. In the copper development of microstructure with increased deformation rate was observed.

Effect of grain size and annealing texture on the cyclic response and the substructure evolution of polycrystalline copper

In attempting to interpret the mechanical response of polycrystalline copper, for which the results in the literature show marked scatter, the effects of microstructure on the cyclic behavior and the substructure evolution of copper polycrystals have been investigated. The microstructure is described by a complex factor—grain size and texture combined. It is found that there is a very significant effect of microstructure in the cyclic response of copper at low and intermediate strain amplitudes, where dislocation structures which localize deformation are expected to be present. In general, the cyclic response of coarse-grained copper shows a much more pronounced cyclic hardening and higher saturation stresses than those for fine-grained copper. This behavior is associated with a well defined hard 〈111〉−〈100〉 fiber texture, inherited in the coarse-grained material after annealing at relatively high temperatures. The multiple slip associated with the 〈111〉−〈001〉 oriented grains homogenizes the deformation very early, resulting in strong cyclic hardening, and a faster substructure evolution into cell structure.

Application of atomized copper powder in obtaining copper-graphite contacts

The method of decomposing salts makes it possible to obtain materials which, by their tribotechnical and electrocontact properties, are not inferior to the standard materials for electric brushes brands MG, MGSOA. The oriented laminated structure of fine-grained copper in graphite causes the formation of surface layers that are characteristic of normal mechanochemical wear. This improves the wear resistance of the material and stabilizes its electrocontact characteristics.

Unusual Combination of High Strength and Ductility in New Precipitation-Hardenable Nickel Silvers

A new series of fine-grained precipitation-hardenable copper alloy is presented. They are characterized above all by an excellent combination of high strength and ductility, and good resistance to atmospheric and tap-water corrosion. Since precipitation is sluggish, alloys do not have to be solution treated after final shape has been given, which reduces considerably the danger of distortion. Furthermore, because of a compensating mechanism in relaxation between matrix and precipitate, dimensional changes during aging are negligible. Finally, machining and cold forming tests under way suggest strongly that these forming processes are readily carried out prior to aging.

Cuprous hydrometallurgy: Part I. Electrorefining copper via acidic solutions of cuprous sulphate containing organic nitriles

Cuprous sulphate is stable in acid solutions containing organic nitriles. Such solutions may be used as electrolytes in the electrorefining of copper much like the aqueous cupric sulphate electrolytes. High quality fine-grained copper is deposited from cuprous sulphate electrolytes in a one-electron process offering savings in energy or time compared with the conventional two-electron process. The effect of nitriles on the cell voltage, optimum current density and role of additives is considered and optimum electrolyte compositions and cell arrangements are proposed.

Structure and property relationships for bulk electrodeposits

The properties of bulk electrodeposits depend on structure. Fine-grained deposits exhibit greater strength than coarse, columnar structures. For example, the tensile strengths of fine-grained copper and nickel reach values as high as 90 000 and 150 000 psi, respectively, in comparison with only 25 000 and 50 000 psi for the coarser-grained deposits. Analogously, the tensile strengths of fine-grained cobalt, gold, iron, and silver can be two to five times the strength of the coarse-grained counterpart. Nickel containing 0.02% sulfur (as nickel sulfide) exhibits a tensile strength as high as 235 000 psi. Some metals deposited at a high rate (> 0.001 in./min) are finer grained and stronger than their counterparts deposited conventionally at a rate < 0.00005 in./min. The physical properties of the fine-grained structures are dependent on the conditions adopted for refining grain size. High density, low electrical resistivity, and good thermal stability can be obtained with conditions that avoid undesirable inclusions.

Production and mechanical behavior of very fine-grained copper

Production and mechanical behavior of very fine-grained copper

Structure and Strength of Fine-Grained Copper and Silver Prepared by Vacuum-Deposition

Polycrystalline copper and silver films, about 2 to 10 μ thick, were vacuum-deposited on glass substrates using tungsten baskets. The variations of 0.2% offset yield stresses and microstructures of the films by annealing at various temperatures ranging from 100° to 1000°C were investigated. The grain size, which was about 2000 Å in diameter in an as-deposited state, increased to several microns in diameter after annealing. The grain size and recrystallization temperature were extremely affected by the deposition condition. The recrystallization temperature of copper films of 10−4 Torr rose above 800°C when the deposition was done in a high residual gas pressure. It is inferred that the fine dispersion of oxide in the films is responsible for the rise of the recrystallization temperature. The strength of the fine-grained films was agreed well with that expected from the Hall-Petch relation.