International Annealed Copper Standard Research Articles

Fractal structure and nano-precipitates break comprehensive performance limits of CuCrZr alloys

Modern industrial materials are often required to have excellent comprehensive properties. Contact wire used in high-speed train needs possess high strength and toughness, high conductivity and wear resistance, which are often trade-off with each other. In this work, we constructed a fractal structure with high-density nano-precipitates in CuCrZr alloy via rotary swage plus aging, and break the strength, conductivity and ductility limits of existing Cu alloys. The CuCrZr alloy exhibits unprecedented comprehensive properties of a high ultimate tensile strength of 626 MPa, a ductility of 19% and an electrical conductivity of 82% international annealed copper standard (IACS). Microstructural analysis indicates that the fractal structure and high-density nano-Cr precipitates block and accumulate dislocations, but allow electrons to flow unimpededly along the axis of CuCrZr wire, resulting in the high toughness and conductivity. Our finding verifies fractal structure has the potential to obtain materials with super excellent comprehensive properties.

The promising Cu/graphene composites in situ fabricated by solid organic carbon sources

Copper/graphene composites have attracted extensive attention in electrical materials due to their excellent electrical and mechanical properties. However, graphene is easy to agglomerate and poorly bonded with copper, leading to its performance failing to meet expectations. In this paper, an in-situ fabrication method using solid organic compounds (malic acid, maleic acid, and melamine) as the carbon sources is adopted to achieve the uniform dispersion of graphene and the strong interface bonding between Cu and graphene, and further explore the rules of selecting different carbon sources. The morphology and quantity of graphene and the interfacial structure are deeply analyzed. The three-dimensional high-quality graphene and the strong copper/carbon interface due to the Cu-O-C chemical bond facilitate the Cu/graphene composite fabricated by malic acid to exhibit the best comprehensive performance, the electrical conductivity is 96.40% International Annealed Copper Standard (IACS) and the hardness is 75.13HV..

First-principles study on the high-strength and high-conductivity modification mechanism of C7035 copper alloy by Ni, Si, and Co solid solution

In order to investigate the effects of matrix solid solution, precipitate phases, and microscale interfaces on the mechanical and electrical properties of copper alloys, we employed first-principles calculations based on density functional theory study aimed to understand how alloying elements enhance the strength and conductivity of copper. The results demonstrated that doping Co atoms into the copper matrix using the Dop2 structure model exhibited the most significant improvement in both mechanical and electrical properties. The Young's modulus was doubled compared to pure copper, and the hardness increased several times. The electrical conductivity reached 59.8 % of the International Annealed Copper Standard (IACS), showing a 6.6 % enhancement compared to Si doping. To validate computational results, we conducted experiments that confirmed the accuracy of the predicted mechanical and electrical properties. Furthermore, the introduction of Co effectively reduced electron losses at the interface between the precipitate phase and the copper matrix. The electron transmission rate through the Co2Si (211)/Cu (111) interface reached 78.6 %, representing a 94.1 % improvement compared to the Ni2Si (111)/Cu (111) interface. In conclusion, Co can simultaneously enhance the mechanical and electrical properties of Cu–Ni–Si alloys, providing theoretical guidance for the design and fabrication of high-strength and high-conductivity copper alloys.

Изменение структуры, механических и коррозионных свойств сплава системы Mg–Zn–Zr, подвергнутого равноканальному угловому прессованию

Magnesium alloys are considered promising materials for the production of bioresorbable implants. Their main disadvantages are low strength and corrosion resistance in biological environment. In the work, the authors studied the effect of severe plastic deformation using the equal channel angular pressing (ECAP) method on the structure, mechanical properties, and corrosion resistance of the Mg–8.6Zn–1.2Zr magnesium alloy. It was identified that one ECAP cycle at 400 °C leads to a substantial hardening of the Mg–8.6Zn–1.2Zr alloy by ~10 %, up to 330 MPa. Structural studies showed that dynamic recrystallisation plays a significant role in the structure transformation. ECAP leads to the formation of a bimodal structure with large deformed grains with an average transverse size of 20±4 µm and recrystallised grains with an average transverse size of 6±2 µm. It was found that with a decrease in the strain temperature up to 250 °С, the process of deformation-induced decay of the supersaturated solid solution takes place. Electrical conductivity of a sample after ECAP at 400 °C amounted 29±2 % according to the International Annealed Copper Standard (IACS), while second ECAP cycles lead to an increase in the electrical conductivity up to 32±2 % IACS. Using the electrochemical corrosion method, the authors found that one ECAP cycle at 400 °C leads to a slight decrease in the corrosion resistance of the alloy under study compared to the initial state. The study showed that the corrosion current increases from 24 to 32 µA/cm2, while the subsequent ECAP cycle at 250 °С increases the corrosion current more than twice (up to 57 µA/cm2).

Defect analysis of the Cu-Cr-Zr-Nb alloys prepared by the non-vacuum melting process

The microstructure and properties of the Cu-Cr-Zr-Nb alloys prepared by non-vacuum melting and vacuum melting were compared and analyzed in this paper. The results showed that, compared with vacuum melting, the alloy prepared by non-vacuum melting had a more uneven microstructure and a coarser grain. In the meantime, the alloy prepared by non-vacuum melting stored less energy and had a lower proportion of HAGBs (high-angle grain boundaries), and the texture distribution along the TD and RD directions was not uniform. In terms of properties, the hardness and electrical conductivity of the Cu-Cr-Zr-Nb alloys prepared by non-vacuum melting were lower than those of the alloys prepared by vacuum melting. The electrical conductivity of the non-vacuum melting alloy was only 70.8 %IACS (International Annealed Copper Standard), and the average hardness fluctuated greatly. However, the electrical conductivity of the alloy prepared by vacuum melting could reach 81.0 %IACS, and the hardness was very uniform. Further research indicated that there were cracks and inclusions in the alloy prepared by non-vacuum melting. A large number of ZrO2 inclusions were found along the grain boundary, which demonstrated that the oxide inclusion was the primary cause of the crack formation. On this basis, three important suggestions for the preparation of the Cu-Cr-Zr-Nb alloys by non-vacuum melting were put forward to reduce the cost and improve the properties of the alloys. It provided guidance for developing high-performance Cu-Cr-Zr-Nb alloys by non-vacuum melting.

High-strength and high-conductivity nanotwinned Cu lightly doped with Ni

We utilized a Cu–Ni co-electrodeposition method to enhance the mechanical strength of nanotwinned copper (NT-Cu), achieving an ultimate tensile strength (UTS) of over 866 ± 20.1 MPa, a 13.1% increase from the original NT-Cu (UTS max of 766 ± 2.7 MPa). ICP-MS analysis showed a nickel content of 0.467 ppm. The Cu–Ni alloy also demonstrated an international annealed copper standard (IACS) value of over 81%, outperforming cold-rolled Cu foils in terms of mechanical strength and IACS value. The addition of Ni was to reduce the Cu grain size, and to increase the twin density of the NT-Cu. A modified confined layer slip (CLS) model is proposed to account for the refined microstructure of the NT-Cu-Ni alloys. Therefore, this approach can tailor the microstructure of NT-Cu, increase its strength, and maintain high electrical conductivity, making it a promising option for advanced packaging materials.

Crossing the limits of electric conductivity of copper by inducing nanotwinning via extreme plastic deformation at cryogenic conditions

Cu features excellent electric conductivity, although typically at the expense of favourable mechanical properties. Nevertheless, by optimizing the processing procedure, the mechanical properties can be enhanced while maintaining advantageous electric conductivity, which consequently increases the efficiency of copper wires and leads to their lower weight, as well as lower costs of material and production. The presented study investigates the effects of a thermomechanical manufacturing procedure involving rotary swaging, an industrially applicable intensive plastic deformation method imparting shear mixing and intensive (sub)structure modifications, performed at cryogenic conditions on the microstructures and mechanical and electric properties of Cu conductors. The results showed that the cryogenic swaging resulted in formation of significantly elongated grains with heavily refined cross-sections, which featured the mechanical properties enhanced by almost 200%, and, simultaneously, the electric conductivity of 104.9% IACS (International Annealed Copper Standard). By applying an optimized heat treatment, the electric conductivity even increased to 105.8% IACS, primarily due to structure homogenization and development of twins in the micro, and also nano scales.

Process development for laser powder bed fusion of GRCop-42 using a 515 nm laser source

Copper is widely used in high heat flux and electrical applications because of its excellent electrical and thermal conductivity properties. Alloying elements such as chromium or nickel are added to strengthen the material, especially for higher temperatures. Cu4Cr2Nb, also known as GRCop-42, is a dispersion-strengthened copper-chromium-niobium alloy developed by NASA for high-temperature applications with high thermal and mechanical stresses such as rocket engines. Additive manufacturing (AM) enables applications with complex functionalized geometries and is particularly promising in the aerospace industry. In this contribution, a parametric study was performed for GRCop-42 and the AM process laser powder bed fusion (PBF-LB/M) using a green laser source for two-layer thicknesses of 30 and 60 μm. Density, electrical conductivity, hardness, microstructure, and static mechanical properties were analyzed. Various heat treatments ranging from 400 to 1000 °C and 30 min to 4 h were tested to increase the electrical conductivity and hardness. For both layer thicknesses, dense parameter sets could be obtained with resulting relative densities above 99.8%. Hardness and electrical conductivity could be tailored in the range of 103–219 HV2 and 24%–88% International Annealed Copper Standard (IACS) depending on the heat treatment. The highest ultimate tensile strength (UTS) obtained was 493 MPa. An aging temperature of 700 °C for 30 min showed the best combination of room temperature properties such as electrical conductivity of 83.76%IACS, UTS of 481 MPa, elongation at break (A) at 24%, and hardness of 125 HV2.

Enhancement of ultimate tensile strength and ductility of copper matrix composites using a low content of single-wall carbon nanotubes

Single-wall carbon nanotube (SWCNT) reinforced copper (Cu) matrix composites were fabricated by a simple procedure of rotating mixing and then spark plasma sintering (SPS). It was found that addition of SWCNTs as low as 0.05 wt% can increase the ultimate tensile strength (223.5 MPa) and elongation rate (48.0%) of composites by 20.8% and 57.9%, respectively, relative to those (185 MPa and 30.4%) of pure Cu material, while the composite electrical conductivity retained a high value of 94.3% International Annealed Copper Standard (IACS). Mechanism analyses revealed that there are nanometer Ni particles tightly attached to SWCNTs, which were formed in situ during SWCNT growth by arc discharge method. These nanometer Ni particles promoted the bonding between SWCNTs and Cu matrix, leading to a fracture-mode change from intergranular in pure Cu material to ductile in the composites. The related factors to influence the microstructure of composites were discussed as well.

Single-crystallization of electrolytic copper foils

Depending on the production process, copper (Cu) foils can be classified into two types, i.e., rolled copper (r-Cu) foils and electrolytic copper (e-Cu) foils. Owing to their high electrical conductivity and ductility at low cost, e-Cu foils are employed extensively in modern industries and account for more than 98% of the Cu foil market share. However, industrial e-Cu foils have never been single-crystallized due to their high density of grain boundaries, various grain orientations and vast impurities originating from the electrochemical deposition process. Here, we report a methodology of transforming industrial e-Cu foils into single crystals by facet copy from a single-crystal template. Different facets of both low and high indices are successfully produced, and the thickness of the single crystal can reach 500 µm. Crystallographic characterizations directly recognized the single-crystal copy process, confirming the complete assimilation impact from the template. The obtained single-crystal e-Cu foils exhibit remarkably improved ductility (elongation-to-fracture of 105% vs. 25%), fatigue performance (the average numbers of cycles to failure of 1600 vs. 200) and electrical property (electrical conductivity of 102.6% of the international annealed copper standard (IACS) vs. 98.5%) than original ones. This work opens up a new avenue for the preparation of single-crystal e-Cu foils and may expand their applications in high-speed, flexible, and wearable devices.

Effect of nano-Y2O3 on the microstructure and mechanical properties of Cu-10W composites prepared by spark plasma sintering

Cu-W composites with high strengths and high conductivities have diverse applications. At present, studies on Cu-W composites with low W content (<50 wt%) are scarce. In this study, Cu-10 wt% W (hereinafter referred to as Cu-10W) composites reinforced by nano-Y2O3 particles with various Y2O3 contents were prepared via ball milling and spark plasma sintering (SPS). The effects of different Y2O3 contents (1, 2 and 3 wt%) on the microstructure and mechanical properties of the composites were studied. The results show that the Y2O3 and W particles were uniformly distributed in the Cu matrix. With increasing Y2O3 content, the distribution of Y2O3 changed from dispersion to agglomeration, and the grain size gradually decreased. The hardness and compressive yield strength increased gradually. In addition, the electrical conductivity was maintained above 81.76 %IACS (as stipulated by the International Annealed Copper Standard). For the Y2O3 content of 2 wt%, the density and relative density of the composites reach the maximum values of 9.18 g/cm3 and 98.65%, respectively. At this time, the tensile strength reaches 353.8 MPa. The combination between the matrix and Y2O3 was good, and the composites showed the best comprehensive performance.

DEVELOPMENT of Cu MATRIX COMPOSITE CONTACTORS REINFORCED by NICKEL COATED SiC

In this study, Cu-Ni coated SiC composite samples were produced by electric current assisted sintering (ECAS) method by adding electroless nickel coated SiC powders to copper powders produced by cementation method at the ratios of 0.5, 1 and 1.5 wt%. The relative densities of the produced samples were measured by Archimedes’ principle, their microstructures were examined by SEM-EDS, dominant phases were determined by XRD technique; microhardness and electrical conductivity measurements were made. The relative density of undoped copper was determined as 99.42% and the relative density value of Cu-Ni SiC composite samples decreased to 98.35% at most with increasing SiC ratio. The hardness values of Cu-Ni SiC composite samples increased from 120HV to 145HV with the addition of SiC; electrical conductivity values decreased from 90.41 IACS (International annealed copper standard) to 58.56 IACS.

Manufacturing of High Conductivity, High Strength Pure Copper with Ultrafine Grain Structure

Applications of Copper (Cu) range from small scale applications such as microelectronics interconnects to very large high-powered applications such as railguns. In all these applications, Cu conductivity and ampacity play vital roles. In some applications such as railguns, where Cu also plays a structural role, not only is high conductivity needed, but high strength, high ductility, and high wear resistance are also critical. Current technologies have achieved their full potential for producing better materials. New approaches and technologies are needed to develop superior properties. This research examines a new fabrication approach that is expected to produce Cu with superior mechanical strength, enhanced wear resistance, and increased electrical conductivity. Materials with refined grain structures were obtained by breaking down the coarse-grained Cu particles via cryogenic ball milling, followed by the consolidation of powders using cold isostatic pressing (CIP) and subsequent Continuous Equal Channel Angular Pressing (C-ECAP). The mixture of fine and ultrafine grains, with sizes between 200 nm to 2.5 µm and an average of 500 nm, was formed after ball milling at cryogenic temperatures. Further processing via C-ECAP produced nanostructured Cu with average grain sizes below 50 nm and excellent homogenous equiaxed grain shapes and random orientations. The hardness and tensile strength of the final Cu were approximately 158% and 95% higher than the traditional coarse-grained Cu bar, respectively. This material also displayed a good electrical conductivity rate of 74% International Annealed Copper Standard (IACS), which is comparable to the current Cu materials used in railgun applications.

Influence of Structure Development on Performance of Copper Composites Processed via Intensive Plastic Deformation.

Designing a composite, possibly strengthened by a dispersion of (fine) oxides, is a favorable way to improve the mechanical characteristics of Cu while maintaining its advantageous electric conductivity. The aim of this study was to perform mechanical alloying of a Cu powder with a powder of Al2O3 oxide, seal the powder mixture into evacuated Cu tubular containers, i.e., cans, and apply gradual direct consolidation via rotary swaging at elevated temperatures, as well as at room temperature (final passes) to find the most convenient way to produce the designed Al2O3 particle-strengthened Cu composite. The composites swaged with the total swaging degree of 1.83 to consolidated rods with a diameter of 10 mm were subjected to measurements of electroconductivity, investigations of mechanical behavior via compression testing, and detailed microstructure observations. The results revealed that the applied swaging degree was sufficient to fully consolidate the canned powders, even at moderate and ambient temperatures. In other words, the final structures, featuring ultra-fine grains, did not exhibit voids or remnants of unconsolidated powder particles. The swaged composites featured favorable plasticity regardless of the selected processing route. The flow stress curves exhibited the establishment of steady states with increasing strain, regardless of the applied strain rate. The electroconductivity of the composite swaged at elevated temperatures, featuring homogeneous distribution of strengthening oxide particles and the average grain size of 1.8 µm2, reaching 80% IACS (International Annealed Copper Standard).

Achieving High Strength and High Conductivity of Cu-6 wt%Ag Sheets by Controlling the Aging Cooling Rate.

In this paper, Cu-6 wt%Ag alloy sheets were prepared using vacuum induction melting, heat treatment, and cold working rolling. We investigated the influence of the aging cooling rate on the microstructure and properties of Cu-6 wt%Ag alloy sheets. By reducing the cooling rate of the aging treatment, the mechanical properties of the cold-rolled Cu-6 wt%Ag alloy sheets were improved. The cold-rolled Cu-6 wt%Ag alloy sheet achieves a tensile strength of 1003 MPa and an electrical conductivity of 75% IACS (International Annealing Copper Standard), which is superior to the alloy fabricated with other methods. SEM characterization shows that the change in properties of the Cu-6 wt%Ag alloy sheets with the same deformation is due to a precipitation of the nano-Ag phase. The high-performance Cu-Ag sheets are expected to be used as Bitter disks for water-cooled high-field magnets.

Effect of Process Parameters on the Microstructure and Properties of Cu–Cr–Nb–Ti Alloy Manufactured by Selective Laser Melting

The fabrication of high-performance copper alloys by selective laser melting (SLM) is challenging, and establishing relationships between the process parameters and microstructures is necessary. In this study, Cu-Cr-Nb-Ti alloy is manufactured by SLM, and the microstructures of the alloy are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and electron backscatter diffraction (EBSD). The effects of processing parameters such as laser power and scanning speed on the relative density, defects, microstructures, mechanical properties, and electrical conductivity of the Cu-Cr-Nb-Ti alloy are studied. The optimal processing window for fabricating Cu-Cr-Nb-Ti alloy by SLM is determined. Face-centered cubic (FCC) Cu diffraction peaks shifting to small angles are observed, and there are no diffraction peaks related to the second phase. The grains of XY planes have a bimodal distribution with an average grain size of 24-55 μm. Fine second phases with sizes of less than 50 nm are obtained. The microhardness, tensile strength, and elongation of the Cu-Cr-Nb-Ti alloy manufactured using the optimum processing parameters, laser power of 325 W and scanning speed of 800 mm/s, are 139 HV0.2, 416 MPa, and 27.8%, respectively, and the electrical conductivity is 15.6% IACS (International Annealed Copper Standard). This study provides a feasible scheme for preparing copper alloys with excellent performance and complex geometries.

A Study of Silver Decoration on Carbon Nanotubes via Ultrasonic Chemical Synthesis and Their Reinforced Copper Matrix Composites.

The homogeneous distribution of carbon nanotubes (CNTs) in the Cu matrix and good interfacial bonding are the key factors to obtain excellent properties of carbon nanotube-reinforced Cu-based composites (CNT/Cu). In this work, silver-modified carbon nanotubes (Ag-CNTs) were prepared by a simple, efficient and reducer-free method (ultrasonic chemical synthesis), and Ag-CNTs-reinforced copper matrix composites (Ag-CNTs/Cu) were fabricated by powder metallurgy. The dispersion and interfacial bonding of CNTs were effectively improved by Ag modification. Compared to CNTs/Cu counterparts, the properties of Ag-CNTs/Cu samples were significantly improved, with the electrical conductivity of 94.9% IACS (International Annealed Copper Standard), thermal conductivity of 416 W/m·k and tensile strength (315 MPa). The strengthening mechanisms are also discussed.

Effects of build orientation and heat treatment on microstructure and properties of Cu–Cr–Zr alloy manufactured by laser powder bed fusion

Laser powder bed fusion was utilized to manufacture Cu–1Cr-0.19Zr alloys with varied build orientations (0°and 90°). The build orientation affected the grain orientation and texture of the studied alloy. Cu–1Cr-0.19Zr alloy manufactured in the 0° orientation exhibited an intensive <110> texture. Aging the as-fabricated alloy reduced dislocations and dislocation cells and led to the formation of recrystallized grains and face-centered-cubic structured Cr precipitates (2–7 nm). The mechanical properties and conductivity of the Cu–1Cr-0.19Zr alloy increased with the aging time. The conductivity enhancement was ascribed to the decrease of defect, and impurity scattering. Meanwhile, texture led to the anisotropy of the mechanical property in the vertical and horizontal planes. The optimal aging temperature and holding time were 500 °C and 30 min, the microhardness, electrical conductivity, and yield strength (compression) reached 220.6 HV, 62.1% IACS (International Annealed Copper Standard), and 540 MPa. The softening temperature of the peak-aged Cu–1Cr-0.19Zr alloy was 580 °C, which was enhanced by dispersed Cr precipitates. These findings guide to fabrication of Cu–Cr–Zr alloys by laser-assisted additive manufacturing.

Suppression of discontinuous precipitation and strength improvement by Sc doping in Cu-6 wt%Ag alloys

• Sc doping significantly suppressed discontinuous Ag precipitates in Cu-Ag alloys. • Sc-doping led to a 55 MPa increase in strength, with only a slight decrease in conductivity. • Sc segregation at grain boundaries inhibited the nucleation of discontinuous precipitates • The UTS of Sc-doped samples was 1080 MPa, 205 MPa higher than that of non-doped samples. In low-Ag Cu matrix alloys, the presence of coarse discontinuous precipitates may limit strength. We demonstrated that discontinuous precipitation was suppressed, and continuous precipitation was enhanced by the doping of Cu-6 wt%Ag with Sc. A high-volume fraction of continuous precipitates, which nucleated on {111} planes, led to a 55 MPa increase in strength, with only a slight decrease in electrical conductivity. The addition of Sc inhibited the nucleation of discontinuous precipitates by causing the Sc and the Ag to co-segregate onto grain boundaries, thus forming a thin intermetallic compound layer between grains. After deformation, both discontinuous and continuous precipitates were drawn into Ag fibers. The combination of deformation strain and doping caused an increase in density and a decrease in the diameter of Ag fibers, resulting in about 205 MPa increase in doped samples when the deformation strain reached 4.9. The thinner, denser Ag fibers in the doped samples also caused higher electron scattering at interfaces, leading to electrical conductivity that was 11% IACS lower than in non-doped samples. For reference, 100% IACS (International Annealed Copper Standard) is equivalent to 1.7241 μΩ cm.

Study on the improvement and mechanism of AA6101 electrical conductivity by trace TM (Zr, V, Ti) elements-assisted boron treatment

The transition metal elements (TMs) are one of the most important factors that damage the electrical conductivity (EC) of AA6101. But according to our study, during boron treatment process introducing trace TMs is beneficial to improve boron treatment efficiency and purify the Al matrix. In this work, boron treatment and TM-assisted composite boron treatment are carried out to improve the EC of AA6101 and the influence mechanism of TMs (Zr, V, Ti) on boron treatment is studied in detail. Results show that the EC of AA6101 improves and then decreases with the increasing of B addition, reaching a maximum value of 53.4% International Annealed Copper Standard (IACS) with 0.09% B (all compositions quoted in this work are in wt% unless otherwise stated). But by analyzing the boron reaction products, it can be found that the TM borides are core-shell structure and the core mainly is unreacted AlB2 compounds, thus the boron treatment efficiency is relative low. Based on this, besides 0.09% B addition, different amounts of TMs (Zr, V, Ti) are introduced into Al melts to break the core-shell structure and promote the boron reaction going on. When the additions of Zr, V, and Ti are 0.05%, 0.06%, and 0.03%, the EC of AA6101 can reach 54.2%IACS, 53.9%IACS, and 53.7%IACS, respectively. By comparing it is obvious that Zr-assisted boron treatment is the best and the EC of AA6101 is 8.2% better than AA6101 without treatment (50.1%IACS). On the basis of thermodynamics and dynamics, Zr can replace the TMs on the boride particles, and the replaced TMs continue to react with the unreacted AlB2 in the boride center. Thus more TMs impurities are involved in the reaction and their damage to EC of AA6101 can be reduced. At last, a schematic diagram is drawn to explain the influence mechanism of TMs on boron reaction process, which is useful for the development of conductive Al alloys.