Copper Specimens Research Articles

Demonstration of an integrated-heating load frame for quantitatively assessing microscale tensile properties of copper and Zircaloy-2

Small-scale mechanical testing (SSMT) is of great interest in the nuclear materials community as it permits the use of surrogate irradiation techniques, such as ion beam irradiation when investigating the impact of irradiation damage on mechanical properties. The design of a micro-electro-mechanical-system (MEMS) micro-tensile stage is demonstrated to enable micron-sized specimen testing up to failure under ambient and reactor-relevant temperatures. Copper and Zircaloy-2 microscale specimens, having gauge lengths of 200 μm, gauge widths of 48 μm, and specimen-dependent constant gauge thicknesses of 10 μm to 26 μm, are fabricated using micro-wire electrical discharge machining and focused ion beam milling. From each gauge section, microstructure data is captured prior to testing using electron backscatter diffraction analysis, and an optimized digital image correlation speckle pattern is deposited on the specimen surface. The speckle pattern is tracked during deformation and post-processed to obtain strain-field evolution maps throughout deformation. Strain maps provide a means to account for and explain microstructure-dependent features observed in the captured stress-strain curves. The combination of using micro-wire electrical discharge machining, focused ion beam cleaning, and ion beam induced platinum deposition for micron-sized specimen preparation as well as utilizing microfabrication techniques to fabricate an integrated heating microtensile load frame reported herein serve as a demonstration of SSMT approaches that can be adopted to tackle challenging problems in nuclear materials research, including but not limited to the effects of ion beam irradiation on mechanical performance and providing experimental data to support small-scale modeling efforts of embrittling precipitates or radiation-induced segregation.

Effect of vacuum diffusion bonding on the mechanical and conductive properties of bonded bulk copper single crystals

Recrystallization-free atomic-level (AL) bonding between bulk copper single crystals was achieved by combining chemical mechanical polishing (CMP) and vacuum diffusion bonding. Under various bonding conditions, the bonded copper specimens can be classified into three categories: AL-bonded, HH-bonded, and L-bonded specimens. AL-bonded copper single crystals were obtained by performing bonding under 20 MPa at 600 °C for 60 min, achieving the mechanical and electrical properties that are closest to those of the parent copper single crystal. The AL-bonded interface is characterized by an asymmetrically tilted sub-grain boundary with a 2° misorientation and consists of two sets of edge dislocations with mutually perpendicular Burgers vectors. The formation of the AL-bonded interface depends on two critical factors: the creation of ultra-flat bonded surfaces and performing diffusion bonding within the elastic deformation range. Achieving an ultra-flat surface that eliminates residual stress allows for bonding under relatively low pressure. With a moderate bonding temperature and holding time, it is possible to simultaneously avoid the formation of voids and recrystallizations at the bonding interface, thereby achieving a high-quality AL-bonded interface between bulk copper single crystals.

Understanding the passivation layer formed by tolyltriazole on copper, bronze, and brass surfaces

Tolyltriazole (TTAH) is used industrially as a corrosion inhibitor for copper alloys, particularly in organic media. In this study, the morphology and chemistry of the layer formed by TTAH on copper and copper alloys under realistic conditions is investigated, with focus on the effects due to the presence of tin or zinc in the substrates. A combination of X-ray photoelectron spectroscopy (XPS), medium energy ion scattering (MEIS), and scanning transmission electron microscopy (STEM) has been used. It was found that an inhomogeneous metal–organic layer forms on the surface of copper specimens, likely in the form of copper nanoparticles surrounded by CuxTTAy complexes. This layer increases in thickness for at least 30 days. Chemically, the copper species in the layer are initially in the +2 oxidation state, but after longer exposure to TTAH, mostly Cu(I) is observed. In bronze samples, tin does not appear to segregate to the surface layer. In brass samples, zinc is depleted from the bulk and forms a thicker ZnxTTAy layer.

Dislocation-based entropy as a criterion for fracture

Griffith’s 1920 fracture criteria is well known in the engineering community. Griffith produces a simple formula for the fracture stress of a material using the first law of thermodynamics by relating the decreased elastic energy of an applied load to the increased surface energy of a crack. However, evidence in fatigue research, most notably the concept of fracture fatigue entropy (FFE), suggests that the fracture mechanism is more intimately related to irreversibility and can be treated via the second law of thermodynamics. In this paper, Griffith’s model is approached from the perspective of the second law of thermodynamics, producing a new equation for fracture stress centered on entropy. Fracture tests are performed on 304 stainless steel (SS) and 110 copper specimens. Experimental crack lengths at fracture determined via digital image correlation (DIC) are compared to predicted crack lengths at fracture determined via the entropic fracture stress relation to assess accuracy. Predicted crack lengths at fracture are determined to be accurate to within 2.88% for 304 SS specimens and 7.62% for copper specimens, both of which are comparable to the corresponding accuracy of Griffith criteria predictions. Further, it is shown that the developed entropy model is capable of predicting the entropy-based debonding strength of a material, matching experimental debonding strength values evaluated via DIC to within 25%.

Copper corrosion inhibition in acidic aqueous media through tolyltriazole application: performance analysis

Tolyltriazole (TTA) is recognized as an effective copper corrosion inhibitor in cooling systems due to its low toxicity and versatile properties. With the increasing focus on sustainable development, the employment of compounds of this nature has become increasingly widespread, driving the search for environmentally responsible alternatives. In this context, the aim of this work was to evaluate the efficiency of a corrosion inhibitor formulated with TTA on copper specimens in HCl 0.1 mol L−1 medium. The samples were exposed to the corrosive electrolyte with inhibitor concentrations ranging from 0 to 20 ppm. Electrochemical methods, including open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy were employed for corrosion monitoring. Overall, the results revealed that TTA behaves as a predominantly anodic inhibitor. Additionally, polarization curves demonstrated that within the Tafel region, the inhibitor adsorbs to the copper surface, following the Langmuir isotherm model. Regarding inhibitory effectiveness, the observed values ranged between 81.3 and 96.1%, while morphological analyses indicated the presence of nitrogen on the surface of the copper specimens after electrochemical tests, confirming the formation of a protective TTA film. In conclusion, this study highlights TTA's efficacy as a corrosion inhibitor, demonstrating its significant potential in safeguarding copper against acidic environments.

Characteristic fatigue damage near the Σ3(111) coherent twin boundary in micron-sized copper specimen

To investigate the effect of a Σ3(111) coherent twin boundary on the fatigue damage of micron-sized Cu, a tension–compression cyclic-deformation test was performed on a bicrystal specimen. The fatigue damage (extrusion/intrusion) occurred preferentially around the twin boundary, induced by stress concentration on one side of the specimen due to the deformation constraint between the crystals. Even though stress relaxation occurred on the opposite side, the fatigue damage along the twin boundary penetrated the specimen. The shapes of the extrusion and intrusion of the opposing sides were coincident, and the dislocation density in the damaged region was lower than that in the far region. These results indicate that the dislocations generated at the stress-concentration sites overcame the stress-relaxation effects and traveled along the twin boundary to escape from the opposite side because of the close distance between the surfaces in the specimen. The ease of dislocation ejection promoted the formation of extrusion/intrusion and decreased the fatigue strength of the specimen. The findings will facilitate the development of materials with improved resistance to fatigue damage.

Three-dimensional representative modelling for fretting wear and fatigue of submarine power cable conductors

Submarine power cables (SPCs) for floating offshore wind turbines (FOWT) have received relatively little attention compared to the structural design of wind turbines. This is particularly true for the assessment of fretting-related damage in multi-strand copper wire conductors, due to the complexity of the contact interactions and potentially severe dynamic loading. In this paper, a three-dimensional representative crossed cylinder methodology is introduced to identify potential inter-wire fretting damage. The approach is based on a global–local methodology for FOWTs. Fretting wear testing of crossed cylinder copper specimens are used to characterise the friction and wear behaviour and validate the local fretting wear simulation. A multiaxial wear-fatigue methodology is implemented in conjunction with the global–local methodology for prediction of effects of normal operating and extreme floating wind SPC design load cases. It is shown that gross slip wear has a beneficial effect on predicted fatigue life by about two to three orders of magnitude. The work demonstrates a global–local modelling methodology for design of SPC conductors in floating wind applications.

Comparison of Linear and Nonlinear Twist Extrusion Processes with Crystal Plasticity Finite Element Analysis.

The mechanical characteristics of polycrystalline metallic materials are influenced significantly by various microstructural parameters, one of which is the grain size. Specifically, the strength and the toughness of polycrystalline metals exhibit enhancement as the grain size is reduced. Applying severe plastic deformations (SPDs) has a noticeable result in obtaining metallic materials with ultrafine-grained (UFG) microstructure. SPD, executed through conventional shaping methods like extrusion, plays a pivotal role in the evolution of the texture, which is closely related to the plastic behavior and ductility. A number of SPD processes have been developed to generate ultrafine-grained materials, each having a different shear deformation mechanism. Among these methods, linear twist extrusion (LTE) presents a non-uniform and non-monotonic form of severe plastic deformation, leading to significant shifts in the microstructure. Prior research demonstrates the capability of the LTE process to yield consistent, weak textures in pre-textured copper. However, limitations in production efficiency and the uneven distribution of grain refinement have curbed the widespread use of LTE in industrial settings. This has facilitated the development of an improved novel method, that surpasses the traditional approach, known as the nonlinear twist extrusion procedure (NLTE). The NLTE method innovatively adjusts the channel design of the mold within the twist section to mitigate strain reversal and the rotational movement of the workpiece, both of which have been identified as shortcomings of twist extrusion. Accurate anticipation of texture changes in SPD processes is essential for mold design and process parameter optimization. The performance of the proposed extrusion technique should still be studied. In this context, here, a single crystal (SC) of copper in billet form, passing through both LTE and NLTE, is analyzed, employing a rate-dependent crystal plasticity finite element (CPFE) framework. CPFE simulations were performed for both LTE and NLTE of SC copper specimens having <100> or <111> directions parallel to the extrusion direction initially. The texture evolution as well as the cross-sectional distribution of the stress and strain is studied in detail, and the performance of both processes is compared.

Monitoring and quantification of ultrasonic fatigue damage in copper based on internal friction measurement

Fatigue damage in metals and alloys would reduce their strength and should be identified as early as possible. However, fatigue damage is usually difficult to detect even using advanced nondestructive testing method. Here we developed an automated damping monitoring system for ultrasonic fatigue testing based on a quantitative electromechanical impedance method. During fatigue testing, the damping and resonance frequency of the Piezo actuator/horn/specimen system is measured regularly using an impedance analyzer. When the system damping suddenly increases, it implies that fatigue damage may be generated in the specimen. Separate impedance measurements on the copper specimen in a vacuum chamber show that the internal frictions of damaged specimens are much larger than the fresh specimens. Subsequent X-Ray micro-CT scanning shows that microcracks up to 0.8 mm in length were generated in those fatigued specimens with increased internal frictions. Further tensile testing shows that compared to the fresh specimen, specimens with fatigue damage exhibits reduced tensile strength and elongation at break. Furthermore, the larger the internal friction, the smaller the remaining yield strength and a nearly linear relationship between them holds. Finally, a damage variable DQ is defined based on internal friction which can act as a measure of fatigue damage in metals.

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.

Effect of microstructure refinement of pure copper on improving the performance of electrodes in electro discharge machining (EDM)

The paper presents an analysis of the impact of plastic deformation using hydrostatic extrusion (HE) on the structural, mechanical and functional properties of pure copper for use as electrodes in the process of electro discharge machining (EDM). As part of the research, copper was subjected to the HE process with the maximum cumulative true strain equal to ɛcum = 3.89 obtained in 5 stages. The result was, a refinement of the microstructure with the grains elongated in the direction of extrusion, with a cross-sectional size of d2 = 228 nm. As the obtained material can be potentially used in the process of electro discharge machining, the copper specimens after the HE process were subjected to a comprehensive analysis to determine the mechanical, physical and functional properties of the material. A significant increase in strength (UTS) and yield strength (YS) of the HE-processed copper was obtained, reaching respectively UTS = 464 MPa and YS = 456 MPa at the maximum strain of ɛ = 3.89. Despite the clear strain-induced strengthening of the material, a very high electrical conductivity of not less than 97% was obtained. The electrodes made of copper after HE process have reduced erosion wear while maintaining a comparable or better quality of the machined surface. The best results were obtained for finish machining, where the electrical discharge wear was lower by 60% compared to the electrode made of non-processed copper. In addition, an improvement in the surface quality after the EDM process by 25% was observed when using the HE-processed electrodes.

The transition from used fuel container corrosion under oxic conditions to corrosion in an anoxic environment

AbstractThe conversion of copper oxide films on copper to copper sulfide has been investigated in sulfide‐containing chloride solutions. Single‐phase Cu2O films and duplex films consisting of Cu2O and CuO, and possibly Cu(OH)2, were prepared electrochemically on copper specimens at various applied potentials and characterized using Raman spectroscopy, scanning electron microscopy, and energy dispersive X‐ray analyses. The surface condition of the specimens subsequently exposed to a solution containing sulfide was monitored by measuring the corrosion potential (Ecorr) for various exposure periods, then cathodic stripping voltammetry was performed. Cuprite (Cu2O) was observed to be converted to Cu2S by chemical reaction with sulfide, while the conversion mechanism for the mixed deposit could comprise a galvanic process involving CuII reduction coupled to the formation of Cu2S by the reaction of sulfide with copper within pores in the Cu2O/CuO surface film and a chemical conversion of Cu2O to Cu2S. Cupric hydroxide was not converted to Cu2S on the time scale (24 h) of these experiments.

Crosslinked succinic acid based non-isocyanate polyurethanes for corrosion resistant protective coatings

Non-isocyanate polyurethanes (NIPUs) are considered as safer alternatives to toxic isocyanate-based polyurethanes (PUs). However, NIPU coatings are generally known for their poor water resistance due to the presence of pendant hydroxyl groups in the structure unlike traditional PUs. In this work, solvent-borne crosslinkable NIPU coating formulations were developed in a non-toxic solvent, diethylene glycol diethyl ether, and their coatings properties were evaluated. The crosslinking chemistry involved acid catalyzed transetherification of a commercially available crosslinking agent hexa(methoxymethyl) melamine (HMMM) with the NIPU hydroxyl groups. The crosslinked NIPU coatings showed good thermal stability (up to 245 °C), high pencil hardness (up to 3H), strong adhesion to metal substrates (adhesive strength up to 9.04 MPa), high resistance to water and good salt-water corrosion resistance. The formulations were also applied successfully for dip coating of copper specimens with complex and hard to reach surfaces. Finally, pigmented solvent-borne coating formulations were also demonstrated. All these results highlight the potential of NIPU resins for the application in industrial coatings substituting traditional petroleum-based polyol resins used currently.

Loosely coupled analysis strategy for melt-ablation modeling of thermal protection material in supersonic gas-particle two-phase impingement flow

In this study, a two-way fluid-thermal-ablation loosely coupled analysis strategy is used to investigate the melt-ablation process of the copper specimen plate in the scaled ducted launcher. By coupling a discrete-phase model for simulate the supersonic gas-particle two-phase exhaust plume impingement flow field of a small scaled solid propellant rocket and a solidification/melting model for simulate the melt-ablation process of a copper specimen plate, the ablation depth profile of the copper specimen plate at a burn time of 3.6 s is successfully estimated. The numerical model is validated by experimental-scale test which shows that the simulation results using the two-way fluid-thermal-ablation loosely coupled analysis strategy can accurately predict the ablation depth profile of the copper specimen plate.

Dynamic responses of copper and impact velocity of split Hopkinson pressure bar strikers

Copper high-impact analysis is critical for understanding characterization at dynamic strain rates. The dynamic behaviour of any material is influenced by numerous components of a split Hopkinson pressure bar (SHPB), such as striker forms, striker speed, striker length, bar geometry, and so on. There is also a significant information gap in the literature when it comes to determining the behaviour of copper under high strain rates, especially when the SHPB parameters are varied. Using ABAQUS/Explicit 6.14, this paper numerically investigates the dynamic behaviour of copper under different striker bar shapes (circular flat, circular round, and square) and impact velocities (10, 12.5, 15, 17.5, and 20 m/s). To understand the effects of the specimen's shape under high strain rate loadings, the geometry of the copper specimen is also changed from circular to square. Copper's behaviour was found to be positively sensitive to strain rates, and compressive strength increased by 32%. For the common velocity of the striker, the maximum copper strength was found for a circular flat-shaped striker and the minimum for a circular round-shaped striker. The true yield strength and ultimate strength increase by 8% and 3%, respectively, when the shape of the specimen changes from circular to square.

Multiphysics Simulation and Experimental Investigation of the Densification of Metals by Spark Plasma Sintering

Multivariant experimental investigations and multiphysics microstructural modeling of the spark plasma sintering process of metallic powders have been performed up to a relative density of approximately 80%. In comparison, the effect of sintering temperature, pressure, and particle size on the interparticle contact area growth and axial shrinkage of cylindrical specimens of copper and nickel particles is measured in laboratory scaled tests. Herein, for the first time all relevant for sintering phenomena are considered simultaneously: the fully coupled thermo‐electro‐mechanical modeling of the spark plasma sintering processes, additionally taking into account for lattice, grain boundary, surface diffusion, electromigration, and thermomigration, has been carried out. The computational analysis of various physical phenomena allows to identify dominant and insignificant mechanisms. The two‐level numerical simulation includes the modeling of the sintering setup at the macroscopic level and the neck formation process in particle chain systems at the microscopic level. The results of the numerical simulations show a very good agreement with the experimental data. Therefore, the impact of electrical and mechanical loads as well as of particle size on microscopic distribution of temperature, inelastic strain, and on densification has been studied by the finite element simulations.

Characterization of surface films that develop on pre-oxidized copper in anoxic simulated groundwater with sulphide

Surface films formed on pre-oxidized copper in anoxic simulated groundwater with sulphide were characterized by field emission gun scanning electron microscopy (FEG-SEM), Fourier transform infrared spectroscopy (FT-IR), open circuit potential (OCP) measurements, and via analysing the water chemistry and weight changes in the specimens. Additionally, films developed under identical conditions on pre-oxidized and ground copper specimens were characterized by glow discharge optical emission spectroscopy (GDOES). The results revealed that the sulphide content in the groundwater significantly influences the morphology, composition and thickness of the surface film. The build-up of Cu2S was evidenced at the sulphide contents of 32 mg/L and 320 mg/L. GDOES depth profiling revealed that sulphur and oxygen coexisted in the film all through its thickness, yet the surface was essentially rich in sulphur. The results from characterization are presented in detail in this paper and discussed from the perspective of capabilities of the used methods.

Optimization of Johnson-Cook Constitutive Model Parameters Using the Nesterov Gradient-Descent Method.

Numerical simulation of impact and shock-wave interactions of deformable solids is an urgent problem. The key to the adequacy and accuracy of simulation is the material model that links the yield strength with accumulated plastic strain, strain rate, and temperature. A material model often used in engineering applications is the empirical Johnson-Cook (JC) model. However, an increase in the impact velocity complicates the choice of the model constants to reach agreement between numerical and experimental data. This paper presents a method for the selection of the JC model constants using an optimization algorithm based on the Nesterov gradient-descent method. A solution quality function is proposed to estimate the deviation of calculations from experimental data and to determine the optimum JC model parameters. Numerical calculations of the Taylor rod-on-anvil impact test were performed for cylindrical copper specimens. The numerical simulation performed with the optimized JC model parameters was in good agreement with the experimental data received by the authors of this paper and with the literature data. The accuracy of simulation depends on the experimental data used. For all considered experiments, the calculation accuracy (solution quality) increased by 10%. This method, developed for selecting optimized material model constants, may be useful for other models, regardless of the numerical code used for high-velocity impact simulations.

A novel approach for evaluating creep damage and cavitation in copper bicrystals subject to constant load

Creep in metal alloys is an important failure mode for high temperature and stress applications, but despite extensive study it is still not fully understood, particularly the early stage of creep cavity formation. This paper describes a novel constant load cantilever beam test to investigate creep damage and cavitation at grain boundaries in copper bicrystals. Bicrystals of copper have been prepared with the grain boundary oriented normal to the beam long axis, allowing the development of damage at a single boundary to be studied. Tests were conducted at a temperature of 285°C in a vacuum of 10−10 MPa. Creep cavitation is observed in copper bicrystals of {001} and {111} orientation with a 22° rotation at the boundary. We compare these data with observations for a polycrystalline copper specimen.

Two Coupled Analysis Strategies for Melt-Ablation Modeling of Thermal Protection Material in Supersonic Gas-Particle Two-Phase Impingement Flow

In this study, two analysis strategies were used to investigate the melt-ablation process of the copper specimen plate in the scaled ducted launcher. The reliability of the simulation results of the two analysis strategies was confirmed by comparing the two-way fluid-thermal-ablation coupled analysis (two-way FTA-CA) strategy with two-way fluid-thermal-ablation loosely coupled analysis (two-way FTA-LCA) strategy. Then, the accuracy of the FTA-LCA strategy was validated by comparing the simulation results of the FTA-LCA strategy and experimental results from the experimental scale test. Finally, the FTA-LCA strategy used in this study can not only estimate the impingement surface heat flux into the copper plate when the inverse heat conduction analysis (IHCA) is not possible, but also provide the analysis solution accuracy and the considerable gain in computational efficiency for predicting the long-duration ablation problem in supersonic gas-particle two-phase exhaust plume impingement flow.