Pure Copper Specimens Research Articles

Microstructures and mechanical properties of pure copper manufactured by high-strength laser powder bed fusion

Pure copper is widely used in motor windings, heat exchangers and aerospace engines because of its high electrical and thermal conductivity. High-strength laser powder bed fusion (HS-LPBF) not only allows rapid production of components with complex geometry and high spatial resolution, but also offers various advantages such as small focal spot diameter, fine powder, and small layer thickness, providing advantages for forming complex structural parts in fields such as engines and heat exchangers. A single factor single layer experiment was performed by varying the hatch spacing (H), and the range of hatch spacing was determined according to the overlap rate. The degree of influence of process parameters on the relative density of pure copper specimens was analyzed using an orthogonal experiment, and a comparative study of the phase composition, microstructure and mechanical properties of pure copper specimens was carried out by varying the laser power. The characteristics of pure copper formed by HS-LPBF were analyzed. In addition, the effect of heat treatment on the microstructure and mechanical properties of pure copper specimens was investigated, and the fracture morphology of the specimens was observed comparatively. The results show that the HS-LPBF technique can effectively increase the energy density and improve the specific surface area of the powder and the laser absorptivity due to its small focal spot diameter, fine powder and layer thickness, thus reducing the minimum energy required to melt pure copper powder. The optimum process parameters were obtained by orthogonal experiment with a relative density of 98.1 % of the specimen. The highest hardness, ultimate tensile strength and elongation were obtained at a laser power of 260 W with 84 HV, 320 MPa and 17.8 %, respectively. This ultimate tensile strength is 18 % higher than the highest ultimate tensile strength that has been reported so far. In addition, the average grain size of the optimal specimens was 3.6 µm. Mechanical properties such as hardness, tensile strength and elongation of pure copper parts can be significantly improved by precisely controlling the process parameters, in particular laser power and hatch spacing.

Investigation on the microstructure evolution and mechanical properties of electromagnetic rail material in a launch environment

The failure issue of electromagnetic railgun rails is a widely researched problem, but effective research methods are lacking in studying the microstructure of rail materials. The high current and high strain rate tensile (HCHST) testing platform was designed to simulate the high current density and high strain rate deformation service conditions of pure copper rails used in electromagnetic guns. The microstructural and mechanical properties of commercially pure copper were analyzed using TEM and EBSD under high current density (2680 A/mm2) and various high strain rates (ε̇=3404s−1,ε̇=6808s−1)using the HCHST test platform. The obtained results were then compared with those obtained from the as-received state and the quasi-static current-assisted tensile (QCAT) test. The findings indicate that the deformation mechanism of pure copper specimen under HCHST is similar to that of QCAT, where dislocation and slip are the main mechanisms. However, distinct differences in microstructure were observed. Specifically, a significant number of dislocation walls were present in the grains under QCAT, whereas numerous dislocation cells were formed in the grains under HCHST. In the high-current density environment of 2680 A/mm2, as the strain rate increased, the number of dislocation cells increased while their size decreased. The grains became extremely refined, and the KAM value also increased. Furthermore, the Vickers hardness of pure copper significantly improved after undergoing the HCHST. Based on the experimental findings, it was observed that during the service process of the pure copper rail in electromagnetic railguns (under the influence of high current density and high strain rate deformation), the surface of the rail material experienced significant dislocation entanglement. This resulted in a significant increase in the strength and hardness of the surface of the rail with high strain rate deformation. However, the uneven distribution of strength and hardness throughout the surface layer of the rail eventually made it more susceptible to deformation and failure.

Microstructure development and mechanical behaviour of pure copper processed by the novel TWO-CAP procedure

AbstractIn this study, thin-walled open channel angular pressing (TWO-CAP) technique was applied to pure copper specimens as a novel severe plastic deformation (SPD) method. The TWO-CAP process was applied to the specimens up to four passes. After each pass, the microstructural and mechanical characterization of the material was investigated by tensile and hardness tests along with OM, SEM, EDS, TEM and XRD analyses. As a result, a highly increase in the mechanical properties was obtained, in addition satisfactory grain refinement was observed in microstructures. Strength and hardness values were positively affected from the minimizing the grain sizes after TWO-CAP process. Another reason of the improvements in mechanical properties can be explained as the increase in dislocation density. Furthermore, the effect of the TWO-CAP process on the dislocation density of the material has been demonstrated by XRD and TEM analyses in nanoscale. Moreover, the strain equation has been developed analytically and the effect of each pass on strain was calculated. Finally, the effect of the process on the stress-strain properties of the material was examined by the numerical analysis method and the study was verified.

Quantitative investigation on deformation mechanism and dynamic recrystallization during localized adiabatic shearing of single crystal copper

The adiabatic shearing of single crystals is realized by using large-sized columnar crystalline pure copper specimens prepared by directional solidification and designing hat-shaped sample to make the shearing region inside a grain under shock loading with split Hopkinson pressure bar (SHPB) in the present work. The pure copper hat-shaped specimens are loaded at strain rates of 6.5, 8.2, and 9.1 × 104s−1 respectively by SHPB, then the microstructure of sheared zone is investigated with optical microscopic (OM) as well as transmission electron microscopic (TEM) and its evolution process is quantitatively analyzed. The results showed that the flow stress increase with the increasing of strain rate, and the highest flow stress are 618.6, 460.6 and 410.3 MPa, respectively. There is no twinning at 6.5, 8.2 × 104 s−1 due to the highest flow stress cannot reach the twinning critical stress of 517.3 MPa. Although the highest flow stress reached 618.6 MPa that exceed the twinning critical stress, the force acting on the twinning dislocations and slipping dislocations could not satisfy the twinning condition Ftwin > Fslip due to the strong <001> texture of the directional solidification, so there is no twinning at 9.1 × 104 s−1. Slip is the dominant deformation mechanism at those three high strain rates. The large-sized dislocation cells at the edges of the ASB gradually transformed into elongated dislocation cells in the middle at strain rate of 6.5 × 104 s−1. There are equiaxed grains with size of 100–200 nm in the middle region of the ASB. The instantaneous grains refinement from 428 μm to 100–200 nm is the result of dynamic recrystallization of pure copper under its recrystallization temperature (542 K) caused by adiabatic shearing. The sub-grains were formed at 91 μs, and then changed from sub-grains to equiaxed recrystallized grains with size of 100–200 nm grains at 108 μs within the whole shearing time of 141 μs

Experimental investigation on the electrical, thermal, and mechanical properties of laser powder bed fused copper alloys

This paper presents a thorough investigation of the material characteristics of laser powder bed fused copper alloys. Three different copper alloys, i.e., pure copper, with phosphorus and zinc acting as the main alloying elements, were investigated. The research started by characterizing the starting copper powders and then identified the best process windows for laser powder bed processing to obtain samples with the highest density. Based on the results of process optimization, the electrical, thermal and mechanical properties, i.e., tensile strength, resistance to indentation, and roughness, were characterized. The experimental data showed a maximum relative density of approximately 91% for both alloyed powders, while that of the pure powder was limited to 84.6%. The presence of pores is considered the main limiting factor that inhibits the electrical conductivity, which is up to 68.4 IACS% for the Zn-added powder, and the resistance to indentation, in which the resistance to indentation of pure copper is half that of the zinc-alloyed powder. The tensile properties experience anisotropy caused by the manufacturing process itself, as highlighted by the X-ray diffraction analysis carried out after the samples were fabricated. The zinc-added powder shows the best tensile properties, reaching a tensile strength of 400 MPa, which is almost twice that of traditional annealed bulk copper (i.e., 210 MPa). Finally, the roughness is still far from that achievable with classical subtractive techniques, with values of approximately 7 μm for the best pure copper specimens.

Investigation on the roll-to-plate imprinting of metallic surface micro dimples

Large-area functional metallic surface microstructures have been increasingly utilized in various industrial fields. As an efficient and economical method in fabricating large-area functional metallic surface microstructures, the roll-to-plate (R2P) imprinting process with the flat die was proposed to experimentally fabricate functional micro dimple arrays on the surface of the metallic substrate. The effects of the rolling direction, die cavity aspect ratio, die feature density and grain sizes on the forming results were investigated using pure copper specimens with different grain sizes. The transfer ratio of surface structures decreases with the increase of the die feature density and die cavity aspect ratio, respectively. The flowing differences of material in the rolling direction and transverse directions lead to the inconformity of section profile of formed dimples in the two directions. The depth of dimples in the rolling direction is prominently greater than that in the transverse direction. The depth difference of dimples in the two directions increases with the increase of rolling depth and reduces with the increase of die cavity width. The surface morphology of formed specimens obviously depends on the material flowing direction, grain sizes and rolling depth. The surface roughness, surface roughness scatter and flatness of the formed specimens increase with the grain size. The symmetry of cross sectional micro hardness distribution on both sides of the formed dimple in the rolling direction is poorer than that on both sides of the formed dimple in the transverse direction. The asymmetry of cross sectional micro hardness distribution on both sides of the formed dimple in the rolling direction becomes more prominent with the increase of grain sizes.

Effect of the build orientation on mechanical and electrical properties of pure Cu fabricated by E-PBF

Electrical conductors are usually made of pure copper because this material shows outstanding electrical conductivity (IACS > 100%). Additive manufacturing can be used to further improve the performances of such electrical conductors because it enables to consider sophisticated geometries impossible to be fabricated by conventional processing routes such as casting, machining or hot forming. In the present work, Electron Beam Powder Bed Fusion is optimized to achieve dense pure copper specimens (relative density >99.9%). Only few residual spherical pores inherited from the as-received powder particles are detected in the samples as nicely revealed by X-ray microtomography scans. Three different build orientations, namely 0{\textdegree}, 45{\textdegree} and 90{\textdegree} with respect to the build direction are produced. The microstructures are characterized using optical microscopy and EBSD measurements. The electrical conductivity is measured using the Eddy current method as well as the four-probes method while the mechanical properties are assessed using Vickers microhardness and tensile mechanical testing. The electrical and mechanical performances are discussed in the light of the microstructural characterizations, and further compared with a cold-worked Cu-ETP sheet subjected to an annealing treatment. It demonstrates that E-PBF is able to reliably produce components made of pure Copper whose properties equal those of pure copper fabricated by more conventional processing routes, regardless of the build orientation.

Mechanical and electrical properties of additively manufactured copper

Additive Manufacturing (AM) has become the new paradigm of design and production strategies. While structural and functional materials are the most implemented ones, it is also possible to manufacture parts using precious metals, being copper one of the most interesting. Among AM technologies, the novel Atomic Diffusion Additive Manufacturing (ADAM) has recently included this material between available ones. ADAM is free from thermal and energetic issues caused by high reflectivity and conductivity of copper which other AM encounter. Therefore, it could be a great alternative to manufacture pure copper. In this work ADAM was used to fabricate pure copper specimens in order to measure electrical and mechanical properties. The influence of a machining post processes in strength and ductility is also discussed. Results are compared with wrought C1 1000 copper and published results of other AM technologies. Despite the newness of ADAM, significant improvement in surface roughness and comparable results in other properties was observed. However, further research shall be done to optimize the manufacturing parameters in order to increase the relative density value, as it was found to be significantly lower than in other AM technologies.

Experimental study of the simultaneous effects of severe plastic deformation and secondary radial strain on copper

Due to the widespread use of copper wires in electrical power transmission, the need for raw materials with a homogeneous structure and high strength while maintaining their conductive properties is of high importance. The present study investigates the production of copper wire with improved mechanical properties and homogeneous microstructure due to its nanometre-sized structure. Therefore, the commercial pure copper specimens were subjected to severe plastic deformation (SPD) by means of equal channel angular pressing (ECAP) during four steps at ambient temperature. Due to the creation of a structure with elongated grains in the ECAP process, the deformed specimens were subjected to the direct extrusion operations; thus, a more homogeneous structure was created in them due to the appearance of a secondary radial strain. The obtained results indicate that by applying the simultaneous effects of SPD and direct extrusion on the microstructure, the mechanical properties such as strength and hardness have improved significantly, while the electrical conductivity of pure copper decreased slightly. The outcome can be used as an alternative to current methods for producing high-strength copper wires with suitable electrical conductivity properties.

Effects of electric current on the plastic deformation behavior of pure copper, iron, and titanium

Uniaxial tension tests were performed on pure polycrystalline copper, iron, and titanium specimens with various applied constant (dc) current levels and at matching temperatures, i.e., zero current with temperature histories matched to the current tests. The experiments achieved uniform strain, current density, and temperature conditions along the specimen gage length for unambiguous interpretation of the test data. The results showed non-thermal current effects only with the titanium; 20% reduction in ultimate strength with respect to the strength from the matching temperature tests was observed as well as significant inhomogeneous grain growth. No discernable changes in microstructure were observed in specimens deformed at matching temperatures or with applied current but no deformation (matching temperatures). The electron-wind and local Joule heating mechanisms for electrically-assisted deformation (EAD) do not produce effects large enough to explain the observed titanium results. Dislocation scattering by thermal phonons and electrons associated with the radial and axial heat fluxes generated in the titanium tensile specimens with bulk Joule heating is suggested as a potential mechanism for the observed EAD effects. The experimental results and the possible link to thermal phonon/electron scattering suggests several new avenues of research for understanding EAD of metals.

The effect of SiC nanoparticles and sintering temperature on the structural and wear properties of Cu–MWCNTs–SiC hybrid nanocomposites

Abstract SiC nanoparticles play an important role in Cu–MWCNTs nanocomposites. So far, the effect of SiC volume fraction has not been considered on the properties of Cu–MWCNTs–SiC hybrid nanocomposites. Copper-based hybrid nanocomposites with 2 vol.% carbon nanotubes and 1–3 vol.% SiC nanoparticles were prepared via powder metallurgy. The composite powders were compacted and then sintered at 850, 900 and 950 °C for 1 h. Increasing the volume fraction of SiC nanoparticles restricts the grain growth, decreases the friction coefficient, and increases the hardness and wear resistance of prepared nanocomposites. The coefficient of friction and wear rate of Cu–MWCNTs–SiC hybrid nanocomposites decreased with increasing SiC content. Nanocomposites sintered at 900 °C exhibited higher hardness and wear resistance compared to other samples. The highest hardness and wear resistance were related to the Cu-2 vol.% MWCNTs-3 vol.%SiC hybrid nanocomposite sintered at 900 °C, which shows approximately 24 and 78% improvement over the pure copper specimen, respectively. Wear resistance and hardness were reduced for samples sintered at 950 °C.

Effects of ultrasonic shot peening process parameters on nanocrystalline and mechanical properties of pure copper surface

In this paper, the effects of ultrasonic shot peening (USP) and various process parameters on grain refinement, surface hardness, and tensile properties of pure copper surface layers were studied. USP was employed to obtain a grain-refined strengthening layer on the surface of pure copper, and the grains size of the strengthening layer were less than 10 nm, and the thickness of the grain-refined strengthening layer can reach 338 μm. The influence law of process parameters on microstructure was acquired. The hardness of surface increased by 233.5%, from 42.6 HV to 142.1 HV, the influence law of process parameters on surface hardness was grained. Obviously, it was found that the tensile strength was increased from 263 MPa to 308 MPa, which was 17.1% higher than that of the original pure copper specimens by using USP stretch on both sides of the tensile specimens. The influence law of process parameters on tensile strength was obtained. When the peening duration was 120 s, the optimal tensile strength can be obtained, sufficient plasticity can be retained meanwhile.

Bee pollen extract as an eco-friendly corrosion inhibitor for pure copper in hydrochloric acid

Herein, bee pollen extract (BPE) was assessed for its performance as a green inhibitor of copper corrosion in acidic media. Gas chromatography mass spectrometry was used to identify the major components of BPE. Multiscale testing techniques, i.e. weight assessment, potentiodynamic polarisation tests, and electrochemical impedance spectroscopy, were employed to explore the corrosion properties of pure copper specimens in 1 M HCl with 0–7 g/L BPE. The adsorption of BPE on the copper surface fitted a Langmuir-type isotherm. BPE behaves as a mixed-type inhibitor that effectively decreases the corrosion of pure copper metal surfaces in 1 M HCl. Increasing the concentration of BPE increases its inhibition efficiency; at 7 g/L BPE, a high inhibition efficiency of 94.5% was attained. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy were employed to analyse the copper surface. The inhibitive properties of BPE on pure copper corrosion are attributed to the adsorption of antioxidants and phenolic compounds on the copper surface. This study provides insight into the efficiency of BPE as a potential corrosion inhibitor of copper in acidic environments.

The Meso-inhomogeneous Deformation of Pure Copper under Tension–Compression Cyclic Strain Loading

The investigation based on experiments and crystal plasticity simulation is carried out to undertake research on meso-deformation inhomogeneity of metals under cyclic loading at grain level. Symmetrical tension–compression cycle tests are performed on pure copper specimens to observe the inhomogeneous distribution of slip deformation and its evolution with cycle number. Cyclic hardening process and stable hysteretic behavior of pure copper under cyclic loading are simulated by applying a crystal plasticity constitutive model including nonlinear kinematic hardening associated with the polycrystalline representative volume element (RVE) constructed by Voronoi tessellation. Inhomogeneous deformation processes of materials under six different strain amplitudes are simulated by 1600 cycles, respectively. We discuss the variation law of the inhomogeneous meso-deformation distribution of material with the increase in cycle number, and research the rationality of characterizing the inhomogeneous deformation distribution and variation with the statistical standard deviation of the micro-longitudinal strain or the statistical average of the first principal strain based on the statistical analysis of the inhomogeneous deformation of the polycrystalline RVE model during the cycling process. It is found that these two parameters are related to and approximately inversely proportional to the length of measuring gauge.

Microstructure changes in HPT-processed copper occurring at room temperature

In the present work, the long-term stability of ultrafine-grained (UFG) copper at room temperature was investigated. The pure copper specimen was processed by 10 revolutions of high-pressure torsion (HPT) at room temperature. This procedure imposes an equivalent strain of about 300 to the material sample. In the region of these large strains, a saturation in grain size refinement occurs. UFG copper, deformed up to the region of microstructure saturation, was subsequently annealed at room temperature for 6 years. Microstructure changes of HPT-processed copper were investigated by means of 2D and 3D electron back scatter diffraction (EBSD) and also by transmission electron microscopy.It was found that the UFG microstructure of copper with saturated HPT-grain sizes coarsens significantly during long-term storage at room temperature. The analysis of grain volumes showed that the boundaries of coarse grains often contain flat segments with the coincidence site lattices (CSL) Σ3 and Σ9. The misorientation distributions revealed that most boundaries in the annealed microstructure are low energy grain boundaries of these kinds. However, groups of fine grains that are surrounded by random boundaries can also be found in the microstructure. Furthermore, 3D EBSD data were analysed in order to obtain a statistical microstructural information. The microstructure contains a high number of fine grains, but they form only a minority of the investigated volume. Quantitative geometrical characteristics of grain boundaries including CSL were described and interpreted.

Synthesis, Structure and Mechanical Properties of Bulk “Copper-Graphene” Composites

Abstract Bulk copper, copper-graphene and copper-graphite composites were produced from copper-thermally expanded graphite (TEG) powder mixtures with 0-3 wt.% TEG contents via modified powder metallurgy process that includes powder milling in a planetary mill at 350 rpm for 5 hours, compaction, and vacuum annealing at 1030 °C for 1 hour. Phase composition and microstructure of the composites were analysed by XRD and SEM techniques. According to Raman spectroscopy, TEG transforms into a few layer graphene flakes in case of composites with 0.1-1 wt.% of carbon additive, while for 3 wt.% of carbon additive it remains in the form of graphite. The addition of 0.1 wt.% TEG results in the tensile strength increase up to 160 MPa (from 93 MPa for pure copper specimen synthesized via the similar synthesis route). Vickers hardness obtained for Specimens under the study is independent fromthe composite composition.

Co-effect of microstructure and surface constraints on plastic deformation in micro- and mesoscaled forming process

The plastic deformation of materials is affected by external boundaries and microstructures, both of which can induce a serious phenomenon, viz., “size effects” in the microforming process. The interaction of these two kinds of size effects, however, is still not clear, thus significantly hinders the understanding and development of the microforming process. In this study, the co-effect of microstructure and surface constraints on the plastic deformation of material was investigated by using the barreling compression tests (BCT) of micro- and mesoscaled cylindrical pure copper specimens. Through comparing the barreling degree and the distribution of deformation bands of compressed specimens in different size scales, a size effect on plastic deformation caused by the interaction of microstructure and surface constraints was observed. To determine the mechanism of the observed size effect, an extended upper bound solution of barreling was firstly developed by employing the surface layer theory and validated by comparing the predicted average and scatter values of barreling magnitude with the experimental measurements in different size scales. Based on the validated solution, the energies dissipated by intergrain restrictions and surface constraints in the deformation of different scaled specimens were obtained and compared, and the mechanism of size effect on plastic deformation was determined as the change of dominating restrictions to grain rotation from intergrain restriction to surface constraints. Furthermore, the critical size scale point for the transformation of dominating restrictions as well as the dependence of the critical size scale point on the shape of the specimen and surface friction was obtained. The research thus provides an in-depth understanding of the plastic deformation in micro- and mesoscaled deformation and thus facilitates the forming of the desired geometry and shape and achieving of the tailored quality of the micro- and mesoscaled deformed parts.

High-temperature internal friction and dynamic moduli in copper

New measurements of dynamic shear and Young's moduli and their associated internal frictions were made with torsional and flexural forced-oscillation methods, respectively, on three polycrystalline specimens of pure copper. The tests spanned the 1–1000 s range of oscillation periods, at temperatures ranging from those of annealing close to the melting point (1050 °C) down to room temperature. A broad internal friction peak, found at temperatures around 700 °C (at 1 Hz) for samples annealed at 1050 °C, is superimposed on a monotonic relaxation background. Non-linear viscoelastic behaviour is observed above strains around 5×10−6. The period- and temperature-dependence of both shear modulus and internal friction is adequately captured by an extended “background plus peak” Burgers model for viscoelastic rheology. Activation energies are found to be around 200 kJ mol−1 for both the high-temperature peak and monotonic damping background, consistent with common diffusional control of both the dissipation background and superimposed peak, plausibly involving stress-induced migration of dislocations. Complementary torsional microcreep tests at selected temperatures reveal that most of the inelastic strain is anelastic (viscous) for loading durations less (greater) than 1000 s. Such linear viscous deformation, observed at low stress in coarse-grained polycrystalline copper, involves much higher strain rates than expected from published rheology, plausibly attributable to the Harper-Dorn mechanism.

Process development of 99.95% pure copper processed via selective electron beam melting and its mechanical and physical properties

Additive manufacturing by selective electron beam melting (SEBM) was used to fabricate pure copper specimens. A process window at process temperature of 530 °C, gives the required beam powers and deflection speeds for manufacturing dense specimens (>99.5%). The microstructure of SEBM specimens was analyzed by using optical and scanning electron microscopy (SEM). Electrical conductivity, thermal conductivity, hardness, and mechanical performance were investigated by using eddy current, laser flash analysis, Vickers hardness and tensile tests, respectively. It was found that the variation of beam power and scan speed results in different microstructures from columnar to nearly equiaxed grain. The electrical conductivity of SEBM-processed specimens was above 58 MS/m (>100 IACS) while their hardness was around 55 HV0.05 and 46 HV5 without any dependency on processing parameters within the process window. The tensile tests revealed how vertical cracks affect the mechanical strength under tensile loading condition. The results of this study not only show a reliable process window but also introduce the links between processing parameters, defect formations, conductivity and mechanical strength of pure copper specimens manufactured by SEBM.

Evaluation of effect of crystal grain size on nonuniform deformation of polycrystalline pure copper specimen inducing stress gradient

Evaluation of effect of crystal grain size on nonuniform deformation of polycrystalline pure copper specimen inducing stress gradient