Pure Copper Specimens Research Articles

Nucleation and growth process of defect clusters in copper during helium ion irradiation

The formation process of interstitial dislocation loops in copper under He + ion irradiation has been studied by using transmission electron microscopy. Wedge shaped specimens of pure copper are subjected to irradiation with 5 to 100 keV He + ions at irradiation temperatures between 300 to 570 K. The minimum thickness were interstitial loops are formed increases with increasing He + ion energy and irradiation temperature, although this thickness scarcely depends on He + ion dose rate. The density of loops shows a linear increase against dose for irradiation with 20 and 30 keV He + ions but has a higher order dependence with respect to doses greater than 2 under irradiation with 5 and 10 keV He + ions. On the basis of the results induced by He + ion irradiation, we have concluded that a low fraction of high energy PKAs play an important role for the nucleation of interstitial loops for energies higher than about 20 keV.

The influence of anodic current on surface and bulk deformation at the crack tip of pure copper in 3.5% NaCl solution

The speckle-interferometry technique (SPI) was used to investigate the influence of anodic current on bulk deformation in the plastic zone at crack tip of corrosion fatigue by comparing the crack tip opening displacements of pure copper specimens in air and in 3.5% NaCl solution. In order to distinguish the different influences of anodic current on the bulk deformation and the surface deformation at crack tip, comparative analyses have been made by measuring the surface strain distributions near crack tip. After applying anodic current, both the plastic zone size and the strain on the surface ahead of crack tip increased significantly. The results indicated that the anodic current has no obvious influence on the deformation of internal material in the plastic zone at crack tip: anodic dissolution can release surface strain hardening and enhance the crack tip surface deformation but it cannot influence the mechanical behavior of internal material in the crack tip plastic zone directly.

Characterization of High Strength Cu/Ag Multilayered Composites

ABSTRACTIn this study, electrodeposition was employed to produce Cu-Ag multilayered nanocomposites using a single-bath cyanide solution. The silver and the copper layers were applied by electroless deposition and galvanostatic electrodeposition methods, respectively. The as-deposited composite showed a very high strength, which was increased upon annealing at 104°C. Annealing at 149°C caused the strength to drop to a level comparable to the strength of electrodeposited pure copper specimens. In this paper, the effect of heat treatment on the mechanical properties and structure of Cu-Ag multilayered nanocomposites is discussed.

Microstructure of copper and nickel irradiated with fission neutrons near 230°C

The microstructures of pure copper and nickel specimens were examined by transmission electron microscopy (TEM) following irradiation at ∼ 230°C in a mixed spectrum fission reactor to damage levels between 0.01 and 0.25 displacements per atom (dpa). A high density of small stacking fault tetrahedra (SFT) and dislocation loops was observed in both materials, and a moderate density of small voids was observed in the irradiated copper specimens. From a comparison with published studies, the proportion of SFTs and dislocation loops in copper was observed to be nearly constant over a wide range of damage levels at temperatures between 200 and 250°C. This suggests that nucleation and growth of interstitial loops to visible sizes is rather difficult in copper in this temperature regime. On the other hand, the loop size and density in nickel increased steadily with increasing dose. The defect clusters in nickel formed a {001} planar wall pattern which became visible after damage levels of ∼ 0.1 dpa. Defect cluster patterning was not observed in the irradiated copper specimens.

Effects of fission neutron and 600 MeV proton irradiations on microstructural evolution in OFHC-copper

Specimens of pure copper (oxygen-free high-conductivity grade) were irradiated with fission neutrons and 600 MeV protons. Fission neutron irradiations were carried out at 523 K in a temperature-controlled rig to fluences of ~ 5 × 10 23 and ~ 1.5 × 10 24 n/m 2 ( E > 1 MeV), corresponding to displacement doses of ~ 0.1 and 0.3 dpa, respectively. Irradiations with 600 MeV protons were carried out at 623 and 673 K to a dose level of ~ 0.5 dpa. Specimens irradiated with neutrons as well as protons were investigated by transmission electron microscopy (TEM). Quantitative determinations were made of defect clusters and cavities formed during irradiation. In the neutronirradiated copper, the swelling is found to be significantly enhanced in a relatively wide zone immediately adjacent to grain boundaries. TEM results demonstrate that the damage accumulation in copper irradiated with 600 MeV protons is significantly different from that observed in copper irradiated with fission neutrons. The implications of these results are discussed.

Defect microstructure in copper alloys irradiated with 750 MeV protons

Transmission electron microscopy (TEM) disks of pure copper and solid solution copper alloys containing 5 at% of Al, Mn, or Ni were irradiated with 750 MeV protons to damage levels between 0.4 and 2 displacements per atom (dpa) at irradiation temperatures between 60 and 200°C. The defect cluster density in copper was observed to be constant for irradiation temperatures below about 130°C, and to decrease with increasing temperature above 150°C. About 60% of the defect clusters in copper were resolvable as stacking fault tetrahedra (SFT). Cavity formation was observed for irradiation temperatures above about 150°C. The dislocation loop and network densities were relatively low in all of the irradiated pure copper specimens. Contrary to expectations, the loop density and size both decreased with increasing irradiation temperature. Solute additions did not have any significant effect on the total density of small defect clusters, but they did cause a significant decrease in the fraction of defect clusters resolvable as SFT to ~ 20 to 25%. In addition, the dislocation loop density (> 5 nm diameter) was more than an order of magnitude higher in the alloys compared to pure copper.

Gross slip criteria in fretting

One of the most important characteristics in fretting is the transition from mixed stick-slip conditions to gross slip, as given by the corresponding regime boundary in fretting maps. The regime boundary is determined by the critical values of frequency, normal force, tangential force amplitude and displacement amplitude. Three sets of criteria for incipient gross slip have been studied in the present investigation: fretting scar morphology, tangential force and displacement amplitude interrelations, and fretting energy dissipation. A fully computerized fretting tester has been used, in which the relative displacement between the specimens can be very accurately controlled and measured. Tangential force and relative displacement measurements can be made with resolutions of 2 nm and 5 mN respectively. Pure copper (UNS C11) specimens were studied. Post-test studies of fretting scars were performed by SEM. With some practice, it is possible to identify scar morphologies characteristic of the different regimes. The last two criteria were compared by plotting tangential force amplitude and energy dissipation together as functions of displacement amplitude in so-called FED (force energy displacement) diagrams. Some FED diagrams display force curves without a well-defined critical force amplitude, rendering the force criterion difficult to apply. The energy curves, however, always have a sharp bend, corresponding to a change in energy dissipation characteristics at the gross slip transition. The energy criterion occurs for a lower critical displacement amplitude than the force criterion (when applicable). A possible explanation of this observation is discussed.

Microcreep deformation measurements by a moire method using electron beam lithography and electron beam scan

Microcreep deformations in pure copper specimens are studied by a new moire method. In this method, a fine micrograting prepared by electron beam lithography is used as a model grating, and a scanning exposure ofthe primary electron beam in a scanning electron microscope (SEM) as a master grating. The scanning exposure of the electron beam on the specimen with the model grating produces moire fringes of bright and dark lines formed in response to the different amounts of the emitted secondary electrons for each primary electron. This new method makes it possible to obtain a clear and fine moire fringe without an image-processing system and to observe the moire fringe pattern and the SEM image at the same time. By this method, the inhomogeneous microcreep deformations such as grain boundary sliding, coarse slip, and localized strain are measured with high accuracy. It is confirmed that the creep strain is nonuniform even in the same grain and the strain distribution is caused mainly by the grain boundary sliding.

組合せ繰返し荷重下の切欠き材における分布微小き裂のモデル化に基づいた余寿命評価

A procedure to evaluate residual life under cyclic combined loadings was established for a given initial state of distributed small cracks. Distributed cracks at the initial stage were modeled as straight-line cracks by using an image-processing technique. The algorithm for the analysis of the crack growth after the initial stage was constructed by taking account of both modes of the propagation as a single crack and the coalescence between propagating cracks. Fatigue tests under combined axialtorsional loadings with constant and variable amplitudes were also conducted using cyclindrical specimens of pure copper with circumferential blunt notches. The fatigue life was correlated with the equivalent plastic strain range. When Compared for the same value of the parameter, the fatigue life became longer with increasing shear component in the stress state at the notch root, while no significant difference was observed between two loading modes of constant and variable stress amplitudes. The fatigue life defined by the formation of crack with a specific length was evaluated based on the proposed procedure. The predicted life almost coincided with the experimental data. Cracking morphology was also simulated by using the present model to show good correspondence with experimental observations.

Void swelling in copper and copper alloys irradiated with fission neutrons

Specimens of pure copper and copper alloys (Cu5Ni, CuCrZr) were irradiated with fission neutrons. Radiation damage microstructures were determined by transmission electron microscopy (TEM). The change in volume due to irradiation was obtained by density change measurements. The void nucleation and growth are found to be significantly affected by the presence of 5% Ni; the effects observed in the present experiments are directly opposite to the findings reported earlier on the Cu-5% Ni alloy irradiated with 1 MeV electrons. The swelling is found to be significantly reduced in CuCrZr alloy. The implications of these results are discussed in terms of spectrum and rate effects.

Chemical composition of regions alloyed by DIGM or DIR

The zinc concentrations of zinc-rich regions formed in a pure copper specimen by diffusion induced grain boundary migration (DIGM) and diffusion induced recrystallization (DIR) with a zincification technique are observed to be typically lower than that of the CuZn zinc source alloy. This phenomenon in the Cu(Zn) system has been analyzed on the basis of a new model to evaluate the chemical driving force of the reactions. The activity of zinc in the zincification atmosphere is assumed to be constant during the reaction. A contribution of the zinc atoms, which diffuse from the atmosphere into the specimen, to the Gibbs energy change of the reaction is considered in the model. The molar Gibbs energy of the copper-rich solid solution phase has been described using a subregular solution model. The experimental results have been accounted for rather well in DIR but not in DIGM. On the other hand, a rather satisfactory agreement between calculation and experiment for DIGM has been obtained through consideration of the effect of an elastic stress on the Gibbs energy of the alloyed phase.

AC Impedance Study of Cu and Cu‐Ni Alloys in Aerated Salt Water: I . Pd Coating and Corrosion Product Stripping

Electrochemical impedance spectroscopy measurements were conducted on rotating disk specimens of pure copper and commercial 90‐10 and 70‐30 copper‐nickel alloys over a 28 day period while immersed in an aerated aqueous 3.4% solution, after vapor deposition of a Pd layer and finally after stripping the detachable corrosion products. The results indicate that for pure copper only the inner corrosion product layer impedes the corrosion reaction whereas for the more corrosion resistant Cu‐Ni alloys, the porous, outer corrosion product layer accounts for the majority of the corrosion resistance. Contributing factors in the case of the Cu‐Ni alloys are the availability of electrons and catalytic sites within the pore structure especially in the vicinity of the inner/outer layer interface and the diffusion of dissolved oxygen within the pore electrolyte to these sites, the latter being the rate‐limiting step.

走査型電子顕微鏡を用いたモアレ法による微視的変形挙動の観察

A new Moiré method using a scanning electron microscope has been developed for the measurements of micro-deformation. In this method, the model grid is fine parallel lines of metal deposited on a specimen, and as a master grid, the electron beam of a SEM is used. The scanning of electron beam on the specimen with the model grid constructs a Moiré fringe. This fine Moiré fringe in a small area makes it possible to determine the distribution of strain around a small notch, the deformation within a grain and grain boundary sliding.For demonstrative experiments, tensile and creep tests of polyimide resin and pure copper specimens were carried out. In the tensile test of a polyimide resin specimen with a small hole, an observation of the electron beam Moiré fringe was performed in-situ in a SEM during loading. The Moiré fringes for copper specimens were observed after high temperature tensile test (673K) and interrupted creep test (723K and 30MPa). It is found that electron beam Moiré fringes are fine and clear enough to measure the strain distribution in a small area (about 500μm square) around a hole in a polyimide resin specimen. The strain distribution around a small hole was calculated from an analysis of the fringes and a strain contour map was constructed.The Moiré fringe in the copper specimens shows complicated patterns due to some metallurgical behaviours. The pattern was analysed. Grain boundary sliding could be measured with high accuracy from the displacement of Moiré fringe at grain boundary, and deformation in a grain and coarse slip bands could be observed from change in the Moiré fringe patterns in relation to micro-deformation modes. Also inhomogenious deformations at triple points and rotation caused by grain boundary slidings in a crept specimen were observed using this method.

Creep behavior of copper under plane stress state

Abstract The aim of this paper is to present results of creep experiments carried out on thin-walled tubular specimens of pure copper under combined tension and torsion at 573 K. The experimental program consists of creep tests for the material in the virgin state, and for the same material prestrained plastically at the room temperature by uniaxial tension or by pure torsion. The modified Norton's law, based on experimental observations, was proposed to describe the rate of secondary creep. This modification is based on the assumption that the material parameters may be expressed as the functions depending on the direction of the loading stress vector. Results are discussed in terms of a creep surface concept. The changes in size and shape of the creep surfaces caused by plastic prestrains express the evolution of the initial creep surface for virgin material.

組合せ荷重を受ける純銅の環状切欠き材の疲労における微小き裂の成長挙動と寿命特性に関する研究

Fatigue tests were conducted using solid cylindrical specimens of pure copper with circumferential blunt notches subjected to combined axial-torsional loadings. The behavior of crack growth was observed by a plastic replication technique, and the property of fatigue life was investigated. The cracking at notch root was identified as an intergranular type. The dominant morphology of crack growth was found to be the coalescence of distributed small-cracks, while some difference was observed depending on the stress multiaxiality. The fatigue life was correlated with the equivalent stress of the Mises type and the maximum shear stress. The fatigue life for the same value of each stress parameter became longer as increasing shear component in the stress state at notch root.An analytical procedure for the crack growth at notch root was established by using a model based on the competition between the coalescence growth and the propagation of a dominant crack. Characteristics of intergranular cracking at the notch root and its dependence on the stress state were very well simulated by the present analytical model. Fatigue lives in several test conditions were statistically estimated by a simulation of the Monte Carlo type. The prediction with the simulated scatter-bands almost coincided with the experimental results.

二軸応力下の弾塑性疲労き裂の伝ぱ挙動

Fatigue crack propagation tests were conducted using thin-walled tubular specimens of pure copper under combined in-phase axial-torsional loadings. In large scale yielding situations, the crack growth behavior under biaxial stresses was investigated based on the elastic-plastic fracture mechanics. The crack morphology was found to be a bent-type in the combined loadings and a branch-type in the torsion case. Cracks were found to propagate in such direction that the Mode II component of the stress intensity factor was minimized. By using a devise to detect the opening and sliding displacements at the center of crack, the deformation behavior of bent-or branch-cracked specimens was also examined to evaluate the crack opening point. It was noted that tails were observed near both tips of the hysteresis loop in the case of torsion. The correspondence between these tails and the crack closure was discussed in the relation with the opening and closing behaviors of ideally elastic cracks. The effective stress intensity factor ΔKIeff of Mode I was calculated by taking account of experimental observations mentioned above. When ΔKIeff was employed to correlate the growth rate, good correlation was not seen because of gross plasticity. A tentative procedure to estimate the J-integral range ΔJ was proposed for the bent crack. The growth rate of bent crack was correlated very well with ΔJ estimated by the proposed procedure.

The interaction between oxygen and bismuth in dilute solution in copper at 1300 °C

The activities of bismuth (in the range 0.0021 < XBi< 0.0053) and oxygen (in the range 3 X 10−4 < Xo < 0.044) in liquid copper at 1300 ° have been measured by equilibrating pure copper specimens with gaseous atmospheres of known oxygen potential and partial pressure of bismuth. The value of γ Bi o in liquid copper at 1300 ° was obtained as 3.09 and the variation of γBi with mole fraction of oxygen was obtained as log γBi = −0.91Xo + 0.49, which yields ɛ O Bi = −2.1. The observed variation of log γo with mole fraction of bismuth is widely scattered but is in fair agreement with the thermodynamically-consistent expression, log γo = −0.9LYBi − 0.51.

弾塑性衝突する物体の衝突端応力変動

In the present study, a new method for measuring the time-variation of stress at the impact end in the elastic-plastic collision of a body against another body was developed and the duration of impact was discussed.Firstly, the simple method for measuring the duration of impact, called the sensing cylinder method, was proposed. The sensing cylinder was confirmed by calibration tests to be effective for measuring not only the duration of impact but also the impulsive force generated at the impact end of a body.Secondly, as an application of the measuring method, plastic impact tests were made on pure copper and aluminum specimens with several different lengths. The time-variation of stress at the impact end of the bars colliding with the sensing cylinder and the duration of impact were measured under various impact velocities. The experimental results were compared with the theoretical ones based on the strain-rate dependent theory of plastic wave propagation. Close agreement between the observed and the calculated values was obtained.

Formation of secondary defects in copper by 14 MeV neutron irradiation and their effects on microstructure evolution

Pure copper specimens were irradiated at 25, 200 and 400°C by 14 MeV neutrons using RTNS-II to the dose of 3.6 × 10 22 n/m 2 and their damage structure was examined by means of transmission electron microscopy. At 25 and 200°C, stacking fault tetrahedra (SFT), partially dissociated Frank loops, aggregates of vacancies, and interstitial loops are nucleated by cascade collapse. They have a tendency to be formed as a group up to about 10. Because SFT are very stable under irradiation, excess interstitials corresponding to the vacancies retained in SFT are accumulated in the matrix and form their clusters. Interstitial loops nucleated near a dislocation grow preferentially by absorbing the interstitials migrating towards the dislocation. Voids were observed at 400°C. They play a very important role in void swelling at high dose.

A simple law of steady-state creep for material with anistropy introduced by plastic prestraining

The Odqvist theory is generalized by employing a plastic prestrain-induced anisotropy tensor of rank four, which is a linear combination of fourth rank tensors formed by the isotropic tensor δ ij and the prestrain effect tensor e( . The constitutive equation is verified by uniaxial creep experiments carried out on thin-walled tubular specimens of pure copper deformed previously at room temperature under combined tension and torsion stresses.