Papers by Keyword: Copper (Cu)

Abstract: The aim of present research was to study the effect of the position of the tool relative to the support backing plate of the FSW machine on the formation of defects and on alterations of the microstructure and mechanical properties of friction stir welds in phosphorus-deoxidised copper (Cu-DHP) thin sheets of 1 mm thick. The welds were carried out using position control conditions; distances between the tool and the backing plate of 0.1 mm, 0.075 mm and 0.05 mm were used. The formation of defects like continuous voids along the weld is very influenced by the tool position, though the heat-input plays an important role in the process. Large grain refinement was observed in the nugget of the welds; the change of the relative tool position has little effect on this grain refinement. Substantial hardening was observed in the thermomechanically affected zone (TMAZ) of the welds. The welds exempt of defects, such as continuous voids, attained a little tensile strength overmatch condition.

Abstract: The aim of the present study was to produce high speed steel – tungsten carbide – copper composites, which should have acceptable density, wear resistance and good sliding prosperities. Various amounts of WC powder were added to the HSS powder prior to compaction. The following compositions were investigated: 100% M3/2, M3/2 + 10% WC and M3/2 + 30%WC. The mixtures were prepared by mixing for 30 minutes in the 3-D pendulum motion Turbula® T2C mixer. Then the powders were cold pressed in a rigid cylindrical die at 800 MPa. Both green compacts and pre-sintered compacts (pre-sintering condition: 1150°C in vacuum for 60 minutes) were infiltrated with copper. The whole infiltration process was carried out in vacuum better than 10-3 Pa. Pre-weighed preforms of copper were carefully placed on top of the rigid skeletons in which porosity were predetermined, heated up to 1150°C, subsequently held at temperature for 15 minutes, and cooled down with the furnace to the room temperature. The dilatometer was used to detect some reaction in the sintering. The changes in as pressed and as sintered density, hardness, bending strength and tribological properties are discussed in this work.

Abstract: Copper and its alloys are part of common used metals in the microelectronic industry. Copper uses, in microelectronic industry include interconnection and electronic packaging. The presence of copper in different alloys creates galvanic cells, which causes rising in corrosion rates. This rising leads to failure of microelectronic devices. The ability of controlling the amount of copper ions Cu (II) bath system has been carried out. The sorption of Cu (II) ions depends on pH, being maximum (73%) at pH=5 and pH=10. In solution of pH 5, the Cu (II) sorption capacity increases with the increase of copper initial concentration, leading to the conclusion that the chelating ion exchanger under study could be used in processes of Cu (II) separation and preconcentration. The Cu (II) ions equilibrium distribution between solution phase and sorbent phase has been described by means Langmuir isotherm model. The calculated value of Gibbs free energy (ΔG=-13.975 KJmol), confirms the affinity of the ion exchange resin with hydroxamic acid and amidoxime groups towards Cu (II) ions. The type of corrosion mechanism and its rate of attach depend on the exact nature of the environment (air, soil, water) in wich the corrosion takes place.

Abstract: With prices for metal resources such as nickel and molybdenum soaring, there is a heightened sense of crisis concerning resource scarcity. While Type304, the most common stainless steel, offers excellent corrosion resistance, its price is affected significantly by the cost of nickel because of its 8% nickel content. The stainless steel that has the same corrosion resistance as that of Type304 and does not contain nickel and molybdenum has been required. JFE Steel Corporation has developed a new 21%Cr-0.4%Cu stainless steel, the world’s first ferritic stainless steel, which offers equivalent corrosion resistance to Type304 while containing absolutely no nickel or molybdenum, two rare metals. The newly developed steel contains 21% chromium with the addition of 0.4% copper. The development of the steel is based on a new discovery that the passive films of stainless steels could be strengthened by the synergy effect of high chromium content and copper addition. Copper addition enriches the chromium content in passive films after field exposure. Newly developed 21%Cr-0.4%Cu stainless steel is adopted for many applications as a substitution for Type304, including commercial kitchenware, building materials and industrial machinery. The steel is expected to be a new standard of a ferritic stainless steel as a substitution for Type304.

Abstract: Quickness of fracture of Al oxide film is important especially for vacuum free Al/Cu bonding. Displacement amount and rate relate closely with fracture of oxide film and create clean surface. Displacement history during bonding process under static bonding load was measured for displacement control systematically. Displacement history under static load consists of three stages with creep and liquefaction. Higher bonding load increased displacement rate of each stage and decreased the thickness of Al oxide film grown by air heating. Suitable hearing time for bond also was shortened by increment of bonding load. Two types of displacement control were designed from these experimental results. One was the accelerated displacement rate control, another was the cyclic displacement control. Fracture of Al oxide film and liquefaction of bonding surface occurred at lower displacement than static load by each displacement control.

Abstract: Diamond-particle-dispersed copper (Cu) matrix composites were fabricated from Cu-coated diamond particles by spark plasma sintering (SPS) process, and the microstructure and thermal properties of the composites fabricated were examined. These composites can well be consolidated in a temperature range between 973K and 1173K and scanning electron microscopy detects no reaction at the interface between the diamond particle and the Cu matrix. The relative packing density of the diamond-Cu composite increases with increasing sintering temperature and holding time, reaching 99.2% when sintered at a temperature of 1173K for a holding time of 2.1ks. Thermal conductivity of the diamond-Cu composite containing 43.2 vol. % diamond increases with increasing relative packing density, reaching a maximum (654W/mK) at a relative packing density of 99.2%. This thermal conductivity is 83% the theoretical value estimated by Maxwell-Eucken equation. The coefficient of thermal expansion of the composites falls in the upper line of Kerner’s model, indicating strong bonding between the diamond particle and the Cu matrix in the composite.

Abstract: Friction powder processing (FPP) has been developed based on the principle of friction stir welding (FSW) or friction stir processing (FSP). The FPP is a method to design the properties of the processed area by performing FSP after powder with a controlled composition is placed in the gap between two plates. The FPP experiments were performed using a tool with the shoulder diameter of 15mm and the probe diameter of 6mm. The tool traveled at 100mm/min and rotated at 1500rpm. A1050 aluminum was used as the plate. Pure Al powder (89μm average grain diameter) and pure Cu powder (106μm average grain diameter) were used as the additives. When using pure Al powder, the pure Al powder left in the base metal after the first pass is sufficiently stirred by performing the second pass and then a good joint without defects is obtained. However, more than three passes are not effective for improving the strength of the welded area. When using pure Cu powder, nanoscale Al2Cu precipitates are uniformly formed in the stir zone, and accordingly, the hardness is significantly increased.

Abstract: High purity aluminum (Al) and copper (Cu) single crystals of different crystallographic orientations were processed for one pass by equal-channel angular pressing (ECAP). The deformed structures were examined using orientation imaging microscopy (OIM) and transmission electron microscopy (TEM). This paper examines the experimental results in terms of the values of the shear factors based on simple shear theory.

Abstract: To stimulate bone regeneration, the design of bioactive implants is a great challenge in current orthopedic research. We reasoned that implants should be suitable both to stimulate osteogenic differentiation of mesenchymal stem cells and prevent infections at the site of implantation. Therefore, we focus on copper ions, which are known to exert antimicrobial effects. On the other hand, copper is essential for the cell physiology, including the formation of the extracellular matrix. We studied the influence of copper ions on mesenchymal stem cells at various concentrations and identified the limits of copper concentrations for cell survival. Below the critical concentration for cell survival we analysed proliferation and osteogenic differentiation of the cells in the presence of copper ions. We found that copper stimulated the proliferation of the mesemchymal stem cells at 0.1 mM. Osteogenic differentiation decreased after 14 days at a concentration of 0.05 - 0.1 mM copper ions in osteogenic medium measured by the expression of osteogenic proteins, like alkaline phosphatase (ALP), bone sialoprotein (BSP) and collagen I (COL). We argue that at the implant surface a higher concentration of copper could prevent biofilm formation of bacteria and physiological concentrations in the vicinity of the implant would stimulate stem cell expansion. Together, copper is an interesting agent to control both bacteria and stem cells in the field of implant technology.

Abstract: The Cu-line patterns with different linewidth were deposited by radio-frequency sputtering and defined by photolithography lift-off process. The residual stress was evaluated with X-ray diffraction technique and the results show that the Cu-line patterns are in a biaxial stress state and the stress values have a great dependence on linewidth. Further analysis reveals that the intrinsic stress has a main effect on changes of residual stress; however, the thermal stress plays a key role on anisotropic contribution of residual stress in directions along and across the Cu line. The variation of intrinsic stress correlates well with crystal orientation of the Cu line, and the linewidth seems to be the most crucial parameter for evolution of both texture and stress.