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Cold welding on cogged surfaces is a technology developed by researchers from Robotics and Welding Department, Dunarea de Jos University of Galati. Easily deformable samples, having plane surfaces, are pressed on cogged surfaces of harder samples. The paper presents several experimental results regarding mechanical resistance on cold welding achievement. Welded joints between aluminum and copper, brass, carbon steel, stainless steel have been obtained. The maximum mechanical strength is obtained at the deformation rates 20...30%, value obviously much lower that the one characterizing the usual cold welding (minimum 70%). While the tensile strength of the joint is low (around 10% of the tensile strength of the parent metal), the shearing strength is much relevant.

In this study, Co/WSi-CoWSi nanocomposite was synthesized via mechanical alloying and heat treatment. In order to fabricate bulk composite, 50-h-milled powders were cold pressed and subsequently sintered at 1150 °C for 4 h in Ar atmosphere. Phase development and structural changes were investigated by x-ray diffraction technique and scanning electron microscopy. After various milling times, the powders were investigated by differential thermal analysis and microhardness measurements. The starting powder mixture has two allotropic structures of Co (fcc and hcp). After 10-h milling, an allotropic transformation takes place in Co (fcc to hcp), and a composite microstructure consisting of cold-welded Co, W, and Si phases is formed. After 20 h, new peaks related to WSi appeared in x-ray diffractograms. Increasing milling time to 50 h caused the formation of (Co, W, and Si) solid solution, WSi, and CoWSi phases. DTA analysis of 30- and 50-h-milled powders confirmed an increase in the degree of ordering. The 50-h-milled powders exhibited high microhardness value of about 1050 HV. XRD result of sintered material demonstrated that only ordered Co/WSi-CoWSi nanostructured composite is present. Consolidated sample showed 12% porosity. Nanoindentation results showed that the sintered composite an exhibited a high hardness of 700 HV with an elastic modulus of 107 GPa. [ABSTRACT FROM AUTHOR]

This paper presents the study of the process of assembling metal sheets by using brazing of joints through cold welding. The processing technology is a normal drawing procedure. This paper explains schematically the drawing process. Aluminium and copper zinc alloys were used in order to observe the increase of the age-hardening response in brazed alloys. Of great importance is the filler material and especially the way in which it diffuses in the base materials. In this study, the material used was correctly selected, the bimetallic sheets were brazed properly and the behavior of the assembled sheets was according to standards. [ABSTRACT FROM AUTHOR]

In this paper, the effects of residual stresses on the ultimate strength of stiffened cylinders are numerically investigated with an emphasis on shakedown which might occur during the service of these structures. Residual stresses caused by two types of actions, namely, cold bending and welding, are simulated with simplified approaches in numerical analysis. Cold bending stresses are simulated by simulating cold rolling and elastic springback until the desired curvature for cylindrical shell is obtained. Welding is simulated by applying cooling down to a certain temperature on the elements adjacent to stiffener-shell joints to obtain weld-shrinkage with realistic magnitudes. Six small-scale externally pressurized ring-stiffened cylinder models are utilized to evaluate the appropriateness of the method for inclusion of welding residual stresses in numerical analysis by comparing the experimental and numerical results. Ultimate strength analyses are then performed for a reference ring-stiffened cylinder model under radial pressure and stringer-stiffened cylinder under axial loading. To assess the effect of shakedown, after applying cyclic compressive loading to the ring-stiffened cylinder model, the level of stress relief and the change in the ultimate strength are evaluated. [ABSTRACT FROM AUTHOR]

In this work, mechanical alloying (MA) technique, which involves repeated cold welding, fracturing and re-cold welding of powder particles, was used to produce molybdenum disilicide (MoSi2) starting from elemental powder mixtures of Mo and Si. The effects of composition of starting materials on the formation mechanism and phase formation were investigated. Two different molar ratios of Mo:3Si and Mo:4Si were prepared in addition to the stoichiometric powder mixture Mo:2Si. Intermittent sampling was done from 4 to 20 h. Samples were characterized by using X-ray diffraction (XRD)/scanning electron microscopy analyses and crystallite size calculated was based on the conventional Scherrer method. With stoichiometric powder mixture, MoSi2was synthesized based on the mechanism of mechanically induced self-propagating reaction (MSR). Increasing Si contentclearly delayed theMSR and the reactants were gradually converted to both α-MoSi2and β-MoSi2phases over a relatively long time. Agglomeration was noticed in samples, even though with different extents. The samples were then heat treated at 900°C. The phase transformation and crystallite size evolutions of the heat-treated powders were characterized by XRD. Final product of Mo:2Si mixture included Mo5Si3compound, while for other compositions with extra Si the final product was α-MoSi2and the excess Si. [ABSTRACT FROM PUBLISHER]

Abstract: As the scale and complexity of products such as aircraft and cars increase, demand for new functional processes to join mechanical parts grows. The use of plastic deformation for joining parts potentially offers improved accuracy, reliability and environmental safety as well as creating opportunities to design new products through joining dissimilar materials. This paper aims to provide an overview of the state of the art in such joining processes, including cold welding, friction stir welding, self-pierce riveting, mechanical clinching and joining by forming. The paper includes description of the mechanism of joint formation, and analysis of joint performance and applicability. [Copyright &y& Elsevier]

Abstract: Carbon nanotube reinforced copper composites are expected to have superior mechanical and thermal properties. Consolidation of copper–carbon nanotube composite powder is the commonly used technique but uniform distribution of carbon nanotubes in copper matrix remains a challenge. In this study, copper–carbon nanotube composites reinforced with 0.2, 5 and 10vol.% single walled carbon nanotubes and 5 and 10vol.% multi-walled carbon nanotubes were processed by high energy milling of pure copper powder with carbon nanotubes. Constituent powders were milled in Attritor mill for 20h and powder samples were collected after every 5hour intervals. The composite powders had flake like morphology after prolonged milling. The SEM micrographs of the cross-section of powders revealed layered structure. The particle size distribution showed an increase in the average particle size with increasing milling time for all composite powders except for copper–10vol.% single wall carbon nanotube. The cold welding and fracturing phenomena of copper–carbon nanotube powders during milling are influenced by the quantity and type of carbon nanotubes. The higher volume fraction of single walled carbon nanotubes has suppressed the cold welding and enhanced the fracturing of copper–carbon nanotube composite powders. [Copyright &y& Elsevier]

A weld repair technique to be used without post-weld heat treatment has been developed for use on grade 91 steel. The approach makes use of standard (non- modified) 9CrMo weld metal. The work has extended an approach used successfully on the low alloy steel ½CrMoV, which utilised a low strength 2CrMoL weld metal, to the more advanced steel grade 91, using an equivalently lower strength weld metal, standard (non-modified) 9CrMo. This has considerably lower creep strength than matching modified 9CrMo weld metal. Two variants of standard 9CrMo weld metal were chosen for investigation: a specially commissioned low carbon 9CrMoL version, with carbon below the normal minimum for this grade of weld metal (0·05 wt-%), and a conventional batch of 9CrMo weld metal, but selected to have carbon in the bottom half of the normal range. Comparison between the 9CrMoL weld metal and the standard 9CrMo weld metal, on the basis of residual stress level and creep and fracture toughness properties, has shown the latter to be the better option. The most likely repair scenario envisaged was to a retrofit grade 91 header on a UK coal fired power station. The goal was to achieve a lifetime for such a repair greater than the 4 year period between major overhauls for a typical power station of this type, corresponding to >20 kh operating hours. [ABSTRACT FROM AUTHOR]

Cold welding defect is the most common defect in electro-fusion (EF) joint for connecting polyethylene (PE) pipe. In our previous study [1], the cold welding defect is successfully inspected by an eigen-line method based on phased array ultrasonic testing technology. However, limited research has been reported on the acceptance criterion of cold welding defect in EF joint. In this paper, the bonding strength of EF joint is measured using a peeling test. The bonding energy of welding interface is calculated both by phenomenological model and deformation energy analysis method. EF joints with different degrees of cold welding are made and used for peeling tests. The results show that the bonding energy of fused interface rises rapidly after bonding and then goes through a plateau region. The starting point of the plateau region in the bonding energy versus welding time curve is regarded as the minimum required welding time of EF joint. Based on bilinear fitting, the acceptance criterion of cold welding defect is proposed. [ABSTRACT FROM AUTHOR]

In this research, the application of equal channel angular extrusion process to produce both the cold-welded and diffusion-bonded Al/Cu bimetallic rods is assessed. The joints shear strength for both of the methods are measured and compared. The microstructure examinations were also carried out using scanning electron microscope equipped with EDX system and x-ray diffraction analysis. The results exhibit that the strength of the bond in cold-welded specimens is dependent on the amount of stretch and pressure at the materials interface. But in the diffusion-bonded specimens, it is depended on the struggle between the oxidation rate of the mating surfaces accompanied by inter-metallic compounds formation and the aluminum and copper atoms ability to diffuse in the joint interface. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, ball milling was employed to coat titanium carbide (TiC) powder on AISI D2 steel specimens. During the milling, TiC powder adhered on the surface by a combination of mechanical deposition, wear, cold welding and fracturing processes. Structure of the coatings at various stages was studied by X-ray diffraction and scanning electron microscopy (SEM). Composition of the coatings was analyzed by energy dispersive X-ray spectroscopy. Their hardness was also measured. It was found that structural and morphological characteristics of the coatings were affected by milling time. With increasing the milling time from 5 to 20h, average thickness of the coatings increased from 10 to 90μm and, thereafter, it decreased, which indicated that, during the initial stages of milling, cold welding was prominent; but, on further milling, fracturing became the predominant phenomenon. It was also observed that substrate hardening enhanced hardness of the coatings. Scratch test was used to evaluate the coating adhesion in different conditions. [Copyright &y& Elsevier]

In this study, FSW of AISI 1080 high carbon (0·85 wt-%) steel was carried out at a temperature below its AC1 under two sets of conditions, one entailing natural cooling and the other rapid cooling with liquid CO2. The joint structures and mechanical properties obtained under both sets of conditions were investigated, whereupon it was found that defect free joints can be successfully fabricated under either. The resulting joint microstructures mainly consisted of grain refined ferrite with some globular cementite. Higher (harder) joint microhardness profiles were obtained under liquid CO2 cooling below AC1 than under natural cooling below AC1. In tensile testing, all joint fractures were observed to occur in the base metal. Also, stir zone tensile strength and toughness were found to be higher in liquid CO2 cooled samples (820 MPa and 76·7 mm N respectively) than in naturally cooled samples. Note that in both cases, the joints were formed at temperatures below AC1. [ABSTRACT FROM AUTHOR]

A new cold nanowelding technique for cetyltrimethylammonium bromide (CTAB)‐stabilized colloidal nanorods in water is reported. This technique leads to the formation of micrometric nanowires by end‐to‐end self‐organization and welding of nanorods. This cold welding strategy could be generally applicable to colloidal nanoparticles and opens new outlooks for the bottom‐up fabrication of nanodevices using colloidal building blocks. [ABSTRACT FROM AUTHOR]

Deformation, strength, dynamic-mechanical, and adhesive properties of polymers based on thiirane and oxirane mixtures were studied. The character of changes in indicators of properties on the ratio of the components in a mixture, as well as the duration and temperature of curing, was found to be quite complicated. [ABSTRACT FROM AUTHOR]

Abstract: The article presents the effect of mechanical activation on the growth kinetics of boride layer of boronized AISI 4140 steel. The samples were boronized by ferroboron+(SiO2–Na2O) powders for 873–1173K temperature and 2, 4, 6 and 8h times, respectively. The morphology and types of borides formed on the surface of AISI 4140 steel substrate were analyzed. Layer growth kinetics were analyzed by measuring the extent of penetration of FeB and Fe2B sublayers as function of treatment time and temperature in the range of 873–1173K. High diffusivity was obtained by creating a large number of defects through mechanical activation in the form of nanometer sized crystalline particles through the repeated fracturing and cold-welding of the powder particles, and a depth of 100μm was found in the specimen borided by the 2h MA powders, for 4h and 1073K, where 2000–2350 HV were measured. Consequently, the application conditions of boronizing were improved by usage of mechanical activation. The preferred Fe2B boride without FeB could be formed in the boride layer under 973K boronizing temperature by mechanically activated by ferroboron+sodium silicate powder mixture due to the decrease of the activation energy. [Copyright &y& Elsevier]

This research investigates the effects of natural aging and cold working prior to artificial aging on microstructures and mechanical properties of Al-4.6Cu-0.5Mg-0.5Ag alloy. Mechanical properties relative to microstructure variations were elucidated by the observations of the optical microscope (OM), differential scanning calorimeter (DSC), electrical conductivity meter (pct IACS), and transmission electron microscopy (TEM). The results showed that natural aging treatment has little noticeable benefit on the quantity of precipitation strengthening phases and mechanical properties, but it increases the precipitation strengthening rate at the initial stage of artificial aging. Cold working brings more lattice defects which suppress Al-Cu (GP zone) and Mg-Ag clustering, and therefore the precipitation of Ω phase decreases. Furthermore, more dislocations are formed, leading to precipitate the more heterogeneous nucleation of θ′ phase. The above-mentioned precipitation phenomena and strain hardening effect are more obvious with higher degrees of cold working. [ABSTRACT FROM AUTHOR]

Silver nanowires are joined and form monocrystalline V‐shaped or zig‐zag silver prisms. Selective activation of surfaces and self‐orientation of lattices promote the joining of silver nanowires under cold conditions. [ABSTRACT FROM AUTHOR]

Abstract: The mechanochemical synthesis of a La0.67Ce0.21Nd0.08Pr0.04Ni5 intermetallic is studied. The intermetallic is synthesised from a mixture of LaNi5 and La0.25Ce0.52Nd0.17Pr0.06Ni5. The processes controlling the mechanical alloying are characterised as a function of integrated milling time (t m). Effects of fracture and cold welding on the sample are identified by scanning electron microscopy. Compositional, microstructural and structural changes are analysed by energy dispersive spectroscopy and X-ray diffraction. The powder obtained has a particle size distribution of 9±1μm with an average crystallite size of 370±10Å and strain >10%. The intermetallic compound is annealed in Ar to increase crystallite size and to release strain. The structure is refined by the Rietveld method. Cell parameters are a =4.982(2)Å and c =3.980(9)Å, respectively. The advantage of the synthesis method using intermetallics instead of metals/alloys is discussed along with the characteristics of the powder obtained. [Copyright &y& Elsevier]

We describe a synthesis of Au wavy nanowires in an aqueous solution in the presence of cetyltrimethylammonium bromide (CTAB). The resultant Au nanowires automatically separated from the solution and floated at the air/water interface. We investigated the formation mechanism by characterizing the samples obtained at different stages of the synthesis. Both particle attachment and cold welding were found to be involved in the formation of such nanowires. Based on X-ray photoelectron spectroscopy and thermogravimetric analysis the CTAB molecules adsorbed on the surface of a Au nanostructure went through a change in structure from a bilayer to a monolayer converting the Au surface from hydrophilic to hydrophobic. As a result the Au wavy nanowires were driven to the air/water interface during the synthesis. This growth mechanism is potentially extendable to many other systems involving small surfactant molecules. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports for the first time synthesis of free standing nano-crystalline copper crystals of a ∼30–40nm by ball milling of copper powder at 150K under Argon atmosphere in a specially designed cryomill. The detailed characterization of these particles using multiple techniques that includes transmission electron microscopy confirms our conclusion. Careful analysis of the chemistry of these particles indicates that these particles are essentially contamination free. Through the analysis of existing models of grain size refinements during ball milling and low temperature deformation, we argue that the suppression of thermal processes and low temperature leads to formation of free nanoparticles as the process of fracture dominates over possible cold welding at low temperatures. [Copyright &y& Elsevier]

Abstract: In solid-state welding, temperature generally has an important role (diffusion, recrystallization, etc.) however, a mechanical loading is also necessary for breaking down the thin oxide layer (Al2O3) which naturally covers aluminium alloys. As the oxide layers have a melting point of around 2000°C meanwhile aluminium alloys generally melt at only 600°C; the heat supply alone cannot lead to the welding and a mechanical loading is always needed. This work aims at understanding the influence of the mechanical loadings on the formation of metallic bonds. To this end a new weldability test has been introduced. A symmetric cyclic shear is run on the welding interface without external heat supply. A tube-shaped sample is cut through its cross-section and undergone both a compression and a cyclic torsion loading. The influence of some parameters has been studied. Among them, surface condition (roughness and cleanliness), torsion angle (low amplitude) and number of cycles are the most significant. The welded joints have been then mechanically tested and microscopically observed (FEG-SEM and EBSD): the joining is achieved on a 1.5μm thick layer, as things stand, on about 50% of the welding interface. Moreover, a thermomechanical model concludes that the internal intrinsic heat involved in this experimental process is too low to imply a significant increase of temperature in the specimen; thus the joining is only achieved due to mechanical effects of elastoplastic type. [Copyright &y& Elsevier]

Polyethylene (PE) pipes are widely used in transporting natural gas since 1960s. However, there are few published literatures on method for safety assessment of PE pipes. This paper introduces recent work in developing ultrasonic nondestructive testing (NDT) equipment and research on safety assessment of electrofusion (EF) joints of PE pipes. According to the geometrical characteristics and ultrasonic response, defects in EF joints can be divided into four categories, i.e., poor fusion interface, voids, structural deformity, and over welding. The defect of the poor fusion interface includes three typical forms, i.e., cold welding, unscraped oxide skin, and contamination of the fusion interface. Cold welding, which is the most common and dangerous defect, has been successfully detected by using ultrasonic NDT equipment and assessed with a patented cold welding Eigen-line method. [ABSTRACT FROM AUTHOR]

The welding on cogged surfaces between aluminium and copper to be useful so as to replace the mechanical aluminium-metal contact with the copper-metal contact. The possible applications in this respect have been analyzed for the following concrete directions: The welding of electric aluminium conductor bars; The sheathing of electric aluminium conductor bars; The sheathing of the aluminium clips. The contact electric resistance measurements made with a CA 10 Microhmeter indicates negligible values of 1-5 µΩ. These values are constant in time during the exploitation of the electrical contact (tests during months of exploitations were also performed). The temperature in the contact area was measured with a Therma Cam PM 675 PAL thermographic camera. The efficiency of the sheathing is obvious if we were to consider the overheating inside the substation with only 3°C as compared to the 30-40°C normally existing there in the case of classical joints.. [ABSTRACT FROM AUTHOR]

Welding by cold pressing on cogged surfaces, produces the joint of a component made from an easy deformable metal by pressing on the cogged surface of a harder metal component. Different welds between aluminium (the easy deformable component) and copper, brass, steel, stainless steel (harder component, cogged on the contact surface) can be obtained. The experimental results show that the weld can be achieved at lower deformation rates than in the classical cold welding case. The weld is obtained only by deforming the aluminium component at a deformation rate of 20 … 20%. The welding on cogged surfaces of materials with different plasticity makes possible the production of bimetallic or multilayer elements. The weld tensile strength is up to 10% of aluminium ultimate tensile strength, better results being obtained for the shearing strength. A thermal treatment can be used to double the joint resistance, by activating the materials diffusion on the contact surface. The weld contact electric resistance is negligible, recommending the process for producing dissimilar elements used in electrotechnics.. [ABSTRACT FROM AUTHOR]

Abstract: In this research, it is shown that the production of bimetallic Al/Cu rod by cold ECAE process is feasible. The mechanism of the cold weld between the copper sheath and aluminum core is assessed using the characteristics of the mating surfaces both theoretically and by examining the SEM micrographs of the peeled surfaces. It is shown that the stretch produced by the shear strain in the process leads to the fracture of the work-hardened layer of the mating surfaces and then by extruding the virgin metal through the cavities of the cracks a cold weld is developed between the sheath and core of the rod. To achieve the cold weld, a threshold surface stretch of about 59% is required. It is shown that the decrease in die angle leads to a higher welding strength. Moreover, the presence of outer angle (ψ) impairs the quality of the weld. [Copyright &y& Elsevier]

A versatile approach to Rb atomic vapor cell construction is proposed and tested. The construction method employs pinch-off copper cold-welds and epoxy to create hermetic seals between dissimilar geometries and materials. Accelerated testing revealed expected lifetimes of 3 days at 90 °C operation and in excess of 1 yr at 25 °C operation. The reaction of Rb with epoxy was determined to be the largest contributor to failure. [ABSTRACT FROM AUTHOR]

Purpose - The purpose of this paper is to focus on the fabrication of SAC nanocomposites solder and discuss the effects of nanoCu addition on the structure and properties of resulted nanocomposite solder. Design/methodology/approach - Ball milling is a nonequilibrium processing technique for producing composite metal particles with submicron homogeneity by the repeated cold welding and fracture of powder particles. This method is believed to offer good processablity, precise control over the solder composition, and produce more homogeneous mixture. Findings - It is found that the melting temperature, the wetting behaviour, and hardness are improved when the Cu nanoparticles are added. Originality/value - So far, no work has been done on the preparation of Cu nanoparticle added composite by ball milling. This paper presents the fabrication of Sn-Ag-Cu nanocomposite solders in a planetary ball mill process, and the data are compared with related researches done. [ABSTRACT FROM AUTHOR]

Abstract: 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 0.6wt.% TiH2 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 TiH2 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. [ABSTRACT FROM AUTHOR]

Abstract: The microstructure, mechanical properties, and wear behavior of two key components of a hinge fabricated from a metal injection molding process that was then sintered and heat treated under various conditions were analyzed using an optical microscope, a pin-on-disk tester, an open-closed reciprocal wear tester, and a scanning electron microscope. Optical photomicrograph revealed a serious decarburization in the sintered component, suggesting that an increase in carbon content would be necessary to improve mechanical properties. At the initial stage of the open-closed reciprocal wear test, the obverse inclined planes of both components exhibited plastic deformation and depression. As the number of test cycles increased, an increase in cold welding, metal adhesion, spalling, delamination, and surface fatigue was observed, triggering a decrease in metal thickness, which in turn altered the shape of the components. In this study, the optimal parameters to satisfy commercial application requirements were obtained when the components were carburized at 870°C for 30min, quenched in oil, and finally tempered at 250°C for 1h. [ABSTRACT FROM AUTHOR]