Changes in the microstructure and various properties of heavily cold–rolled Cu–Zn system alloys with added small amounts of Ag were systematically investigated. While a typical heterogeneous–nano （HN） structure was evolved in all the alloys, the texture and ratio of the microstructural components developed were slightly varied depending on the added amount of Ag and Zn. The characteristic “eye”–shaped twin domains tended to evolve more significantly with increasing addition of these elements. Thermal stability of the HN structure appeared to be improved by Ag addition. This was due to grain–boundary segregation of Ag, which enabled sufficient age hardening. The grain–boundary segregation in the HN structure also resulted in the improvement of electrical conductivity. In this way, all the alloys showed quite high–tensile strength over 900 MPa along transvers direction with superior electrical conductivity around over 30％IACS. Maximum tensile strength achieved was 990 MPa with 34.5％IACS for Cu–30 mass％Zn–1 mass％Ag alloy.

The Cu−Cr−Zr alloy is a typical precipitation–strengthening alloy with excellent properties such as high strength, high thermal conductivity, high electrical conductivity, and so on. Recently, there has been an increasing demand for cost reduction, miniaturization and thinning due to the increase in copper bullion prices accompanying the increase in global demand. Therefore, it is required to improve the aging characteristics such as higher strength, higher electrical conductivity and shortening aging time. In this study, we focused on RMA–CREO process, which is a process of forming evaluate organization through introducing remarkable distortion by rotate deformation, as a method to improve properties, and investigated the effect of the two–step aging on properties of this alloy. It was confirmed that the combination of aging of 623 K and 773 K shortened the aging time. As a result of observing the microstructure before the aging using the backscattered electron diffraction method with a scanning electron microscope, it was confirmed that distortions were accumulated in the grains of the specimen subjected to the RMA–CREO process. From the differential scanning calorimetry and the microstructure observation with a transmission electron microscope, it was confirmed that chromium was precipitated in the grains and at the low–angle grain boundaries by the preliminary aging. From the above results, it was suggested that shorten precipitation was promoted by defects such as low–angle grain boundaries introduced by RMA–CREO process became precipitation sites and led to the aging time.

Cu–Ni–Si alloys have been used for electronic devices such as semiconductor lead frames because Cu–Ni–Si alloys have excellent electrical conductivity and strength. It is well known that Cu–Ni–Si alloys are strengthened by fine precipitates of δ–Ni₂Si (orthorhombic crystal structure) during aging treatment. There are many reports about mechanical properties of Cu–Ni–Si alloys, however, a few papers are dealt with crystal structure evolution of both matrix and precipitates using high resolution transmission electron microscope (HRTEM). In this work, Cu–3.8mol％Ni–1.8mol％Si (42NS) alloy having Ni/Si = 2, were prepared and hardness test and microstructure observation of alloy were performed to investigate the precipitates in high Ni and Si content alloy. In as quenched samples, coarse or fine intermetallic compounds were remained in 42NS alloy. They are mostly identified as δ–Ni₂Si by scanning electron microscope–energy dispersive X–ray spectroscopy (SEM–EDS) technique. In aged samples, fine precipitates were confirmed by TEM and HRTEM observation. Fine precipitates increased with increasing of aging times.

The effect of addition of third element on hardening behavior and microstructure in Cu–42 mass％Zn alloys have been investigated using hardness measurement and transmission electron microscopy (TEM) observation. The peak hardness during annealing and the number density of α–phase per unit area (N) in 0.1 mass％Mn–bearing alloy were highest among all alloys. Many striations which have been considered as the periodicity of 9R structure were observed in the α–phase. The number density of striations in α–phase per unit volume (Nv) and the ability of hardening (ΔHV) at peak hardness were calculated. Nv and ΔHV showed the linear relationship. There were a lot of striations in α–phase at the early annealing time, and the number of these striations decreased with increasing annealing time. According to the analysis of selected area electron diffraction (SAED) patterns obtained for these α–phase, transition time from 9R structure to fcc structure has been detected by the changing of angles in SAED patterns as the same as previous report for 60/40 Cu–Zn alloys.

Nb₃Sn high–field superconducting coil generates a strong magnetic field for confinement of a fusion plasma in an International Thermal Fusion Reactor (ITER). Nb₃Sn wire rods have excellent high magnetic field characteristics and good mass productivity, while in real environments, damage to the wire rod due to mechanical and thermal deformation is large, and deterioration of the critical current density (J_c) is a problem. It is reported that addition of In showed improvement in J_c as well as increase in strength by solid solution compared with addition of Zn. In this study, three types of wire rods, Nb/Cu–16Sn–0.3Ti, Nb/Cu 14Sn–2In–0.3Ti and Nb/Cu–10Sn–5In–0.3Ti, were prepared and the effect of In addition on the microstructure of Nb₃Sn filament was investigated．

Solid solution copper alloys for connectors are required to have both strength and stress relaxation resistance. Stress relaxation resistance can be improved by low–temperature annealing after cold rolling because dislocations annihilate with recovery. The dislocations formed during deformation can be classified into SS (statistically stored) and GN (geometrically necessary) dislocations. Based on the thermal stability and mobility of each dislocation, it is necessary to investigate the effects of the changes in densities of SS and GN dislocations caused by the low–temperature annealing on the stress relaxation property. The changes in strength and stress relaxation resistance of solid–solution Cu–Mg and Cu–Sn alloys with the low–temperature annealing were investigated. The SS and GN dislocation densities of solid solution were analyzed by using both X–ray diffraction and EBSD (electron backscatter diffraction) methods, and the dependence of the SS and GN dislocation densities on the low–temperature annealing temperatures was clarified. It was confirmed that the SS dislocation density decreased with increasing the low–temperature annealing temperatures, while the GN dislocation density remained constant. Therefore, it was understood that the GN dislocations have little effect on the stress relaxation, while the SS dislocations are mainly responsible for the stress relaxation. also found that the stress relaxation resistance of the Cu–Mg alloy was superior to that of Cu–Sn alloy, and this was mainly due to the low SS dislocation density.

Our group has developed age–hardenable Cu–Ni–Al alloys with excellent tensile strength of over 1400 MPa, excellent discoloration resistance, and non–magnetism, which are useful for leaf springs in Voice Coil Motor (VCM) modules of smartphone cameras. The alloys are fabricated by aging, severe cold rolling, and the final annealing process. There are two unique phenomena in the fabrication processing：One is softening in severe cold rolling and the other is significant hardening in the final annealing. In this study, we attempted to elucidate the softening and hardening mechanism by revealing microstructural changes during the processing via conductivity measurements, and TEM, XRD, and 3DAP tomography analysis. Fine Ni₃Al particles with an fcc ordered structure were dispersed in the Cu matrix after aging. Not only the Cu matrix, but also the Ni₃Al particles were sheared and deformed by severe cold rolling. It was also confirmed that the ordering degree of Ni₃Al particles was reduced by severe cold rolling. The Ni₃Al particles did not change significantly in size and morphology after the final annealing, but their ordering degree was partially restored. Therefore, it can be proposed that the disordering of Ni₃Al particles causes to degradation of age–precipitation strengthening and to softening by severe cold rolling. The significant hardening by the final annealing should be caused by the recovery of ordering degree of Ni₃Al particles.

The influence of substitution of Co for Ni in Cu–Ni–Si alloy on work and precipitation hardening was investigated using Cu–1.5Ni–0.36Si, Cu–0.75Ni–0.75Co–0.36Si and Cu–1.5Co–0.36Si alloys (in mass％). The alloys were peak–aged at 550°C and then cold–rolled to various rolling reductions. The larger the Co content was, the higher the precipitation hardening attained at peak aging. On the other hand, the work hardenability of the alloys decreased in the order of Co substitution. Based on the hypothesis that the yield stress after the thermomechanical treatments was mainly contributed by the precipitation strengthening and work (dislocation) strengthening, the effects of the substitution of Co for Ni on the strength of the alloys were discussed by the estimation of each contribution. The amount of precipitation strengthening was estimated from the volume fractions of precipitates obtained by electrical resistivity measurements. The estimates exhibited the same tendency as the actual age–hardening. Also, the amount of dislocation strengthening was estimated from the dislocation density derived from X–ray diffraction measurement. The amount of work hardening observed was in qualitatively accordance with the estimated dislocation strengthening. However, the sum of estimated precipitation and dislocation strengthenings showed a different tendency from the measured yield stress. Therefore, solid solution strengthening and grain refinement strengthening should be considered.

The microstructure and mechanical and electrical properties of two kinds of high concentration Corson alloys, which contained different amounts of Co substitution in Ni, were systematically investigated. After 90％ cold rolling, a heterogeneous–nano (HN) structure, composed of “eye”–shaped twin domains, shear bands and conventional low–angle lamellae, was fully developed in both alloys. The substitution of Co increased the volume fraction of the twin domains. Moreover, pre–aging treatment of the alloys before the cold rolling further enhanced the volume fraction of the twin domains. The alloys with and without pre–aging treatment were subjected to principal aging at various temperatures after the cold rolling. The peak hardness and electrical conductivity increased by the effects of pre–aging. And the peak–aged Co–substituted alloys exhibited superior balance of mechanical/electrical properties than that in the alloy without Co substitution. Nevertheless, the difference in the amount of Co substitution did not significantly affect the properties since the solvus of the δ phase in the alloys were almost unchanged by the Co substitutions.

The effects of the existence of precipitates on the development of heterogeneous–nano (HN) structure in a Cu–Ni–Si system alloy were systematically investigated using a Cu–4.0 mass％Ni–1.1 mass％Si alloy. After solution treatment, the specimens were aged at 733 K for various periods up to 10.8 ks and then cold–rolled to a reduction of 93％ in thickness. The microstructure and mechanical properties of the rolled specimens were examined. After 70％ cold rolling, the specimens with the aging for 3.6 ks, the HN structure consisting of conventional lamellae parallel to the rolling direction, shear bands inclined from an angle to the rolling direction and deformation twin domains surrounded by the shear bands were well–developed. On the other hand, the HN structure formed in the specimen without the aging before the cold rolling was relatively vague. The HN structure developed more clearly in the specimens with increasing the rolling reduction. However, the area fraction of the twin domains in the 3.6ks–aged specimen cold–rolled to 93％ were decreased compared with the 70％ cold–rolled one. The microhardness of the alloy accordingly decreased from 307 Hv to 290 Hv. It is inferred that the shear bands were formed more densely in the 3.6 ks–aged specimens than in the un–aged specimen due to the precipitation strengthening as well as the more significant work hardening during the cold rolling. The more densely developed shear bands could cause the subdivision of the twin domains and thus result in a decrease in the area fraction of the twin domains and hardness in the specimen cold–rolled to 93％.

The heterogeneous–nano (HN) structure consisting of “eye”–shaped twin domains, shear bands and lamellar grains is developed by heavy cold rolling of FCC metals and alloys with low stacking fault energy, and it provides superior strength/ductility balance. In this study, a Cu–Zn system alloy was subjected to two different rolling methods, and the effects of rolling methods on the development of the HN structure and mechanical properties were investigated. Some specimens were subjected to conventional unidirectional rolling up to a 90％ reduction in thickness. The others were cross–rolled to 90％, in which the rolling direction was rotated by 90° for each rolling pass. The 90％ cold rolling by both methods successfully introduced the typical HN structure. The cross–rolled specimen exhibited more isotropic mechanical properties than those of the unidirectionally rolled one. The more isotropic mechanical properties of the cross–rolled specimens were attributed to the more isotropic microstructure developed.

Heavily and simply cold–rolled Cu alloys with ultra–low stacking fault energy exhibit superior strength/ductility balance. The excellent mechanical properties are attained by the formation of a heterogeneous–nano （HN） structure consisting of twin domains, shear bands, and lamellar grains. In this study, using a Cu–Zn system alloy, two specimens with different initial textures were subjected to cold rolling. One has a strong <001> texture along the normal direction (ND) of the rolling surface, and the other has a <111> texture. Then, the effects of the initial texture of specimens on the formation of deformation twins in the early stage of cold rolling were precisely investigated. Also, the microstructure and mechanical properties of the alloys with finally developed HN structure after 90％–cold–rolling were examined. At the early stage of rolling, the mechanical twinning occurred more frequently in the specimen with <001> texture than in the <111> one. The difference in the twinning frequency can be reasonably explained by the significant difference in the ratio of the Schmid factor for twinning partial to the one for the perfect dislocation. On the 90％ cold rolling, the <001> specimen exhibited better strength/ductility balance than that of the <111> specimen since the <001> one has a higher volume fraction of the deformation twin domains. It can be concluded that the initial texture of the specimen before the cold rolling plays an important role in the mechanical properties of HN structured materials via the formation of the twin domains.

Morphology of eutectic in a hypoeutectic Cu–Zr alloy can be changed to various structures dependent on plastic deformation methods. This study reports morphological evolution of eutectic caused by unidirectional– and cross–rolling in a hypoeutectic Cu–2.7at.％Zr alloy. A graph–based method was applied to analyze the SEM images to characterize the morphological evolution of eutectics in terms of orientation, length, thickness, and connected structure of eutectics. Before rolling processes, an as–cast Cu–2.7at.％Zr alloy possessed a net–like morphology of eutectic with random orientations. The morphology of eutectic changed to the elongated and oriented one along the rolling direction by the unidirectional–rolling, and one along the two rolling directions by the cross–rolling. Variations of electrical conductivity by the unidirectional– and cross–rolling were also discussed based on the morphological evolution of eutectic.

Copper and copper alloys exhibit wide varieties of deformation textures depending on the chemical compositions and production process. Precise analysis and modeling of texture evolutions are important for developing the various copper alloys efficiently. In this study, we conducted in–situ neutron diffraction experiments during tensile tests of pure Cu and Cu–Mg alloy at iMATERIA beamline in J–PARC (Japan Proton Accelerator Research Complex). Texture evolutions of the copper alloys were evaluated by a time–of–flight neutron diffraction method. Neutron shielding sheets were used to mask areas of the tensile specimens to maintain a constant volume section for analyses. These careful measurements revealed that increasing rate of <111> component during tensile deformation of pure copper was higher than that of Cu–Mg alloy in larger strain region (above 0.22 in true strain), whereas the increasing rates of pure copper and Cu–Mg alloy were similar in smaller strain region (below 0.22 in true strain). We also conducted the crystal plasticity finite element calculation of tensile behaviors of the copper alloys. The initial crystal orientations that well reproduced initial textures of in–situ experiments were used for the calculation. Same material parameters of crystal plasticity were used for pure copper and Cu–Mg alloy. Texture evolutions of calculation results qualitatively agreed with experimental results. Under the present calculation condition, the increasing rate of <111> component of Cu–Mg alloy was higher than that of pure copper as opposed to the experiments.

Discontinuous precipitation (DP) generated in an age-hardenable copper-titanium (Cu-Ti) alloy and its magnesium (Mg)-doped analog were thoroughly explored in a comparative study by advanced electron microscopy using focused ion beam specimens extracted from the bulk. Transmission electron microscopy (TEM) as well as scanning transmission electron microscopy (STEM) in combination with energy-dispersive X-ray spectroscopy (EDS) allowed us to describe and differentiate real microstructures of the DPs formed in the alloys. The Cu₉₆Ti₄ solid-solution alloy, when subjected to a prolonged aging treatment at 450°C for 100 h, had lamellar aggregates resulting from DP along the grain boundaries, consisting of an FCC-Cu solid-solution phase (denoted by α-Cu_ss) and a stable Cu₄Ti intermetallic phase (β-Cu₄Ti), while those in the ternary Cu₉₄Ti₄Mg₂ counterpart also had similar lamellar aggregates, but consisting anomalously of two distinct FCC-Cu solid-solution phases with different Ti-solute contents, without causing the β-Cu₄Ti plates to coexist. On the basis of these observations, the possible effects of Mg-doping on the DP behavior in the Cu-Ti alloy were elucidated and the structural environment of the DPs, which may result in relatively higher mechanical capabilities, was also discussed.

The phase diagram of Cu–Ni₃Al pseudo–binary system was experimentally determined using fully heat–treated Cu–(26.7 to 94) at.％ Ni₃Al alloys, via microstructural observation and quantitative analysis such as TEM–EDS, DSC, and electrical resistivity measurements. The Cu–Ni₃Al pseudo–binary system exhibited a eutectic–type phase diagram with a three–phase coexistence region of Liq. + γ–Cu solid solution (Cu_ss) + γ’–Ni₃Al. As the (Ni+Al) content in the Cu–Ni₃Al alloys increased, the microstructure transited in the order of γ single–phase, eutectic (γ+γ’) two phases, primary γ’ + eutectic (γ+γ’) phases, and γ’ single phase. The melting start and end points of Cu–Ni₃Al alloys monotonically increased from 1084°C to 1380°C with increasing the (Ni+Al) content. The solid solubility of (Ni+Al) content in the γ phase C_(Ni+Al) could be described by the Arrhenius–type equation of ln C_(Ni+Al) = 5.50–2637/T, (T：absolute temperature), which indicated that the γ single–phase region had a relatively large temperature–dependence. Whereas, the maximum solubility of Cu in γ’ phase was approximately 14 at. ％, which was not significantly decreased with the temperature decreased.

In a superconducting magnet using Nb₃Sn wire, a strong electromagnetic force called hoop force is generated when the magnetic field becomes higher and the diameter becomes larger, and this electromagnetic force causes a large strain in the wire, resulting in a problem of degradation of superconducting properties．In order to solve this problem, it is necessary to increase the strength of Nb₃Sn wire. In this study, we conducted a basic research to evaluate the metallurgical structure and mechanical properties of copper alloys of various compositions to strengthen the copper matrix after superconducting phase formation．

Ni–bronze has relatively high strength among copper alloys, but heat–treated materials may be used instead of as–cast materials in order to further increase the strength. In addition, bronze–based members are often used as so–called sliding members, and improvement in friction characteristics is also required. The authors investigated the hardness of Cu–Ni–Sn alloys with and without sulfur as a function of aging condition, and found that the optimum condition of aging ranged at 350°C for temperature and from 20 to 30 h for time, with little effect of sulfur. However, it is necessary to study the impact resistance and friction characteristics as mechanical properties. In this study we evaluated the impact resistance and friction characteristics of the sulfide–dispersed Ni bronze specimens heat–treated optimally by means of Charpy impact test and pin–on–disk sliding test, respectively. As a result, impact value was higher than that of current Cu–Sn base alloys, in spite of a decrease by aging treatment. During the sliding test, sulfides caused formation of a thick film along the sliding direction on the specimen surface, resulting in achievement of stable friction phenomena.

It is required that polycrystalline copper alloys used for electronic components reveal good mechanical and electrical properties. For example, high stress relaxation characteristics are required in copper alloys used for connecter terminals. However, residual stresses which are related to stress relaxation characteristics are unclear in those alloys. In order to analyze the residual stresses of polycrystalline materials, the 2D method is useful, since it provides the three–dimensional stress tensor in microscopic area. Residual stress characteristics in Cu–Mg alloys heat–treated at 250°C, 300°C, and 350°C and deformed in tensile machine at speed of 0.1 mm/min were investigated in this study, to reveal the mechanism of stress relaxation of heat treatment and stress inducement by elongation. And stress ellipsoid was calculated by stress tensor. It indicates the magnitudes, direction, and tensile or compression of principal stresses, and it can evaluate the contribution of shear stress. Normal stress and principal stress are nearly equal values and directions in all samples. It indicates tensile stress by tensile machine affect normal stress directly, and contribution of shear stress is small. So, tensile deformation of crystal lattice is mainly occurred, effect of shear deformation is small. Also, as the temperature of heat treatment is higher, normal stress, its direction is equal to tensile direction, is increased. As higher heat treatment temperature is effective to stress relaxation, the interaction of residual stress and tensile stress is small. These results reflect the change of stress field in measurement area. And results of re–measured residual stress in all samples reproductively were obtained.

Microstructure, electrical conductivity, and mechanical properties of aged Cu–Ca alloys were investigated. In Cu–0.1 at. ％Ca alloy and Cu–0.5 at.％Ca alloy after 90％ cold rolling, Cu₅Ca intermetallic phase was observed with about 1.3 µm and 4.5 µm in diameter in the Cu solid solution phase, respectively. By aging at 200, 300, and 400℃, the electrical conductivity increased, but the hardness significantly decreased, which was due to recovery and recrystallization. However, the higher the Ca content, i.e., the higher the volume fraction and larger the size of Cu₅Ca phase, the higher the softening resistance. In Cu–0.5 at.％Ca alloy, the tensile strength of 382 MPa and the electrical conductivity of 93％IACS were obtained after 90％ cold rolling. By aging at 200 or 300°C, the tensile strength and the electrical conductivity lie in the range of 266–382 MPa and 93–100％IACS, respectively.

Cu–Zn alloys possess excellent workability and low cost, however, stress corrosion cracking resistance is poor compared to other Cu alloys. Many studies on stress corrosion cracking of Cu–Zn alloys have found that addition of Si and P to Cu–Zn–Sn alloys improves resistance to stress corrosion cracking and bending workability, but the mechanism for improving bending workability has not been elucidated yet. The purpose of this study is to evaluate the effect of the addition of Si and P on the bending workability of Cu–Zn–Sn based alloys.

In this study, we investigated the strength, bending workability, crystal orientation and microstructure of Cu–Zn–Sn–Si–P alloys processed with different rolling reduction ratios. Cu–Zn–Sn–Si–P alloys showed better bending workability and higher strength than Cu–Zn–Sn alloys. Cu–Zn–Sn–Si–P alloys also possessed small lattice strain and large crystallite size after rolling, which implies that shearing strain was suppressed from accumulating in the crystal grains and rather contributed to the formation of deformation twins. It was, therefore, concluded that the slip deformation was suppressed and the crystal grains were miniaturized by the introduction of twin boundaries, as a result, both the bending workability and the strength could be improved at the same time in Cu–Zn–Sn–Si–P alloys.

Accurate prediction of the spring properties of the terminal in the connector is required for the terminal design and development spring material. Responses of stress – strain for three spring materials of copper alloy thin sheet, Cu–Ni–Si alloy, Cu–Ni–Sn–P alloy and Cu–Zn alloy were determined with in plane tensile–compression tests. Stress softening behavior by Bauschinger effect was obtained at the compression loading after the prior tensile loading and unloading. V–bending terminal specimens were formed from these spring materials, and their force – stroke relations in a reverse direction to the V–bending direction were determined twice. The force – stroke relations were characterized by the degrees of stress softening. The experimental spring properties of the V–bending terminals for the Cu–Ni–Si alloy were accurately predicted by FE simulation using Yoshida–Uemori model.

We investigated whether high–quality fine copper wire could be manufactured at a low cost by combining three–roll rolling and die wire drawing. The roundness, surface quality, mechanical properties, and processing cost of fine wires finished from a copper wire rod by three–roll rolling and to the conventional die drawing method were compared. It is more difficult to obtain an exceptionally high quality of fine wires in terms of roundness value and surface quality by only three–roll rolling. However, the rolled wire is self–annealed by processing heat, so there is no need for the intermediate annealing work that is normally performed in the subsequent process on the troublesome task of threading wire to the die, so workability and productivity are improved while manufacturing cost is reduced. These are advantageous points. It was clarified that extremely high–quality copper fine wire can be manufactured at a low cost by first reducing the diameter of the rolled copper wire to 1.8 mm by the three–roll rolling method and then drawing the wire using the die.

When considering the strength required for structural materials, the first requirement is the ability to permanently hold stress under static loads. In order to achieve carbon neutrality, there is a need for lean and extreme design. It is important to evaluate the flow stress by removing the strain rate dependence of the material from the results of uniaxial tensile tests at quasi–static strain rates. In this study, the athermal stress component (stress independent on strain rate) of cold–rolled phosphor bronze sheet for springs (JIS–C5210–H) was evaluated using stress relaxation tests and extrapolation by curve fitting. It was found that about 90％ of the 0.2％ proof stress observed in the uniaxial tensile test at quasi–static strain rate was the athermal stress component. It was also found that the thermal stress component (stress dependent on strain rate) accounted for about 10％ and could not be generally ignored. Therefore, it is suggested that evaluation of the athermal stress component is effective as one of the direct methods to evaluate the static strength of structural materials.

The effect of temperature and phosphorus addition on the surface tension of molten Cu-P alloys were measured by the oscillating droplet method using the electromagnetic levitation technique. We successfully measured the accurate surface tension of molten samples that were sufficiently above the liquidus temperature. The surface tension of liquid copper was determined in its pure state, which is free from any contamination, such as oxygen adsorption and chemical reaction with the supporting material. The surface tension of the molten sample was decreased as phosphorus addition was increased. The surface tension of molten Cu-P alloys was well expressed as functions of temperature and of phosphorus activity from the measurement results using the Szyszkowski model. Furthermore, the enthalpy and entropy change in phosphorus adsorption on liquid copper were also estimated.

This study experimentally investigated the heat transfer coefficients and flow patterns of falling film evaporation of HFO refrigerant R1336mzz(E) as test refrigerant on a horizontal smooth tube with outer diameter of 19 mm. The experiments were carried out at a saturation temperature of 15 °C and film Reynolds number range of 50-1000. In the experimental conditions, the droplets, disturbed columns, and discrete droplets were observed. There was no difference in the transition of the flow pattern due to the heat flux. The heat transfer coefficients dramatically decreased due to the increase in the dry patch area at low film Reynolds number region. The dry patch area increased with increasing heat flux at the low film Reynolds number region. At the low heat flux condition, the heat transfer coefficient increased as the film Reynolds number decreased except for the region where dry patches occurred. The heat transfer coefficients were enhanced with increasing heat flux due to promotion of nucleate boiling.

Since the soaring price of copper during these years, demands to increase material strength and lower material costs have been driving manufacturers to develop high strength copper alloy tube with thinner wall–thickness for heat exchangers. It has been confirmed that the strength of Cu–Ni–P alloy is increased by precipitation strengthening even after brazing. Corrosion resistance evaluation is also necessary for the development of copper alloy tubes for air conditioners. The main corrosion problem of copper tube for air conditioner is ant’s nest corrosion. It is also known that stress corrosion cracking (SCC) occurs in phosphorus deoxidized copper, which is classified as pure copper alloy, when tensile stress is applied in ammonia–gas atmosphere. Since the precipitation state of Cu–Ni–P alloy differs depending on the heat treatment conditions, it is important to focus the corrosion resistance when the cooling rate after heating is substantially varied. In this study, we investigated the effects of heat treatment conditions on ant’s nest corrosion vulnerability and SCC susceptibility using a Cu–0.93mass% Ni–0.24mass% P copper alloy tube. Ant’s nest corrosion test found that the corrosion morphology of furnace cooled material, air cooled material, and water quenched material exhibited a hemispherical shape, showing immunity to ant’s nest corrosion. These were considered to be the effect of high phosphorus content in the alloy. Stress corrosion cracking test under tensile stress in ammonia–gas atmosphere revealed that grain boundary cracking was observed in all of the furnace–cooled, air–cooled, and water–cooled material. Above all, water quenched material achieved highest SCC resistance, which had withstood more than 10 times longer than furnace cooled material.

Brazing is the main method used to connect copper tubes in heat exchangers of air–conditioning and sanitary equipment, and leakage accidents have occurred due to grooving corrosion on the copper tube near the brazing parts. The corrosion progressed by the galvanic action, in which copper was the anode and brazing filler metal was the cathode. Here, we studied the effects of solution flow, solution conductivity, and types of ions on grooving corrosion on the copper tube near the brazing parts by electrochemical measurement of copper plate, copper tube and brazing filler metals. In the test, we used BCuP–2 and BCuP–3 as brazing filler metals. The results showed that the brazing filler metals and the carbon film on the inner surface of the copper tube affected corrosion potential in tap water. The corrosion current density increased with increasing conductivity on actual tube and BCuP–2. The effects of solution conductivity and types of ions on corrosion current density were greater for BCuP–3, and it was thought to be that silver contained in the brazing filler metal influenced the effect.

We examined the suppression of type I” pitting corrosion in copper tubes used for heat transfer in cooling water systems with absorption chillers. We have developed a new water treatment chemical that could inhibit this pitting corrosion. Previously, we investigated the effects of cooling water quality on the effects of the water treatment chemical, and reported a tendency for corrosion inhibition with increasing calcium hardness. In addition to calcium, silicate has been reported as a corrosion inhibitor in water quality components, but there have been no reports regarding the relationship between silicate and water treatment chemical with regard to effects of silicate on pitting corrosion. In this study, the effects of calcium hardness and silicate concentration on the carbon film–dependent pitting corrosion inhibitory effects of water treatment agents for cooling water systems were investigated. The results showed that the breakdown potential increased with increasing silicate concentration, and silicate was effective in preventing corrosion by the water treatment agent. In addition, when the silicate concentration was high, the potential tended to be low when the calcium hardness was high, and conversely tended to be high when the calcium hardness was low. These observations suggested that film formation differs depending on the ratio of calcium to silicate present. The anticorrosion effect was considered to be due to the synergistic effect of 1–hydroxyethane–1,1–diphosphonic acid (HEDP), benzotriazole (BTA), calcium hardness, and silicate contained in the water treatment chemical.

Residual carbon on the inner surface of copper tubes is one of the causes of pitting corrosion. In evaluation tests of pitting corrosion resistance, the original pipes used in actual equipment were applied for the test specimens. The occurrence of micro–mounds on the inner surface of specimen was investigated after the short time filling test using special solution mixed with various ratios of factors that promote or inhibit corrosion. As the result, it was found that the pitting corrosion resistance should be evaluated by the number of occurrence of micro–mounds in size of 50 to 400 μm under the concentration of corrosive anion at 100 mg/L in special solution. In addition, differences in the amount of residual carbon caused differences in the occurrence of micro–mounds and the form of corrosion over time was differed due to the differences in the amount of residual carbon. It was concluded that this test in a short time should be useful to evaluate the pitting corrosion resistance of copper tubes.

In opened circulator cooling system, water treatment should be conducted to prevent pitting corrosion of copper tube and generation of Legionella spp. In this system ionic components in cooling water are gradually concentrated by evaporation of the water and the high concentration may affect the pitting corrosion and the number of Legionella spp. Suitable treatment of the cooling water is required in which some chemicals are added to solve the two problems. In this study, field tests were conducted using copper plates and tubes with different amounts of residual carbon. Comparison between the results of the tests in flowing and stagnant water suggested that corrosion evaluation was made possible by the stagnant–water test using the copper tubes. The pitting corrosion evaluation and Legionella spp. measurement were conducted at 10 points with different water qualities by the stagnant–water test in which the newly developed water treatment chemical was added. The results showed that the developed water treatment chemical achieved excellent performance on pitting corrosion prevention and on maintaining Legionella spp. below the limit of detection at all the locations.

A real–time imaging electrochemical measurement system was developed for an in–situ observation of brass dezincification corrosion. This system allows for a video recording of brass cross–section under galvanostatic polarization. The progress of erosion associated with the dezincification corrosion in the depth direction on the brass cross–section was successfully observed from the video recording during the measurement. The erosion depth at each measurement time could be estimated from the cross–section images, indicating that the erosion depth was drastically increased at arbitrary time under galvanostatic polarization. It suggested that the erosion rate in the depth direction is strongly related to the dissolution behavior of zinc and copper from brass surface, namely, the preferential dissolution and the simultaneous dissolution. The relation between the dissolution behavior and the electrode potential of brass under galvanostatic polarization was discussed.

A tin–bearing αBrass, αCu–Zn–Sn alloy, which is an αCu–Zn alloy with about 1 mass％ Sn added to increase the strength, shows good spring properties, but has high susceptibility to stress corrosion cracking (SCC)．The co–authors have found that the addition of Si and P to the αCu–Zn–Sn alloys significantly improves its SCC susceptibility. The objective of this study is to elucidate a mechanism by which the susceptibility is improved by the addition of Si and P. αCu–Zn–Sn alloy specimens with different concentrations of Si and/or P were prepared. The change over time in the anodic current density of the specimen bent to apply tensile stresses on the surface was measured in 0.1 M NaNO₂ solution under a constant potential. After the measurement, the components of the films formed on the specimen was analyzed by Raman spectroscopy. The concentration depth profile and the surface distribution of elements for the formed films were measured by XPS and EPMA respectively. The composition at the cross–section of the film sliced by FIB milling technique was analyzed by EDS. The results suggested that the addition of Si and P enhanced the protective properties of the surface film for the αCu–Zn–Sn alloy, suppressed the occurrence of local corrosion leading to the initiation of SCC, and prompted the repairing of the locally broken–down film by depositing as a silicon oxide or a phosphate film respectively. It was considered that low SCC susceptibility of the αCu–Zn–Sn alloys with Si and P is brought by the synergistic effect of these added elements.

In this study, we investigated the degradation behavior of contacts based on the contact resistance and temperature change during high current using Sn plating used in automotive terminals. In the non–sliding energization test, there was a positive correlation between the current value and the temperature rise, and it was confirmed that the temperature rise exceeded 20°C and the contact resistance decreased. It is considered that the plating softened, and the contact area was deformed due to the effect of current generation caused by increased current value. And the contact resistance decreased due to the increase in contact area. Next, it was confirmed that the slight sliding wear phenomenon as in the well–known low current energization occurs in the energization accompanied by sliding. However, the higher the current value, the shorter the number of slides until the base material is exposed. Under the high–current condition, the heat effect is large, which accelerated the softening and melting of the contact area and accelerated the abrasion of the plating.

Based on these results, the higher the current value, the higher the calorific value generated, which causes the plating film to soften and an increment in contact area. Therefore, it is expected that the plating wear will progress more, especially under the slight sliding conditions caused by the vibration of the vehicle body, and the result is consistent with the concern in actual use.

An investigation was carried out of the effects of sliding cycles and contact load on electrical contact resistance behavior of reflowed tin plating in reciprocating slide wear test. This paper discusses and reports experimentally observed results on electrical contact resistance behavior and wear behavior of reflowed tin plating during slide wear test with a varying load. Electrical contact resistance was measured via a four–terminal method by re–contacting the wear marks of samples after the slide wear test.

The main results are summarized as follows：(a) Electrical contact resistance increased with decreasing load and a larger number of sliding cycles. (b) This is conjectured to be due to deposition of tin oxides with a larger number of sliding cycles. (c) It is conjectured that tin oxides deposited more easily at the contact area with decreasing load. This is conjectured to be due to reduced discharge of tin abrasion powder outside the contact area due to decreased load.

The purpose of this study is to clarify the effects of electroplating conditions and the graphene size on the properties of Ag–Graphene composite films that electrodeposited on Cu alloy as terminals and/or connectors for automobiles. It was found from the measurement results of electrical contact resistance that the conductivity of the Ag–Graphene composite films was highly dependent on the current density during electroplating. The electrical contact resistance of the Ag–Graphene composite films decreased gradually with plating current density, giving a lowest value of 0.25 mΩ at 0.5 N, or in other words, improving the conductivity for 59％ than the pure Ag film. This can be attributed to the fact that the composited graphene sheets had fewer defects when the current density was increased. Moreover, the conductivity or the electrical contact resistance stability can be maintained even after heating at 200°C for 1000 h due to the excellent thermal stability of graphene. Furthermore, it was also found from wear tests that the graphene size included in the composite films plays a significant role in the abrasion resistance of the Ag–Graphene composite plating films. In particular, the Ag–Graphene (3–5 μm) composite film exhibited the best wear resistance, with a 69％ reduction in the friction coefficient and a 95％ reduction in the worn amount after sliding friction for 100 cycles under 3 N.

This study is aimed at fabricating Sn–Graphene composite films on Cu alloys by hybrid electroplating method and clarifying the factors that affect the properties as automotive connectors. The graphene content in composite films was dependent on the current density during electroplating as well as graphene size. It was confirmed from GD–OES and Raman analysis that graphene exists not only on the outermost surface but also inside the composite films, with better crystallinity for the larger size or domain. The Sn–Graphene composite film exhibited lowest electrical contact resistance of 0. 61 mΩ (0.5 Ν), which reduced 32–34％ compared to pure Sn plating films due to the high conductivity of the graphene in the Sn film. In particular, the contact resistance value of Sn–Graphene composite film remained much lower than that of pure Sn film even after heat resistance test at high temperature above 200 °C for more than 70 h. This is because the graphene sheets suppressed effectively the Cu–Sn alloying progress of the plating film during heating. Moreover, it is found from fretting corrosion tests that the Sn–Graphene (3–5 mm) exhibited excellent stability with unchanged contact resistance upon sliding, in comparison to the significant increase for pure Sn film in a short period, which can be attrubuted to the inclusion of graphene in the wear powder between the connectors.

In order to prevent the spread of infectious diseases, it is important to prevent the spread of pathogens. Pathogens transmit through frequently hand touched environmental surfaces such as the surfaces of doorknobs and handrails. Introducing antibacterial metallic materials to environmental surfaces is therefore expected to inhibit transmission of pathogens by sterilizing the surfaces. Copper alloys are frequently used because of their high strength, and workability. Among copper alloys, brass is commonly used for environmental surfaces. The brass surface is oxidized by oxygen in the air but few studies have considered the oxides on the brass surface. Since zinc is antibacterial, not only copper oxides but also zinc oxides likely affect the antibacterial properties, and a more effective antibacterial brass surface can presumably be achieved. The object of this study is to propose a treatment method that improves the antibacterial properties of brass surface. Heat–treated brass specimens were immersed in citric acid solution for 24 hours. The specimens were then subjected to X–ray photoelectron spectroscopy analysis, antibacterial tests by the film contact method, and measurements of the amount of ions eluted from specimen surfaces by ICP–MS. It turned out that zinc ions inhibited the antibacterial action of copper ions. The antibacterial mechanism of solid copper seemed to be different from that in the ion solution. An increase in the total ratio of Cu and Cu2O improved the antibacterial properties of brass.

Exposure to pure copper (Cu), Cu containing alloy surfaces, or cupric (Cu²⁺) ion containing solutions is toxic to microorganisms including bacteria and cyanobacteria. The present study describes the effect of Zn²⁺ ions on Cu²⁺ ion induced toxicity and structural changes in cyanobacterium Synechococcus elongatus PCC7942 (S. elongatus). Cyanobacteria were treated with aqueous Cu²⁺, Zn²⁺ and Ni²⁺ ion containing solutions mimicking the metal ratios in pure Cu (C1020), brass (C2600, C2680, C2200, C2300, C2801), and nickel silver (C7521, C7701). Cells were observed by fluorescent and electron microscope. Chemically fixed and high–pressure frozen cells were used for ultra–structural observations by TEM. Co–localization of elements including Cu, Zn, and P was observed by EDX elemental mapping. Zn²⁺ ions at more than 0.13% were found to have a protective effect against DNA damage caused by Cu²⁺. When cells come in contact with a specific range of Zn²⁺ concentrations (0.13 to 0.2%) in the solution, cyanobacterial cells go through a transient DNA compaction. Zn²⁺ ions colocalized with DNA; however, ROS formation was not significantly changed with Zn²⁺ ion percentage increase.

Free–cutting brass contains 3％ lead to obtain excellent machinability, but because lead is harmful to the human body, lead regulations are being tightened in Europe, starting with the 2010 and 2014 lead control laws for drinking water–related equipment in the United States, and including RoHS regulations, ELV regulations, and the 4MS Positive List. Being affected by these increasingly strict lead regulations in Europe and the United States, demand for brass with significantly reduced lead content is on the rise.

In order to meet the needs of the times, the authors have developed the world’s first lead–free, free–cutting α+β brass “62.5Cu–1Si–Zn alloy” with a lead content of less than 0.1％.

As a result of investigating the machinability of this alloy by comparing it with CW510L, it was demonstrated that the quality of machined products made of the 62.5Cu–1Si–Zn alloy is good due to reduced cutting resistance realized by shear type chips that can be generated by the action of Si solid–solubilized in the β–phase, the presence of fine P compounds, and the effect of fine α–crystal grains.

Brass that contains lead is called free-cutting brass, and because it boasts good machinability, which allows fine cutting, it has long been used in a variety of applications. However, lead is known to have negative impacts on the environment. Today, regulations such as the EU’s RoHS Directive limit the use of brass containing lead. So, cutting work must be performed on lead-free brass. However, compared to leaded brass, lead-free brass has very poor machinability. Therefore, to perform cutting work on such lead-free brass without causing adverse effects on the environment, it is necessary to improve its machinability. With this in mind, we have developed brass that uses silicon as a substitute for lead. Adding silicon to the β-phase of brass has been reported to lower the stacking fault energy (SFE). This is because a lower SFE causes the chips formed during cutting to break off short, thus decreasing the cutting resistance. However, there have been no reports on the cutting characteristics (including drill lifespan, cutting resistance, and chip condition) during microdrilling of fine holes in silicon brass.

In this study, we compared the cutting characteristics during microdrilling of fine holes in leaded brass and brass with silicon added to either the α-phase or the β-phase of the solid solution. The results revealed that the addition of silicon to the β-phase led to nearly the same drill lifespan as that for leaded brass. This is due to the lower SFE. However, with silicon brass, chips tend to stick to the drill flank and increase the cutting resistance （thrust force）. Moreover, both leaded brass and silicon brass produce folded chips. However, in the case of leaded brass, this folding occurs due to the solid lubrication action of the lead, whereas for silicon brass it is caused by the lower SFE, which makes it easier for shear failure to occur. Thus, similar folding can be caused by different mechanisms.

Generally, brass with lead added is called free–cutting brass and is used for various parts such as water supply parts. However, lead is regulated in many countries because it has an adverse effect on the human body. Under regulations, various types of lead–free brass have been developed by copper and copper alloy manufacturers. Among them, lead–free Brass with Bi, which has similar characteristics to Pb, has been developed and put into practical use. It has good machinability and has machinability close to that of free–cutting brass. However, there are still many unclear points such as the difference in cutting mechanism between lead–free Brass with Bi and free–cutting brass and the machinability improvement mechanism. In this study, for the purpose of examining the effect of Bi on machinability in cutting of lead–free Brass with Bi, we performed experiments of turning and two–dimensional cutting about lead–free Brass with Bi and free–cutting brass with Pb. As a result, it was found that Bi in lead–free Brass with Bi has almost the same effect of reducing frictional force and shearing force as Pb. Similar to Pb, the Bi system improves chip fragmentation due to Bi stress concentration in the tissue, and the difference in chip fragmentation from the Pb system may be due to the distribution of Bi particles. In addition, there was a difference in the state of additives between Bi and Pb on the newly formed surface of chip. However, in the lubrication action between the tool and the chips, the difference between Bi and Pb in the elongation of the additive on the new chip surface does not affect the friction reduction effect, and it is considered that a sufficient effect is obtained in Bi as well.

Recently, the electrification of vehicles has been progressing toward carbon neutrality. As the electrification of cars progresses, the number of copper bar junctions will increase. It’s junction’s point of view, welding with fiber laser is attractive because of its deep welding depth, narrow heat affected zone and productivity.

On the other hand, when we weld copper plates with the conventional IR fiber laser, a large amount of spatter and welding defects occur. To suppress this welding defect, we tried to weld copper plate with the fiber laser which adopted beam mode control technology or blue–IR hybrid laser. As a result of that, we succeed suppressing the welding defects. We assumed it was caused by the opening around the keyhole in the molten pool.

Copper alloys with excellent machinability and thermal conductivity are widely used as piping materials, and brazing is used as the connection method. Ants’ nest corrosion is one of the causes of corrosion damage to copper pipes. Corrosion resistant copper alloys have been developed by adding a small amount of various elements to pure copper to suppress the occurrence of ant’s nest corrosion. However, there are many unclear points about the brazing properties of these corrosion resistant copper alloys.

In this study, brazing was performed using corrosion resistant copper alloys, and the microstructure of the cross section of the brazed part was observed using optical microscope and EPMA elemental analysis. The corrosion resistant copper alloys used were one copper alloy with Mn and the other a copper alloy with P. In addition, the area of the fillet was measured evaluated the brazing–ability.

As a result, it was confirmed that braze joints using BCuP–8 had better brazing–ability than those using BAg–7. It was also found that Mn in the pure copper matrix had a negative effect on brazing–ability. Furthermore, it was found that Mn added to the pure copper base metal had a strong influence on brazing–ability in the brazing material with Cu solid solution as the primary crystal. On the other hand, P contained in the pure copper base metal, P was detected at the interface between the brazing layer and the base metal. Therefore, good brazing–ability was obtained.

To examine the effect of bond strength at the Cu/Cu bonded joint interface of formate coated Cu nanoparticles, the interfacial microstructures and fractured surfaces of joint were observed using SEM. Cu nanoparticles surface was modified by immerse to room temperature formic acid for predetermined time. Bonding process was performed at bonding temperature of 523〜723 K under a load of 20 MPa (bonding time of 15 min). By applying the metal salt coating treatment, a good bonding interface with fewer voids was obtained compared to the case without treatment. From the experimental results, it is found out that formate coating process is effective at removing oxide film and substitution to a metal salt on the Cu nanoparticles surface.

In recent years, in order to reduce the use of fossil fuels, the electrification of automobiles and other vehicles using renewable energy sources has been promoted. For example, in the electronics industry, high–density, high–integration packaging technology is required, and power semiconductors are the mainstream, especially in inverters and converters used in hybrid and electric vehicles. A connection method that can withstand the operating temperature of power semiconductors is necessary, but no established connection method has yet been found. Therefore, direct solid phase bonding is a promising bonding method, and various bonding methods have been investigated, such as the metal salt generation bonding technique. The metal salt generation bonding method has been investigated for solid phase bonding of Cu, but it is not suitable for electronic packaging because the bonding time is long and the bonding is done in a vacuum. In this study, we investigated short–time bonding in air using the pulse heat bonding method, which utilizes the formation and decomposition reaction of metallic salts.

Brass has been used for piping components because of its excellent machinability and workability. In recent years, due to the revision of the Drinking Water Quality Standards Law, the weighted average value of Pb in brass used for piping components 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. In the case of a combination of Pb-free free-cutting brass and stainless steel, it is necessary to clarify “the effect of the difference in thermal conductivity between the two on the brazing process” and “the effect of added elements such as Bi and Si on braze ability,” but it is not known. In this study, brazing was performed at controlled temperatures by changing the volume ratio and temperature conditions.

Interfacial reaction between molten brazing filler metal/stainless steel occurred slightly at 680°C for 20 minutes. So that sound brass/stainless steel brazed joint was not obtained. According to cross-sectional microstructure observation results and EPMA elemental analysis results at the brazed joint at 830°C, Bi alloy layer at the brazed joint and Ni disappearance layer at the interface between brazed layer and stainless steel base metal were recognized under uniform heating condition during brazing. On the other hand, under non-uniform heating condition, sound brazed joint was obtained.

Brass has excellent ductility and workability. To comply with environmental regulations, such as water quality standards, Pb–free brass containing Bi and Si has been put into practical use. However, brass soldering using lead–free solder is required for actual use. In our laboratory, we conduct soldering and brazing experiments using pure copper and Pb–free brass. These experiments yield a large amount of data. However, the experimental results confirmed that the wetting spread was nonuniform when the brazing material penetrated. The reason for this nonuniform wetting has not yet been clarified. Therefore, this study aims to quantitatively clarify the cause of nonuniform wetting during soldering and brazing by comparing the data from previous studies using parallel two–plate test specimens. The experimental results using specimens with various modifications suggest that the nonuniform wetting is caused by the temperature distribution in the gap and the gap shape. The gap shape was found to have a greater effect on wetting than temperature distribution.

Stud welding has been widely used for the welding of bar to plate. However, it is difficult to weld dissimilar metals in this method. Thus, the authors have begun to examine the welding of the dissimilar stud joints using friction welding. In the present study, stud joints of copper–chromium alloy bar to SUS304L stainless steel plate were friction welded. In all joints, even burrs were generated from the bar side and the plate side did not deformed, and there were no cracks at the weld interface. The heat affected zones of the copper–chromium alloy bar side was significantly softened. Joint strength was evaluated by tensile testing, fatigue testing and bending testing. In the tensile testing, all joints were fractured near the weld interface, and the maximum tensile strength was 350 MPa. In the fatigue testing, joints were fractured in the softened area of the copper–chromium alloy bar near the weld interface, and the fatigue limits of joints were 39–43 MPa. In the bending testing, all joints were cracked near the weld interface at the bending angle of 50–55 degree.

Oxygen–free copper is widely used in ultra–high vacuum equipment and heat sinks because of its high thermal and electrical conductivity and low gas release in vacuum. On the other hand, due to the low mechanical strength of oxygen–free copper, copper alloys such as chromium copper alloys are attracting attention. However, although joining methods have been established for pure copper and oxygen–free copper, chromium copper alloys are difficult to weld because of their poor weldability and large thermal conductivity. In this study, solid phase bonding was attempted by heating and pressurizing the base metal of chromium copper alloy without melting. As a joining method for chromium copper alloys, we used sodium hydroxide and formic acid to reduce and remove the oxide film on the joining surface, with the aim of producing joints with higher joining strength.