Cold-rolled Copper Research Articles

Effects of cold rolling path on recrystallization behavior and mechanical properties of pure copper during annealing

The recrystallization behavior, grain boundary characteristic distribution, and mechanical properties of pure Cu sheets that were subjected to different cold rolling paths, and then annealed at 400 °C for 10, 30, 60, and 420 min, were investigated. Different rolling paths changed the grain boundary orientations of cold-rolled copper, causing recrystallized grains to nucleate and grow in an oriented manner. However, the evolution of the texture indicated that cold-rolled copper with different rolling paths did not show an obvious preferred orientation after annealing. The RD-60 specimen exhibited the smallest grain size (6.6 μm). The results indicated that the grain size and low-Σ CSL grain boundaries worked together to provide RD-60 samples with appropriate mechanical properties and high plasticity. The yield strength, ultimate tensile strength, and elongation of RD-60 sample were 81 MPa, 230 MPa, and 49%, respectively. These results could provide guidance for tuning the microstructures and properties of pure Cu foils, as well as designing fabrication routes for pure Cu foils through processes such as rolling and drawing.

The Influence of Crystal Orientation and Thermal State of a Pure Cu on the Formation of Helium Blisters

The factors that influence the formation of helium blisters in copper were studied, including crystallographic grain orientation and thermomechanical conditions. Helium implantation experiments were conducted at 40 KeV with a dose of 5 × 1017 ions/cm2, and the samples were then subjected to post-implantation heat treatments at 450 °C for different holding times. A scanning electron microscope (SEM) equipped with an electron backscatter diffraction (EBSD) detector was used to analyze the samples, revealing that the degree of blistering erosion and its evolution with time varied with the crystallographic plane of the free surface in different ways in annealed and cold rolled copper. Out of the investigated states, rolled copper with a (111) free surface had superior helium blistering durability. This is explained by the consideration of the multivariable situation, including the role of dislocations and vacancies. For future plasma-facing component (PFC) candidate material, similar research should be conducted in order to find the optimal combination of material properties for helium blistering durability. In the case of Cu selection as a PFC, the two practical approaches to obtain the preferred (111) orientation are cold rolling and thin layer technologies.

Comparing the properties and growth of graphene on electrolytic and rolled Cu foils by chemical vapor deposition

In this work, we use electrolytic copper foils as substrates for the deposition of graphene by chemical vapor deposition. We investigate the effects of preannealing conditions, methane injection time, and temperature to synthesize graphene with a similar quality as when grown on cold-rolled copper. We find that the electrolytic copper foil’s annealing conditions and CH4 injection temperature determine the quality of graphene.

Comparison of a copper processed by asymmetric unidirectional rolling (AUR) and cross rolling (ACR): Strain distribution, microstructure, texture, and mechanical properties

In this work, the effect of strain path on the strain distribution, microstructural evolution, crystallographic texture, and mechanical behavior of electrolytic tough-pitch copper was investigated by simulation and experimental procedures. The asymmetric unidirectional and cross rolling processes with a thickness reduction of 90% were performed at room temperature. The asymmetric cross-rolling (ACR) gives much better through-thickness uniformity of shear strain distribution compared to the asymmetric unidirectional-rolling (AUR). The average equivalent strain of AUR and ACR after 90% rolling reduction was 3.99 ± 1.22 and 3.66 ± 0.26, respectively. Both AUR and ACR processes improved the particle distribution in the matrix. However, the particle distribution of the AUR sample was slightly more uniform compared to the ACR sample. The shape of primary grains in the AUR copper was straight while that in the ACR sample was zigzag. The average dislocation density of the AUR sheet was larger than that of the ACR sample (2.41 × 1016 m−2 vs. 2.31 × 1016 m−2). The major recrystallization mechanism in the AUR and ACR samples was discontinuous and continuous dynamic recrystallization, respectively. The main deformation textures (Copper, S, and Brass components, and α and β fibers) were weak in both samples due to the domination of recrystallization and shear textures in the cold-rolled copper. The recrystallization texture components in the upper region were stronger than in the lower region. The uniformity of the microhardness profile of the ACR sample was more than that of the AUR sample. The AUR sample had a larger strength and a smaller ductility compared to the ACR sample. The results showed that the strain path of asymmetric rolling was effective on the strain-hardening behavior of copper during the tensile test. The fractograph of the ACR sheet exhibited ductile dimples. However, the fractograph of the AUR sample revealed many ductile shear dimples and flat surfaces.

The Influence of Adventitious Carbon Groups on the Wetting of Copper: A Study on the Effect of Microstructure on the Static Contact Angle.

Tuning of the wetting behavior of metallic surfaces by chemical and topographical modification has become popular in recent years. Still, there is a lack in the understanding of fundamental relations between intrinsic properties of the material and its resulting water contact angle. It is widely accepted in the literature that transitions from a hydrophilic to increasingly hydrophobic behavior upon exposure to ambient conditions happen due to the adsorption of adventitious hydrocarbons. In order to investigate the role of metallic bulk microstructure in the wetting behavior and its transition properties, we created three different grain sizes and deformation states on copper by preparation combined with heat treatment. We found that for freshly prepared surfaces, differences in the wetting behavior show a higher static contact angle for mechanically prepared surfaces with a fine-crystalline deformation layer compared to the electropolished cold-rolled copper sheet and the annealed defect-free coarse-grained surface. Already after five days of storage time, most of this difference vanishes, and all surfaces show a wetting behavior with a contact angle in the range of 97-100° after 30 days. Though long-term wetting behavior seems largely independent of microstructure, correlated XPS measurements showed an increased adsorption of organic contaminants of the mechanically polished surface. Preparation-induced near-surface defects seem to accelerate adsorption, while varying grain size and slight bulk deformation from rolling processes did not show significant effects. Complex relations between the amount of adsorbed carbon and the polarity of the adsorption film were found to depend on the sample age and influence the contact angle.

Chemical Vapor-Deposited Graphene on Ultraflat Copper Foils for van der Waals Hetero-Assembly.

The purity and morphology of the copper surface is important for the synthesis of high-quality, large-grained graphene by chemical vapor deposition. We find that atomically smooth copper foils—fabricated by physical vapor deposition and subsequent electroplating of copper on silicon wafer templates—exhibit strongly reduced surface roughness after the annealing of the copper catalyst, and correspondingly lower nucleation and defect density of the graphene film, when compared to commercial cold-rolled copper foils. The “ultrafoils”—ultraflat foils—facilitate easier dry pickup and encapsulation of graphene by hexagonal boron nitride, which we believe is due to the lower roughness of the catalyst surface promoting a conformal interface and subsequent stronger van der Waals adhesion between graphene and hexagonal boron nitride.

Twinning during recrystallization and its correlation with the deformation microstructure

The formation of annealing twins during recrystallization in a cold-rolled copper single crystal has been studied. A new method is proposed to classify annealing twins according to their orientation relationship with the surrounding deformed matrix. A statistical analysis based on the new classification method shows that during growth of a recrystallized grain, twinning occurs more frequently on twinning planes close to one of the {111} planes of the deformation microstructure, and most frequently when the {111} plane is the dominant slip plane of the deformed matrix for the present single crystal. The differences in morphology for different types of twins are discussed based on growth selection criteria. The study highlights the importance of the local deformation microstructure on the formation of annealing twins.

Non-uniform Grain Boundary Migration During Static Recrystallization: A Cellular Automaton Study

During static recrystallization, grains often have non-constant and non-uniform growth rates, significantly affecting the recrystallization kinetics and the microstructure after recrystallization. A cellular automaton model was employed in order to evaluate the relative influences of gradients of stored energy, grain boundary curvature, and heterogeneity of grain boundary mobility on the non-uniform migration of grain boundary segments, leading to the formation of protrusions and retrusions. Electron back-scatter diffraction measurements of a cold-rolled copper microstructure served to feed the model. Orientation maps obtained after partial recrystallization were used to assess the model outcome. The model was capable to predict the shapes of recrystallized grains with retrusions and protrusions. Effects of different model assumptions were compared to reveal individual contributions of different factors to grain size distribution, grain shape and boundary roughness. The model predicted a decreasing average grain growth rate as a result of the progressive immobilization of an increasing fraction of grain boundary segments. The model prediction was compared with experimental results, explaining the origin of stationary boundaries and indicating some further improvements necessary to reach quantitative agreement.Graphical

Self-organized criticality – a model for recrystallization?

Abstract A novel X-ray diffraction method, allowing the position-resolved imaging of a polycrystalline specimen using the diffracted radiation, was applied for in situ investigation of recrystallization of cold-rolled copper. A large area of the specimen could be observed simultaneously, yielding information about nucleation and growth of many individual crystallites. The recrystallization process showed a stochastic behavior which can be described by the model of self-organized criticality.

Effect of Substructure on Hardness and Conductivity of Copper During Annealing

In the present investigation, the effect of substructures on hardness and conductivity during partial annealing of cold-rolled copper was studied. Substructures were observed after annealing at lower temperature; however, the annealed sample (at higher temperature) was mostly free from substructures. Therefore, it is proposed that the restoration mechanism at lower temperature envisages recovery in copper; however, it is partial recrystallization at higher temperature. There was an increase in hardness observed at lower temperature due to higher fraction of substructures, while an increase in conductivity was observed at higher temperature due to partial recrystallization. It was confirmed that the twin boundaries produced during cold rolling provided dislocations pinning, leading to greater tensile strength.

The role of surface morphology on nucleation density limitation during the CVD growth of graphene and the factors influencing graphene wrinkle formation

ABSTRACTCVD graphene growth typically uses commercially available cold-rolled copper foils, which includes a rich topography with scratches, dents, pits, and peaks. The graphene grown on this topography, even after annealing the foil, tends to include and reflect these topographic features. Further, the transfer of such CVD graphene to a flat substrate using a polymer transfer method also introduces wrinkles. Here, we examine an electropolishing technique for reducing native foil defects, characterize the resulting foil surface, grow single-crystal graphene on the polished foil, and examine the quality of the graphene for such defects.

Adiabatic shear deformation behaviors of cold-rolled copper under different impact loading directions

Adiabatic shear deformation behaviors in cold-rolled copper under different impact loading directions were systemically investigated in this paper. Split Hopkinson Pressure Bar (SHPB) system was used for the dynamic test. The microstructure and microtexture of the received shear localization regions were investigated by optical microscopy (OM), electron backscatter diffraction (EBSD) technique and microhardness tests. Three hat-shaped specimens were cut from cold-rolled copper sheet with the direction with an angle of 0° (RD sample), 45° (RD-45° sample) and 90° (TD sample) from the rolling direction within the rolling plane. The stress-strain curves indicate that the mechanical properties of the cold-rolled copper sheet show regularity in the work hardening dominated stage and that the shear stress of TD sample is the highest in that of the those three. OM results show that the morphology of adiabatic shear band in three samples shows differences that their deformation processes fall into two categories, pure relative shearing in RD sample and relative shearing with rotation in RD-45° and TD sample. EBSD results reveal that ultrafine grains with high-angle-boundaries are found within the adiabatic shear bands in three samples. The microhardness measurements show that the microhardness of shear region in three samples are significant higher than that of other regions. However, the size of grains within the shear band in RD sample are much larger than that in the other two samples. Microtexture analysis reveals that the grain orientations inside the shear band in three samples show similar characteristics that the <110> direction tends to parallel to the local shear direction and the {111} and {100} planes tend to parallel to the local shear plane. The calculated results show that rotational dynamic recrystallization can take place in the shear band.

Relationship between Dislocation Density and Antibacterial Activity of Cryo-Rolled and Cold-Rolled Copper.

In the present work, cold rolling and cryo-rolling were performed on 99% commercially pure copper substrates. Both cold and cryo-rolling processes caused severe plastic deformation that led to an increase in dislocation density by 14× and 28× respectively, as compared to the pristine material. Increases in average tensile strengths, by 75% (488 MPa) and 150% (698 MPa), were observed in the two rolled materials as the result of the enhancement in dislocation density. In addition to strength, enhanced antibacterial property of cryo-rolled copper was observed in comparison to cold rolled and pristine copper. Initial adhesion and subsequent proliferation of bio-film forming Gram-positive bacteria Staphylococcus aureus was reduced by 66% and 100% respectively for cryo-rolled copper. Approximately 55% protein leakage, as well as ethidium bromide (EtBr) uptake, were observed confirming rupture of cell membrane of S. aureus. Inductively coupled plasma-mass spectroscopy reveals higher leaching of elemental copper in nutrient broth media from the cryo-rolled copper. Detailed investigations showed that increased dislocation led to leaching of copper ions that caused damage to the bacterial cell wall and consequently killing of bacterial cells. Cryo-rolling enhanced both strength, as well as antibacterial activity, due to the presence of dislocations.

Diffusion bonding of aluminum-magnesium using cold rolled copper interlayer

Diffusion bonding, due to improving the dispersion of brittle intermetallic compounds, reducing the process energy and increasing the bonding strength of aluminum-magnesium joints, is widely used. In the present study, the commercially pure aluminum and magnesium bulks were successfully diffusion bonded at different strain values (0, 30 and 60%) at 480 °C and different holding times in two cases of without interlayer and with cold rolled copper interlayers. The results of the microstructural study using scanning electron microscopy (SEM) showed that, in interlayer-used bonding, the increase in the strain value of copper interlayer led to a wider joint diffusion layer. The results of the micro hardness test indicated that the hardness of the bonding interface in interlayer-used bonding, decreased in comparison with the non-interlayer bonding state. Moreover, the shear strength test showed that, as the holding time in the non-interlayer state increased, the strength decreased and in the case of interlayer-used bonding, increased time and strain resulted in increased strength of the Al-Mg bond. By rolling the interlayer to different values, the structural and mechanical properties of the Al-Mg diffusion bonding can be adjusted.

Importance of Non-uniform Boundary Migration for Recrystallization Kinetics

Recrystallization kinetics is studied by three characterization methods: post-mortem electron microscopy, in situ three-dimensional X-ray diffraction (3DXRD), and ex situ electron microscopy. Cold-rolled copper is used as a model material. The post-mortem analysis shows that the average migration velocity of unimpinged recrystallizing boundaries decreases strongly with annealing time, leading to a low Avrami exponent. For individual grains, the in situ 3DXRD measurement reveals that the growth rates decrease significantly shortly after nucleation. This is explained by the ex situ characterizations, which show that different segments of the recrystallizing boundaries migrate with significantly different velocities, and some boundaries, although unimpinged, remain stationary. This non-uniform migration of recrystallizing boundaries leads to an amoeba-like growth, and is proposed to be responsible for the decrease of the average boundary migration velocity, because the fraction of slowly moving/stationary boundaries increases during the recrystallization. Reasons for stationary boundaries are discussed based on a quantitative analysis of the local deformed microstructure. It is concluded that non-uniform boundary migration has a significant influence on recrystallization kinetics and needs to be included in recrystallization models.

Effect of electric-current pulses on structural changes in cold rolled copper at different initial temperatures

The influence of external current electric fields on the mechanical properties of metals and alloys has been studied for a long time. The effects of electric-current pulses (ECPs) on materials structure were attributed to an increase in the mobility of dislocations in the presence of the electric current (an effect sometimes referred to as “electron wind”) and subsequent acceleration of the formation of recrystallization nuclei. At the same time, it has been demonstrated that the Joule heat induced by ECP has some impact on the recrystallization microstructure of the material. What makes the dominant contribution to the structural changes taking place in the material, Joule heating or "electron wind", remains still unclear. The aim of this work was to determine the effect of Joule heating by electric-current pulses on the evolution of grain structure at different initial temperatures in copper specimens. For this purpose, copper samples were rolled to a 90% thickness reduction and then pulsed at two initial temperatures of the specimens, 20°C and -170° C, the latter being achieved by cooling with liquid nitrogen. As the integral current densities 0.449 × 105 A2s mm-4 for initial room temperature and 1.052 × 105 A2s mm-4 for initial temperature -170oC were attained, the material was recrystallized completely. The microstructural changes are compared to similar observations for static recrystallization and explained in terms of Joule heating.

Effects of lubricants on the rolling performances of cold rolled copper strips

Two parameters in rolling process, the forward slip value (Sh) and the minimum rolling gauge (hmin) were tested using a 4-high rolling mill in order to investigate the rolling performances of cold rolled copper strips under different lubricating conditions viz, lubrication with (i) base oil, (ii) base oil with 0.5wt.% oiliness, (iii) base oil with 0.5wt.% dialkyldithiophosphateester(DDE) and (iv) base oil with 0.25wt.% DDE and 0.25wt.% molybdenum dialkyldithiophosphate (MoDDP). The surface roughness of rolled copper strips was measured by a laser scanning confocal microscope. The surface morphologies of copper strips were observed by a scanning electron microscopy (SEM) and the compositions of the surface residues were analyzed with an energy dispersive spectrometer (EDS). Results showed friction coefficients, which were calculated by Sh with different lubricants ranged from 0.067-0.302. The surface topography of copper strips showed smooth and the plowing wear was finer. Meanwhile, when the lubricant was base oil with 0.25wt.% DDE and 0.25wt.% MoDDP, the hmin of copper reached 19μm, a value satisfied the copper foil conduction. However, with the addition of EP additives, the topographies showed some grind pits at local region. Indicating that EP additives containing P, S, Mo moieties possess a better thickness-reducing performance, but cause corrosion at the same time.

In Situ XRD Studies of the Process Dynamics During Annealing in Cold-Rolled Copper

The dynamics of the release of stored energy during annealing along two different crystallographic planes, i.e., {111} and {220}, in deformed copper have been investigated using in situ X-ray diffraction measurements at 458 K and 473 K (185 °C and 200 °C). The study has been carried out on 50 and 80 pct cold-rolled Cu sheets. The microstructures of the rolled samples have been characterized using optical microscopy and electron backscattered diffraction measurements. The microstructural parameters were evaluated from the X-ray diffractogram using the Scherrer equation and the modified Rietveld method. The stored energy along different planes was determined using the modified Stibitz formula from the X-ray peak broadening, and the bulk stored energy was evaluated using differential scanning calorimetry. The process dynamics of recovery and recrystallization as observed through the release of stored energy have been modeled as the second-order and first-order processes, respectively.

Development of special lubricant for the copper belt cold rolling

Purpose Aiming at the high temperature, high speed, high precision and high surface quality of the copper belt cold rolling, the purpose of this paper is to develop a new type of lubricant for cold rolled copper belt. Design/methodology/approach The component of the developed oil was determined based on the physical and chemical properties of the base oil and the tribological properties, the oxidation resistance properties, the rust resistance properties, the anti-foam properties, the demulsibility and the other properties of the additives. The orthogonal experiment method was used to determine the optimum adding amount of the additives; finally, the developed oil formulation was determined. Findings The physical and chemical experiment results show that the developed oil has a good performance of oil film bearing capacity and oxidation resistance. The simulation of rolling experiment found that the developed oil can significantly reduce rolling pressure and effectively reduce the friction in the process of rolling. Originality/value The experimental results show that the developed oil has excellent performance and can meet the requirement of lubrication in the process of cold rolling copper belt.

Line-Profile Analysis Combined with Texture Analysis for Characterizing Dislocation Distribution in Texture Components of Cold-Rolled Copper Sheets

Abstract We described a newly developed characterization technique that dislocation density could be individually determined for each texture component of plastically deformed metals by combining the line-profile analysis with the texture analysis by using X-ray diffraction. This method was applied to major texture components of cube, copper, and brass evolved in cold-rolled copper sheets. The Warren–Averbach procedure using two diffraction peaks was used for estimating the dislocation density. An increase in the dislocation density with the rolling reduction was evaluated for individual texture components. Although the individual texture components underwent the different slip paths, the dislocation densities in these texture components were almost comparable; however, the non-texture component was shown to have a higher dislocation density than the texture components. The recovery and recrystallization proceeded preferentially in the non-texture component.