High Purity Copper Single Crystals Research Articles

Lattice rotations during channel-die compression at high strain rates in copper single crystals of {110}, {112} and {123} orientations

The microstructure and texture evolutions of high purity copper single crystals of Br(1-10)[112], C(112)[11-1] and S(346)[63-5] initial orientations were investigated to evaluate the influence of high strain rate on the intensity of twinning and shear banding. The samples were deformed up to 60% in a channel-die at a strain rate of 7 × 105 s-1 using explosive energy to propel the punch. The microstructure was characterized by optical microscopy as well as scanning and transmission electron microscopy. High strain rates of deformation of C and S-oriented single crystals lead to massive deformation twinning. Despite the identification of three families of compact clusters of twins of two generations, the microstructure and texture of both single crystals are practically dominated by the twinning on only one co-planar slip plane. The common rotation of twin-matrix layers, within the narrow area, combined with deformation twinning in the re-oriented matrix are responsible for final SB texture formation. This mechanism contributes to the formation of orientations from the neighborhood of the {110}<100> orientation. The {110}<112> orientation, stable during deformation in channel-die in the range of ‘conventional’ strain rates, lost its stability giving rise to intense twinning and deformation bands across the deformed specimen.

Deformation of copper single crystals: Comparison of experimental results with crystal plasticity simulations

A combined experimental and numerical study on deformation behaviour of single crystal copper is presented in this paper. High purity copper single crystals were fabricated and subjected to uniaxial compression loading at quasi-static strain rate. The stress-strain responses along four different crystallographic orientations were then extracted after determining the initial orientation by Laue Back-Refection technique. In order to study and compare the responses, a phenomenological crystal plasticity model was described and implemented in a crystal plasticity finite element based code. The key description of the model follows a generalized yield criterion that incorporates non-Schmid effects assuming cross-slip plays an important role on orientation dependence of the material. Using the model, the stress-strain responses of four different crystallographic orientations were investigated. Investigations were also carried out on the shape change of the deformed crystals along with lattice orientation mapping. Finally, details of slip activities of the deformed crystals were determined by comparing the orientation of slip lines with the theoretical traces of possible crystallographic planes. The identity of the experimentally determined active slip modes was matched with those determined by the simulations.

Microstructure and microtexture evolution during strain path changes of an initially stable Cu single crystal

The microstructure and microtexture evolution in a deformed Goss oriented crystal were characterized after a sample rotation and consequent change in strain path, over a range of scales by optical microscopy, high resolution scanning electron microscopy equipped with field emission gun and electron packscattered diffraction facilities and transmission electron microscopy orientation mapping. High purity copper single crystals with initial Goss{1 1 0}〈0 0 1〉 orientation were channel-die compressed 59% to develop a homogeneous structure composed of two sets of symmetrical primary microbands. New samples with ND rotated orientations of Goss{1 1 0}〈0 0 1〉, brass{1 1 0}〈1 1 2〉, M{1 1 0}〈1 1 1〉 and H{1 1 0}〈0 0 1〉, were then cut out and further compressed in channel-die by a few per cent. The change in flow stress could be correlated with the change in dislocation substructure and microtexture, particularly along shear bands initiated by the strain path change. In the H{1 1 0}〈0 1 1〉 and M{1 1 0}〈1 1 1〉 orientations, the flow stress increased by Taylor factor hardening then decreased by intense macroscopic shear band (MSB) formation. In the softer brass orientation and in the absence of Taylor factor hardening, more diffuse MSB formation occurred. The local rotations in the band were used to deduce the possible local slip systems initiated during the strain path change.

Sub-Grain Size and Hall-Petch Relation in Pure Copper Single Crystals

The effect of sub-grain on the yield stress of pure copper single crystals with the [253] orientation was investigated by using the etch pit technique. The single crystal plates were successfully prepared from the seed crystals, which were produced at the melting temperature of 1473 K by the Bridgeman method. The present investigation confirmed the Hall-Petch relation concerning the effect of sub-grain boundaries on the macroscopic yielding of pure copper. The result derived from the extrapolation of the relationship of critical resolved shear stress (CRSS) and the initial dislocation density and sub-grain size is in good agreement with the evaluation in high purity copper single crystals of low dislocation density.

An Investigation of Deformation in Copper Single Crystals Using Equal-Channel Angular Pressing

This paper describes experiments in which high purity copper single crystals of two different orientations were processed for one pass by equal-channel angular pressing (ECAP) and the deformed structures were examined using optical microscopy (OM), orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). The first single crystal (0° specimen) was oriented within the entrance channel of the die so that the {111} slip plane and the &lt;110&gt; slip direction were parallel to the theoretical shear plane and shear direction, respectively. The second crystal (20° specimen) was oriented with the {111} slip plane and the &lt;110&gt; slip direction rotated by 20° in a clockwise sense from the theoretical shear plane and shear direction, respectively. For the 0° specimen, after passing through the shear plane there were two crystallographic orientations representing the initial orientation and an orientation rotated by 60° in a counter-clockwise sense from the initial orientation. For the 20° specimen, there was an orientation rotated by 20° in a counter-clockwise sense from the initial orientation after passing through the shear plane.

Orientation dependence of nanoindentation pile-up patterns and of nanoindentation microtextures in copper single crystals

We present a study about the dependence of nanoindentation pile-up patterns and of microtextures on the crystallographic orientation using high purity copper single crystals. Experiments were conducted on a Hysitron nanoindentation setup using a conical indenter in order to avoid symmetries others than those of the crystal structure. Orientation measurements were conducted using a high resolution electron back-scatter diffraction technique for the automated acquisition of texture mappings around the indents. Simulations were carried out by means of a 3D elastic–viscoplastic crystal plasticity finite element method which takes full account of crystallographic slip and orientation changes during indentation. The experiments as well as the simulations show that the pile-up patterns on the surfaces of (0 0 1)-, (0 1 1)- and (1 1 1)-oriented single crystals have four-, two-, and sixfold symmetry, respectively. The different pile-up patterns can be explained in terms of the strong crystallographic anisotropy of the out-of-plane displacements around the indents. Pronounced accumulation of material entailing characteristic pile-up patterns occurs along the intersection vectors between the primary crystallographic slip planes and the indented surface planes.

An Investigation of Deformation in Aluminum Single Crystals Using Equal-Channel Angular Pressing

This paper describes experiments in which high purity copper single crystals of two different orientations were processed for one pass by equal-channel angular pressing (ECAP) and the deformed structures were examined using optical microscopy (OM), orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). The first single crystal (0° specimen) was oriented within the entrance channel of the die so that the {111} slip plane and the slip direction were parallel to the theoretical shear plane and shear direction, respectively. The second crystal (20° specimen) was oriented with the {111} slip plane and the slip direction rotated by 20° in a clockwise sense from the theoretical shear plane and shear direction, respectively. For the 0° specimen, after passing through the shear plane there were two crystallographic orientations representing the initial orientation and an orientation rotated by 60° in a counter-clockwise sense from the initial orientation. For the 20° specimen, there was an orientation rotated by 20° in a counter-clockwise sense from the initial orientation after passing through the shear plane.

Directional annealing of cold-rolled copper single crystals

The effects of annealing temperature, hot zone velocity and temperature gradient ahead of the hot zone on the microstructure of directionally-annealed, cold-rolled, high-purity copper single crystals were investigated. Columnar grains were observed at an optimum hot zone velocity that increased with increasing annealing temperature and decreasing temperature gradient. Equiaxed grains were formed both when the velocity of hot zone movement was low, and when it exceeded the maximum growth rate of grains. The number of twin boundaries per unit area decreased with increasing hot zone velocity, increasing temperature gradient and decreasing annealing temperature. The results are explained in terms of the effects of annealing temperature and temperature gradient on the grain boundary mobility and the nucleation of new grains and twins.

Two-channel DC-SQUID picovoltmeter for the measurement of low-field Hall coefficient and electrical resistance from 4.2 to 100 K

A two-channel DC-SQUID voltmeter developed for the measurement of low-field Hall coefficient and electrical resistance of high-purity copper single crystals between 4.2 and 100 K is described. The noise is 1.8 pVHz −1/2 at 4.2 K and increases to 12 pVHz −1/2 at 100 K. A sample current up to 2.5 Å and a magnetic induction up to 60 mT can be applied.

Experimental Evidence of Kink Relaxation and Kink Resonance in Dislocations of FCC Metals

Many papers have been devoted to the motion of dislocation lines in crystals. The string model and the kink model presented the most relevant theoretical approach. However, each model independently can not describe all experimental data. In this paper is presented experimental data of logarithmic decrement associated to dislocation lines, measured in Hz and MHz ranges, on high purity copper single crystals plastically deformed by compression and torsion at room temperature. The experimental data obtained for the Bordoni Peak, analyzed on the basis of the kink model, shows the predicted temperature dependence of the effective enthalpy, a evidence of the kink diffusion mechanism. The data can be well fitted over all temperature range investigated, assuming the contribution of kink relaxation and kink resonance aging simultaneously. From the last mechanism a temperature dependent kink density is assumed. This procedure allows to explain the width and the asymmetry of the Bordoni peak.

Defect Cluster Structure and Tensile Properties of Copper Single Crystals Irradiated With 600 MeV Protons

AbstractThe defect microstructures and tensile properties of high purity copper single crystals have been studied after irradiation at room temperature with 600 MeV protons in the dose range from 10-3to 10-1dpa. The defect number density N of clusters shows a linear dependence with dose up to a saturation value of 4×1023m-3, with a broad transition region between doses of 3×10-3and 10-1dpa. The increase in critical resolved shear stress (CRSS) induced by the irradiation is proportional to the square root of the dose, up to a dose of 7×10-3dpa. These results are compared to those of both fission and fusion neutron irradiations, showing that in room temperature irradiations at low fluences, no recoil spectra effects can be detected.

The Bordoni Relaxation in High Purity Copper Single Crystals at Low Frequencies

The aim of this work is to explore the low-frequency spectrum of 5N pure copper in a sub-resonant pendulum which allows in situ cycled torsion deformation and recovery. Samples were taken from the same single crystals used for ultrasonic attenuation studies in order to compare both results in an Arrhenius plot. In one sample prepared by electro-erosion, polished with nitric acid, recovered 4 hours at 650°C in preliminary vacuum and 1, 4 and 9% deformed at room temperature, the spectra show a main Bordoni peak whose height increases with deformation, and additional peaks in the 40-65K range, as important as the Bordoni peak, which are due to impurities generated during the preparation of the sample. In an uncontaminated sample cut by diamond disk, polished with a mixture of nitric, phosphoric and glacial acetic acids, and water, recovered in 5.10 -6 mmHg vacuum, deformed 3 and 5%, the internal friction spectra show the main Bordoni peak as the principal effect, accompanied by a defect modulus. The study of the influence of different parameters such as the amount of deformation, the amplitude and frequency of oscillation, the temperature rate and the recoveries may be an interesting contribution to the characterization of the Bordoni peak.

Dislocation behavior and surface morphology of high purity copper single crystals fatigued at low-strain amplitude at elevated temperatures: Hidaka, K. Diss. Abstr. Int. (Dec. 1992) 53 (6), 135 pp

The characterization of critical levels of microstructural damage that can lead to fatigue-crack propagation under high-cycle fatigue loading conditions is a major concern for the aircraft industry with respect to the structural integrity of turbine engine components. The extremely high cyclic frequencies characteristic of in-flight loading spectra necessitate that a damage-tolerant design approach be based on a crack-propagation threshold, ΔKTH. The present study identifies a practical lower-bound large-crack threshold under high-cycle fatigue conditions in a Ti–6Al–4V blade alloy (with ∼60% primary α in a matrix of lamellar α+β). Lower-bound thresholds are measured by modifying standard large-crack propagation tests to simulate small-crack behavior. These techniques include high load-ratio testing under both constant-R and constant-Kmax conditions, performed at cyclic loading frequencies up to 1 kHz and R-ratios up to 0.92. The results of these tests are compared to the near-threshold behavior of naturally-initiated small cracks, and to the crack initiation and early growth behavior of small cracks emanating from sites of simulated foreign object damage.

Effects of neutron and gamma irradiation on the dislocation relaxation peak in very pure copper single crystal of 〈110〉 concentration

The effects of neutron and gamma irradiation on the height and temperature of the dislocation relaxation peak (Bordoni peak) have been studied in four very high purity copper single crystals having the orientation 〈110〉. Two crystals have width to length ratio 1:10 and the other two 1.3:1. Samples with different width to length ratio were used so that different dislocation loop lengths could be achieved by initial prestrains. In all samples the peak height and the peak temperature were reduced by irradiation. The samples with width to length ratio 1:10 exhibited a larger peak, due to the longer loops created in them. Gamma irradiation was found to have more effect on the characteristics of the peak than neutron irradiation. The results were in full agreement with the kink pair generation model.

THE EFFECT OF GAMMA IRRADIATION ON THE DISLOCATION RELAXATION PEAK OF COPPER

The effect of gamma irradiation on the dislocation relaxation maximum, i.e. the Bordoni peak, of two high purity copper single crystals of orientation &lt;110&gt; has been studied at a frequency of 10 MHz. It was found that as the irradiation dose increases the Bordoni peak height [Formula: see text] and its temperature Tm decreases in both specimens. A specimen of width to length ratio 1:10, i.e. easy glide, seems to be more sensitive to gamma irradiation than one of aspect ratio 1.3:1. The peak height and its temperature in the former specimen was found to be always higher than in the latter when both were irradiated with a similar dosage. The relation between [Formula: see text] and the gamma irradiation dose is of the form [Formula: see text] where y equals 1.4 or 1.5 depending on the mechanical treatment. Moreover, the study suggests that Q−1 is proportional to the dislocation loop length L in the form [Formula: see text] where n has values of 1.4 and 1.5 which agrees with the pair-kink generation model first proposed by Seeger.

Positive and negative surface induced deviations from Matthiessen's rule in thin copper wires

We have measured the electrical resistivity ϱ (d, T) of polycrystalline copper wires with diameter d comparable with the residual electron mean free path 1 E = 71 μm in the temperature range 4.2–35 K. The deviation from Matthiessen's rule caused by the surface scattering of the conduction electrons is examined and found to be negative in samples with d > 1 E. The magnitude of the surface-induced T 2 contribution to the resistivity of samples with d < 1 E increases linearly with (d/1 E) − 2 3 and supplement our recent results on high purity copper single crystals.

De Haas-van Alphen measurements of sub-grain misorientations in dislocated copper

De Haas-van Alphen measurements have been made of the angular distribution of sub-grains produced in dislocated high-purity copper single crystals bent about a (111) axis. The results are compared with models in which misorientations are formed by dislocations produced in various (121) directions depending on the resolved shear stress due to bending. The method has been shown to be an accurate probe of the distribution of misorientations in bent crystals, and is capable of measuring the components of misorientations in any direction by suitable choice of the crystal zone in which the direction of the magnetic field is varied. However, some discrepancies exist between the predicted values of the misorientations and the experimental data which are thought to be due to the inherent unrepeatability of producing dislocations, and hence misorientations, by bending. Reasons for the unrepeatability are discussed.

PVDF-Transducers for MHZ-Pulse-Echo Attemiatopm Measurements in Metals at Low Temperatures (Advantages and Limits)

Piezoelectric PVDF-foils have been tested as transducers for pulse-echo sound attenuation measurements at 10 to 200 MHz between 4 and 300 K. Their performance is compared with that of quartz transducers. Measurements of dislocation resonance absorption in high-purity copper single crystals are used to demonstrate that the thin foil PVDF transducers, in contrast to quartz transducers, cause no measurable dislocation effects due thermal expansion mismatch between sample and transducer, e.g. during cooling to low temperatures. However, measurements of the frequency dependence of attenua tion show that foil resonance and foil-X/ 4 interference effects have to be considered carefully with respect to measurements of stress amplitude, frequency and temperature dependence of attenuation.

Erosion of copper single crystals under conditions of 30° incidence

High purity copper single crystals were eroded at 30° to a (111) face using glass spheres 210 μm in diameter travelling at a velocity of 133 m s −1. Detailed scanning electron microscopy of both eroded surfaces and metallographic sections has been performed together with transmission electron microscopy of erosion debris. It was observed that there was extensive surface shear that led to ripple formation, folding of the surface, subsurface crack propagation and material loss by flaking similar to delamination wear. Direct evidence was obtained for recrystallization of the surface layers.

Mechanisms of solid particle erosive wear for 90° impact on copper and iron

High purity copper single crystals and fully annealed polycrystalline α-Fe were eroded by glass spheres 70 μm in diameter suspended in an argon gas stream and travelling normal to the target surface at 122 m s −1. Detailed scanning electron microscopy of eroded surfaces, together with transmission electron microscopy of erosion debris, was performed. It was observed that the surfaces developed a stable hill-and-valley topology not reported previously. The mechanism of material removal was plowing on the hillsides and flaking due to subsurface crack propagation in the valleys. Subsurface voids were created independently of second-phase particles and evidence existed for a local temperature rise at the surface.