Ultrafine-grained Copper Alloy Research Articles

Effects of Stacking Fault Energy and Solute Atoms on Microstructures of Ultrafine Grained Copper Alloys Processed by Severe Plastic Deformation

Effects of Stacking Fault Energy and Solute Atoms on Microstructures of Ultrafine Grained Copper Alloys Processed by Severe Plastic Deformation

Investigation of superplasticity of ultrafine-grained copper alloys obtained using the ECAP

The paper describes the results of experimental studies of the superplasticity of ultrafine-grained (UFG) high-purity copper, as well as UFG copper alloys Cu-Ag and Cu-Cr. The study shows that the introduction of small (up to 0.1 wt.%) additives of alloying elements leads to an increase in the ductility of UFG copper at elevated temperatures. An increase in the concentration of alloying elements complicates the process of plastic flow of UFG copper at elevated temperatures due to the difficulty in grain-boundary sliding.

Preparation of ultrafine-grained copper alloy by annealing treatment after multi-directional compression

Ultrafine grained(UFG) metallic materials arouse a great interest due to their excellent mechanical properties.The UFG materials,produced by severe plastic deformation(SPD) technique such as channel angular pressing(ECAP) and high-pressure torsion(HPT),exhibit obvious improvement in strength but a large decrease in their thermal stability and ductility.In this article,an UFG QBel.7 copper alloy with good comprehensive properties was prepared by multi-directional compression (MDC) at room temperature and subsequent annealing at high temperature.The deformed and subsequent annealed microstructures were investigated by OM.TEM and SEM/EBSD techniques.The integrated flow curves plotted over a number of compression passes increase to a maximum at moderate strains of 1 to 2 followed by steady-state-like flow at high cumulative strains.Fine grains were not observed even at a higher cumulative stain of￡￡=4.8,although there were many sub-grains when the samples were deformed to￡s=2.4.This indicates that the dynamic recrystallization or recovery was completely inhibited by fine precipitates.Static recrystallization(SRX) of the MDCed structure at 973 K was also investigated.With the increment of cumulative strains,the effect of grain refinement became more obvious,but the thermal stability was getting worse.At a medium strain of∑e=2.4. the minimal grain size of 0.8μm could be developed with an excellent combination of properties.The formation of ultrafine grains is attributed to the development from low-angle boundaries to medium angle boundaries to large angle boundaries.The change of the average grain size with annealing time could be divided into three stages:a recovery period for grain refinement,rapid grain refinement and normal grain growth.

Ultrafine-Grained High Strength Cu-Ni-Si Alloys

Ultrafine-grained (UFG) pure copper has been in the focus of materials scientists over the last two decades, however ultrafine-grained high-strength copper alloys have scarcely been processed or characterized so far industrially.In this contribution, UFG copper alloys, especially Cu-Ni-Si alloys, being well known as ideal materials for electromechanical connectors, springs and leadframes, are presented. Precipitation hardened Cu-Ni-Si alloys are a well established and technologically important class of materials for a wide range of applications where high strength and good conductivity are required. Yield strength and fatigue properties of metallic alloys can be significantly enhanced by severe plastic deformation methods. In contrast to other strengthening methods such as solid solution hardening, severe plastic deformation leads to a weaker decrease of electrical conductivity and is therefore a means of enhancing strength while maintaining acceptable conductivity for current bearing parts and components. Characterization of these materials after severe plastic deformation by swaging, wire drawing and subsequent aging was carried out using conductivity-, hardness-and tensile tests as well as highly-resolved microstructural characterization methods.The results reveal that UFG low alloyed copper alloys exhibit impressive combinations of properties such as strength, conductivity, high ductility as well as acceptable thermal stability at low and medium temperatures. By a subsequent aging treatment the severely plastically deformed microstructure of Cu-Ni-Si alloys can be further enhanced and thermal stability can profit from grain-boundary pinning by precipitated nanoscale nickel silicides.

Enhanced strength and electrical conductivity in ultrafine-grained Cu-Cr alloy processed by severe plastic deformation

The influence of severe plastic deformation on strength and electrical conductivity in the Cu-Cr copper alloy has been studied. Microstructure of ultrafine-grained samples was investigated by transmission electron microscopy and X-ray diffraction with special attention on precipitation of small chromium particles after various thermal treatments. Effect of dynamic precipitation leading to enhancement of strength and electrical conductivity was observed. It is shown that ultrafine-grained samples enable to demonstrate the combination of enhanced thermal stability up to 500°C, high ultimate tensile strength of 790-840 MPa and enhanced electrical conductivity of 81-85% IACS. The contributions of grain boundaries and precipitates to enhanced properties of ultrafine-grained copper alloy are discussed.

Ultrafine Grained Copper Alloys Processed by Continuous Repetitive Corrugation and Straightening Method

A growing trend to use new copper-based functional materials is observed recently world-wide. Within this group of materials particular attention is drawn to those with ultrafine grain size of a copper matrix. This study was aimed to investigate mechanical properties, electrical conductivity and microstructure in strips of precipitation strengthened copper alloys processed by continuous repetitive corrugation and straightening (CRCS). Tests were performed with the copper alloy strips using original die set construction installed on tensile testing machine. The microstructure was investigated using optical and electron microscopy (TEM and SEM equipped with EBSD). Proposition of semi industrial application of this method have been also presented. The CRCS process effectively reduced the grain size of a copper alloy strips, demonstrating the CRCS as a promising new method for producing ultra fine grained metallic strips.

Thickness Reduction Effect in Obtaining Ultrafine-Grained Microstructure from Oxygen-Free Copper Using High-Ratio Differential Speed Rolling

This study has demonstrated a novel method of fabricating ultrafine-grained oxygen free copper sheets by applying high-ratio differential speed rolling (HRDSR) at room temperature that induces severe plastic deformation. Temperature rise of the sample due to friction and plastic deformation during deformation by HRDSR was significant such that beyond a thickness reduction > 65%, the grain refining efficiency was reduced. The proposed processing method holds great potential for continuous production of ultrafine-grained copper alloy sheets.

Formation of fivefold deformation twins in an ultrafine-grained copper alloy processed by high-pressure torsion

Fivefold deformation twins (DTs) are formed in an ultrafine grain, with a size of ∼100 nm, of a Cu–16 at.% Al alloy processed by high-pressure torsion. Formation occurs through the sequential emission of partial dislocations from grain boundaries and other multiple twin boundaries. These observations confirm the emission of partial dislocations from multiple-fold nodes which can be attributed to increased twinnability via the introduction of Al atoms which lower the driving force for partial emission.

Fabrication of Ultrafine Grained Copper Alloy by 3-Layers Accumulative Roll-Bonding Process

The 3-layers accumulative roll bonding process (ARB) has been attempted to increase the strength of copper alloy (Cu-0.02wt.%P) by refining grain size. The 3-layers accumulative roll bonding was conducted up to 7 cycles at room temperature without lubrication. Microstructural evolution of the copper alloy with the number of the 3-layers ARB cycles was investigated by optical microscopy (OM), transmission electron microscopy (TEM), and electron back scatter diffraction (EBSD). The average grain size has been refined from 20 μm before ARB to 170 nm after 7 cycles of 3-layers ARB. More than 70% of ultrafine grains formed by 3-layers ARB were composed of high angle grain boundaries. The average misorientation angle of ultrafine grains was 30.7 degrees in the center of the specimen. Tensile strength after 7 cycles of 3-layers ARB was 605 MPa, which is about 3.2 times higher than the initial value.

Ultrafine Grain Evolution in Copper Alloys Induced by Mechanisms of Continuous Dynamic and Static Recrystallization

New thermo-mechanical processes (TMPs) to produce ultrafine-grained copper alloys utilizing continuous recrystallization (cRX) were proposed. These methods stand on our hypothesis that the evolution of ultrafine grains can be evolved by a mechanism of cRX even during severe plastic deformation at ambient temperature. A TMP of warm compression of 10 to 20 % of Cu-1.7mass%Fe alloy followed by annealing was cyclically repeated. The slight reduction, low-temperature annealing and pinning of grain boundaries by precipitates efficiently impeded occurrence of discontinuous recrystallization (dRX). The evolved substructures with nodes of the Fe precipitates gradually changed to new grains surrounded by low- and high-angle boundaries with increasing number of the repeated processes. Ultrafine grains with average size of 0.7 m were successfully evolved. However, the onset of dRX triggered extended grain coarsening accompanied by grain-boundary migration under conditions of insufficient annealing temperature and large pass stain. Another TMP cycles of cold rolling and annealing also induced fine-grained structure of about 0.6 m. The above results improved that ultrafine grain refinement can be realized simply by a mechanism of cRX even in the metallic materials with low stacking fault energy.

Increasing the ductility of ultrafine-grained copper alloy by introducing fine precipitates

We fabricated ultrafine-grained (UFG) Cu–Cr–Zr alloy including fine second-phase particles via an accumulative roll-bonding process and subsequent aging treatment. The nanosized precipitates dispersed within the UFG matrix significantly enhanced strain hardening, resulting in the simultaneous improvement of uniform elongation and tensile strength.

Annealing Characteristics of Nanostructured Cu-Fe-P Alloy Processed by Accumulative Roll-Bonding

Annealing characteristics of a nanostructured copper alloy processed by accumulative roll-bonding (ARB) were studied. A nano-grained Cu-Fe-P alloy processed by 8 cycles of the ARB was annealed at various temperatures ranging from 100 to 400 degrees C for 0.6 ks. The sample still showed an ultrafine grained (UFG) structure up to 250 degrees C, however above 300 degrees C it began to replace by equiaxed and coarse grains due to an occurrence of the conventional static recrystallization. The hardness of the annealed copper decreased largely above 300 degrees C. These annealing characteristics of the UFG copper alloy were compared to those of a high purity copper.