Copper Grain Growth Research Articles

Yield Point Phenomenon Induced by Twinning Accompanied by Abnormal Grain Growth in Fine-Grained Copper

In this study, an equiaxed fine-grained copper specimen was fabricated by powder injection molding, followed by hot isostatic pressing. The specimen showed a yield point phenomenon with a Lüders-type deformation during a uniaxial tensile test. This study aimed to identify the cause of the yield point phenomenon in the fine-grained copper specimen. First, the Lüders band was designed to partially propagate within the gauge section through an interrupted uniaxial tensile test equipped with a digital image correlation system. The microstructures of the Lüders and non-Lüders band regions were compared by electron backscatter diffraction. It was observed that self-annealing was accelerated by the applied stress in the Lüders band region. Consequently, the microstructure of the Lüders band region transformed into a bimodal structure composed of fine grains and abnormally coarse grains containing numerous large twins. Identification of active twin variants in the abnormally coarse grains suggested that a significant tensile strain can be accommodated by this twinning. Based on these results, it was confirmed that the strain burst generated by the sudden occurrence of numerous large twins induces the yield point phenomenon in the fine-grained copper.

Blue laser welding of low thickness Ni-coated copper and mild steel for electric vehicle (EV) battery manufacturing

Modern advancements in blue lasers offer a promising alternative to conventional infrared laser welding of highly-reflective battery materials. In this study, a high-power blue laser system was used to weld the low thickness Ni-coated copper and mild steel used in 18650-type cylindrical cells. The effect of laser power on the penetration depth, interface width, and weld bead quality was studied. The weld microstructure was characterized by employing optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The mechanical performance of the welds was evaluated through peel testing and microhardness measurements. The results show that the penetration depth and weld width increased with laser power. Increasing the laser power to more than 1.3 kW resulted in a damaging effect on weld bead quality creating defects such as crack, under-fill, and distortion due to excessive heat input. Weld samples fractured in the heat-affected zone of Ni-coated copper during peel testing due to grain growth in copper. The maximum peel strength of 158.8 N was achieved for the 1.2 kW sample. The formation of a composite microstructure between Cu and Fe with a higher hardness than parent metals was observed inside the weld nugget. The hardness of this zone increased with the laser power due to an increase in the amount of Fe, reaching 185 HK for the 1.5 kW sample. By exposure to a corrosive environment, the peel strength drastically decreased and the failure occurred at the weld interface. For the 1.2 kW sample, the peel strength was reduced to around 57 N. The process initially developed for coupons of Ni-coated copper and mild steel was further tested on the positive and negative tabs of 18650-type cylindrical cells. The weld microstructure showed a lack of defects. However, due to varying thicknesses and associated heat sinks further process refinement is required for optimum joint quality.

The Ultrahigh-Rate Growth of Nanotwinned Copper Induced by Thiol Organic Additives

Incorporation of high-density coherent twin boundaries into copper grains can improve the physicochemical properties of copper. However, the scheme to synthesize such an attractive structure by high-speed direct-current electrodeposition is not adequately understood. Here we provide the first report for a facile strategy to induce the growth of nanotwinned copper grains with adding sufficient amount of the thiol organic molecule and discover that columnar nanotwinned copper can actually be deposited at an average growth rate up to 130 nm·s−1 via the direct-current electroplating. We confirm that the Cu+ concentration during the cupric ion reduction is crucial in the mechanism of twin formation. The high coverage of thiol-chloride bridges greatly accelerates the Cu2+/Cu+ reduction rate and promote the quantity and stability of Cu+ intermediates during electrodeposition. The concentrated thiol-chloride-Cu+ intermediates at the cathode surface/vicinity enable the formation of high-density nucleation sites for copper deposition and reduce the interfacial energy via stress releasing, leading to the formation of the nanotwinned structure. Ultimately, transformation into the microstructure with large columnar grains filled with high-density twin boundaries becomes the most thermodynamically favorable path for copper nucleation and growth.

Reduced Graphene Oxide–Refined Cu Matrix Composites: An Experimental and First‐Principles Study

AbstractReduced graphene oxide/copper matrix composites (RGO/Cu) are successfully fabricated via powder metallurgy methods. Composite powders of electrolytic Cu and 0.5 or 1.0 wt% graphene oxide (GO) are prepared by high‐energy ball milling. The composites are then consolidated using hot‐press sintering with a pressure of 22 MPa at 800 °C under a vacuum of 2 × 10−2 Pa. Microstructural observations of the RGO formed from GO show that it is located along the Cu grain boundaries and CuO nanoparticles distributed inside the Cu grain. The average grain sizes are 30.11 (pure Cu), 24.75 (0.5 wt% RGO/Cu composites), and 19.66 µm (1.0 wt% RGO/Cu composites). The Vickers hardness and tensile strengths of the RGO/Cu composites are higher than those of pure Cu. Theoretical research based on first‐principles calculations shows that oxygen atoms from the decomposition of GO react with Cu to form CuO nanoparticles. This secondary phase behaves as a pin that hinders the growth of copper grains. The covalent bonding between RGO and Cu slightly limits the movement of neighboring Cu atoms. More importantly, the grain refinement mechanism is related to the RGO retarding the diffusion of Cu atoms along the interface of copper grains due to its large activation energy.

Numerical Simulation of Grain Refinement of Pure Copper Solidified under Pulsed Magnetic Field

Grain refinement of pure copper solidified with the low voltage pulsed magnetic field (LVPMF) has been achieved in our previous experiments. To further study the influence of solidification condition on the as-cast structure and the relevant mechanism, the numerical investigation of grain growth of pure copper under LVPMF was conducted in the present work. The calculation result indicates that the temperature field and the cooling rate in the melt of pure copper become more uniform for the condition with LVPMF, meanwhile the cooling rate of melt in central region is much higher than the case without LVPMF. It is found the grain refinement by LVPMF is strongly related to the cooling condition. For the case without LVPMF, the larger the cooling rate is, the smaller the arm spacing of columnar grain structure. Under the LVPMF, the solidification pattern changes to equiaxed grain structure and the better grain refinement can be achieved with lower cooling rate.

Effect of initial texture on deformation-induced grain growth in pulsed electrodeposited microcrystalline copper

ABSTRACTOwing to the presence of large fraction of grain boundaries, deformation-induced grain growth is commonly observed in fine-grained electrodeposited metals. Here we demonstrate that microcrystalline copper (d∼1–10 µm) with different textures produced by electrodeposition exhibit significant deformation-induced grain growth in tension by coalescence along with twin boundary migration and detwinning. Oriented growth with the formation of a cube texture was noted in the deformed samples. There was an increased fraction of twin boundaries with large angular deviation from Brandon's criterion during deformation.

The effect of bismuth on microstructure evolution of ultrafine grained copper

The effect of bismuth on the microstructure evolution of ultrafine grained copper at elevated temperatures has been studied. Ultrafine grained copper polycrystals were produced employing the High-Pressure Torsion technique. Bismuth had little effect on kinetics of recrystallization and grain growth of as-processed copper. Bi-rich intergranular films at the grain boundaries were observed in the samples annealed between 700 and 900°C. Complete wetting of the grain boundary triple junctions by the Bi-rich liquid phase was observed at the temperatures below the onset of complete grain boundary wetting. We attributed the fact that Bi does not affect the kinetics of grain growth to the abundance of twin boundaries not affected by Bi segregation.

Microstructural and kinetic investigation on the suppression of grain growth in nanocrystalline copper by the dispersion of silicon carbide nanoparticles

In this paper, the thermal stability and grain growth kinetics of nanocrystalline Cu, reinforced with SiC nanoparticles and obtained using a mechanical milling process, were investigated during isothermal annealing. The presence of the nanoparticles in the nanocrystalline copper matrix resulted in a significant decrease in grain growth, the formation of partially textured microstructure and twin boundaries at higher temperatures, and an increase in the volume fraction of recrystallized grains, as estimated by grain orientation spread, in comparison to unreinforced Cu during annealing. The lower volume fraction of recrystallized grains at higher temperatures was attributed to dynamic recovery. Normal grain growth was observed in the annealing range of 400–600°C, and significant abnormal grain growth was observed at higher temperatures. An analysis of the grain growth kinetics in the temperature range of 400–600°C revealed a time exponent of n≈3.6 and activation energy of ≈34kJmol−1, based on the parabolic equation. The calculated activation energy for grain growth in the SiC dispersion strengthened Cu was found to be less than that of nanocrystalline Cu. The low activation energy and high thermal stability were attributed to high lattice strain and the retarding effect of nanoparticles by the Zener mechanism.

Synergistic effects of gelatin and convection on copper foil electrodeposition

Copper foil electrodeposition has been explored using a pure titanium rotating disk electrode (RDE) in acidic electrolytes containing gelatin and/or chloride ions under different convection conditions. In the plating bath without gelatin, the results indicate that stronger convection promotes hydrogen evolution, which reduces the current efficiency during copper plating. Gelatin restrains the growth of copper grains in the lateral direction parallel to the surface. This results in grain refinement on the shiny side, an increase in local grain misorientation and in internal stresses on both the shiny and the matte side, and a reduction in their internal stress difference. At strong convection conditions and with gelatin present, copper deposits as strip-like grains along the centrifugal direction of the cross section, and finally forms a spiral-shaped pattern on the matte side. The causes of these features are discussed in detail. The combined influences of hydrogen and gelatin adsorption are further elaborated in a model for a copper deposition. The current investigation suggests that a moderate convection (somewhat lower than 1000rpm) and a concentration of 2ppm gelatin in the plating bath are sufficient for copper foil fabrication in the presence of chloride ions (20ppm).

Oxidation-assisted graphene heteroepitaxy on copper foil.

We propose an innovative, easy-to-implement approach to synthesize aligned large-area single-crystalline graphene flakes by chemical vapor deposition on copper foil. This method doubly takes advantage of residual oxygen present in the gas phase. First, by slightly oxidizing the copper surface, we induce grain boundary pinning in copper and, in consequence, the freezing of the thermal recrystallization process. Subsequent reduction of copper under hydrogen suddenly unlocks the delayed reconstruction, favoring the growth of centimeter-sized copper (111) grains through the mechanism of abnormal grain growth. Second, the oxidation of the copper surface also drastically reduces the nucleation density of graphene. This oxidation/reduction sequence leads to the synthesis of aligned millimeter-sized monolayer graphene domains in epitaxial registry with copper (111). The as-grown graphene flakes are demonstrated to be both single-crystalline and of high quality.

The kinetics of grain growth in near-micrometre grain size copper produced by spark plasma sintering

Samples of copper with a grain size in the near-micrometre regime and in a nearly fully recrystallized condition have been prepared by a spark plasma sintering (SPS) process. The thermal stability of these samples in the temperature range from 950 to 1050 °C has been investigated by an analysis of the kinetics of grain growth, based on microstructural measurements using electron backscatter diffraction. In the temperature range from 950 to 1000 °C the activation energy for grain growth is approx. 300 kJ mol-1, corresponding to a value one and a half times the activation energy for self-diffusion in pure copper. In the temperature range from 1000 to 1050 °C the activation energy for grain growth is found to decrease, although annealing in this temperature range additionally results in non-uniform grain growth. For preparation of samples with a desired uniform grain size at present the best method appears to be via control of the temperature during the SPS process.

Influence of the gas phase composition on the properties of bimetallic Ag/Cu nanomaterials obtained via chemical vapor deposition

The carboxylate compounds [Ag(μ-O2CC2F5)]n and [Cu{CH2C(H)SiMe3}(μ-O2CC2F5)]m were used as precursors in chemical vapor deposition (CVD) for the preparation of bimetallic Ag/Cu nanomaterials. The composition and thermal stability of the copper and silver species transported in the gas phase were studied using mass spectrometry (EI-MS) and variable-temperature IR spectroscopy. The bimetallic [AgCu(O2CC2F5)2] carboxylate, which influences the properties of the resulting materials, was formed in the gas phase. The growth of rods and large copper grains on the silver surface was observed. Analyzing the morphology using scanning electron microscopy (SEM) and atomic force microscopy (AFM) indicated that the nAg/nCu molar ratio determined the composition of the gas phase, which affected the structure, grain size, and packing density of the Ag/Cu materials.

Cryogenic indentation-induced grain growth in nanotwinned copper

Nanocrystalline copper thin films with as-deposited Σ3 twin boundaries were indented while immersed in liquid nitrogen. Quantification using precession-enhanced electron diffraction determined the crystallographic texture and grain-to-grain misorientation of the undeformed, pile-up and compressed regions. Grains in the undeformed region retained a high density of Σ3 recrystallization twins, whereas the pile-up showed significant coarsening, prevalent Σ7 subgrain formation and a decrease in twin boundaries. The abnormal grain growth is attributed to a detwinning mechanism. The compressed region showed significant grain refinement.

Mechanism of film growth of pulsed electrodeposition of nanocrystalline copper in presence of thiourea

This article reports the effect of addition of small amount of thiourea on mechanism of film growth, levelling and grain refinement of pulsed electrodeposition of nanocrystalline copper on stainless steel substrate using simple aqueous acidic copper sulphate solution prepared from 0.25 M CuSO4·5H2O and 0.5 M H2SO4. The amount of thiourea used in the electrolyte is 0 and 36 mg/l. The results indicate the change in morphology of the deposits with addition of thiourea leading to dendrite free copper deposits. The growth mechanism of the copper deposition is found to change from Volmer–Weber type to Frank-Vander Merwe type making the deposits smoother when deposited with thiourea addition. A small amount (36 mg/l) of thiourea addition leads to decrease in the average grain size of copper from 1160 nm to 14 nm. The results clearly reveal the formation of nanocrystalline copper by addition of thiourea with three orders of magnitude reduction in grain size as compared to the sample deposited without thiourea. Preferential segregation of sulphur (present in thiourea) along the grain boundaries of nanocrystalline copper is shown by energy filter imaging using ultra high resolution transmission electron microscope (TEM), thereby restricting the growth of copper grains during pulsed electrodeposition.

Influence of Ar+ Energy of Bombardment Cu Target and Low Energy Assisted Bombardment on Cu-W Thin Film Structure by Ion Beam Sputtering

This paper is to study the influence of Ar+ energy of bombardment Cu target and low energy assisted bombardment on Cu-W film structure in the preparation of Cu-W thin film by dual ion beam sputtering technique with iron as the substrate and argon as ion source. The results shown : when Ar+ energy of bombardment tungsten target is about 3keV, the beam of copper target is 20mA, Ar+ energy of bombardment Cu target is 1kev, 1.5kev and 2keV respectively, Cu-W thin film prepared by ion beam sputtering exists with the skeleton of tungsten in amorphous phase mixing with copper grains; with the increase of Ar+ energy of of bombardment copper target, the grain size of copper increases slightly; influenced by crystal defects and lattice distortion, copper diffraction peak offsets a little. Low energy assisted bombardment helps to increase grain growth of copper and can decrease crystal defects and lattice distortion. But with excessive energy, thin film fails to deposit.

EFFECTS OF MICROSTRUCTURE ON TENSILE STRENGTH OF ELECTROFORMED COPPER

The electroformed copper with various microstructures are fabricated under conditions of non-agitation and ultrasonic agitation according to the demand of the electroforming micro components. The microstructure of the electroformed copper layer was observed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The preferred orientations of the layer were characterized by X-ray diffraction (XRD). The tensile strength was evaluated with a tensile tester. It was found that the copper layer preferentially grow along the (220) plane during the electroforming process, and the ultrasound-assisted technique led to a highly preferred orientation. The effects of ultrasonic vibration increased the chance of nucleation and controlled the excessive growth of copper grains during electroforming process. The microstructure of copper electroformed under condition of ultrasonic agitation is made up of regular columnar crystals, and its tensile strength increased by 40% in comparison with that of under condition of stationary state.

Numerical simulation of solidification morphologies of pure copper by vacuum continuous casting using cellular automaton model and its experimental verification

The purpose of this study was to predict the morphologies of the solidification process for pure copper using vacuum continuous casting (VCC) and to verify its accuracy by comparing these findings with observed experimental results. A finite differential method and a cellular automaton (CA) model were used to simulate the macro-temperature field for nucleation and grain growth of pure copper using real data from actual casting operations. From the observed experimental results, the drawing speed of the VCC process was considered as the fundamental parameter. With the increase of drawing speed, morphologies of the copper changed and the position of the liquid–solid zone moved closer to the orifice of the mould. The solidification morphologies simulated with the CA model were in good agreement with the results from the actual casting experiment.

Dislocation-assisted grain growth in nanocrystalline copper under large deformation

Dislocation plasticity conventionally induces textures in polycrystalline metals after a large deformation . We used parallel molecular dynamics to simulate the plastic deformation of nanocrystalline copper to an isochoric stretch up to 100% logarithmic strain. We found that the movements of partial dislocations that dominate the deformation process do not lead to texture formation. The grain size distribution becomes extremely inhomogeneous. By observing the structural evolution, we demonstrate that grain growth assisted by partial dislocations suppresses the texture formation.

D-36 Grain Growth and Texture Sharpening in Copper, Nickel and Palladium Thin Films, Investigated by Non-Ambient X-ray Diffraction Measurements

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Abnormal grain growth in alumina dispersion-strengthened copper produced by an internal oxidation process

Cu–2.7 vol.% Al2O3 (15 nm) composite was synthesized by an internal oxidation and hot extrusion process. The grain growth at elevated temperatures was studied and compared with extruded copper powder. Abnormal grain growth via a mechanism analogous to that of site-saturated phase transformation was observed. The critical grain size for the abnormal growth was determined to be 1.1 ± 0.2 μm. The growth rate decreased with time until the grain size approaching a final value ranging from 7.9 to 13.3 μm depending on the temperature.