Cold Welding Process Research Articles

Cold welding of copper nanowires with single-crystalline and twinned structures: A comparison study

In this article, molecular simulations were adopted to explore the cold welding processes of copper nanowires with both single-crystalline and fivefold twinned structures. It was verified that the twinned nanowires exhibited enhanced strength but lowered elastic limit and ductility. Both nanowires could be successfully welded through rather small loadings, although their stress–strain responses toward compression were different. Meanwhile, more stress was accumulated in the twinned nanowire due to repulsive force of the twin boundaries against the nucleation and motions of dislocations. Moreover, by characterizing the structure evolutions in the welding process, it can be ascertained that perfect atomic order was finally built at the weld region in both nanowires. This comparison study will be of great importance to future mechanical processing of metallic nanowires.

Size effect on cold-welding of gold nanowires investigated using molecular dynamics simulations

The size effect on the cold-welding mechanism and mechanical properties of Au nanowires (NWs) in head-to-head contact are studied using molecular dynamics simulations based on the second-moment approximation of the many-body tight-binding potential. The results are discussed in terms of atomic trajectories, slip vectors, stress, radial distribution function, and weld strength ratio. Simulation results show that during the cold-welding process, a few disordered atoms/defects in the jointing area rearrange themselves and transform into a face-centered cubic crystalline structure. With an increase in contact between the two NWs, dislocations gradually form on the (111) slip plane and then on a twin plane, leading to an increase in the lateral deformation of 4-nm-wide NWs. The effect of structural instability increases with decreasing NW width, making the alignment of the two NWs more difficult. The elongation ability of the welded NWs increases with increasing NW width. Smaller NWs have better weld strength.

Microstructural and microanalysis investigations of bond titanium grade1/low alloy steel st52-3N obtained by explosive welding

Explosive welding is a solid state welding process that is used for the metallurgical joining of two or more dissimilar metals. In this process, forces of controlled detonations are utilized to accelerate one metal plate into another. As a result, an atomic bond is created. It is considered as a cold-welding process since it allows metals to be joined without losing their pre-bonding properties. The metal plates are joined under the influence of very high pressure which causes local plastic deformation and grain refining at the bond interface. Moreover, between the parent and flyer plate some local melting zones are formed. The explosively cladded steel plates are used in the chemical, petrochemical and nuclear industry due to their good corrosion resistance and mechanical properties.In this work, microstructural and chemical analyses of clad plates obtained by the explosive method are presented. The clad plates studied were made of titanium grade 1 explosively bonded with a thin layer of st52-3N low alloy steel. The microstructure was evaluated using light (LM) and scanning electron microscopes (SEM), while chemical composition was assessed using energy dispersive spectroscopy (EDS). It was found that the bond area had different microstructure, chemical composition and microhardness than the bonded materials. In the junction between the base steel and the cladding, a strongly defected transient zone with altered chemical composition in comparison with the bonded metals was revealed.

Preparation and Characterization of Cerium (III) Doped Captopril Nanoparticles and Study of their Photoluminescence Properties

AbstractIn this research Ce3+ doped Captopril nanoparticles (Ce3+ doped CAP-NP) were prepared by a cold welding process and have been studied. Captopril may be applied in the treatment of hypertension and some types of congestive heart failure and for preventing kidney failure due to high blood pressure and diabetes. CAP-NP was synthesized by a cold welding process. The cerium nitrate was added at a ratio of 10% and the optical properties have been studied by photoluminescence (PL). The synthesized compounds were characterized by Fourier transform infrared spectroscopy. The size of CAP-NP was calculated by X-ray diffraction (XRD). The size of CAP-NP was in the range of 50 nm. Morphology of surface of synthesized nanoparticles was studied by scanning electron microscopy (SEM). Finally the luminescence properties of undoped and doped CAP-NP were compared. PL spectra from undoped CAP-NP show a strong pack in the range of 546 nm after doped cerium ion into the captopril appeared two bands at 680 and 357 nm, which is ascribed to the well-known 5d–4f emission band of the cerium.

Fabrication and analysis of thin-film GaAs solar cell on flexible thermoplastic substrate using a low-pressure cold-welding

We present flexible thin-film GaAs solar cells fabricated on thermoplastic substrates by a low-pressure cold-welding and epitaxial lift-off process. The use of polyethylene terephthalate (PET) film as a flexible substrate enables cold welding (130 °C) of gold layers between a thin-film GaAs solar cell and PET film with very low mechanical pressure (0.4 MPa), due to their thermoplastic properties. The feasibility of the proposed technique was demonstrated by fabricating GaAs single junction solar cells (without antireflection coating) on PET film, having an efficiency of 13.2%. The fabricated solar cell also showed a stable performance after 2000 cycles of bending.

Investigation of Cold Pressure Welding: Cohesion Coefficient of Copper

Joining materials by forming is an interesting approach to the manufacture of hybrid (multi material) parts. By establishing a cold pressure weld between metallic surfaces, high quality joints with superior properties can be achieved. Reliable cold welding conditions are difficult to set up, however, since the weld initiation requires extraordinary clean, virtually sheer surfaces. Until today such conditions could only be achieved under a high vacuum conditions. Various studies on cold pressure welding reported that under vacuum welds can be established at significantly lower deformation than in a normal atmosphere. Since adverse deformation is currently needed in industrial cold pressure welding processes like the cold roll cladding of metal bands, a new process with in-line electrochemical surface treatment, is investigated. The ECUF process is intended to supply clean and thereby highly activated surfaces to the cold pressure welding process.This paper presents first results on the weld-ability of copper specimens with regard to the influence of the welding environment: air, argon and KCl solution. Butt welds were made by pressure welding of previously fractured specimens.

Nanoscale Understanding of Bond Formation during Cold Welding of Aluminum and Steel

Cold welding, e.g. by cold forging, is a smart manufacturing technology, enabling novel multi material designs. A material combination, which is particularly attractive for manufacturing, though challenging to handle in a cold welding process, is steel and aluminum. We investigate the bond formation between cold forged C 15 (mainly primary heat treated) and AW 6082. Analysis starts with numerical simulations using the finite element analysis (FEA) to identify optimum conditions for bond formation. The bond strength was determined by tensile tests from samples eroded from the cold-welded specimen. Best performing samples showed a maximum tensile strength of ~200 MPa with ductile failure in the AW 6082. Transmission electron microscopy (TEM) inspection of the bonded area between aluminum and steel show a reaction layer consisting of iron and aluminum of few nm thickness throughout the sample. The formation of such a reaction layer is hypothesized to be crucial for bond formation.

Molecular dynamics understanding on tensile behaviours of cold welding experiments of oriented ultra-thin gold nanowires

A molecular dynamic study on cold welding experiments of ultra-thin gold nanowires in <100> orientation was carried out at room temperature to understand their tensile behaviours. In order to investigate the size effects on cold welding, four kinds of ultra-thin gold nanowires with different diameters are simulated and analysed respectively. We studied the principle of cold welding through observing how the nanowire lattices evolve during the processes of cold welding and stretching. The strain–stress curves of single nanowire and welding nanowire are obtained and analysed, and then the young’s modulus and yield strength are compared each other with corresponding diameters. The observation from the simulation results gives that the atoms in the solder joints would regroup into new lattices during cold welding processes. For the nanowires with small diameters, including Φ3 nm and Φ4 nm, the mechanical properties, such as the young’s modulus, yield strength and yield strain, are all different between single nanowire and welding nanowire with the same diameter, and the single nanowire holds greater ones. As the nanowires’ diameters larger than 4 nm, their mechanical properties are almost the same in the elastic period with corresponding diameters.

Joining with electrochemical support (ECUF): Cold pressure welding of copper

Joining metals using electrochemical support (ECUF) is a new process for cold pressure welding sheets and parts. This new process is based on an electrochemical in-line surface treatment followed by incremental pilger rolling. The ECUF process intends to cold pressure weld materials under optimized conditions. Oxide layers on metal surfaces are known to inhibit the formation of cold pressure welds. The in-line electrochemical treatment will be used to remove these surface oxides for specific engineering metals and alloys. Hence, an improved pressure weld formation at lower forces and smaller reduction ratios is expected for the electrochemically treated surfaces. Using a more flexible pressure welding process, the number of applications could be greatly improved. First tests with copper were performed to analyse the efficiency of the proposed electrochemical surface treatments. Two electrochemical treatments, the cathodic oxide-reduction and cyclovoltammetric oxide-reduction, were compared with conventional treatments (degreasing and scratch brushing) regarding their influence on the cold pressure welding process of copper. The weld strength of lap welds has been investigated as well as the necessary reduction threshold to form a weld. It was found that the electrochemical oxide reduction resulted in higher weld strength. The results of scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDX) indicate that surface oxides were successfully removed by the electrochemical surface treatments.

Molecular Dynamics Studies of Cold Welding of FCC Metallic Nanowires

The atomistic-scale cold welding processes for metallic nanowires (NWs) are studied using embedded-atom molecular dynamics (MD) simulations. The mechanical behavior and structural evolution of the FCC metallic nanowires, including Au, Ag, and Cu materials, that experienced a mechanical stretching break and solid-phase pressure welding process, were investigated. The welding temperatures (Tw) ranging from 100 to 900 K were systemically investigated on the effects of welding strength. The ratio of welding strength, Rws, defined as the ratio between the welding strength and the original yield strength of NWs, was employed to identify the welding quality. Simulation results show that the Rws of Au NWs is better than those of Ag and Cu welded at room temperature; however, for welding at high temperatures (600~900 K) the Rws value of Ag NWs is the best. The Rws values of Au NWs using cold welding show less variance than with high temperature welding, reflecting that the application of cold-welding on the Au NWs is highly feasible. The Rws values for NWs with small diameters are generally higher than those with large diameters. The breaking places of the tensile test for the post-welded NWs didnt occur at the welding region, indicating that the broken wires can be robustly reconnected through solid-phase mechanically-assisted welding methods.

폐가공송전선 Al선재 냉간접합 특성

The new recycling technology for aged Aluminum wires in overhead conductor have been carried out. We are attempting to develop remanufacturing method for them for more effective way of recycling in stead of its conventional remelting process. The weld of aged aluminum wires play a vital role in remanufacture process. The paper investigates the mechanical properties during cold welding process of aged Aluminum wire. The tensile tests and microscopic analysis results are discussed to underscore the hardening features of welded aluminum wire. Various graphs are presented accompanied by discussion about their relevance on the process.

Investigation of nanostructure formation mechanism and magnetic properties in Fe45Co45Ni10 system synthesized by mechanical alloying

Mechanism of nanostructure formation and magnetic properties in Fe 45 Co 45 Ni 10 alloy synthesized by high energy milling has been explored in this study. Our results suggested a simultaneous increase in the dislocation density and formation of low-angle grain boundaries when one of the cold welding or fracturing process was predominant (up to 2 h of milling). This was followed by a steady state between cold welding and fracturing (2 to 35 h), which coincided with high angle grain boundaries formation. After milling for 10 h, dissolution of Co and Ni in Fe, correspondingly, resulted in a bcc solid solution. The powders exhibited a minimum grain size of ~ 10 nm and lattice parameter of ~ 0.28512 nm after 35 and 20 h, respectively. Alloy formation enhanced magnetization saturation to about 186 emu/g and grain size refinement decreased coercivity to approximately 32 Oe. Our results suggested a simultaneous increase in the dislocation density and formation of low-angle grain boundaries when one of the cold welding or fracturing process was predominant (up to 2 h of milling). This was followed by a steady state between cold welding and fracturing (2 to 35 h), which coincided with high angle grain boundaries formation. ► We divide nano-structure formation during mechanical alloying into two stages. ► We determine alloying sequence as Co → Ni → Fe. ► Rigorous increase in volume fraction of grain boundaries leads to lattice expansion. ► Alloy completion increases magnetization saturation.

Research and Development of High Energy Pulse Precision Cold–Welding Technology

High energy pulse precision cold–welding technology is a new welding technology that using high-energy pulsed, which arc produced between tungsten electrode and the workpiece, to melt the base metal and welding wires quickly. The quality and accuracy of this technology are equal to laser welding. It can repair the surface of parts, pitting, cracks and other defects of special-shaped surface. This article discusses research process of the High energy pulse precision cold–welding technology and its working principle, performance characteristics and equipments. It also presents the technology of cold welding materials and processes to explore the High energy pulse precision cold–welding technology’s potential application and future development in the field of surface engineering.

A novel method for producing of steel tubes with Al foam core

In this study, the aluminum foam filling steel tube was produced by powder metallurgy and cold welding process. By this method, Al powder mixed with 0.6 wt.% TiH 2 powder and then pressed into the steel tube. This filled tube was treated in temperature above aluminum melting point for releasing the hydrogen gas by decomposition of TiH 2 particles for providing of foam production conditions. For the first time, the steel tube with Al foam core produced by this method, without using of binder or fitting. Main advantage of these filled tubes is high energy absorption. Energy absorption is very useful in automobile and railway industry. Lightweight is another advantage of these tubes for these applications. It is found that the Al foam filling steel tubes absorb higher energy with respect to the sum of the energy absorptions of the steel tube and aluminum foam alone.

Anisotropic nanostructured magnets by magnetic-field-assisted processing

It has been a great challenge to produce anisotropic nanocrystalline bulk magnets. In this paper, we report our recent work in preparing anisotropic bonded magnets consisting of SmCo5 nanocrystalline particles. The work involved synthesis of nanocrystalline hard magnetic SmCo5 particles by ball milling in the presence of a magnetic field. Structural and magnetic characterizations show the alignment of the c-axis of the SmCo5 grains upon the magnetic-field-assisted ball milling, while the grain size was controlled under 15 nm. The formation of the texture may be attributed to the effect of magnetic fields on the grain orientation during the cold welding process during ball milling. The as-milled particles were then compacted under a magnetic field with a binder to form bonded bulk SmCo5 nanostructured magnets. X-ray diffraction patterns show c-axis alignment in the bulk magnets, which was consistent with the magnetic measurements.

Adhesion and the cold welding of gold-silver thin films

This paper presents the results of a combined experimental and theoretical study of adhesion in cold-welded Au–Ag interfaces that are relevant to the fabrication of organic electronic structures. Focused ion beam /transmission electron microscopy and electron energy loss spectroscopy techniques are used to reveal interfacial impurities associated with the cold welding of nanoscale Au and Ag thin films. A theoretical model is also developed and used to predict the contact profiles around impurities between cold-welded thin films. The model is shown to provide new insights into how adhesion affects the surface contacts that occur during cold welding. The implications of the results are then discussed for the design of cold-welding processes.

Cold welding sealing of copper-water micro heat pipe ends

The quality of micro heat pipe(MHP) is strongly affected by sealing technology. Based on the analysis of requirements of sealing technology, a cold welding technology was presented to seal MHP. In the cold welding process, compression force was used to flatten micro groove copper(MGC) tube. Then the bonding of MGC tube was reached because of intensively plastic deformation of MGC tube under pressure. It is found that the plastic deformation area of the cold welding of MGC tube can be divided into three sections. The deformation of micro grooves in each section was investigated; the influence of the dimensions of cylindrical heads on the weld joint shape and strength was studied; and a comparison between smooth copper tube and MGC tube was done. The results show that a groove compression stage exists in the cold welding of MGC tube besides a flattened stage and a melting stage.

Molecular dynamics investigation of patterning via cold welding

We perform a series of molecular dynamics simulations of a subtractive cold-welding patterning process. The effects of film thickness and work of adhesion between the thin film and substrate are examined. For small works of adhesion, the film elastically debonds from the substrate before the onset of plastic deformation inside the film during stamp retraction. A simple model is proposed to describe the debonding and deformation of the film. The model provides an analytical framework that describes the playoff between adhesion, yield strength, and film thickness in determining the debond length of the film induced by stamp retraction.

Material flow and hardening at butt cold welding of aluminium

The paper investigates the material flow and the hardening during butt cold welding process of 99.5% Al bars. The material flow inside and outside the bars is described both experimentally and theoretically, with important conclusions on the relation between the material deformation and hardening. The Mechanically Affected Zone (MAZ) is identified, defined and described for the first time through the FEM based analysis of the strain–stress field, and validated through the hardness field. The analytical description of the strain state, the hardness tests, and the experimental relation between the material hardness and the strain state are used to validate the FEA results. Tensile tests, microscopic and macroscopic analysis results are discussed to underscore the material flow and hardening features. Various parametric graphs are presented accompanied by discussion about their relevance on the process and equipment design.

FEM model of butt cold welding

Butt cold pressure welding is a solid state manufacturing process with several important applications, but with a gap in its fundamentals. This paper presents a new approach of the research in the field, bringing both theoretical and practical original contributions to the knowledge and creating the bases for the development of new processes addressing modern materials. First, an overview of finite element method (FEM) used in butt cold welding is presented. Correlation between stresses and material deformation is further addressed. Original indicators related to cold welding process initiation are introduced: critical deformation, welding critical stress and welding critical radius. The paper brings an original interpretation of cold welding process based on FEM model and on microstructural considerations. Results of mechanical tests and of macro- and microscopic analysis are provided to validate the model.