International Annealed Copper Standard Research Articles

Ultra-high flatness and conductivity of copper electrodeposits obtained by nano-twinned/fine-grained double layer electrodeposition

Electrodeposited copper (Cu) is utilized as an electrical interconnect material in electronic devices. In high-frequency signal transmission, the skin effect of current conduction is becoming more pronounced, necessitating higher requirements for conductor’s surface roughness and conductivity. In this study, we fabricate a double-layer copper (dl-Cu) consisting of highly flat fine-grained copper (fg-Cu) on top and perpendicular nano-twinned copper (pnt-Cu) at the bottom through two-step electrodeposition. The overall grain growth into large grains is achieved by annealing, and reverse dissolution before electrodeposition of fg-Cu is found to eliminate the interface of fg-Cu and pnt-Cu. The surface roughness of dl-Cu is only 4.65 nm, and the conductivity after annealing reaches 95.5 % of the international annealed copper standard.

Enhanced electrical and mechanical properties of additively manufactured pure copper with green laser

The effort to improve the additive manufacturing (AM) of copper, which is essential in various industrial sectors, has led to the exploration of green laser powder bed fusion (GL-PBF). By using a high-energy green laser, we overcome the challenges posed by the high reflectivity of copper, which has previously hindered achieving the desired component densities and functionalities through AM. This study uncovers the key role of GL-PBF process parameters on the densification, microstructure, surface roughness, mechanical properties, and electrical conductivity of pure copper parts. Our findings demonstrate that optimizing GL-PBF parameters can achieve copper components with over 99.9 % relative density and 98 % international annealed copper standard (IACS) electrical conductivity. The combination of comprehensive experiments and finite element modeling also reveals how the critical role of defect morphology in affecting electrical conductivity. This work contributes to the broader application of AM technologies, especially for high-reflectivity metals, and also provides new insights into how these defects affect conductivity and should be controlled during the AM process.

Combined experimental and computational investigation of precipitation behaviour and mechanical properties in a novel Cu–Ni–Si–Co alloy: effect of solution treatment temperature

ABSTRACT Cu alloys are extensively utilized in electronics for heat exchangers, electrical conductors, automotive connectors, and electrical contacts. To meet the demands of miniaturization, these alloys must exhibit enhanced strength and electrical conductivity. We investigated the microstructural and precipitation properties of the Cu–Ni–Si–Co alloy at the solution treatment temperature (1,050°C). We subjected the alloy to cold rolling and ageing. The secondary-phase particles dissolved completely at higher temperatures, increasing the concentrations of the Ni, Si, and Co solutes within the Cu matrix. This enhanced supersaturation facilitated higher precipitation during ageing, resulting in fine (Ni,Co)2Si precipitates with a number density of 12.3 × 1010 cm−2. The alloy was strengthened by the Orowan mechanism and exhibited good electrical conductivity. Moreover, nanoscale (Ni,Co)2Si precipitates were formed. We achieved the highest hardness of 251 hV and an electrical conductivity (EC) of 51% International Annealed Copper Standard (IACS).

Laser powder bed fusion of pure copper using ring-shaped beam profiles

Additive manufacturing of copper using laser powder bed fusion (PBF-LB/M) enables the production of highly complex components. However, processing of copper by means of near-infrared laser radiation is challenging due to its absorptivity of only 5%–20%. Using a keyhole welding process with a Gaussian intensity distribution increases the absorptivity up to 53% due to multireflection. This enables the production of components with a density larger than 99.5% and electrical conductivity larger than 90% of the International Annealed Copper Standard (IACS), but this type of welding leads to keyhole porosity due to keyhole instabilities. One way of counteracting is the use of a heat conduction welding process. However, due to the Gaussian intensity distribution, it is not possible to supply sufficient energy to eliminate lack-of-fusion porosity and concurrently avoid the formation of a keyhole. Ring-shaped beam profiles have proven their advantages in stabilizing the PBF-LB/M process with a tendency toward higher laser power, but pure copper has not yet been processed in this way. Therefore, this study investigates the potential of three ring-shaped beam profiles to produce specimens with a density of more than 99.5% and their respective electrical conductivity using a laser power of up to 1300 W. In order to understand the underlying welding process, the weld geometry of single-tracks is analyzed. Specimens with a density of up to 99.77% and an electrical conductivity of up to 101.62% IACS are produced, whereby the material properties and welding regime depend on the selected ring-shaped beam profile.

Arc erosion behaviour of Cu–diamond composites at different load voltages in air atmosphere

ABSTRACT To investigate the arc erosion performance of Cu–diamond composites, Cu–5vol.-% diamond composites were fabricated using the hot-pressing sintering method. Compared to pure copper, Cu–5vol.-% diamond composites exhibited improvements in Brinell hardness of 60.1 HB. The relative density and electrical conductivity of Cu–5vol.-% diamond composites were 97.54% and 83.29% IACS (International Annealing Copper Standard), respectively, with no significant decrease compared to pure copper. The thermal conductivity was 423.48 W·(m·K)−1, showing a slight enhancement. The effect of different load voltages on the arc erosion behaviour of Cu–5vol.-% diamond composites was investigated. Experimental results indicated that as the voltage rose from 3 to 7 kV, the breakdown strength decreased from 7.164 × 106 V m–1 to 2.535 × 106 V m–1, while the arc duration increased from 21.752 × 10−3 s to 28.864 × 10−3 s, and the breakdown current rose from 10.8 to 27.2 A. Additionally, the presence of diamond particles enhanced the viscosity of the molten pool, thus the splashing phenomenon of copper liquid during arc discharge was not obvious, indicating that the material loss was small. Few cracks and holes were detected. The Cu–5 vol.-% diamond composites possess good resistance to arc erosion.

Electrodeposition of Nanotwinned Cu Foils with Different Microstructures

In recent years, electric vehicles have been considered one of the most forward-looking industries in the world. In 2023, electric vehicles have occupied 16% of the light vehicle sales market. The expansion of the electric vehicle market is expected due to the goal of 2050 net zero emissions. This has led to increased performance requirements for automotive lithium batteries (LIBs). In general, copper foil is an important material for LIB anode current collector. Since The volumetric expansion during the charge-discharge cycles of LIBs introduces significant stress, the resulting large stress may damage the copper foil at the anode, causing the battery to eventually fail. Therefore, the mechanical properties of the copper foil need to be enhanced. In this study, different organic additives are added during electrodeposition to increase the mechanical strength of the nanotwinned copper (NT-Cu) foil while still maintaining good electrical conductivity. With organic additive B, the ultimate tensile strength (UTS) can be increase to 750 MPa, yield strength (YS) to 550 MPa, with an increase of 66% and 74 % compared to the Cu foils fabricated by additive A, and the international annealed copper standard (IACS) remains at 83.7%. Facilitated by focused ion beam (FIB), in the case of organic additive A, its microstructure is columnar nanotwin copper, and for additive B, its microstructure is a mixture of columnar nanotwin copper and fine grains. The difference of the microstructure contributes to the additional strength. Furthermore, linear sweep voltammetry (LSV) analysis is used to illustrate the relationship between type of additives, tensile strength, and reduction potential. Figure 1

Design strategy to simultaneously enhance electrical conductivity and strength: Cold-drawn copper-based composite wire with in-situ graphene

We proposed a unique wire-production process by rolling up and drawing chemical vapor deposition copper/graphene (Cu/Gr) foils, and a good strength-conductivity trade-off was achieved originating from the dispersed Gr in Cu matrix and the high-quality heterointerfaces. The 1.14 mm cold-drawn composite wire exhibited a tensile strength of 455 ± 5 MPa and a conductivity of 98.18 ± 0.16 % of the International Annealed Copper Standard (IACS), and the tensile strength was 250 ± 2 MPa with a satisfied electrical conductivity of 101.68 ± 0.52 % IACS upon annealing. The microstructure involution during the preparing process was revealed, and the reinforcement mechanisms in the yield strength and conductivity due to the introduced Gr were clarified. The results indicated that the Gr plays a role in pinning dislocations and preventing grain boundary movement during deformation and the subsequent annealing, thereby enhancing the strength of the Cu matrix. Meanwhile, the Cu-Gr coupling interfaces exhibited an electronic doping effect, enhancing the conductive properties. Our work presented a feasible method for preparing Cu/Gr composite wire with comprehensive electrical conductivity and strength optimization.

Precipitate-mediated enhancement of mechanical and electrical properties in HPTE-processed Al–Mg–Si alloy

In this study the effect of high-pressure torsion extrusion (HPTE) and artificial aging (AA) on the strength and electrical conductivity of an Al–Mg–Si alloy was investigated. The resulting material shows remarkable improvement in ultimate strength reaching 380 MPa and in electrical conductivity with 53 % IACS (International Annealed Copper Standard), after post-processing aging at 160 °C for 10 h. X-ray diffraction analysis and electron backscatter diffraction were employed to analyze the structure of the alloy caused HPTE followed by AA. Transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy were used to study the morphology, elemental composition, and crystal structure of the secondary phases. The study confirms that Guinier-Preston (GP) zones and nano-scale precipitates created during the deformation and subsequent heat treatment are evenly distributed inside the grains. Chemical composition analysis of the precipitates indicated the presence of one main phase based on the Mg/Si ratio coexisting with a low volume fraction of other phases in this Al grade. High-resolution TEM revealed precipitates either with a partially ordered structure or a fully crystalline structure. Strength and electrical conductivity modeling were carried out based on the microstructural characterization results. The findings of this study indicate that HPTE together with thermal treatment has the potential as new approach for processing of commercially significant aluminum alloys.

Precipitation behavior and properties change of Cu–3Ti–2Ni alloy during aging process

The microstructural evolution of Cu–3Ti–2Ni alloy under primary and secondary cold rolling combined aging was investigated through various characterization techniques including transmission electron microscopy (TEM), scanning electron microscope (SEM), and X-ray diffraction (XRD). Additionally, the electrical and mechanical properties during different stages of aging were examined to reveal the organizational changes and performance variations of Cu–3Ti–2Ni alloy under primary and secondary aging. This study revealed that the alloy exhibited optimal primary aging performance at 450 °C for 4 h, with a strength of 954 MPa and an electrical conductivity of 21.5 %IACS (International Annealed Copper Standard for Conductivity). In comparison to primary aging, both strength and electrical conductivity were effectively improved under secondary aging conditions. The optimum secondary aging process was determined to be aging at 400 °C for 3 h, resulting in a strength of 1133 MPa and an electrical conductivity of 24.2 %IACS. During the aging process, the matrix witnessed the formation of numerous elliptical disc-shaped NiTi and Ni3Ti phases. Notably, the interface of NiTi phases exhibited a stronger coherency effect compared to Ni3Ti. β′-Cu4Ti precipitated uniformly within the matrix during aging, enhancing the alloy's strength. A recovery and recrystallization process occurred during aging, leading to the formation of sub-grains within the matrix.

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.