Pure Copper Surface Research Articles

Effect of stabilizing heat treatment on condensation heat transfer performance of laser micro-/nano-textured copper surface

The surface reforming method of metal superhydrophobic surface usually utilizes organic matter, which has the problems of serious environmental pollution, high thermal resistance, low processing efficiency, as well as easy to fall off. According to the application requirements of steam condensation heat transfer on copper surface, a laser micro-/nano-texturing technology assisted by green post-processing method is proposed in this study. In this technology, a nano-second laser was used to texture the surface of pure copper, which will undergo heat treatment to prepare a superhydrophobic surface with micro-/nano-level structures. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyze the microstructure changes. A contact angle tester was used to measure the wettability of the surfaces and surface Gibbs energy. Furthermore, steam condensation system was set up to assess surface heat transfer performance. The results show that the laser micro-/nano-textured copper surface has a superhydrophilic contact angle of 4°; after heat treatment, it reaches 161° and became a superhydrophobic surface. As the heat treatment promotes fully oxidation of the textured copper surface, the surface energy is greatly reduced. Due to the formation of nanoscale CuO “clusters” transferred from laser-textured Cu2O by heat treatment, the superhydrophobic surface blocks the growth of condensate droplets and increases the condensation heat transfer coefficient by 4 times to 730.4 W m−2 K−1. It provides a green non-chemical treatment method for heat transfer applications of copper alloy components in the fields of energy, chemical engineering, refrigeration, microelectronics, and batteries.

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.

Improvement of Wear Resistance in Laser Shock-Peened Copper Contacts

This study investigated the influence of laser shock peening without coating (LSPw/oC) on the degradation of copper electrical contacts. A theoretical calculation of the plastic-affected depth (PAD) induced by LSPw/oC was performed, based on the laser-induced plasma pressure along with the Hugoniot elastic limit of our LSPw/oC experimental conditions. The theoretical PAD was obtained approximately 650 µm from the surface for the LSPw/oC at the laser energy density of 5.3 GW/cm2. Various characterization methods such as the Vicker’s hardness test, residual stress test, and electron backscattered diffraction (EBSD) mapping indicated the PAD may play a significant role in laser induced effective depth for LSPw/oC. At a laser energy density of 5.3 GW/cm2, the laser shock-peened copper showed approximately double the surface hardness as compared to the pure copper. This was attributed to grain refinement, which was confirmed by measuring average grain sizes, and by observing mechanical twin structures from the EBSD analysis. Additionally, a compressive residual stress was induced down to the PAD but gradually switched to a tensile residual stress below PAD. The surface hardening effect conferred by LSPw/oC to the pure copper surface resulted in excellent wear resistance, i.e., a low coefficient of friction and wear loss. As a result, the contact exhibited lower electrical resistance following the fretting friction test compared to pure copper; this would result in a significant delay in electrical contact failure.

Enhanced pool boiling performance of a porous honeycomb copper surface with radial diameter gradient

Boiling heat transfer (BHT) is widely used in industry and in our daily lives, and it can be enhanced by micro/nano structures. Previously, porous honeycomb copper surfaces have been proven to significantly enhance BHT performance, but how a radial pore diameter gradient affects BHT is still unknown. In this paper, two porous honeycomb copper surfaces with uniform pore diameters of 60 and 120 μm, respectively (named Sample#U1 and Sample#U2), were prepared using the electrochemical deposition method. On this basis, a porous honeycomb surface with a radial diameter gradient was prepared by infusing liquid onto the reaction surface during the deposition process. The range of pore diameters from the center to the edge was 60–120 μm (named Sample#G1). Pool boiling experiment results showed that the sample with the radial diameter gradient had superior heat transfer performance. Sample#G1, with the smallest pores at the center and largest pores at the edge, had a maximum nucleate BHT coefficient hMNB of 16.1 W•cm–2 K–1, which was about 1.4 times that of Sample#U2, 1.5 times that of Sample#U1, and 3.5 times that of a pure copper surface. It was assumed that surfaces with a radial diameter gradient had a superior rewetting ability, and this was confirmed in a capillary wicking experiment. The K/Reff of the sample with the radial diameter gradient was larger than those of the samples with uniform diameter, which indicated that a radial diameter gradient surface could quickly accelerate the replenishment of water in pool boiling. A porous structure provides pores and cavities, which was benefit for activate bubble nucleation under a low superheat. Sampe#G1 had the lowest ΔTONB. The bubble dynamics also proved that the sample with the radial diameter gradient had a faster bubble growth speed than those with a uniform diameter, resulting in faster heat removal.

Experimental investigation of pool boiling characteristics of surfactant solutions on bi-conductive surfaces

In this study, we conduct pool boiling experiments on pure copper and bi-conductive surfaces using sodium dodecyl sulfate as the surfactant and focus on the bubble behaviors and heat transfer performance of the solutions at the boiling crisis. In comparison with the deionized water, the surfactant solutions are found to effectively enhance the boiling heat transfer at low and medium heat flux. This could account for more active nucleation sites and less bubble coalescences, which can accelerate the formation and departure of bubbles. However, as mushroom bubbles are more easily formed in the surfactant solutions with the increase of the heat flux, the rewetting effect of the heater surface is inhibited, and the CHF is lower than that of the deionized water. For the bi-conductive surface, the CHF is found to be improved in the boiling of the surfactant solution compared with the smooth cooper surface, and the heat transfer deterioration are slowed down during the boiling crisis. Moreover, it is found that the low-thermal-conductivity material can hinder the lateral heat transfer, ensuring the generation of small bubbles and inhibiting the expansion of the dry-out area.

An experimental study on a rapid micro imprinting process

Abstract Large-area micro features have been studied a lot due to their diverse functions and vast application prospects in many industrial clusters. Even though many methods have been developed, a flexible fabrication method which could be easily applied on curved surfaces has not been found. In the present work, a rapid micro imprinting (RMI) process employing periodic dynamic load and the feed of workpiece was proposed and studied. A RMI experimental platform was firstly developed and micro dimples arrays were successfully manufactured on the surface of pure copper. Through observation, the forming process of a micro feature was analyzed to consist of impacting and exiting stage. During the exiting stage, the affected zone of the moving imprinting tool was characterized and divided into ploughing-affected zone (PAZ) and deformation-affected zone (DAZ). The comprehensive effects of the tool’s geometry, grain size and process parameters on the forming results were investigated thoroughly by experiments. It was found the tool’s fillet can improve the forming depth but also result in step-shaped features on the wall area of micro dimples. Though increasing the grain size can improve the forming depth, it can enhance the risk of crack in the ploughed surface. Furthermore, the deviation of forming depth was revealed to change with the grain size and reach the highest value at a critical value close to the diameter of the tool feature, which was further discussed in terms of the inhomogeneous material properties influenced by grain size. Finally, based on the analysis of the process parameters including the feed speed and imprinting frequency on the forming depth and undesirable geometry, a process map was plotted to provide guidance for manufacturing micro dimples with reduced undesirable geometry.

Light-induced enhancement of critical heat flux on TiO2 coatings with specific surface topology

Although many studies have been carried out to explore boiling heat transfer enhancement via thin-film coating, few studies have concentrated on the precise control of the microstructure, and hence the surface properties, of the coatings and the relationship of the surface properties with the resultant heat transfer performance. Herein, we employed two methods, atomic layer deposition (ALD) and magnetron sputtering (MS), to prepare TiO2 thin layers on copper substrates. The optical properties and surface topographies of the coatings made by the two methods were investigated with ultraviolet–visible spectra, scanning electron microscopy, and atomic force microscopy. It was found that the microstructure and hence the surface wettability of the coating could be precisely controlled using UV light irradiation. The hydrophilicity over the surfaces obtained by different methods increased in the order of non-coated < MS < ALD. Both the coating thickness and surface topology played an important role in the boiling heat transfer process. Significantly, the sample with the thinnest TiO2 coating of 40 atomic layers deposited via the ALD method showed the best heat transfer performance, with a critical heat flux (CHF) 68% higher than that of the pure copper surface. We believe this work provides valuable guidance for improving surface modification methods for enhanced boiling heat transfer.

Study of laser cladding Fe–Co duplex coating on copper substrate

Fe-Co duplex coating has been successfully deposited onto pure copper surface by Nd:YAG laser cladding. The morphology and microstructure were investigated by optical microscopy (OM), scanning electron microscopy (SEM) and x-ray diffraction (XRD). Mechanical properties of the samples have been evaluated by microhardness measurement and wear properties. Experimental results showed that the coating was free of cracks and voids, and good metallurgical bonded to the substrates. The surface of the Fe–Co duplex coating was mainly composed of α-Co solid solution, CoCx, Fe0.64Ni0.36 and a number of carbides. The microhardness of the Co-based coating reached 438.6 HV0.2, which was about 5 times of Cu substrate (90.5 HV0.2). The wear test showed the average wear rate of Fe-Co duplex coating was 19.8% of that of copper matrix. The hardness and wear resistance of the Fe-Co duplex coating was significantly improved.

Visualization of Patterned Modified Surfaces in Condensation and Frosting States

In this study, a novel, thorn-shaped, containing, hydrophilic, and hydrophobic surface is proposed to have a better condensate drainage characteristic and to delay the required time for frosting. By using a hydrophilic and hydrophobic mixed thorn-shaped surface created by screen printing, the design makes use of the differences in the wettability gradient to achieve rapid condensate drainage and to lengthen the time for frosting. The results of a frosting experiment indicated that the droplet adsorption and combination and discharge effect in the thorn sample were substantial. The drainage effect increased the surface renewal rate and inhibited ice layer growth on the thorn sample by 52.4% compared with that on pure copper surface. The heat transfer coefficient of the thorn sample during frosting was approximately 16.2% higher than that of pure copper surface. In addition, the defrosting results indicated that the defrosting time of the thorn sample was almost equal to that of the pure copper sample. However, large droplets were easily stagnated at the structural junction due to contact angle hysteresis after defrosting.

Initial Corrosion Behavior of Pure Copper in Atmospheric Environment

The corrosion behavior of pure copper with sodium chloride deposition and without sodium chloride deposition in atmospheric environment was studied by 500h environmental corrosion test and linear polarization test in laboratory, as well as characterization of corrosion products by SEM and XRD. The results showed that pure copper displayed good corrosion resistance in inland atmospheric environment without pollution. After depositing NaCl salt to the surface of pure copper, the corrosion current density increases sharply and plenty of corrosion products is formed on the surface of the sample, consisting of CuO, Cu2O and CuSO4·H2O.

Wear Resistance of Ni-Based Alloy Coatings

In this paper, nickel-based alloy coatings were deposited on the surface of pure copper by jet electrodeposition. The wear resistance of the coatings was studied by a material surface comprehensive performance tester under dry sliding. Hardness testing, friction, and wear testing were performed to characterize the microhardness, surface morphology, and wear resistance of the coatings. The results indicated that adding Fe and W could refine and purify the microstructure. The coatings with additions of 5 wt.% Fe and 7 wt.% W exhibited the highest wear-resistant properties. Moreover, new compound phases NiO, Fe2O3, and WO3 were found on the surface coatings, such that the microhardness was higher than that in the other coatings. Detailed discussions on the influences of Fe and W on the sliding wear are presented.

Influence of chlorides and phosphates on the antiadhesive, antibacterial, and electrochemical properties of an electroplated copper-silver alloy.

Antimicrobial surfaces such as copper alloys can reduce the spread of pathogenic microorganisms, e.g., in healthcare settings; however, the surface chemistry and thus the antibacterial activity are influenced by environmental parameters such as cleaning and disinfection procedures. Therefore, the purpose of the present study was to assess how copper-complexing compounds (chlorides and phosphates), common to the clinical environment, can affect the surface chemistry and the antiadhesive and antibacterial properties of a newly developed antibacterial copper-silver alloy and the single alloying metals. The authors demonstrated that the antiadhesion efficacy against S. aureus 8325 was the highest when the copper-silver alloy and copper surfaces (four- and two-log bacterial reduction compared to stainless steel controls, respectively) were exposed to chloride-containing suspensions. This was explained by the electrochemical activity of copper that dissolved as Cu+, highly toxic to the bacterial cells, in the presence of Cl- and eventually formed a chlorine- and oxygen-rich layer with the incorporation of phosphorus, if also phosphates were present. If chlorides were omitted from the wet environment, there was no difference (P > 0.05) in bacterial counts on copper-silver alloy, copper, silver, and AISI 316 stainless steel control surfaces, due to the fact that no oxidizing conditions were established and therefore there was no dissolution of copper ions from copper-silver alloy and copper surfaces. However, under dry conditions, copper-silver alloy and pure copper surfaces were antibacterial also in the absence of chlorides, suggesting a marked difference between dry and wet conditions in terms of the interactions between surfaces and bacteria. The authors conclude that an attentive design of control policies integrating disinfection interventions and antimicrobial surfaces, such as the copper-silver alloy coating, can be a beneficial solution in fighting the spread of antibiotic resistant bacterial strains and potentially reducing the number of disease outbreaks.

Antimicrobial properties of ternary eutectic aluminum alloys.

Several Escherichia coli deletion mutants of the Keio collection were selected for analysis to better understand which genes may play a key role in copper or silver homeostasis. Each of the selected E. coli mutants had a deletion of a single gene predicted to encode proteins for homologous recombination or contained functions directly linked to copper or silver transport or transformation. The survival of these strains on pure copper surfaces, stainless steel, and alloys of aluminum, copper and/or silver was investigated. When exposed to pure copper surfaces, E. coli ΔcueO was the most sensitive, whereas E. coli ΔcopA was the most resistant amongst the different strains tested. However, we observed a different trend in sensitivities in E. coli strains upon exposure to alloys of the system Al-Ag-Cu. While minor antimicrobial effects were detected after exposure of E. coli ΔcopA and E. coli ΔrecA to Al-Ag alloys, no effect was detected after exposure to Al-Cu alloys. The release of copper ions and cell-associated copper ion concentrations were determined for E. coli ΔcopA and the wild-type E. coli after exposure to pure copper surfaces. Altogether, compared to binary alloys, ternary eutectic alloys (Al-Ag-Cu) had the highest antimicrobial effect and thus, warrant further investigation.

Efficient fabrication of gradient nanostructure layer on surface of commercial pure copper by coupling electric pulse and ultrasonics treatment

Severe plastic deformation can be easily produced on metal surfaces by coupling the micro thermal shock from high peak pulse current and the micro mechanical shock from ultrasonics. Moreover, an efficient method for preparing a gradient nanostructured metal surface by coupling electric pulse and ultrasonics treatment (CEPUT) is developed in this study. The variation in microstructure and hardness of the specimen are investigated by electron backscatter diffraction, transmission electron microscope, X-ray diffraction, and nano-indentation measurement. Results showed that on the treated copper surface with CEPUT, the original grain boundaries are no longer recognized, the average grain size decreases from 48.77 μm to 39.22 nm, and the thickness of severe plastic deformation layer reaches to approximately 500 μm. Moreover, the hardness reaches to 2.105 GPa, and CEPUT also reduces the texture in the sample surface. A computational model is developed and the grain refinement mechanism is proposed to describe the electrical-thermal-mechanical phenomena during CEPUT. The proposed simple and cost-effective method of grain refinement and to produce the graded materials is effective, especially in the materials of high thermal and electrical conductivity.

Experimental Investigations on Subsequent Yield Surface of Pure Copper by Single-Sample and Multi-Sample Methods under Various Pre-Deformation.

Using copper thin-walled tubular specimens, the subsequent yield surfaces under pre-tension, pre-torsion and pre-combined tension-torsion are measured, where the single-sample and multi-sample methods are applied respectively to determine the yield stresses at specified offset strain. The rule and characteristics of the evolution of the subsequent yield surface are investigated. Under the conditions of different pre-strains, the influence of test point number, test sequence and specified offset strain on the measurement of subsequent yield surface and the concave phenomenon for measured yield surface are studied. Moreover, the feasibility and validity of the two methods are compared. The main conclusions are drawn as follows: (1) For the single or multi-sample method, the measured subsequent yield surfaces are remarkably different from cylindrical yield surfaces proposed by the classical plasticity theory; (2) there are apparent differences between the test results from the two kinds of methods: the multi-sample method is not influenced by the number of test points, test order and the cumulative effect of residual plastic strain resulting from the other test point, while those are very influential in the single-sample method; and (3) the measured subsequent yield surface may appear concave, which can be transformed to convex for single-sample method by changing the test sequence. However, for the multiple-sample method, the concave phenomenon will disappear when a larger offset strain is specified.

Doping and oxidation effects under ambient conditions in copper surfaces: a “real-life” CuBe surface

The CuBe surface oxidizes in air similarly to a pure copper surface and contaminants do not affect its electronic properties.

Pure and Oxidized Copper Materials as Potential Antimicrobial Surfaces for Spaceflight Activities.

Microbial biofilms can lead to persistent infections and degrade a variety of materials, and they are notorious for their persistence and resistance to eradication. During long-duration space missions, microbial biofilms present a danger to crew health and spacecraft integrity. The use of antimicrobial surfaces provides an alternative strategy for inhibiting microbial growth and biofilm formation to conventional cleaning procedures and the use of disinfectants. Antimicrobial surfaces contain organic or inorganic compounds, such as antimicrobial peptides or copper and silver, that inhibit microbial growth. The efficacy of wetted oxidized copper layers and pure copper surfaces as antimicrobial agents was tested by applying cultures of Escherichia coli and Staphylococcus cohnii to these metallic surfaces. Stainless steel surfaces were used as non-inhibitory control surfaces. The production of reactive oxygen species and membrane damage increased rapidly within 1 h of exposure on pure copper surfaces, but the effect on cell survival was negligible even after 2 h of exposure. However, longer exposure times of up to 4 h led to a rapid decrease in cell survival, whereby the survival of cells was additionally dependent on the exposed cell density. Finally, the release of metal ions was determined to identify a possible correlation between copper ions in suspension and cell survival. These measurements indicated a steady increase of free copper ions, which were released indirectly by cells presumably through excreted complexing agents. These data indicate that the application of antimicrobial surfaces in spaceflight facilities could improve crew health and mitigate material damage caused by microbial contamination and biofilm formation. Furthermore, the results of this study indicate that cuprous oxide layers were superior to pure copper surfaces related to the antimicrobial effect and that cell density is a significant factor that influences the time dependence of antimicrobial activity. Key Words: Contact killing-E. coli-S. cohnii-Antimicrobial copper surfaces-Copper oxide layers-Human health-Planetary protection. Astrobiology 17, 1183-1191.

In situ investigation of copper corrosion in acidic chloride solution using atomic force—scanning electrochemical microscopy

The anodic dissolution of pure copper surfaces in acidic chloride solution has been monitored in-situ using combined atomic force − scanning electrochemical microscopy (AFM-SECM). Here, the initial studies performed on model copper-modified substrates have been extended to the investigation of bulk copper samples used in industrial settings. The local release of Cu2+ ions was monitored through electrochemical reduction and deposition of the metal ions on the conductive frame of the AFM-SECM probe. Simultaneous monitoring of the topographical changes due to the corrosion process allowed the distinction and correlation of local passivation and pitting phenomena. The extent of the attack was estimated by anodic stripping of the copper metal deposited at the probe.

Influence of in-plane stress state on sliding contact fatigue damage of metallic surfaces

Current study investigates stress-dependent fatigue wear mechanism of pure copper surfaces in ambient environment. The stressed copper surface by a unique bending fixture is subjected to sliding motion of the atomic force microscope probe. Wear volumes are determined at different contact loads with variable bending stresses. Experimental results indicate that the surface damage is accelerated under compressive stresses and suppressed under tensile stresses with the similar contact pressures. A numerical model of fatigue stress intensity factor at the subsurface crack is proposed to explain the stress-dependent fatigue damage mechanism. The numerical study agreed compressive surface stress accelerates fatigue wear. Consequently, experimental and numerical studies on dry sliding contact damage concludes a significant dependence of the surface stress on ductile metal surface.

Study on Wear Behavior of Gradient Nanocrystalline Structure on Pure Copper Surface Induced by Burnishing

Study on Wear Behavior of Gradient Nanocrystalline Structure on Pure Copper Surface Induced by Burnishing