Cu–Ni–Si alloys have been used for electronic devices such as semiconductor lead frames because Cu–Ni Si alloys have excellent balance of 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, 4 kinds of Cu–Ni–Si alloys, 31NS alloy, 42NS alloy, 53NS alloy and 74NS alloy having Ni/Si＝2, were prepared and hardness test and microstructure observation of those 4 alloys were performed to investigate the effect of Ni and Si content on age–hardening behavior and microstructure. In as quenched samples, coarse or fine intermetallic compounds were remained in all alloys. 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, and they are mostly identified as δ–Ni₂Si. Fine precipitates increased with increasing of Ni and Si content.

The Nb₃Sn high magnetic field superconducting coil creates a strong magnetic field to confine the fusion plasma in the International Thermonuclear Reactor (ITER). Nb₃Sn wire has excellent high magnetic field characteristics and productivity, but in the actual environment, it is greatly damaged by mechanical and thermal strains, and there is a concern that the critical current density (Jc) may deteriorate. When Zn was added as a solute element to the Cu–14 mass％ Sn alloy used in the usual bronze method, the Zn equivalent became about 27 mass％, and the Nb₃Sn phase was formed after the heat treatment. The strength of Nb₃Sn wire rod is increased by the solid solution of Zn. Currently, as a further improvement, the addition of In, which is expected to be more solid solution strengthened than Zn, has been reported. Addition of In can be expected not only to strengthen the solid solution but also to improve the Jc characteristics. This study will investigate the effects of In addition to bronze using TEM and SEM microstructure observation of Nb₃Sn filaments fabricated by heat treatment of Nb/Cu–10Sn–5In–0.3Ti (mass％) ultrafine multi–core wire.

The heterogeneous–nano (HN) structure consisting of twin domains, shear bands, and lamellar grains developed by heavy cold rolling of FCC metals with low stacking fault energy is known to provide extremely high strength. In the present study, the effects of the rolling pass schedule on the development of HN structure and the mechanical properties in a Cu–38mass%Zn alloy were investigated. Two different rolling pass schedules were conducted； one was conventional unidirectional rolling (1–DR) up to 90% reduction in thickness, and the other was the two–directional rolling (2–DR) , in which the specimen was unidirectionally rolled to 25% reduction, then rotated 90° around the rolling direction, and subsequently, unidirectionally rolled up to total reduction of 90%. At total reduction of 50%, the number of grains with deformation twins in the 2–DR specimen was comparably higher than that in the 1–DR one. Further cold rolling up to 90% produced the HN structure in both specimens. The size of twin domains in the specimen fabricated by 2–DR was finer and their volume fraction was larger than those in the specimen processed by 1–DR. Also, the 2–DR specimen exhibited a better strength–elongation balance than the 1–DR specimen. It can be concluded that the finer size and larger volume fraction of the twin domain effectively improved the strength–elongation balance in the 2–DR specimen.

Wires of a Cu–3.8wt% Zr alloy were produced by conform extrusion followed by wire drawing up to 0.2 mm in diameter (S wire), or by conform extrusion and subsequent annealing during wire drawing up to 0.2 mm (IA wire). The effects of microstructure on the strength and electrical conductivity of the S and IA wires were investigated. The severely drawn S and IA wires had a mixed microstructure consisting of a Cu parent phase with fine grains, fibrous eutectics elongated along the drawing direction, and granular eutectics. The 0.2% proof stress (σ_0.2) and tensile strength (σ_u) of the S and IA wires increased monotonically with increasing drawing ratio (η). The S wire with η=7.8 exhibited large values of σ_0.2=1080 MPa and σ_u=1320 MPa. The S and IA wires having the mixed microstructure are strengthened primarily by high density of dislocations and grain refinement in the Cu phase and by the presence of fibrous and granular eutectics. The electrical conductivity (E) of the S wire increased in the early stage of wire drawing and then began to decrease, dropping to 42% IACS at η=7.8. The increase in E is caused by refining of the eutectics, which was formed during casting, toward the granular or fibrous form. The E value of the IA wire after annealing was high, 72%IACS, and then decreased as η increased. Values of E of the S and IA wires with the mixed microstructure was estimated by applying rules of mixtures. The estimated values of E are in agreement with the measured values of E. It is shown that the presence of the fibrous and granular eutectics significantly increases the electrical conductivity.

The effect of the amount of Mn on the microstructure evolution of the Cu–Mn alloy processed by ECAP has been investigated focusing on the solid solution effect. The samples used were pure Cu, Cu–1at% Mn, Cu–10at% Mn, and Cu–15at% Mn, and they have little difference in stacking fault energy. ECAP processing was performed for 0–8 Pass followed by Vickers hardness test, tensile test, and SEM/TEM. As the amount of Mn increased, the persistent increase of hardness until 8 passes and the reduction of the final grain size was evident while the hardness of pure copper and 1at%Mn alloys saturated with 3 to 4 passes. The results of the tensile tests after ECAP for 8 passes showed persistent strain hardening in high Mn contents as compared with that in pure copper and low Mn and indicated suppression of dynamic recovery. It is considered that this is because the rearrangement dislocations was suppressed by the atomic size effect of the solid solution atom rather than difference in stacking fault energy in the late stage of processing.

The effect of stacking fault energy and solid solution effect on the ultrafine grained (UFG) structural evolution during equal channel angular pressing (ECAP) was studied focusing on the transformation from dislocation cell structures to grain structures. To attempt to separate and compare both effects, pure Cu, pure Ag, Cu–Al alloys and Cu–Mn alloys were chosen for materials because the SFE of Cu–Al alloys decreases with increasing Al concentration whereas that of Cu–Mn alloy remains constant with increasing Mn concentration. The results show that the grain size was smaller and the hardness was higher with increasing solute concentration regardless of low or high SFEs. The final grain size of Cu–10Mn reached 71 nm, and this value was smaller than that of Cu–6.8Al which has lower SFE and was assisted by deformation twinning. A decrease of SFE influenced decreasing dislocation cell size associated with the formation of deformation twinning and shear bands in the early stage of ECAP, but had little influence on decreasing grain size in the later stage. In contrary, the presence of solute atoms facilitated the accumulation of dislocations and led to decreasing cell size in the early stage, and delayed the saturation of microstructures due to suppressed dynamic recovery in the later stages.

To elucidate the relationship between dislocation evolution in solid–solution copper alloys and plastic deformation modes, the dislocation evolution of the tensile deformed and cold–rolled Cu–2 at%X (X＝Sn, Mg) alloys were investigated by using X–ray diffraction (XRD) line–profile analysis and electron backscatter diffraction (EBSD) analysis. The plastic deformed Cu–2 at% Sn alloy exhibited higher hardness than the Cu–2 at% Mg alloy. Correspondingly, it was confirmed that the total dislocation density, which was analyzed by XRD line–profile analysis, in the Cu–2 at% Sn alloy was higher than that in the Cu–2 at% Mg alloy. The larger size effect of tin in the copper matrix reduced the mobility of dislocations, and more dislocations were formed to compensate the lower mobility of dislocations in the Cu–2 at% Sn alloy. The cold–rolled alloys exhibited higher hardness than the tensile deformed alloys. This is due to the higher dislocation density of the cold–rolled alloys. It was also confirmed that the dislocation rearrangement was retarded in the cold–rolled alloys, in comparison with the tensile–deformed alloys. It is considered that the intersection of dislocations occurred more frequently in the cold–rolling deformation than in the tensile deformation. Consequently, the mobility of dislocations decreased in the cold–rolled alloys, and the lower mobility of the dislocations would result in the dislocation multiplication. While the XRD line–profile analysis can evaluate the total dislocation density, which is the sum of geometrically necessary dislocation (GND) density and statistically stored dislocation (SSD) density, the GND density can be selectively evaluated from kernel average misorientation in the EBSD analysis. Interestingly, the total dislocation density depended on the plastic deformation modes, whereas the GND density of the cold–rolled alloys was almost comparable to that of the tensile deformed alloys. Thus, the higher dislocation density of the cold–rolled alloys is considered to be originated from the higher the SSD density.

The effects of amount of solute atoms on the formation of heterogeneous–nano structure in Cu–Ni–Si system alloys was investigated using Cu–2.01mass%Ni–0.44mass%Si, Cu–3.03mass%Ni–0.65mass%Si, Cu–3.60mass%Ni–0.77mass%Si, and Cu–4.2mass%Ni–0.91mass%Si alloys. All the alloys were subjected to solution–treatment and subsequent cold–rolling up to a reduction of 90% in thickness. In each alloy, conventional lamellae parallel to the rolling direction were formed after cold rolling. As the Ni and Si contents increased, in addition to the lamellae, shear bands with an angle to the rolling direction and deformation twin domains surrounded by the shear bands were formed, eventually leading to the development of distinct heterogeneous–nano structure. The Cu–4.2mass%Ni–0.91mass%Si alloy after the cold rolling was aged at 450°C for 5 min, and an excellent tensile strength of 964 MPa was achieved.

Effects of pre–aging of Corson alloys with high concentrations of Ni and Si (Cu–4.2mass%Ni–0.93mass%Si) followed by heavy cold rolling and full–aging on strengthening were systematically investigated. Especially, development of heterogeneous–nano (HN) microstructure was focused. And the relationship of mechanical/electrical properties was precisely examined. The pre–aged alloys exhibited a considerable strengthening after 90% cold rolling. This was attributed to the increase in the volume fraction of deformation twin domains in the HN microstructure after cold rolling as well as the precipitation strengthening. The sample prepared by a thermo–mechanical process via pre–aging at 723 K, subsequent cold rolling and full–aging at 673 K for 600 s exhibited the best strength/conductivity balance with an ultimate tensile strength (UTS) of 1096 MPa and electrical conductivity (E) of 29%IACS. When examined the effects of solid–solution (SS) temperature on the microstructure and properties, SS at 1223 K derived finer grain size than at 1323 K and the achieved best balance of UTS and E with 1061 MPa and 33%IACS. Therefore, grain refinement prior to pre–aging had no significant effect on strengthening but contributed to modification of electrical conductivity.

A Laser Metal Deposition (LMD) has been proved a potential technique for the fabrication of tool steel. Commercially available H13 tool steel powders were used to build a rectangular deposit in two ways of laser cladding. Assuming solid cooling of hot–working die, the base plate was a 10mm–thick pure copper. By parallel line scans of ϕ1.1 laser beam, gas–fed powders were deposited and ended up a chevron shape. Alternatively 8mm–oscillated beam scan was dragged on laid powder layers, and nearly rectangular shape was obtained with stacking seven 1mm–thick powder layers. The heat input 2.5kJ/g is necessary for the shaping, and laser power has to be controlled considering the heat from a previous layer. A convolute interface was formed with a copper plate and the hardness of martensite microstructure was mostly higher than that of quenched and tempered H13 except the lower few layers.

In order to reveal the change in electrical resistivity and strengthening due to plastic deformation and microstructural evolution, investigation of mechanical and electrical properties was performed. From microstructural observations, it was found that the heterogeneous–nano structure having “eye”–shaped twin domains was formed of which volume fraction becomes largest at 90% of rolling reduction. Ultimate tensile strength increases with increasing rolling reduction and reaches about 735 MPa at 90% and 95% reductions. The electrical resistivity measured at 77 K changes from about 39.6 nΩm to about 61.9 nΩm, and correspondingly, the conductivity at 293 K changed from about 28.0%IACS down to about 19.9%IACS. When compare the total changes in electrical resistivity before and after reduction of 80%, the latter was larger. The more obvious changes in mechanical and electrical properties over reduction of 80% are associated with the formation of heterogeneous–nano structure in addition to increasing dislocation density.

Heavily cold–rolled Cu–Ni–Si alloys with low concentrations of Ni and Si were aged at relatively low temperatures and the changes in the microstructure and properties were systematically investigated. Heterogeneous–nano structure was inhomogeneously developed as well as a typical low–angle lamellar structure in all the alloys by the cold rolling. The evolution of the heterogeneous–nano structure, which induced grain subdivision, was more evident in the alloys with higher contents of Ni and Si. The alloy with added largest amounts of additive elements exhibited highest tensile strength with moderate ductility, i.e., good balance of mechanical properties. However, it showed early softening because of lower thermal stability owing to finer grain size, Therefore, full–ageing seemed to be difficult. Even while rather good mechanical properties were attained by the combination of heavy cold rolling and low–temperature ageing of Cu–Ni–Si alloys with low concentrations of Ni and Si, it was revealed that a suitable ageing condition is highly required for the further improvement of their properties.

Low Ti content Cu–Ti alloys with small additions of Co and Ag, i.e., Cu–Ti–Co and Cu–Ti–Co–Ag alloys, were heavily cold rolled. A typical lamellar structure as well as heterogeneous–nano one was developed in both alloys. Increment of the lamellar spacing during low temperature aging was effectively suppressed by Ag addition. Both alloys exhibited well–balanced properties of tensile strength over 1 GPa, ductility over 10% and electrical conductivity over 20%IACS were achieved after peak aging, all which exceeded those of the commercial Cu–Ti alloys with relatively higher concentrations of Ti. However, Ag addition more emphasized the above properties. These specific properties attributed to the heterogeneous–nano structure which induced matrix strengthening and homogeneous precipitation instead of Spinodal decomposition.

Effects of Be content and heat–treatment conditions on development of heterogeneous–nano structure and mechanical properties of Cu–Be alloys were systematically examined. With increasing Be concentration from 0.4 to 2.14 in mass%, volume fraction of “eye”–shaped twin domains developed in the 90% cold–rolled samples increased up to 4.9%. In addition, the volume fraction further increased to 7.1% when Co was excluded although Be concentration was 1.86 mass%. Therefore, increase in Be content promotes mechanical twinning, in contrast, precipitates appear to impede it. Still more, it was revealed that excess Be was consumed for formation of γ– and β–phases in the Cu–Be alloy with 2.14 mass% Be. Age hardenability at 588 K was more significant with increasing Be content, even while increment in tensile strength was not substantial. And these tendencies were more emphasized when solution treated at higher temperatures and for longer period of time. The highest tensile strength achieved was 1.7 GPa of the Cu–Be alloy with 2.14 mass% Be when tested along transverse direction, which is slightly higher than 1.5 GPa when tested along rolling direction. The above experiments indicated important role of age hardenability as well as the volume fraction of “eye”–shaped twin domains.

Microstructures and mechanical properties of Cu–Be–Co alloys having four different Be contents and prepared by simply heavy cold rolling (CR), were systematically investigated. The cold–rolled alloys exhibited excellent mechanical properties due to the development of heterogeneous–nano (HN) structure during CR, which consists of rhombic deformation twin domains surrounded by shear bands and further embedded in conventional lamella. The strength of each alloy increased with increasing Be content. The volume fraction of twin domains in each alloy was quantitatively evaluated by texture analyses. It increased with increasing Be content rapidly from 0.40 mass% to 1.27 mass% and was gradually up to 2.14 mass%. The latter stagnation was attributed to the formation of coarse particles of intermetallic phases, which inhibited the formation of the HN structure. It revealed that the change in strength was correlated well with the volume fraction of twin domains.

Among copper alloys, Cu–Ni–Sn alloys are applied as a relatively high–strength material such as one for bearing for connecting rods of automobile engines and the like. There are an increasing number of cases in which these as–cast copper alloy castings, which conventionally have not been heat–treated, are subjected to solution treatment or aging treatment in order to further increase the strength. However, when considering the use as a material for bearings and other sliding components, further improvement in frictional performance and wear resistance is required both in the forms of a material and a member. Therefore, in this study, we focused on sulfide–dispersed alloy created by applying dispersion of sulfide that contributes to the improvement of frictional performance of Cu–Sn alloys to Cu–Ni–Sn alloys. By adding sulfide while the copper alloy is molten, the sliding characteristics of the alloy can be improved since sulfide, which acts as a solid lubricant, is uniformly dispersed over the as–cast structure. However, although it is known that the matrix structure changes when this alloy is heat–treated, there are few studies about the influence of sulfide on the matrix structure. Therefore, the purpose of this study is to evaluate the influence of sulfide on a Cu–Ni–Sn–S alloy based on the change in hardness by heat treatment. As a result of the study, we have discovered that, the spherical sulfide captured between the Cu–Sn dendrites of an as–cast material maintains a spherical shape without significantly moving from its original position or growing bigger even through heat treatment, and is present both inside the recrystallized grains and at grain boundaries and that sulfide has little influence on changes in hardness. Further, it is presumed that the cracks generated during aging treatment correspond to the quenching cracks generated by segregation of points or elements such as tin at grain boundaries.

At the moment, Nb₃Sn superconducting wires are world–widely made by the bronze method, which is the fabrication process of Nb₃Sn superconducting phase through the diffusion reaction at the interface between Nb filaments and bronze (Cu–Sn) alloy matrix. In general, a small amount of Ti is added to the bronze matrix, because Ti substitution to the Nb₃Sn crystal structure increases the upper critical field (B_c2) as well as it promotes the formation of Nb₃Sn phases. Meanwhile, Ti addition should also affect microstructures and mechanical properties of a bronze alloy itself. In this study, the effect of Ti addition on microstructures and mechanical properties especially at elevated temperatures were investigated.

Microstructural evolution and changes in hardness and electrical conductivity of a cast hypoeutectic Cu–2.7at%Zr alloy processed by high–pressure torsion (HPT) were investigated. The cast alloy had a net–like microstructure composed of a primary Cu phase and a eutectic consisting of layered Cu and Cu₅Zr phases. The Cu and Cu₅Zr phases in the eutectic had a cube–on–cube orientation relationship. The cast alloy with the hardness of 137 HV exhibited a value of electrical conductivity of 32%IACS. With increasing the number of HPT–revolutions, the eutectic was severely sheared and elongated along the rotational direction. In addition, mechanical dissolution of the Cu₅Zr phase into the Cu phase by HPT was confirmed after 5 HPT–revolutions through XRD measurements and TEM observations. After 20 HPT–revolutions, the Cu phase was significantly refined and formed the lamellar structure having an average grain size of 15 nm. The electrical conductivity decreased and saturated at a value of 8%IACS after 50 HPT–revolutions. The significant decrease in the electrical conductivity was primarily attributable to the mechanical dissolution of the Cu₅Zr phase into the Cu phase by HPT, followed by the formation of nanocrystalline Cu–Zr supersaturated solid–solution alloy with the hardness of 430 HV.

The frequency bands used for the autonomous driving of cars and the 5G/6G communications are increasing. In response to the frequency increasing trend, the FPC (Flexible Printed Circuit board) with low transmission loss has been developed recently. Therefore, it is important to optimize the material factors, such as grain size, surface roughness, electric conductivity, and purity of the copper foil for low transmission loss in high frequency bands.

In this study, multiple copper foils having various material factors without surface treatment were examined to compare the influence of the material factors of the copper foils on the transmission characteristics.

As the results, it was found that the grains being more than 10 μm in diameter don’t affect high–frequency transmission characteristics. On the other hand, smaller surface roughness and the higher electrical conductivity at room temperature showed better high–frequency transmission characteristics. It is considered that the surface roughness is the major factor to affect the transmission loss, since the skin depth at several tens of GHz and surface roughness of copper foil for FPC are comparable.

The effects of composition and microstructure on temperature dependence of electrical resistivity in Cu–Xmol%Mn–Ymol%Ni alloys (X=12.0〜12.9, Y=1.6〜3.8) were studied. It was found that the amount of Mn added follows Linde’s rule, while the amount of Ni added does not in the resistivity of these alloys. In these alloys, the resistivity increased from 0 to about 50°C and decreased from about 50 to 150°C monotonically. The higher the temperature at which the resistivity reached its maximum was, the smaller the resistivity change from 0 to 150°C became. Moreover, it was found that the resistivity change increases with the addition of Mn, while it decreases with the addition of Ni. In terms of the microstructure, the fine recrystallized grain and the strain by cold working made the resistivity change larger. In Cu–12.5Mn–2.6Ni, it was clear that it is effective to reduce the amount of Mn, increase the amount of Ni, and make the recrystallized grain coarser, in order to reduce the temperature change of the resistivity from 0°C to 150°C.

Refrigerant leakage of an air conditioner caused by formicary corrosion has been found more in highly airtight and highly heat–insulating houses. Our initial survey indicated that the leakage cases occurred chiefly in the houses in which a large amount of Japanese cypress wood was used. To clarify the corrosivity of these environments, 24 samples of condensed water were collected from the indoor units of air–conditioners with and without refrigerant leakage and they were analyzed by ion chromatography. The chemical composition of the water extracts from the sawdust produced from Japanese cypress and Japanese cedar wood before application of the termite repellent was also investigated. Furthermore, the corrosivity of those extracts to the copper tube was assessed. The pH of the condensed water collected from highly airtight and highly heat–insulating houses ranged from 4.6 to 5.2, which was significantly lower than the pH of 5.7 to 6.9 of those found in the general wooden house. Ion chromatography detected much more formic acid and acetic acid in the condensed water from leaked air–conditioners. Laboratory corrosion test showed that formicary corrosion developed in C1220 tubes that were exposed in the test cell filled with Japanese cypress sawdust, but not with Japanese cedar. The chemical analysis revealed that the water extracts from the Japanese cypress sawdust contained 33 mg/L of formic acid and 115 mg/L of acetic acid and the pH of the extracts dropped down to 4.3, suggesting that volatile substances contained in the Japanese cypress affected the formicary corrosion of the copper tube. Another corrosion test for C1220 tubes exposed to the vapor in touch with 1vol% formic acid solution with different pH demonstrated that formicary corrosion occurred when the pH was equal to or lower than 5. These results suggest that pH measurement of condensed water is an effective technique for detecting the potential risk of refrigerant leakage caused by formicary corrosion.

Ant’s–nest corrosion forms three–dimensional and complex pits in a copper tube. This corrosion gives fatal damage to air conditioners. Although improvements in material design and operating environment have been proposed for avoiding this corrosion, there are some practical problems associated with operation cost and performance of the corrosion inhibition.

This paper proposed a new method for inhibiting the ant’s–nest corrosion by applying repetitive heating and drying during operation of the copper tube. It was confirmed that this method exhibited reliable performance toward corrosion inhibition without requiring special materials or surface treatments. SEM and CT scanning system were performed to analyze morphology of the corrosion pits. EDS was employed to analyze chemical composition inside the pits. The results confirmed that the repetitive heating and drying causes restoration of corrosion inhibition.

The C–ring sample was immersed in a solution containing ammonia and tetraamine copper ion in order to reproduce the stress corrosion cracking (SCC) of pure copper tubes in the liquid phase. The test solution was prepared by dissolving copper sulfate in ammonia solution and contains free ammonia by adding the surplus ammonia solution. Stress corrosion cracking (SCC) occurred in the copper tube immersed in the solution containing more than 3.0 mol/L free ammonia and 5.0 g/L copper ion. The SCC occurred in the ammonia solution was accompanied by tarnish film and intergranular corrosion. No SCC occurred in the low phosphorous deoxidized copper tube containing 0.007% P and oxygen–free copper tube without P, while the SCC occurred in the high phosphorous deoxidized copper tube containing 0.023% P that tempers is 1/2H. The SCC also occurred in the ammonia solution when the diameter of the C–ring specimen was tightened more than 0.7 mm. From this study, a method for reproducing SCC of pure copper tube in solution by C–ring test was established.

Strength–improved α Cu–Zn–Sn, which is an alloy of α brass (Cu–Zn) and about 1 wt% of Sn, is one of promising materials for electronic connectors. Although α Cu–Zn–Sn is not as susceptible to stress corrosion cracking (SCC) as α brass, further improvement of the susceptibility has been desired. Recently, it was reported that the time to fracture by SCC of α Cu–Zn–Sn in an ammonia gas atmosphere was extended about 10 times by adding 2 wt% of Si and 0.05 to 0.10 wt% of P. However, the mechanism by which the addition of Si and P improves SCC susceptibility has not been clarified. In this study, we focus on the effect of phosphorus and investigate why the addition of P improves the SCC susceptibility of α Cu–Zn–Sn. The polarization measurement and the SCC test at a constant potential are carried out in a sodium nitrite solution, which is known as a SCC environment for α–brass. Followings are investigated： changes in the polarization characteristics of α Cu–Zn–Sn–P with 0 to 0.20 wt% of P and in the time to fracture at a constant potential by adding several concentrations of disodium hydrogen phosphate (DSHP) to the sodium nitrite solution. The results of these electrochemical measurements suggested that the improved SCC susceptibility of α Cu–Zn–Sn–P was caused by the formation of a protective film consisting of phosphate products at a crack tip and subsequently the prevention of crack growth.

This study was performed to examine type I pitting corrosion in copper tubes due to the synergistic effects of water quality and carbon film produced by the influence of oil and heat treatment. Although carbon film was considered to be one factor responsible for pitting corrosion, the relationship between the amount of carbon film and corrosion was not well understood. Therefore, a simple method for quantifying carbon film is required. In this study, we first examined copper tubes with unknown residual carbon amounts by X–ray photoelectron spectroscopy (XPS) and the conventional procedure. The results were the same by both procedures, confirming that the residual carbon amount can be determined by XPS. Next, we investigated the effects of carbon films on the corrosion behavior of copper tubes utilizing galvanic current measurements and polarization curve measurements. The carbon area ratio was dependent on galvanic current. Polarization curve measurements were closely correlated with galvanic current measurements, indicating that polarization curve measurements could be used to determine the relationship between the area ratio of the carbon film and galvanic current density.

It was known that one of the causes of pitting corrosion of copper tubes was residual carbon on the inner surface of copper tube. As a test for evaluating pitting corrosion resistance, electrochemical behavior was investigated using a mixture of corrosion promoting and corrosion inhibiting factors. In addition, immersion tests were conducted to confirm the effect of the compositional change of corrosive anions. There was a difference in electrochemical behavior and surface condition after the test due to the difference in the amount of residual carbon, and the possibility of pitting corrosion increased as the time for the spontaneous electrode potential to stabilize became shorter. Corrosive anions, especially sulfate ions, were considered to affect the electrochemical behavior.

This study was performed to investigate corrosion protection of pipe materials used in cooling water systems. The chemical composition of the water affected the corrosion phenomena. The pattern diagrams, such as hexa diagrams and trilinear diagrams, of the major components in the water are well known. In this study, hexa diagrams and trilinear diagrams of the major components (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^–, SO₄^2– and HCO₃^–) were drawn based on the results of analysis at each water source, and we investigated the relationships between the corrosion phenomena and the pattern diagrams of the water. The results indicated clear relationships. Water quality can be classified into five patterns according to the pattern diagrams：Ca–Cl or Ca–SO₄ type, Ca–HCO₃ type, Na–Cl type, Na–HCO₃ type, and intermediate type. The water qualities at the two locations of the corrosion survey were classified as Ca–HCO₃ type and intermediate type, and the galvanized steel pipe showed good corrosion resistance in Ca–HCO₃ type. In addition, the results of electrochemical measurements showed that a stable film tended to form on the copper tube in the Ca–HCO₃ type.

Microbiologically influenced corrosion (MIC) is rapid deterioration of structural materials induced by action of microorganisms in environment. In such a case, microbial adhesion and proliferation on material surface is a precursor to corrosion initiation, then if the material is stainless steel, its open circuit potential can be ennobled. Therefore, significant biofilm formation on metal surfaces and open circuit potential ennoblement of corrosion resistant steels are recognized as indicators of MIC risk.

There are many lab scale studies for the correlation between microbial adhesion on materials and initiation of MIC. However, there are few studies investigating correlation between metallurgical factors of structural materials and microbial amount or flora on the surface in actual environments.

We are conducting systematic research focused on material types or alloying elements in order to investigate how such metallurgical factors affect microbial activity in field. In this report, the corrosion behavior was examined by corrosion engineering methods such as potential measurement and weight loss evaluation. Then the microbial amount and microbial flora adhered on copper, carbon steel, and stainless steel coupon in a freshwater were evaluated by genetic analysis method.

Water model experiments for bubble flotation have been performed on polyethylene particle removal under N₂ gas injection stirring condition. The effect of gas flow rate, particle diameter and liquid height on removal rate has been investigated. It was found that the removal rate constant increases with increasing gas flow rate, particle diameter and decreasing with liquid height. The removal rate constant showed almost zero apparently in the case without oil layer because re–entrapping to the bulk liquid. A mathematical model based on bubble flotation theory was developed to represent the experimental data. The model calculated values were generally in agreement with the experimental values and were found to be valid.

In the additive manufacturing (AM) process for metallic materials, solidification takes place from solid/liquid interfaces after local melting. For controlling microstructures of materials processed by AM, it is important to know how the structures form. However, as molten metal is optically opaque, it is difficult to ascertain not only the solidification process, but also how metallic materials melt. In the present study, in–situ observation of melting and solidification behaviors of Cu powder induced by laser irradiation was carried out by time–resolved X–ray imaging using synchrotron radiography. In the growth process of the melt pool by laser irradiation, the liquid phase of the melt pool did not move to Cu powders, but they were attracted to the melt pool by such means as electrostatic attraction. A powder–free zone formed in areas near the melt pool, which was one of the causes of defects in metallic products processed by AM. Despite steady laser scanning, a continuous melt pool did not form； rather, single tracks formed by repeated formation of melt pool, unification and solidification. The growth direction of grains in the melt pool changed due to changes temperature distribution, gradient and heat flow.

High entropy alloys (HEAs) with Cu as the main constituent element were investigated focusing on the distribution of Cu in the ingots in this study. Based on the taxonomy of HEAs, the HEAs with Cu elements for casting materials were classified into two groups. The two groups were：(1) HEAs whose main constituent elements were 3d-transition metals such as Co, Cr, Fe, Mn, Ni, Cu (3d-HEAs), and (2) HE brasses based on Cu-Zn alloy system and HE bronzes based on Cu-Sn and/or Cu-Al alloy systems. Focusing on 3d-HEAs with Cu, the distribution of Cu in the ingots showed the following tendency：(1-1) the segregation from dendrite to the residual liquid, resulting in the formation of a Cu-rich interdendrite region in the ingots；(1-2) liquid phase separation resulting in the formation of a Cu-rich liquid, which formed a macroscopically phase-separated structure；(1-3) the dispersion of fine Cu particles embedded in the solid solution matrix.

Influence of torsional moment on strain, hardness and microstructure of Cu–35mass%Zn alloy workpiece was investigated in cold upsetting. The cylindrical workpiece was simultaneously compressed in axial direction with a speed of 0.1mm/s and twisted around the compression axis with a speed of 0.5 rpm. The torsional motion was either one–way with a maximum angle of 180° or cyclic alternating with a maximum amplitude angle of 45°. The Vickers hardness of the workpiece forged with a reduction in height of 60% was improved by approximately 7% and reduced heterogeneity of the distribution by approximately 25% by applying torsional moment. The strain distribution of the forged workpiece calculated by finite element analysis agreed with the hardness distribution of the forged workpiece measured by experiment. The shear texture in the microstructure of the forged workpiece increased approximately 20% by applying torsional moment with torsional angle of higher than 15°.

As vibration while rolling reduces productivity and strip quality, causes of vibration and measures for normalization have been investigated and reported so far. Most of those vibration related report cases of large sized mill for steel strip production, and cases of medium sized mill were rare. In this study, characteristics of vibration in medium sized cold strip rolling mill have been investigated. A specification of medium sized cold strip rolling mill and a kind of rolling condition for copper alloy strip were assumed, and the natural frequency of various kinds of vibration have been calculated theoretically based on those assumption. The vertical displacement natural frequency of a 4HI type mill and a 6HI type mill have been calculated based on mass–spring model. As cold strip rolling is conducted under front tension and rear tension, deflective strip vibration is easy to occur. The strip deflective natural frequency while rolling has been calculated. Also natural frequency of torsional system of the mill has been reported.

In general, sustained vibration of rotating system is mainly resulted from resonance or self–excited vibration. On both cases, vibration frequency is close to natural frequency, and vibration is easy to occur at lower natural frequency. Natural frequency of medium sized strip mill has lower natural frequency compared to that of large sized steel mill, so the former mill has stable tendency usually.

Copper alloys used in lead frames are required to have high electrical conductivity and strength, as well as good solder heat resistance; however, the degradation mechanism of solder heat resistance has not been clarified. In this study, we examined the solder/substrate interface of Cu–Fe–P alloy after the solder heat resistance test and investigated the effects of processing strain and aging temperature. Fe–precipitates originating from the alloy were agglomerated near the solder/substrate interface due to the Kirkendall effect. The formation of the voids was observed when there were large processing strain and fine precipitates, resulting in poor solder heat resistance. By contrast, when there was almost no processing strain, no voids were found, resulting in good solder heat resistance. Good solder heat resistance was also obtained when the aging temperature was high. Coarse precipitates were observed near the interface and are likely to cause uniform interdiffusion of Cu and Sn atoms compared to the case where fine precipitates existed, resulting in improved solder heat resistance. These findings suggest that processing strain and precipitate size are dominant factors in solder heat resistance for precipitate hardening alloys.

Copper alloys with excellent machinability and thermal conductivity are widely used as piping materials, and brazing is used as the connection method. Exposure to running water containing sulfate ions and ammonium ions may cause corrosion damage such as pitting corrosion near the brazed joint of the pipe, leading to leakage of the refrigerant. Therefore, it is necessary to evaluate not only the piping but also the corrosion resistance of the joints of the piping.

In this study, the corrosion resistance of brazed joint to acidic, neutral, and alkaline solutions was measured by an electrochemical method. In addition, the cross–sectional structure was observed to investigate the corrosive behavior of the brazed joint. Using C3604 as a base metal, a single lap shaped brazed specimen was prepared. Phosphorus copper filler metal and silver filler metal were used for brazing. The area was controlled with Kapton tape, and the corrosion resistance of the base metal, brazing filler metal, and brazed specimen was evaluated by the three–electrode method. Furthermore, the cross–sectional structure of the brazed joint was observed using an optical microscope.

From the polarization curve, in the case of fresh water and 0.05 mol NH₃, the current densities of both specimens increased monotonically. In the case of 0.05 mol H₂SO₄, it was found that the brazed specimen was greatly affected by the base metal. From in–situ observation, it was found that Cu and Cu–Zn were preferentially corroded in the brazed specimen. Due to the preferential corrosion of Cu and Cu–Zn, it was considered that the brazing filler metal, base metal, and brazed specimen showed similar corrosion behavior in fresh water and 0.05 mol NH₃.

Many products using Cu such as heat exchangers and electrical wire have been developed, because of high thermal conductivity and electrical conductivity. In recent years, the combination of Cu and Al has been promoted to reduce weight and improve strength. Generally, metallurgical joining using pressure welding or welding is employed for joining dissimilar metal materials. However, most of them have a limited joint design and have a problem that they cannot cope with complicated ones. Therefore, this time, we will try to join with brazing that can handle complicated joint design by a relatively simple method.

On the other hand, there are various problems with brazing of dissimilar metals. In the brazing of Al/Cu, an intermetallic compound is formed at the interface, resulting in a problem that the mechanical properties deteriorate. Furthermore, there is a few gap temperature in liquidus temperature between Al–Si brazing filler metal and Al–base metal. Therefore, temperature control is very important when brazing Al and Cu.

In this study, an Al plate and a Ni–plated Cu pipe were brazed using a brazing furnace capable of high–precision temperature control. As a result, it was found that the appropriate brazing temperature was 858 K. From this, a sound brazed joint could be obtained. Heating time influenced strongly spreading ability of molten brazing filler metal and fillet formability at the brazed joint.

Brass has excellent ductility and workability. Lead–free brass containing Bi and Si has been put into practical use in order to comply with environmental regulations such as water quality standards. For actual use, brass soldering with lead–free solder is required. On the other hand, on–site soldering is generally done using a torch as a heat source. In this torch soldering, a pure Cu pipe is inserted into a brass valve to heat the torch. At this time, heating is performed only from the brass valve side. As a result, the heating becomes uneven, which is different from the general soldering process of furnace brazing.

The purpose of this study was to develop a new test piece and analyze the behavior of molten solder and molten brazing material during joining through in–situ observation experiments.

In this investigation, we proposed a test piece called a groove specimen. The behavior of the molten solder was analyzed using the groove specimen. By installing solder on one side of the groove specimen and heating it, the solder melted and entered the groove. The movement of the molten solder at this time was observed and summarized.

As a result of the experiment, it was confirmed that the behavior of the molten solder differs depending on the base material. Also, there was a difference in the wetting of the solder between the upper part, the middle part, and the lower part in the groove specimen. This was suggested to be different because the shape of the groove specimen was different in each part.

Press–fit connections are expected to replace soldering in the mounting of power modules. In the present study, the effect of contact resistance on temperature and microstructural development at the press–fit contact interface under high current loading were investigated. The larger the diameter of the through–hole into which the press–fit terminal is inserted, the lower the contact pressure and the higher the resistance of the press–fit connection. When a current of 100 A was applied, the temperature of the press–fit connection reached approximately 100°C, although it depended on the contact resistance. The intermetallic compounds were formed at the contact interface by loading high current, which decreased the contact resistance.

The relationship between the joint strength and the deformation heat input in the upset stage, and that between the joint strength and the upset burn–off length, were examined for friction–welded joints of C1100 tough pitch copper to S15CK carbon steel. Joint strength was evaluated by tensile tests and fatigue tests. It was found that both the deformation heat input in the upset stage and the upset burn–off length correlated well with joint strength, and when the deformation heat input in the upset stage or the upset burn–off length exceeded a certain value, a stable tensile strength was obtained, although it was not possible to classify joints into tensile–fracture modes. Additionally, it was possible to obtain joints that have a fatigue limit which was almost the same as that of the C1100 base metal when the deformation heat input in the upset stage or the upset burn–off length exceeded a certain value. However, due to the joints having a fatigue limit that was almost the same as that of sound joints despite the low fatigue strength at low cycles, it was difficult to evaluate fatigue strength only by the fatigue limit.

Demands for platings with high wear resistivity are increasing for battery terminals used in electric vehicles. Silver–Graphite composite plating (AgC) has higher wear resistivity than formerly used Silver–Antimony alloy plating, when the plating is used at both plate (male terminal) and indent (female terminal) side. In this study, we researched the wear resistivity of combination of platings, inspected the cause of the test results, and measured the characterisitics of the newly achieved plating.

We found that AgC needs further improvement when used only at indent side. The cause of decrease in wear resistivity is that since plating is easily deformed by contact load, AgC is scraped out from contact area before its lubricating effect is active. We increased the hardness of the silver plating to prevent deformation, and developed hardened AgC plating with excellent wear resistivity. Moreover, it also has very low insertion force and excellent fretting corrosion reisitivity compared to other platings such as gold, silver and tin.

In conclusion, hardened AgC plating has an excellent characteristic unaccomplished by former platings, which is expected to be applied to various terminals that require high contact reliability.

Influence that the electric current gave on the degradation of tin plates contact was investigated. In this report, the contact resistance behavior under electrical current test and the observation of the contact area after electrical current test were investigated. The electrical current conditions were 100A, 200A and 300A.

From the result of the electrical current test, the decreases in contact resistance from 0 seconds to 5 seconds increased with the increase of electric current. The Joule heat increases when electric currents increase. As a result, it is considered that the conditions of contact between female embossment and the male receptacle suddenly changed.

The contact resistance after electrical current test at 100A was high. On the other hand, the contact resistance after electrical current test at 200A and 300A became equal and was lower than that of 100A. In addition, a contact area after electrical current test at 200A and 300A were bonded by molten tin.

Influence of Cu–Sn intermetallic compound surface form on a fretting corrosion phenomenon of reflowed tin plating was investigated. This paper reports and discusses experimentally observed results on contact resistance behavior and wear behavior during fretting corrosion testing using samples with different surface roughness. Cu–Sn intermetallic compound plating was prepared to eliminate the influence of the dispersed state of tin and Cu–Sn, intermetallic compound. The main results are summarized as follows. (a) The results of the fretting corrosion test showed the peak value of contact resistance decreased with the rough–surface samples. (b) The rough–surface samples had both convex and concave areas. It is thought that the convex areas promote the discharge of tin abrasion powder to the outside of the contact area or to concave areas.

Effects of current density and plating time on structures and resin adhesion properties in roughening copper plating for improving a resin adhesion were studied. As the current density of the plating increased, the number density of plated granular copper particles increased, and rough surface was formed. As the plating time became longer, the plated granular copper particles became larger and surface roughness increased. As the arithmetic mean height (Sa) increased, the shear strength increased and reached a maximum at Sa：400 to 500 nm. The reason of decreased shear strength is the surface convex portion is excessively enlarged, so that the gap between the copper particles is closed and the bonding area with the resin is reduced. The roughening copper plating showed high resin adhesion even after moisture sensitivity tests, because the increase in the bonding interface suppressed an infiltration of water. Moreover, even noble metal plating over the roughening copper plating, the resin adhesion was high, and good results were shown even after the moisture sensitivity tests.

Based on these results, it is possible to provide a lead frame with excellent adhesion to resin even in a high temperature and high humidity environment by roughening copper plating.

Reactive oxygen species (ROS) formation and subsequent damage in Synechococcus elongatus PCC 7942 (S. elongatus) cells after contact with metal ions in aqueous solutions were studied. Percentage ratios of divalent metal ions in aqueous solutions were used to mimic the metal ratios in pure copper (Cu), brass (C2600) and nickel silver (C7701 and C7521). The interactions between the generated ROS and cell components such as DNA and polyphosphate bodies (PPBs) in S. elongatus cells were observed by fluorescence microscopy, and the localization of ROS was confirmed at the ultra–structural level by staining cells with 3,3’–diaminobenzidine hydrochloric acid (DAB), which was oxidized by ROS and subsequently DAB–osmium black deposits were produced during post fixation with osmium tetroxide. Co–localization of elements including Cu, Zn, and P was observed by EDX elemental mapping. TEM observation of DAB treated cells successfully showed the locations of ROS accumulation on and in metal ion treated cyanobacterial cells. 0.3% of divalent Cu ions (Cu²⁺) caused excessive production of ROS on the cell wall, penetration of ROS into the cell, and DNA damage. When 0.13% of divalent Zn ions (Zn²⁺) were present in the solution in addition to 0.3% Cu²⁺, DNA structures were protected in a compacted shape, although ROS formed inside the cells to some extent. That phenomenon also occurred in the presence of both Zn²⁺ and divalent Ni ions (Ni²⁺) in the solution in addition to Cu²⁺, but only when the percentage of Zn²⁺ was higher than a certain level. When cyanobacteria came in contact with 0.09% of both Zn²⁺ and Ni²⁺ and 0.3% Cu²⁺, DNA was severely damaged although ROS formation was reduced. This leads to the hypothesis that DNA in cyanobacteria cells is possibly damaged by two different mechanisms under metal ion stress : 1) by metal ions inducing an excessive amount of ROS and/or 2) by some direct effect of the metal ions with less production of ROS. After the metal ion treatment, Cu and Zn co–localized with P at some sites. This observation indicates the ability of inorganic PPBs to attract metal ions. The presence of PPBs in bacteria cells may thus reduce the antibacterial effect of treatment by metal ion solutions and on certain Cu–based alloy surfaces.

One of the major routes by which pathogenic microorganisms spread out is propagation through frequently hand touched surfaces. It is expected that introducing antibacterial metallic materials, such as copper and copper alloys, on frequently hand touched surface will keep environmental surfaces sterilized and prevent the spread of pathogen. When copper and copper alloys are used for frequently hand touched surfaces, their surfaces can be soiled due to human contact. As surface soling reduces antibacterial properties of copper and its alloys, it is necessary to clean the surfaces. Although cleaning removes contaminants on surfaces, the detergent used for cleaning may corrode copper surface resulting in degradation of the antibacterial properties. In medical facilities, sodium hypochlorite aq. and ethanol aq. are used as detergents. For sodium hypochlorite aq., it has been shown that adding anti–rust is effective for prevention of reduction in antibacterial properties, as well as surface texture, of copper. In this study, we investigated additives for ethanol aq. that keeps surface texture and antibacterial properties of oxygen–free copper. Acid added ethanol aq. was used as a detergent. The specimens were immersed in a detergent for 15 seconds and then dried in air for 1 hour. Such processes, designated as W–D cycles, were cyclically applied for specimens for 168 times. The surface of the specimens deteriorated with W–D cycles except the case that oxalic acid was used as an additive. Antibacterial properties of OFC subjected to the W–D cycles with oxalic acid added ethanol aq. was equivalent to those of OFC kept in air for the same period. Oxalic acid, which is used as food additives, is effective to prevent degradation in antibacterial properties of copper surface caused by wipe cleaning with ethanol aq.

The present study experimentally investigated the falling liquid-film evaporation heat transfer coefficients and flow patterns of R1234ze(E) on a horizontal microscopic-grooved copper tube with an outside diameter of 18.8 mm. The experiments were carried out at a saturation temperature of 15°C, heat flux range of 2.5-30 kWmM^-2, and film Reynolds number range of 50-1000. The effects of film Reynolds number, heat flux, and flow pattern of falling liquid-film on the heat transfer were clarified. As the film Reynolds number increased, the flow pattern shifted from droplets mode to droplets-columns mode, columns mode, columns-sheet mode, and sheet mode. The heat transfer coefficients dramatically decreased due to dry patches observed at low film Reynolds number region. The heat transfer coefficients were affected by flow pattern at low heat flux conditions, while flow pattern did not significantly affect the heat transfer coefficients at high heat flux conditions.

In order to produce thin and small semiconductor packages, leadframes with fine pitch and multi–pin are demanded. So, leadframe materials should possess higher strength, higher electrical conductivity, and excellent etching characteristics. In this study, we successfully developed novel Cu–Ni–Co–Si alloys for high–performed leadframes by optimizing thermomechanical process conditions. The Cu–Ni–Co–Si alloys have tensile strength of 1020 MPa, electrical conductivity of 38%IACS and high heat resistance, which overcome conventional leadframe materials of Cu–Ni–Si alloys. In addition, the Cu–Ni–Co–Si alloys exhibit an excellent etching characteristics comparable to conventional Cu–Ni–Si alloys. The excellent etching characteristics for the alloys can be explained by fine grain size rather than dislocation, precipitates, and grain orientation. Thus, the Cu–Ni–Co–Si alloys are promissing to be applied widely for thin and multi–pin leadframes in ultra–miniaturized communication and information devices.

In recent years, demands for miniaturization and multi–polarization of automotive connectors have grown, along with increasing needs for highly integrated electronic devices in vehicles. For this reason, copper materials for connectors are required to have high strength, high electrical conductivity, high stress relaxation resistance, and excellent bending workability. Among various solid solution strengthening copper alloys, Cu–Mg alloy was found to exhibit excellent balance between strength, electrical conductivity, stress relaxation resistance, and bending workability. With Cu–Mg alloy rolled at 98.4%, the rolling texture formed by heavy cold rolling was deliberately utilized, and the optimum characteristics for small terminals；tensile strength of 1016 MPa, electrical conductivity of 40% IACS, residual stress rate of 71%, and bending workability of R/t=0；was obtained.

We investigated the influence of the largest crack on the critical current and n–value that is the index of the sharpness of the transition from the superconducting state to the normal conducting one in the copper stabilized coated superconducting tape with multiple cracks, by simulation using a model sample consisting of short sections that have a length L₀ and contain one crack of different size in each. The voltage probes were set in step of the distance L=L₀ and 3L₀. In the case of L=3L₀, the region between the voltage probes is composed of 3 sections and, hence, contains 3 cracks of different size. The main results are summarized as follows. (1) With increasing voltage probe distance L, both the average critical current value and the average n–value decrease. This phenomenon becomes more prominent with increasing width of crack size distribution. Also, the n–value is more sensitive to the voltage probe distance than the critical current. (2) In small voltage probe distance in laboratory scale as in this study, the largest crack among the cracks included in the region between the voltage probes has a dominant influence on the determination of the critical current. (3) In the case of L=3L₀, when the sizes of the largest cracks in the regions are the same, the critical current values are nearly the same even when the sizes of the other cracks are different among the regions. In contrast, n–value of the region is high when the size of the largest crack is close to that of other cracks and therefore the V (voltage) – I (current) curve of the largest crack–section is close to the V – I curves of the other sections, but it is low when the size of the largest crack is quite different from the sizes of other cracks and therefore the V – I curve of the largest crack–section is away from that of the other sections．In this way, n–value is dependent on the largest crack size and also on the difference in size among cracks. (4) The upper and lower bounds of the relationship between the critical current and the largest crack size, the relationship between the n–value and the largest crack size and the relationship between the n–value and the critical current can be expressed by the upper–lower bounds approach, in which an extreme situation where the all cracks have a same size gives the upper bound for n–value and the lower bound for the critical current, and another extreme situation where one crack is far larger than other cracks gives the upper bound for the critical current and the lower bound for the n–value. (5) It was shown that the critical current distribution of regions (L=3L₀) with cracks of various sizes can be obtained from the crack size distribution by using the simulation results and the extreme value distribution statistics of Gumbel.