Hayabusa2 is the second asteroid sample return mission in the world following Hayabusa. The target asteroid is (162173) Ryugu, which is a C–type near–Earth asteroid. The most important purpose of this mission is to obtain clues for investigating the origin of the life and water on the Earth. Hayabusa2 was launched on 3 Dec. 2014, and arrived at Ryugu on 27 June 2018, and returned to the Earth on 6 Dec 2020. This six–year mission was perfect, and we were able to get 5.4 g samples of Ryugu. When the samples were analyzed, they were found to contain a great variety of organic matters. However, the origin of life has yet to be elucidated. After returning to the Earth, Hayabusa2 left the Earth again. Since the status of the spacecraft was fine, we have extended the mission, which is called “Hayabusa2 extended mission (Hayabusa2#)”. In the extended mission, Hayabusa2 will flyby (98943) 2001 CC21 in July 2026 and will rendezvous with 1998 KY26 in July 2031. Hayabusa2 has started for the new challenges.

The development research of Cu–Ti alloys for electrical engineering applications copes with two crucial problems. First, Ti solutes in the Cu matrix results in serious loss of electrical conductivity； second, discontinuous precipitation (DP) results in the deterioration of the mechanical properties of the alloy. In this connection, the effect of isothermal aging in a hydrogen atmosphere on the microstructure of an Mg–doped Cu–Ti alloy, under test condition of 450 ˚C for 100 h and hydrogen pressure of 0.6 MPa, were investigated using various electron microscopy and microanalytical technique. During the early stage of aging, the ternary alloy showed almost the same levels of the Vickers hardness as well as the electrical conductivity as those of the binary counterpart without Mg doping. Through this stage, fine needle–shaped metastable β’–Cu₄Ti precipitates were continuously formed, as in the case of the binary alloys subjected to conventional aging in air (or vacuum). After 10 h of aging when the peak–hardness was reached, the Vickers hardness and electrical conductivity of the ternary alloy were recorded at more reduced and elevated levels respectively than in the case of vacuum aging. On further aging, the ternary alloy had the β’–precipitates replaced more increasingly by stable TiH₂ precipitates in the matrix than the binary counterpart, resulting in a more rapid increase of electrical conductivity. It is, thus, suggested that the combined treatments of Mg doping and aging in hydrogen atmosphere can affect significantly the microstructures of Cu–Ti alloys to effectively reduce the negative impact of the Ti solutes in matrix as well as of the DP reaction.

It is known that annealing 60/40 Cu–Zn alloy at relatively low temperatures causes bainitic transformation from the β1’ single–phase state to a plate–like α–phase, which affects the hardness of the brass. In this study, Ag, whose BOP value is comparable to that of Cu and Zn, was selected as an additive element, and the effects of the additive elements on the phase transformation were investigated using micro–Vickers hardness tests, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Comparing the alloys, the highest maximum hardness and the highest number density (N) of α–phase were observed in the 1.0Ag alloy. As quenched (as Q.) sample of 1.0Ag alloy showed the highest hardness value. The TEM observation results showed a stripe–like contrast caused by the 9R structure, which has been reported in this laboratory. A correlation existed between the aging effectivity (ΔHV) from as Q. to the maximum hardness and the density of stripe contrasts per unit volume in α phase.

Solid–solution copper alloys for connector terminals are required to improve stress relaxation resistance. The stress relaxation resistance is affected by grain size and low–temperature annealing condition. The smaller the grain size, the lower the stress relaxation resistance. This is deduced to be due to the increase in the dislocation density associated with the grain size. Dislocations are classified as GN (geometrically necessary) and SS (statistically stored) dislocations. It has been clarified that the low–temperature annealing improves the stress relaxation resistance mainly due to the recovery of the SS dislocations. On the other hand, the effect of the GN dislocations on the stress relaxation is not clearly understood. In general, the GN dislocation density depends on the grain size. Thus, the GN dislocation density was varied by changing the grain size, and its effect on the associated stress relaxation was investigated. The GN and SS dislocation densities of solid–solution Cu–Sn alloys were analyzed by a combination of XRD (X–ray diffraction) and EBSD (electron backscatter diffraction) methods. As the grain size decreased, the SS dislocation density changed little, while the GN dislocation density increased and the stress relaxation resistance deteriorated. The SS dislocations recovered by the low–temperature annealing whereas the GN dislocations did not. It was confirmed that the GN and SS dislocations have different effect on the stress relaxation.

Changes in the microstructure of Cu–Ni–Si alloys in which Ni was partially or totally substituted by Co were investigated. Based on the results obtained, the effects of changes in the amount of Co substitution on precipitation hardening and work hardening were discussed. The size of precipitates in the peak–aged alloys became smaller as the amount of Co substitution was increased. The theoretical value of precipitation hardening (σ_p) estimated from the size of the precipitates increased in proportion to the amount of Co substitution. In addition, the estimates of σ_p decreased with increasing rolling reduction. Thus, it is suggested that the precipitates were sheared by dislocations during cold rolling and partially redissolved into the Cu matrix. The decrease in precipitation hardening associated with the redissolution of precipitates during cold rolling became smaller as the amount of Co substitution increased. The effect of Co substitution on the redissolution of precipitates can be theoretically explained in terms of the size and misfit strain of the precipitates. The sum of σ_p and the estimated value of dislocation hardening became larger as the amount of Co substitution increased and the trend was consistent with the measured value.

Microstructure and mechanical properties of Corson alloys with three different amounts of substitution of Ni by Co were systematically investigated. Shear bands were developed in each alloy during cold rolling. It was found that the highly localized deformation occurred within the shear bands. Nanoindentation hardness tests showed that the hardness within the shear bands was lower at the early stage of rolling than before rolling. The precipitate size in the specimens decreased with increasing the amount of Co substitution and rolling reduction, and the decrease in the size during cold rolling became smaller with increasing Co substitution. Moreover, the number density of precipitates within the shear band was extremely low. Therefore, it was suggested that the precipitates were sheared by moving dislocations and partially redissolved into the Cu matrix within the shear bands. Based on the microstructural observations, the amount of precipitation strengthening was estimated from the Orowan mechanism. The estimates for all specimens increased with rolling reduction, but such an increase must not occur in practice. Therefore, in order to understand the change in precipitation strengthening during rolling, it is necessary to investigate the change in the actual number density of precipitates by direct observation using transmission electron microscopy and etc.

The effects of Al and Fe co–doping with Cu–Ti alloys on microstructure, strength, bend formability, and fatigue properties were investigated. Al and Fe co–doping with Cu–Ti alloys leads to (i) suppression of coarsen discontinuous precipitate β–Cu₄Ti on the grain boundaries, (ii) grain refinement during solution heat treatment caused by pinning effect by FeTi particles, and (iii) formation of extra–precipitates such as Cu₂TiAl in Al–doped alloys and FeTi and (Cu,Fe)₄Ti₃ in Fe–doped alloys. The microstructural evolutions in the Cu–Ti–Al–Fe alloy were contributed to the improvement of strength, bend formability, and fatigue properties, in comparison with those of binary Cu–Ti and ternary Cu–Ti–Al and Cu–Ti–Fe alloys. Especially, fatigue property was significantly improved in the Cu–Ti–Al–Fe alloy, which was explained by suppression of the initiation and growth of fatigue cracks through small Cu₂TiAl particles on the fine grain boundaries. Therefore, it can be concluded that the Cu–Ti–Al–Fe alloy should be expected as an applicable material for compact springs and connectors in information communication devices.

With the miniaturization of electronic parts, the bending ability of copper alloys requires improvement. The bendability of rolled copper alloys is affected by crystallographic orientation, and it was reported that the bendability is related to the Taylor factor. When the Taylor factor of shear strain mode (M_sh) is lower than that of plane strain compression mode (M_p), shear bands might form during bending deformation. In this study, therefore, an index for the possibility of shear band formation, M_p/M_sh, was proposed, and a prediction map for shear band formation was also generated based on the crystallographic orientation analysis. Furthermore, the usefulness of the prediction map was verified by investigating the shear band formation behavior in the 90° W–shape–bent Cu–Ni–Co–Si alloy rolled sheet. The shear bands tended to form near the region with a high M_p/M_sh value. The proposed prediction map for shear band formation can potentially aid the crystallographic orientation control to enhance the bendability of copper alloys.

The dependence of mechanical twinning on the crystallographic orientation at the early stage of rolling was investigated. For this purpose, a copper–zinc alloy plate having a sharp {001} texture on the rolling plane (normal direction∥<001>) was prepared, and the twinning behaviors during rolling were studied in the grains with orientations of rolling direction (RD) parallel to <100>, <210> and <110>. The precise examination revealed that grains with RD∥<110> orientation were most prone to twinning among the three crystallographic orientations. Effects of the development of heterogeneous–nano (HN) structure on the tensile properties were also systematically investigated. As the rolling reduction increased from 50％ to 70％, the tensile strength increased significantly, and the elongation to failure also increased simultaneously. Considering the microstructural changes, the increase in the strength/ductility balance was attributed to the formation of the HN structure. Further rolling up to 90％ resulted in a slight increase in strength and a significant decrease in ductility to about half of the value at 70％. It was suggested that the decrease in the volume fraction of twin domains in the HN structure, instead increase in the other texture components, during the rolling reduction from 70％ to 90％ complicatedly spoiled the strength/ductility balance.

High–temperature deformation and dynamic recrystallization (DRX) behaviors of Cu–Co alloy developed for high–strength copper tube were systematically investigated by hot compression test at temperatures between 1173 K and 1273 K and at various strain rates from 2×10^–4 s^–1 to 2×10^–1 s^–1. All flow curves showed single or multiple peaks accompanied by large flow softening irrespective of temperature and strain rate, indicating extensive occurrence of DRX in all the testing conditions. Even while distribution of precipitates changed depending on testing condition, they did not strongly impede DRX. Deformation and DRX behaviors at such high temperatures of the Cu–Co alloy looked similar to those of pure Cu and Cu–P alloy, which would imply easy hot deformation and microstructural control by DRX. Nevertheless, it was suggested that the precipitates should impede extensive DRX as deformation temperature decreased. Control of deformation conditions is, therefore, indeed important for the present precipitate–harden alloy for the uniform evolution of DRXed structures.

The alloy design of the equiatomic CuSnZn and CuSnAl alloys for the development of the Medium Entropy (ME) bronzes was performed by the empirical alloy parameters. The solidification microstructures of the metallic mold casting ingots in the equiatomic CuSnZn and CuSnAl alloys were investigated by X–ray diffraction, optical and electron microscopy. The repulsive tendency between Sn and other constituent elements was observed in the ingots of equiatomic CuSnZn and CuSnAl alloys, resulting in the Sn–rich liquid formation via the liquid phase separation in the equatomic CuSnAl alloys and the enrichment of Sn element at the inter–dendrite regions of the equiaxis dendrite structure in the equiatomic CuSnZn alloys. The significant segregation tendency of Sn element indicates the difficulty in the development of the equiatomic Cu–Sn–based ME bronzes with a single solid solution phase.

The advancement of electronic devices and their capabilities has driven the demand for specific material property combinations, such as mechanical strength and electrical conductivity, in materials pertinent to device fabrication. To this end, the microstructure and properties of Cu–4.2 at％ Ti alloy sheets, produced through a multi–step process involving over–aging and severe cold rolling, were investigated. The microstructure of the over–aged alloy prior to cold rolling consisted of cellular components with laminated plates of copper solid solution (Cu_ss) and β–Cu₄Ti. When the over–aged alloy was severely cold rolled for a 99％ reduction in thickness, a hierarchical double–phase microstructure was formed parallel to the cold–rolling direction, with Cu_ss bands and two–phase bands containing small β–Cu₄Ti pieces stacked within Cu_ss phase. The strength of the over–aged alloy sheet increased steadily during increasing degrees of cold rolling, caused by a large volume fraction and fine dispersion of hard β–Cu₄Ti pieces and high dislocation density in the Cu_ss matrix. The electrical conductivity decreased in the later stages of cold rolling； however, the conductivity was higher than that of the alloy sheet prepared by peak aging and cold rolling. Eventually, the balance between strength and electrical conductivity of this Cu–Ti alloy was significantly improved by over–aging and severe cold rolling compared to conventional peak–aging and cold rolling processes.

Rectangular–shaped bulky Cu–Be alloy was multi–directionally forged (MDFed) at ambient temperature. While coarse initial grains were gradually fragmented by mechanical twinning with increasing forging cumulative strain, grain fragmentation appeared more proceeded at surface–edge and inner–central regions than at surface–central and inner–edge ones of the MDFed sample. The hardness Hv, therefore, changed much depending on position from 2.69 GPa to 3.02 GPa at cumulative strain of ΣΔε=2.4. Hence, ultimate tensile strength (UTS) showed same tendency that the UTS at the inner–central region (962 MPa) was larger than that at the other regions (818 MPa), i.e., 15％ difference. Nevertheless, the difference in the UTS became much smaller to be 1.39 GPa at maximum and 1.32 GPa at minimum, i.e., 5％ difference, after peak aging at 513 K without showing large difference in the ductility around 4％, which should be due to the difference in the age–hardenability depending on microstructure.

It was investigated that the two–step aging properties of Cu–Cr–Zr alloy applied to continuous remarkable torsional distortion processing (RMA–CREO processing) at 1273 K and by 5, 10, 15 and 20 rpm in rotation rate. After the secondary artificial aging was conducted at 773 K following with preliminary artificial aging at 623 K for 14.4 ks, the peak Vickers hardness was 125 HV for the comparative specimen which solution–heat–treated specimen (ST), and 121, 124, 124, and 126 HV by 5, 10, 15 and 20 rpm, respectively. The electrical conductivity at the peak Vickers hardness was higher for each CREO specimens than for the ST specimen. Furthermore, the secondary aging time to reach the peak Vickers hardness for each CREO specimens was halved compared to the ST specimen.

The strength of Cu–Ni–Si alloy can be improved by finely dispersing a Ni–Si–based compound as a precipitate into the Cu parent phase by heat treatment. In order to investigate the strengthening effect of the precipitate, quantitative evaluation of the size distribution and dispersion state is necessary. In this work, we utilized transmission electron microscopy, small–angle X–ray scattering (SAXS), small–angle neutron scattering (SANS), and atom probe tomography to analyze this Ni–Si precipitated phase. The atom probe tomography results showed two types of the diffusion layers at the interface between the Cu parent phase and the precipitated phases. The alloy contrast variation method based on the difference of SAXS and SANS intensity in absolute units also suggests that the δNi₂Si precipitates are distorted.

Residual carbon on the inner surface of copper tubes is one of the causes of Type I” pitting corrosion, however there are few clear methods for its evaluation. In a previous report, it was reported that a test in which copper tubes were filled with a mixture of H₂O₂, BTA and corrosive anions for one hour enabled the pitting corrosion resistance of copper tubes to be evaluated in a short time (rapid evaluation test). In order to evaluate the correlation between the test’s results and behavior in an actual environment, a three–month water flow test was conducted on copper pipes that had been evaluated in a rapid evaluation test. Rapid evaluation tests assessed samples with residual carbon amounts of 1.1 mg/m² as being in the safe range and above 1.9 mg/m² as being in the critical range. The results were in good agreement with previous reports that pitting corrosion is likely to occur when the residual carbon content is above 2 mg/m². No pitting was observed in samples assessed as safe in field tests, while pitting corrosion was observed in some samples assessed as critical. Agreement between the results of the rapid evaluation test and the field test was observed, and it is expected that the method can be effectively applied in actual environments.

Residual carbon on the inner surface of copper tubes is known to be a cause of pitting corrosion. We showed previously that the rapid filling test was useful to evaluate the pitting corrosion resistance of copper tubes. Immersion tests using the rapid evaluation test solution showed that corrosion occurs on the entire surface of copper tubes with low residual carbon amounts, while those with high residual carbon amounts show pitting corrosion. Therefore, it was necessary to improve the corrosion resistance of copper tubes with high residual carbon amount, which was expected to undergo pitting corrosion. As pitting corrosion occurs when anodes were locally concentrated on part of the metal surface, it had been suggested that anodes be dispersed over the entire surface by the processing of the metal surface. Metal processing had various purposes, including changing the shape and properties of metals, and in this case, leading to desirable surface properties (such as expansion and drawing processes). Here, we focused on the expansion process and its effects on corrosion resistance of copper tubes. As a result, no corrosion was observed in the expanded copper tubes, which was expected to improve corrosion resistance. The composition analysis of the inner surface of the copper tubes showed a peak intensity of Cu₂O only in the expanded copper tubes (no processing), suggesting that an oxide film was formed by the expansion process.

Recently, the leakage was experienced for copper tubes of air conditioning system using well water by corrosion after about seven years services. The corrosion in copper tubes experienced in the outdoor unit of a water–cooled packaged air–conditioner system was localized and penetrated through the tubes thickness. It was inferred that the corrosion was sand erosion due to the fast flow of water and the breakdown of the oxide film caused by the sand. In addition, corrosion in copper tubes was experienced near the heat affected zone at brazed joints of u–bend tubes and connecting tubes for desiccant air–conditioning heat exchangers. This corrosion was considered to be galvanic groove corrosion in brazing part or Type I pitting corrosion, which occurs in a well water environment, because of the potential difference between copper and brazing material in the former and the presence of small mounds of patina products in the latter. It was considered necessary to install sand removal equipment and to change to use the materials with high corrosion resistance.

In this study, we focused on the fact that the solidification structure of brazing filler metals varies depending on its composition and cooling rate, and investigated the effect of the cooling rate during brazing on the relevant corrosion based on the metallurgical structure and corrosion behavior measured by polarization curves. The results showed that the metallurgical structure became finer in the air cooled and ice water cooled the filler metals than in the furnace cooled the filler metals. The microstructure was considered to be two phases of Cu solid solution with Sn and P solid solution and Cu₃P for the filler metal A, and three phases of Cu solid solution with Ag and P solid solution, Ag solid solution and Cu₃P for the filler metal B. Compared to furnace cooling, air cooling was considered to improve the corrosion resistance of the filler metals because Sn and Ag ware finely dispersed throughout the filler metals due to the finer microstructure, while copper base metal corrosion progresses.

In this study, immersion tests and wet atmosphere exposure tests were carried out to investigate the corrosion morphology of copper at different acetic acid concentrations. The results of the immersion tests showed that the corrosion morphology of copper in the gas phase, gas–solution interface and solution phase regions varied with acetic acid concentration in the solution phase. Acetic acid concentrations above 5 vol.% resulted in severe corrosion at the gas–solution interface and significant wall thinning as the acetic acid concentration increased. In particular, a near–hemispherical corrosion pattern was observed in the gas phase and at the gas–solution interface at an acetic acid concentration of 1 vol.%. In wet atmosphere exposure tests, a near–hemispherical corrosion morphology was observed at acetic acid concentrations above 1 vol.%. It is considered that the corrosion form of copper in the immersion test depends on the pH of the test solution.

Water leakage from copper tubes for air conditioners was a problem due to carbon film dependent pitting corrosion, which was caused by the carbon film formed on the inner surface during copper tube production and the quality of the water flowing inside the tube. In the presence of phosphonic acid (HEDP), which was used as a scale inhibitor, silicate ion (SiO₄^4–) and calcium ion (Ca²⁺), which were considered to be corrosion inhibitors, act on the copper plate surface, which was polished and acid washed to remove carbon film as a measure against pitting corrosion. In this study, copper tubes with carbon coating were used to simulate the real environment, and the corrosion inhibition effect of copper in the presence of HEDP, SiO₄^4–, and Ca²⁺ was investigated electrochemically. The anodic polarization curves showed that the current density of the copper tube was lower than that of the copper plate as the Ca²⁺ concentration increased, and that the copper was less likely to dissolve as ions due to the decrease in the current flowing on the copper surface. The above results suggest that the copper tube with carbon film was more effective than the copper plate in inhibiting copper corrosion due to the increase in Ca²⁺ concentration in the presence of SiO₄^4–.

We have been examined the suppression of pitting corrosion in copper tube used for heat transfer in cooling water systems with absorption chillers. The corrosion was caused by the relationship between the carbon film on the copper tube surface and the water quality flowing through the tube. Phosphonic acid, and benzotriazole (BTA) were used as water treatment chemical due to suppress pitting corrosion. We reported silicate ion and calcium ion are effective for the corrosion resistance of copper in the presence of phosphonic acid, and also studied the effect of pH and carbon film. In this study, BTA was added to the system containing these three factors, and the effect of BTA on the corrosion resistance of copper tubes was investigated using electrochemical measurements. As the concentration of BTA increased, the current density was suppressed and the BDP became larger. No significant difference was observed with pH, but there was a difference with and without carbon film. From these results, it was considered that corrosion inhibition is more effective with increasing BTA concentration.

In recent years, due to the expansion of use of heat exchanger and electric vehicle and the growing awareness of environmental issues, there is a need to reduce the cost of copper–based material. Therefore, high–strength copper alloys for thinner thicknesses were developed. In this study, we focused on the difference in aging temperature and Ni/P concentration ratio of Cu-Ni-P alloy, and investigated the influence of the aging properties of Cu-Ni-P alloy. when the concentration ratio of Ni/P was 2, the maximum hardness was about 149 HV, and the conductivity at that time was about 55%IACS, which is the highest hardness value. And the concentration ratio was from 2 to 1 or 3, the hardness decreased and the time to reach the maximum hardness became longer. From the results of thermal analysis by DSC, it was deduced that the amount of Ni₂P and/or Ni₁₂P₅ increased when the concentration ratio of Ni/P was 2.

Brass alloys are well suited for cutting and have superior thermal conductivity；they are widely used as materials for hot–water piping. For piping, brass alloys are combined with stainless steel with superior strength and corrosion resistance by brazing the joints. In recent years, brass with Bi and Sn addition has been developed. When brazing stainless steel and brass with Bi addition, its impact on brazeability is unknown. In the present study, we examined brazing that uses Ag–Cu–Ni brazing filler metal at a high–temperature range and aimed to examine the impact of the brazed joint structure on hardness distribution to determine brazeability.

Results showed that stainless steel and brass with BAg–13a can be brazed at a high–temperature range. However, because molten brazing filler metal reacted with the brass base material, we could not confirm the brazing filler metal layer. Compared with C3604, the brazing filler material exhibited wetness and spread on C6801；however, voids were confirmed. Bi in C6801 migrates to the brazing filler metal layer during the brazing and precipitates during the solidification. The Vickers hardness test showed similar hardness for each brazed joint.

Compositionally complex alloys with the aim of light weight, high strength and high ductility were developed as medium entropy ones using four elements, Cu, Al, Zn and Mg. In order to investigate possibility of improving ductility of the alloys, high temperature deformation and subsequent properties were examined in Cu₄Al₄ZnMg (4411) alloy with the highest compressive strength at room temperature and the fundamental composition CuAlZnMg (1111) alloy. Flow stress had a peak immediately after yield point and decreased gradually with strain in true stress –true strain curve in both alloys. It was found that cracks at the apex of the indentation in the Vickers hardness test, which showed brittle, were also observed in the specimens subjected to high temperature compressive test at various temperatures and strain rates as well as as–cast alloys before the test. Higher fracture toughness was, however, obtained in the specimens after the compressive test compared with ones before in both alloys. This fact suggested desirable possibility of improving ductility by controlling the microstructure through deformation at elevated temperatures.

The reproducibility of stress relaxation behavior over a long period of time and the evaluability of “permanent strength”, which is the residual stress after infinite time, were verified using existing stress relaxation models. Stress relaxation tests were conducted on three different types of ECAPed industrial pure copper specimens, each with different stress relaxation behavior. Stress–relaxation time relationships were analyzed using three types of models： logarithmic and power–law models formulated theoretically, and an empirical exponential model. All of the three models are sufficient to reproduce the stress relaxation behavior, regardless of the relaxation amount and relaxation time, within the range of the experimental data. On the other hand, the permanent strength obtained from extrapolation of the experimental data is correlated with the plastic strain rate at which the stress–relaxation behavior stagnates. In this samples, it is necessary to obtain experimental data from ׄε_p=3×10^–10/s to ׄε_p=8×10^–12/s for the logarithmic and power–law models, and to ׄε_p=2.5×10^–9/s for the exponential model. Therefore, the exponential type is not significantly affected by differences in relaxation behavior, suggesting that it is a highly effective model that can evaluate the permanent strength more validly with shorter experimental data than other models.

A trade–off between mechanical strength and thermal conductivity prevents the achievement of higher thermal conductivity in copper alloys, while maintaining the high mechanical strength of copper at high temperatures, which can result in energy savings and a lower carbon footprint. Oxide dispersion–strengthened (ODS) Cu–xY₂O₃ (x=0, 0.5, 1, 2 wt%) alloys were prepared by mechanical alloying (MA) using a water–cooled high–energy ball milling machine and then sintered with a hot press. The indentation hardness of the sintered materials increased with the amount of Y₂O₃. Microstructural observations revealed that high strengths for the Cu– Y₂O₃ ODS alloys was achieved by both oxide dispersion and fine grains. However, the thermal diffusivity was not simply dependent on the amount of Y₂O₃, which was higher in both Cu–0Y₂O₃ and Cu–1Y₂O₃ but lower in the others. Among the factors affecting the thermal diffusivity, the amount of impurities, such as Fe and Cr, introduced during the MA process are responsible for the higher values of thermal diffusivity in Cu–0Y₂O₃ and Cu–1Y₂O₃. The obtained results indicate that ODS–Cu alloys fabricated by MA and sintering can overcome the trade–off between mechanical strength and thermal conductivity when the solute impurities are suppressed.

The fatigue property of copper foil on Flexible Printed Circuits (FPCs) is a critical factor for the miniaturization and the life of electronic devices. In recent years, as FPCs are adopted for wearable devices, evaluation methods with complex stresses which can predict fatigue properties on actual applications are required. In this report, torsion tests were carried out as a practical method. The influence of cyclic torsional bending on fatigue morphology of copper foil was evaluated. It was found that the rolled annealed copper foil with cubic recrystallized texture showed longer fatigue life than the electro deposited copper foil. Some FPCs were buckled depending on the test conditions. The copper foil with buckling discolored into a periodic X pattern. Although the copper foil without buckling discolored uniformly in the line direction of the circuits in FPC, the degree of discoloration varied depending on the line position. Since persistent slip bands were observed in the discolored areas, it is said that the discoloration state represents the fatigue morphology. The stress distribution by simulation is good agreement with the fatigue morphology.

In response to a move of enacting lead–restricting regulations in Europe, demand for lead–free, free–cutting brass is growing. Amidst such circumstances, the authors developed a lead–free brass C68370 (63Cu–1Si–0.07P–Z) in 2020 consisting of two phases, alpha and beta phases, and containing Si. In order to examine the machinability of this alloy, the authors compared its behavior when drilled using an NC lathe with that of C3604 and CW510L. The result was that C68370 exhibited magnificent machinability, excelling C3604, particularly when drilled at a high feed. This is indicated by the fine vertical grooves generated over the entire surface of its fan–shaped cutting chips. Further, it was revealed that the required power to cut the new alloy was small, and the surface of the inner wall of drill holes was smooth and good since the chips were less likely to get stuck in the holes. It is considered that this improvement in machinability when drilled at a high feed derives from the superb machinability that C68370’s beta phase has due to an addition of Si, and the precipitates present in the alloy that trigger fragmentation of chips, neither of which CW510L or C3604 has.

The use of copper alloys with high mass density will increase with the popularization of electric vehicles. To reduce vehicle weight, high–strength alloys are developed, and the shapes of parts become more complex. As a result, sheet forming of copper alloys becomes more difficult. In the future, sheet forming analysis will be required for copper alloys as it is for general structural materials. To achieve high accuracy in sheet forming analysis, it is necessary to measure the yield surfaces under biaxial stress states. There are few studies on the measurement of yield surfaces and modeling with anisotropic yield functions for copper alloys. The authors proposed a simplified identification method for yield surfaces that does not require the use of specialized material testing equipment. The method uses uniaxial tensile, plane strain tensile, and hydraulic bulge (equibiaxial tensile) tests. The equivalence of plastic work and the associated flow rule are assumed for the yield surface identification. The yield surface can be obtained from the circumscribing polygon of the contour of equal plastic work. In this study, the yield surfaces of tough pitch copper (C1100) and 7/3 brass (C2600) sheets in different work hardening states were measured. The yield surfaces of copper and brass can be approximated by yield functions for aluminum alloys proposed by F. Barlat (Yld2000–2d and Yld2004–18p).

The effect of crystal orientation on Lankford value and drawability in Cu–Ni–Si alloy was investigated. The specimens with a crystal orientation aligned with the BR orientation {362} <853>, R orientation {123} <634>, Cube orientation {001}<100> and RDW {012}<100> were prepared from Cu–2.5wt%Ni–0.6wt%Si alloy ingot by hot rolling, cold rolling, and heat treatment. The average Lankford value was higher in the order of R orientation, BR orientation, RDW orientation and Cube orientation. The drawability was investigated by drawing blanks with diameters of 30.0, 35.0, 42.5 and 45.0 mm using a punch with a diameter of 20.0 mm. The limiting drawing ratio was higher in the order of R orientation, BR orientation = RDW orientation and Cube orientation, and a positive correlation with the Lankford value was observed. The R–oriented material showed higher drawability than C2680R–H which has been often used for drawing.

Influence of roughness of contact surface of C1020 copper and A1050 aluminum sheets on bonding characteristics was experimentally investigated in roll bonding of copper/aluminum/copper laminated sheet at room temperature. The contact surfaces of the sheets were roughened by emery paper and grindstone prior to roll bonding. Minimum reductions in thickness for bonding (higher than 0.9 in area fraction of bonding at the contact surface) were 63%, 55% and 50% in the laminated sheet with no surface treatment (mean arithmetic roughness Ra=0.1 μm), emery paper surface treatment (Ra=1.2–1.7 μm) and grindstone surface treatment (Ra=3.1–3.6 μm), respectively. On the other hand, the bonding strength of the laminated sheet with/without surface treatment was lower than 10 MPa. In roll bonding of the laminated sheet with large interface roughness, the elongation and relative sliding of the sheets at the contact interface of the sheets in rolling direction were reduced to approximately 90% and 35%, respectively. The bonding mechanism of the laminated sheet with large interface roughness was discussed from viewpoints of the deformation and the relative sliding in roll bonding.

We have investigated the formation mechanism of Cu–Sn alloy mesoparticles when tin(II) ethylhexanoate was used as a reducing agent. The addition of tin(II) ethylhexanoate led to the color change of the reaction solution. And the size of the mesoparticles and the primary nanoparticles that compose them were affected by the amount of tin(II) ethylhexanoate. Therefore, tin(II) ethylhexanoate plays an important role in the reduction process of Cu oleate. Furthermore, the reduction of Sn²⁺ ion occurs through the underpotential deposition mechanism. Then, Cu–Sn alloy mesoparticle ink was prepared and used as a bonding material for Cu–Cu joint. The maximum shear stress (τ_max) on the bonding interface reached 37 MPa under the bonding temperature of 350°C and the bonding pressure of 30 MPa in an air atmosphere. The higher the bonding temperature, the larger the τ_max tended to be, but there was no dependence on bonding pressure. Although our Cu–Sn alloy mesoparticles are in the meso–size range, they achieved mechanical strength comparable to Cu nanoparticles in a simple bonding process.

Dissimilar resistance welding of C1020/SUS304 plates was performed with and without interposing Zr₅₅Al₁₀Ni₅Cu₃₀ metallic glass ribbons as interlayers. The joint strength of the welded specimens without the metallic glass ribbons was lower than that of those with the ribbons, when a higher electrode load was applied. Similar load–displacement curves of the tensile shear tests were obtained with interposing the glassy ribbons when lower electrode load was applied. The number of the welded specimens exhibiting joint strength higher than 1000 N increased when a lower electrode load was applied and the metallic glass ribbons were interposed. The reproducibility of load–displacement curves of the tensile shear tests was increased by the glass transition to a supercooled liquid of the metallic glass ribbons upon resistance heating during welding.

Wide bandgap semiconductors such as SiC, GaN, and GaO require advanced bonding methods to meet demands to realize high performance and reliability of these devices. Sinter bonding by copper nanoparticles has major challenge to suppress the oxidation during bonding process. We introduced porous sintered copper layer formed by printing copper nanoparticles paste on a copper substrate, and irradiating a scanning blue laser beam. It was solid–phase bonded to copper chip by vertical excitation of ultrasonic waves. As results, porous sintered copper layer prepared with high laser power condition changed continuous and solid, and was densified after ultrasonic bonding. Under moderate laser power condition (3.6W), cohesive failure appeared in the bond region on both sides of the chip and the substrate, showing ductile fracture. It was suggested that the densification of the copper nanoparticles sintered layer and the low–temperature bonding of copper were achieved simultaneously in a short time due to the extremely high compressive deformability of the porous sintered copper layer worked effectively within the bonding layer and at the bonding interface.

Brass has been used for piping components because of its excellent machinability and workability. Recently, due to the revision of the Drinking Water Quality Standards Law, the weighted average value of Pb in brass used for piping parts is regulated to be less than 0.25 mass%. Therefore, Pb–free free–cutting brass with Bi or Si added as a substitute element for Pb has been developed and put into practical use.

When brass is used for valves, stainless steel with high strength and corrosion resistance may be used for piping. Previous research has revealed “the influence of the difference in thermal conductivity between the two on brazing” and “the behavior of additive elements such as Bi and Si during brazing. We confirmed the phenomenon that Ni disappears from the interface during brazing of stainless steel during brazing of the above. The purpose of this experiment was to elucidate these interfacial reactions.

No interfacial reaction between the molten brazing material (BAg–7) and stainless steel was observed at 710℃. According to the results of cross–sectional microstructural observation and EPMA elemental analysis of the brazed joint at 740°C, a Ni loss layer was observed at the interface between the brazing layer and the base metal under the uniform heating conditions during brazing. The interface reaction between the molten brazing material (BAg–13a) and stainless steel was not confirmed at 740 and 770°C, and at 800 and 830°C, a Ni disappearance layer was confirmed, which was less than in the previous study data.

Generally, brazing is completed when the brazing filler metal penetrates the gap by uniform wetting. It is believed that the joining process is completed with the formation of joint defects “voids” in the process of uniform wetting. However, previous studies have shown that what occurs when brazing is performed is non–uniform wetting. It is suggested that this non–uniform wetting is the cause of void generation.

Wetting and spreading of brazing filler metal is tested on a metal plate, as described in JIS Z 3191. The resulting angle between the molten brazing filler metal and the base metal surface is substituted into the “Young’s equation”. This is used to investigate the wetting of the brazing filler metal. However, this method does not cover the wetting of the molten brazing material as it moves into the gap.

From the results of the experiment, it was found that there are two types of wetting of molten brazing filler metal：“primary wetting” and “secondary wetting.”

In this study, Sn–Graphene (Ag) composite plating films were fabricated on copper alloy substrates using a hybrid plating method, and the effects of addition and concentration of Ag⁺ in plating bath on various properties were investigated. It is found that the defect density of graphene in composite films decreased with increasing Ag⁺ concentration. The as–plated Sn–Graphene (Ag) composite film exhibited excellent electrical contact resistance of 0.49 mΩ, which is 49% lower than those of pure Sn and 20% lower than that of Sn–Graphene composite plating films, and even lower than that of pure Ag plating film (0.61 mΩ). In particular, it was confirmed that the Sn–Graphene (Ag) composite films showed stable resistance in the resistance–load change profiles and even after being heated at 200°C for 150 h. The contact resistance of the pure Sn plating increased more than doubly after the heating test, whereas the Sn–Graphene (Ag) composite films increased only about 30% and maintained the same level of conductivity as the pure Ag plating film, indicating the effective enhancement of conductivity and heat resistance by the inclusion of Ag–doped graphene in Sn matrix plating films even under a long–term high temperature environment.

Copper foil, along with polyimide, has been used as a flexible printed circuits (FPCs) material, contributing greatly to the development of the information society. In particular, since rolled copper foil has excellent flexibility, its use in wearable devices and in–vehicle sensors, as well as smartphones, has begun to increase in recent years. In addition, as the functionality of these devices improves, FPCs with more complex wiring patterns, such as double–sided FPCs and multilayer FPCs, are increasingly being used. In many cases, FPCs with two or more layers of copper foil often require conductive processing, which involves copper plating on the copper foil, and there is concern that the copper plating layer may reduce the flexibility of the FPC.

In this study, we investigated the influence of the plating layer on flexibility by evaluating the flexibility of samples made from three types of copper foils with different crystalline structures (high flexibility rolled copper foil, standard rolled copper foil, and electro–deposited copper foil) that were given a plating layer. At the same time, the effect of the copper foil crystalline structure on the crystal growth of copper plating was also investigated.

As a result, we report that when a high flexibility rolled copper foil was used, the plating structure that grew epitaxially under the influence of the copper foil structure showed high (100) accumulation as well as the copper foil, thereby maintaining high Flexibility.

Silver electroplating films are widely used in various electronic/electrical devices owing to their excellent conductivity. This study is to verify the practicability of Ag–Graphene plating films by using cyanide and cyanide–free plating baths and to investigate the effects of plating bath and graphene inclusion on their properties. Uniform Ag–Graphene composite films with hardness of 130〜155 Hv can be produced in both cyanide and cyanide–free baths containing graphene sheets with mixed sizes. It was found that the conductivity of Ag–Graphene composite films was both improved by combining graphene, up to 35% and 51% in the cyanide and cyanide–free baths compared to the pure Ag film. In particular, the electrical contact resistance of the composite films can be maintained as the same levels as the as–plated states even after heating at 200°C for 1500 h due to the excellent thermal stability of graphene. Moreover, the wear resistance of Ag–Graphene composite films from both plating baths improved greatly and the improvement related to the orientation of graphene sheets in Ag matrix films, which can be controlled by stirring methods. Therefore, the Ag–Graphene composite films can be applied as a promising plating material for improving connecting reliability and reducing power consumption.

The numbers of connector pins for automotive applications have been increasing rapidly. Therefore, it is increasingly important to reduce the insertion force for workability. In this study, we investigated the effect of cold atmospheric pressure plasma treatment on the suppression of adhesion between electroplated materials, and the main cause of increase in the friction coefficient.

The plasma treatments with various gas species were performed on three types of plating：hard Ag, hard Ag–C composite, and Sn. The friction coefficients of the hard Ag and the hard Ag–C composite decreased by the treatments, especially using oxygen–containing gas species. The contact resistance increased after the treatment. The increment of the resistance was smaller at higher contact loads. Oxygen was detected on the surface of the hard Ag and the hard Ag–C composite after the treatment, suggesting that the surface oxidation of Ag is the main reason in the reduction of the friction coefficient and the increase in resistance. The thicknesses of the silver oxide layer were measured to be single nanometers and presumed to be thin enough to be broken on the contact force of the connector, having little adverse effect on the contact reliability. The plasma treatment is highly productive and suitable for continuous processing on automotive connectors that require low insertion force and contact reliability.

This study measured the heat transfer coefficients and visualized flow patterns of falling film evaporation using refrigerant mixture R32/R1234ze(E) as test refrigerant on a horizontal smooth tube with outer diameter of 19 mm. The experiments were carried out at a test pressure of 0.52 MPa and film Reynolds number range of 50–1000. In this experiment, the droplets, disturbed columns, and discrete droplets were observed. Also, there was no difference in the transition of the flow patterns due to the difference in heat flux. The heat transfer coefficients of refrigerant mixture dramatically decreased due to the increase in the dry patch area at the lower film Reynolds number region. At a film Reynolds number of 800, no dry patch occurs even under high heat flux conditions, and the heat transfer coefficients of refrigerant mixture increased monotonically with increasing heat flux.

Correlation between surface microstructure changes and catalytic property in the NO+CO reaction over rolled copper foil was investigated. The reaction characteristics (improvement of activity in hysteresis) of the rolled copper foil were significantly different from those of conventional supported copper catalysts. Comparing the surface structure of the rolled copper foil before and after the reaction, roughening of grain boundaries became more pronounced after the reaction, and also the surface roughening state varied depending on the crystal orientation. Experimental results on the surface reactivity of the rolled copper foil with NO or CO revealed that the cause of the roughening is mainly oxidation by NO. Consequently, the activity was improved because the roughened portion with microfacets (e.g., grain boundaries) formed by the redox process during the NO+CO reaction play an important role as the reaction sites.

In this study, we investigated the effects of the corrosion inhibitor benzotriazole (BTA) with the chemical formula C₆H₅N₃,on the oxidation behavior of copper through microstructure analysis. Our results demonstrate that BTA on copper decreased oxidation rate and alters the morphological characteristics of the copper oxide during oxidation. The biocidal ability of copper was found to be unaffected by the presence of BTA. Our findings suggest that the stability of the interface between copper and its oxide, Cu₂O, is primarily determined by atmospheric pressure rather than the presence of BTA during the oxidation process. This study provides valuable insights into the role of BTA in the oxidation behavior of copper, which can have implications for various applications.

This study investigates the inactivation mechanism of copper and its alloys on Cryptosporidium parvum oocyst infectivity and to evaluate its infectivity in a β–tubulin mRNA expression system using cultured human intestinal epithelial cells. Copper and brass strongly injured the oocyst wall of C. parvum and promoted sporozoite excystation in a short time. This denaturing effect was mediated by ROS produced via the Fenton reaction. The denatured oocysts were not capable of expressing β–tubulin mRNA with a 288 bp intron deletion in cultured cells. These results suggest that copper and brass have the potential ability to denature the wall and sporozoites of C. parvum oocysts via ROS and eliminate their infectivity.

Oxygen–free copper is an integral part of electric vehicles and renewable energy initiatives as the key conductor material owing to its high conductive properties. However, the poor heat resistance and poor stress relaxation resistance properties pose challenges for applications involving heat. This study aims to explore the potential for developing a new pure copper material with enhanced heat resistance and stress relaxation resistance properties while maintaining conductivity. Trace amounts of solute elements Mg, Sn, P, Ti, and Ag were added to oxygen–free copper, and the following results were obtained from the cold–rolled material：

(1) Mg, Sn, P, Ti, and Ag addition below 500 at ppm have little effect on yield strength.

(2) Mg and Ag addition below 200 at ppm have little effect on electrical conductivity.

(3) Mg and Sn addition above 100 at ppm increase the half softening temperature to over 300°C.

(4) Mg, Sn, and Ag addition above 100 at ppm increase the residual stress ratio to over 60%.

(5) Mg and Ag addition have superior balance among electrical conductivity, half softening temperature, and residual stress ratio, particularly, Mg addition of 100 to 200 at ppm exhibit excellent balance.

Novel composite materials of zeolite and polysaccharides were developed for efficient removal of Cu²⁺ ion in aqueous phase. Zeolite–composited alginate free–standing membranes were successfully prepared by chemical cross–linking of dried sodium alginate containing zeolite. Although the combination of zeolite with alginate was found to be advantageous in terms of improved handling, reduced the amount of Cu²⁺ ion–exchange per unit mass. Therefore, zeolite combined alginate free–standing membranes with improved water permeability by the addition of plasticizers were prepared, and their ion exchange capacities were estimated. However, the improvement in water permeability did not result in an increase in ion exchange capacity. Chitosan free–standing membrane containing zeolite was also prepared by a similar method. The ion–exchange capacity of the zeolite composited chitosan free–standing membrane was also determined and found to be improved compared to the zeolite composited alginate membrane. These results suggest the use of membrane substrate with less polarity is effective in reducing ion–exchange inhibition.

We investigated how the addition of indium (In) affects the deformation twinning of copper–indium (Cu–In) alloy through density functional theory (DFT) simulations. The twinnability of Cu–In alloy was compared to that of pure copper, copper–aluminum (Cu–Al) alloy, and copper–zinc (Cu–Zn) alloy. Our results showed that twinnability was greatly improved at two adjacent (111) slip planes with different concentrations of In atoms. Despite having a lower average twinnability than Cu–Al or Cu–Zn alloys, Cu–In alloy exhibited significantly higher twinnability near specific (111) planes with In atoms, which suggests that deformation twins can be easily generated on these planes during the normal deformation process with low strain rate. This study provides insights into the effects of In on the twinnability of Cu–In alloy and has implications for the design of new copper alloys with high mechanical properties.

To improve motor performance, motor magnet copper wires are changing from conventional round copper wires to flat (rectangular) copper wires. The market strict demands on the dimensional accuracy, surface properties, and surface defects of flat drawn copper wires, but there is almost no research on drawing to derive the optimum processing conditions for manufacturing flat wires. In this paper, we have focused on typical flat magnet wire manufacturing processes by multiple times shaped drawing from a round wire, to obtain high–quality flat magnet copper wire. Optimal processing conditions (mother wire diameter, cross–sectional reduction) and derivation of the optimal drawing die shape (angle) were studied. By Finite Element Analysis, we have investigated the possibility of shaped drawing, the lack of thickness, and the dimensional accuracy of the drawn shaped wire, and clarified the optimum processing conditions. In addition, the drawing experiments were carried out to confirm the reliability of the FEM analysis results. Based on these results, we clarified the optimum mother wire diameter, the optimum drawing conditions (die angle and reduction per pass) in the production of flat magnet copper wires.