Cu-10 Wt Research Articles

Quantitative analysis of work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy based on true stress vs strain curves

Quantitative analysis of work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy based on true stress vs strain curves

Influence of initial solid–liquid interface morphology on further microstructure evolution during directional solidification

Preparation of the initial solid–liquid interface on which growth is started is a very critical step in directional solidification experiments. Dedicated experiments concerning preparation of the initial solid–liquid interface morphology and its influence on further directionally solidified microstructure were performed on Cu-20 wt% Sn peritectic alloy in a Bridgman-type furnace. To verify the morphology of the initial solid–liquid interface, steady-state directional dendritic growth was interrupted by thermal stabilization ranging from 0 to 1 h prior to quenching. With thermal stabilization duration increase, the solid–liquid interface morphology degenerated from dendritic to cellular and finally to planar. To verify the influence of the initial state on further solidification microstructure, directional solidification experiments were performed at a low pulling rate of 1 μm/s with different initial solid–liquid interface morphologies. The initial state affects solute redistribution and formation of peritectic coupled growth structure in the subsequent directional solidification process.

Mechanical Properties of Cu–Ag Microcomposites Thermo-Mechanically Processed by Equal Channel Angular Pressing (ECAP)

Equal channel angular pressing (ECAP) combined with intermediate heat treatment was carried out on Cu-15 wt.% Ag at room temperature. ECAPed Cu-15 wt. Ag exhibited ultrafine structure with the shape and distribution of Ag phase dependent on the processing routes. The initial lamellae of Ag phase were elongated along the shear direction and developed into filaments in route A whereas the initial lamellae became finer by fragmentation with no pronounced change of the shape in route Bc. The application of intermediate heat treatment at 330 � C was found to increase the hardness greatly for all three different routes. The network lamella structure usually observed in route C without intermediate heat treatment was not well developed in the specimen with one intermediate heat treatment. The dissolution Ag lamellae with high strain energy and re-precipitation of Ag precipitates is thought to be responsible for the irreversible slip in route C since Ag precipitates in the matrix are likely to act as obstacles to the reversible slip of dislocations, leading to the easier modification of thin-walled network-like structure. The presence of more precipitates in Cu-15 wt.Ag specimens ECAPed with intermediate heat treatment supports the effect of Ag precipitation on the microstructure and the hardness.

Isothermal Peritectic Coupled Growth in Directionally Solidified Cu-20 wt pct Sn Alloy

Isothermal peritectic coupled growth (PCG) has been experimentally observed in directionally solidified Cu-20 wt pct Sn alloy at pulling rate of 1 μm/s under a temperature gradient up to 45 K/mm. The PCG growth interface temperature is determined above the equilibrium peritectic temperature T P. Diffusion coupling at and parallel to the solid/liquid interface necessary for PCG growth above T P is first experimentally proven.

Modification of microstructure and strength/conductivity properties of Cu-15 Ag in-situ composites by equal-channel angular pressing

Equal-channel angular pressing (ECAP) was carried out on Cu-15 wt% Ag in-situ composites at room temperature. The ECAPed Cu-15 Ag in-situ composite exhibited an ultra-fine two-phase structure with the shape and distribution of the Ag phase dependent on the processing routes. In route A, the initial lamellae of the Ag phase were elongated along the shear direction and developed into filaments, whereas the initial lamellae became finer by fragmentation with no pronounced change of the shape in route Bc. The strength/conductivity combination of 743 MPa/78.6 %IACS was attained in Cu-15 Ag processed by route Bc. The strength of Cu-15 Ag ECAPed using route Bc was greater than that ECAPed using route A, suggesting that substructural strengthening combined with precipitation strengthening is superior to interface strengthening. The electrical conductivity decreased more drastically in route Bc than in route C due to the frequent fragmentation of the lamellae in route Bc.

Influence of Stacking Fault Energy on Defect Structures and Microhardness of Cu and Cu Alloys

Nano-structured Cu, Cu-10 wt%Zn and Cu-2 wt%Al with stacking fault energies (SFE) of 78, 35 and 37 mJ/m2, respectively, were preprared through high energy ball milling. X-ray diffraction and Vickers microharness test were used to investigate the microstructure and microhardness of all the samples after ball milling. X-ray diffraction measurements indicate that lower SFEs lead both to decrease in grain size and increase in microstrain, dislocation and twin densities for Cu-10 wt%Zn and Cu-2 wt%Al after 5 h of ball milling. The microhardnesses of Cu-10 wt%Zn and Cu-2 wt%Al reach to nearly the same values of 2.5 GPa after 5 h of ball milling, which is higher than that of Cu of 2.0 GPa. Two factors are considered to contribute to the finer grian size and higher microhardness of Cu-10 wt%Zn and Cu-2 wt%Al: (1) the effect of solid solution strengthening, which result in the interaction of solute atoms with screw dislocations; (2) the introduction of deformation twins during ball milling process by the decreasing of SFE, which results in the grain refinement.

Wear Behavior of the Lead-Free Tin Bronze Matrix Composite Reinforced by Carbon Nanotubes

Copper-coated carbon nanotubes were prepared by the electroless plating route. The structure and component of copper/carbon tubes were characterized using a transmission electron microscope and energy dispersive spectrometer. The results show that the surface of the carbon tubes was covered by the copper particles. Copper/carbon tubes were used as the substitute of part of tin and all of lead in the tin bronze matrix, and the tribological properties of carbon nanotube-reinforced Cu-4 wt pct Sn-6 wt pct Zn composites were studied. The effects of the carbon nanotube volume fraction and sliding distance in unlubricated ball-on-disc wear test were investigated. The 3 vol pct carbon nanotube-reinforced Cu-4 wt pct Sn-6 wt pct Zn composite shows the Vickers hardness of 126.9, which is approximately 1.6 times higher than that of Cu-6 wt pct Sn-6 wt pct Zn-3 wt pct Pb tin bronze. The wear rate and average friction coefficients of 3 vol pct carbon nanotube-reinforced Cu-4 wt pct Sn-6 wt pct Zn composite were lower than those of the Cu-6 wt pct Sn-6 wt pct Zn-3 wt pct Pb tin bronze, respectively.

Influence of Al 2O 3 reinforcement on precipitation kinetic of Cu–Cr nanocomposite

In this paper, the kinetic of precipitation process in mechanically alloyed Cu-1 wt.% Cr and Cu-1 wt.% Cr/3 wt.% Al 2O 3 solid solution was compared using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The ageing kinetics in Cu–Cr and Cu–Cr/Al 2O 3 can be described using Johnson–Mehl–Avrami (JMA) and Sestak–Berggren (SB) models, respectively. These different behaviors have been discussed in details. It was found that in presence of Al 2O 3 reinforcement, the ageing activation energy is decreased and the overall ageing process is accelerated. This behavior is probably due to higher dislocation density previously obtained during ball milling and Al 2O 3–Cu interface. TEM observations confirm that Al 2O 3–Cu interface and structural defects act as a primary and secondary nucleation sites, respectively.

Electromigration in a Sn-3 wt.%Ag-0.5 wt.%Cu-3 wt.%Bi Solder Stripe Between Two Cu Electrodes Under Current Stressing

The electromigration behavior of a Sn-3 wt.%Ag-0.5 wt.%Cu-3 wt.%Bi solder stripe between two Cu electrodes under current stressing at various densities has been investigated for a current stressing time of 72 h and a temperature of 120°C. After current stressing at a density of 1.0 × 104 A/cm2, the solder matrix exhibited a slight microstructural change as well as formation of a distributed Cu6Sn5 phase near the anode-side solder/Cu interface. Upon increasing the current density to 3.9 × 104 A/cm2 and 5.0 × 104 A/cm2, a high density of distributed Cu6Sn5 phase was formed across the entire solder stripe, resulting in pronounced microstructural change of the solder. Hillocks were also formed near the anode-side interface due to accumulation of a Sn-rich phase, a Bi-rich phase, and a distributed Cu6Sn5 phase, while voids were formed in the solder matrix and at the opposite cathode side. The mechanisms of formation of the distributed Cu6Sn5 phase and migration of Bi and Sn are discussed.

Effects of Residual Elements Arsenic, Antimony, and Tin on Surface Hot Shortness

Scrap-based electric arc furnace (EAF) steelmaking is limited by a surface cracking problem in the recycled steel products, which is known as surface hot shortness. This problem originates from the excessive amount of copper (Cu) in the steel scrap, which enriches during the oxidation of iron (Fe) and consequently melts and penetrates into the austenite grain boundaries. In this article, the effects of arsenic (As), antimony (Sb), and tin (Sn) on surface hot shortness were investigated. A series of Fe-0.3 wt pct Cu-x wt pct (As, Sb, or Sn) alloys with x content ranging from 0.06 to 0.10 wt pct was oxidized in air at 1423 K (1150 °C) for 60, 300, and 600 seconds inside the chamber of a thermogravimety analyzer (TGA) where heat is supplied through infrared radiation. Scanning electron microscopy (SEM) investigations show that (1) the presence of Sb and Sn results in severe grain boundary cracking, whereas the presence of As does not, (2) open cracks with Fe oxides were found beneath the oxide/metal interface in the Sb and Sn alloys, and (3) the oxide/metal interfaces for all As, Sb, and Sn alloys are planar. Penetration experiments of pure Cu and Cu-30 wt pct Sn liquid were also conducted in the chamber of a hot-stage confocal laser scanning microscopy (CLSM) in nonoxidizing atmosphere: (1) on the Fe-35 wt pct manganese (Mn) alloys to study the correlation between cracking and grain boundary characters, and (2) on the pure Fe substrates to exclude the bulk segregation effects of Sn on grain boundary cracking. It was found that grain boundary cracking rarely took place on low-energy grain boundaries. The results also suggest that the bulk segregation of Sn in the substrate is not necessary to promote significant grain boundary cracking, and as long as the liquid phase contains Sn, it will be highly embrittling.

Domain Reorientation as a Damping Mechanism in Ferroelastic-Reinforced Metal Matrix Composites

The damping behavior of a model ferroelastic-reinforced–metal matrix composite (FR-MMC) system was examined through the incorporation of barium titanate (BaTiO3) particles into a Cu-10 wt pct Sn (bearing bronze) matrix. The damping properties of the resulting FR-MMC were investigated vs frequency, temperature (above and below the Curie temperature of the ferroelastic reinforcement), and number of strain cycles. Dynamic mechanical analysis (DMA) indicates that the incorporation of the ferroelastic-capable reinforcement significantly augments the damping capability relative to the matrix alone, and also with respect to the damping that would result from the presence of passive composite reinforcements. Neutron diffraction data demonstrate a strong correlation of domain reorientation activity to imposed stress level and demonstrate a degree of reversibility important to the potential practical application of this mechanism of damping.

Spark Plasma Sintering of Nanocrystalline Cu and Cu-10 Wt Pct Pb Alloy

For the first time, we report here that high purity nanocrystalline Cu and Cu-10 wt pct Pb alloys can be densified with more than 90 pct theoretical density at a low temperature of 623 K (350 � C) using spark plasma sintering (SPS) in argon atmosphere at a pressure of 100 MPa. Scanning electron microscopy (SEM) analysis indicates that molten Pb particles travel through Cu grain boundaries, delineating a ‘‘flowlike’’ pattern in the microstructure. An extensive transmission electron microscopy (TEM) analysis of the ultrafine scale microstructure reveals partial wetting of Cu by liquid Pb as well as entrapment of Pb particles within the Cu matrix. The sintering kinetics and microstructural evolution are discussed in reference to the intrinsic characteristics of SPS as well as phase equilibria in the Cu-Pb system. An important result is that high hardness of around 2 GPa is measured in the Cu-10 wt pct Pb nanostructured alloy, SPS at 573 K to 623 K (300 � C to 350 � C).

Strength and thermal stability of Cu-Al<sub>2</sub>O<sub>3</sub> composite obtained by internal oxidation

The objective of the work is to study the effects of the high-energy milling on strengthening, thermal stability and electrical conductivity of Cu-Al 2 O 3 composite. The prealloyed copper powders, atomized in inert gas and containing 3 wt. % Al, were milled up to 20 h in the planetary ball mill to oxidize in situ aluminium with oxygen from the air. Composite compacts were obtained by hot-pressing in an argon atmosphere at 800 °C for 3 h under the pressure of 35MPa. The microstructural characterization was performed by the optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction analysis (XRD). The microhardness, electrical conductivity and density measurements were also carried out. The effect of internal oxidation and high-energy milling on strengthening of Cu-Al 2 O 3 composite was significant, The increase of the microhardness of composite compacts (292 HV) is almost threefold comparing to compacts processed from the as-received Cu-3 wt. % Al powder (102 HV). The grain size of Cu-Al 2 O 3 compacts processed from 5 and 20 h-milled powders was 75 and 45 nm, respectively. The small increase in the grain size and the small microhardness drop indicate the high thermal stability of Cu-Al 2 O 3 composite during high-temperature exposure at 800 °C.

Kinetics of Intermetallic Compound Formation at the Interface Between Sn-3.0Ag-0.5Cu Solder and Cu-Zn Alloy Substrates

The growth kinetics of an intermetallic compound (IMC) layer formed between Sn-3.5Ag-0.5Cu (SAC) solders and Cu-Zn alloy substrates was investigated for samples aged at different temperatures. Scallop-shaped Cu6Sn5 formed after soldering by dipping Cu or Cu-10 wt.%Zn wires into the molten solder at 260°C. Isothermal aging was performed at 120°C, 150°C, and 180°C for up to 2000 h. During the aging process, the morphology of Cu6Sn5 changed to a planar type in both specimens. Typical bilayer of Cu6Sn5 and Cu3Sn and numerous microvoids were formed at the SAC/Cu interfaces after aging, while Cu3Sn and microvoids were not observed at the SAC/Cu-Zn interfaces. IMC growth on the Cu substrate was controlled by volume diffusion in all conditions. In contrast, IMC growth on Cu-Zn specimens was controlled by interfacial reaction for a short aging time and volume diffusion kinetics for a long aging time. The growth rate of IMCs on Cu-Zn substrates was much slower due to the larger activation energy and the lower layer growth coefficient for the growth of Cu-Sn IMCs. This effect was more prominent at higher aging temperatures.

Tensile and Friction Properties of Tin Bronze Matrix Composites Reinforced by Carbon Fibers

Copper-coated carbon fibers and carbon fiber (CF)-reinforced tin bronze matrix composites were prepared by chemical plating and powder metallurgy, respectively. Copper-coated CFs were characterized with field emission scanning electron microscope. The effects of CF volume fraction on the friction properties and tensile properties of the composites were investigated. The results showed that the composites exhibited lower friction coefficient and higher tensile strength than tin bronze 6-6-3 with the chemical composition of Cu-6 wt%Sn-6%Zn-3%Pb. The friction coefficient of the composites decreased with the increasing of the CF volume fraction. The composite with 9 vol.% CFs showed the highest hardness and tensile strength, which were, respectively, about 1.8× and 1.68× higher than those of the tin bronze 6-6-3.

In-Situ Synthesis of Cu/Cr-Al2O3 Nanocomposite by Mechanical Alloying and Heat Treatment

In this article, a novel method has been used to prepare a copper matrix nanocomposite containing Cu-10 wt pct Cr-10 wt pct Al2O3 by heat treatment of the mechanically activated Cu, Al, and Cr2O3 powder mixture. Structural evolutions were investigated using the X-ray diffraction (XRD) technique. The microstructure of samples was examined using scanning electron microscopy (SEM). It was found that during the milling process, Cu(Al) solid solution and Cu9Al4 phase were formed as the intermediate products, and therefore, Al activity was decreased. Hence, the reduction of Cr2O3 with Al was prevented during the ball milling stage. Further heat treatment carried out under argon atmosphere at 900 °C for 8 hours resulted in completion of Cr2O3 reduction by Al.

Influence of External Stress on Discontinuous Precipitation Behavior in a Cu-Ag Alloy

The influence of an applied stress on discontinuous precipitation (DP) has been investigated for a Cu-5 wt pct Ag alloy aged at 573 K. A tensile stress enhances the growth of DP cells in both the loading direction (LD) and transverse direction (TD), but the cell growth rate in the TD, v CT , is faster than that in the LD, v CL . A compressive stress suppresses the cell growth in the TD, but does not significantly influence it in the LD. The tensile or compressive stress tends to produce discontinuous silver precipitates elongated in a $$ \left\langle {110} \right\rangle_{\alpha } $$ direction of the copper matrix in a DP cell, nearly perpendicular to or parallel to the LD. This result, along with the dependence of the cell growth rate on the sense of the applied stress, can be understood through the interaction energy between the external stress and the misfit strains of silver precipitates. An analysis of length-change measurement results has enabled estimation of the ratio of the growth rate of silver precipitates in the TD, v PT , to that in the LD, v PL , under tension or compression. The estimated values of v PT /v PL are in good agreement with the values of v CT /v CL , experimentally obtained, indicating that the anisotropy of the cell growth rate is determined by the growth behavior of silver precipitates.

Effects of Route on Microstructural Evolution and Mechanical Properties of Cu-8 Wt Pct Ag Alloy Processed by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) is applied to investigate the microstructural evolution and mechanical properties of Cu-8 wt pct Ag alloy subjected to one to four passes via four different routes (A, B(A), B(C), and C). It is demonstrated that better mechanical properties, a higher fraction of high-angle boundaries, and a smaller grain size can be obtained most rapidly with route A, whereas the specimen processed by route B(C) contains relatively inhomogeneous microstructure and has poor mechanical properties. The ultimate tensile stress (UTS) of the Cu-Ag alloy processed by route B(C) saturates after four passes; in contrast, the UTS of the Cu-Ag alloy processed by route A increases continuously in relation to the number of ECAP passes. Based on the experimental results, the strengthening mechanisms of the Cu-8 wt pct Ag alloy processed by different routes as well as the efficiency of different routes in refining the binary alloy are discussed.

TEM and electron holography analyses of granular and thin layered Cu–Co magnetic materials

The paper shows the examples of application of transmission electron microscopy (TEM) techniques for characterization of two types of copper–cobalt magnetic nanomaterials: Cu-10 wt% Co granular giant magnetoresistance (GMR) thin ribbons and thin nanocrystalline Co films deposited on Cu substrate. Quantitative TEM microstructural analyses were used for determination of Co particle size distributions in GMR ribbons. It was demonstrated that the relative resistivity depends on the mean diameter of the cobalt nanoparticles. For nanocrystalline thin Co layers, off-axis electron holography was used to investigate their magnetic structure. The mean in-plane component of the magnetic field in cobalt was calculated from the phase gradient.

Análisis de perfiles de difracción de rayos X de una aleación Cu-8% en peso de Cr obtenida por medio de aleado mecánico

El presente trabajo estudia la evolución de la estructura de una mezcla de polvos Cu-8% peso de Cr, aleada mecánicamente, por medio del análisis de perfiles de difracción de rayos X. Se encontró que al aumentar el tiempo de molienda, el tamaño de cristalitas y la energía de falla de apilamiento disminuyeron, y los valores de microdeformación y probabilidad de falla de apilamiento aumentaron. La distribución de cristalitas se desplazo hacia valores menores de tamaño de cristalitas al incrementar el tiempo de molienda. Después de 50 horas de molienda, los datos indicaron que se ha producido una solución sólida de cromo en cobre.