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The Ni coatings were prepared from nickel metal powder and zirconia ceramic balls by mechanical coating technique. The relationship between rotation speed and coatings thickness was studied, the thickness of the coatings was characterized by the weight increase of the zirconia balls after mechanical coating. The composition and microstructure of the coatings with maximum thickness were analyzed by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray Diffraction (XRD). The results revealed that the formation of coatings consists of thickening from the cold welding between Ni particles and the thinning from the exfoliation of coatings work hardening. The thickness of the coatings reaches the maximum when the above two process progress are close to each other. The results proved that higher speed was favor of the coatings formation, the maximum thickness was obtained at the 15 h for rotation speed of 240 rpm, and microscopic images show that the average thickness was about 20 μm.

MnBi-LTP has excellent magnetic intrinsic properties and attractive characteristics as a permanent magnet material. It is necessary to synthesize fine particles of MnBi-LTP with a size close to that of its single magnetic domain (. 500 nm) to improve the magnetic anisotropic characteristics. Although the room-temperature ball milling process has been reported as a common method to reduce MnBi particle size, it has an inevitable limitation in reducing the powder size due to the low milling energy as well as the powder agglomeration by cold welding phenomenon. In this study, we synthesized fine particles of MnBi-LTP by the cryo-milling process at a temperature of 77 K. Phase analysis and magnetic properties were examined as a function of the amount of stearic acid for the cryo-milled powders. As a result, it was found that stearic acid as a surfactant plays an important role in suppressing the decomposition of the magnetic phase that occurs during the cryo-milling process. Consequently, high-purity fine MnBi-LTP particles, with (BH)max of 9.25 MGOe, were obtained through this method. Thus, this indicates that the cryo-milling process has the potential to synthesize fine MnBi-LTP particles with superior magnetic properties.

Oxide dispersion strengthened materials are commonly used for high-temperature applications. Among other possibilities, these oxides are mostly introduced by mechanical alloying comprising cold welding and fracturing of powders by high-impact loads during milling. However, despite their outstanding high-temperature performance, these materials are still not established because of their laborious and thus expensive processing. Therefore, to improve mechanical alloying’s efficiency, the effect of lower milling temperatures is investigated on an oxide-dispersion strengthened high-entropy-alloy in the proposed study. To this end, prealloyed FeCrMnNiCo powders were milled together with yttria at cryogenic and room temperature by using a novel attritor cryomill. Powders milled at both temperatures were subsequently compared regarding their macroscopic morphology, amount and size distribution of detectable yttria as well as defect structure by means of high-resolution scanning electron microscopy and X-ray diffraction, respectively. Investigations showed a significant decrease of powder particle size and an insignificant influence on their aspect-ratio at cryogenic conditions. Furthermore, the phase fraction of detectable yttria got reduced by cryomilling, indicating increased dissolution or at least refinement. Additionally, a higher full width at half maximum accompanied by increased stacking fault probability of the fcc FeCrMnNiCo matrix gained by X-ray diffraction measurements suggests an improved milling efficiency during cryomilling intensified by higher defect density as well as strength of FeCrMnNiCo powders.

Contact dynamic welding failure problems seriously limit the electrical lifetime of electromechanical relay. However, the welding behavior occurred in contact making and breaking process and relevant influencing factors are still unknown. In this article, a series of experiments are carried out in make only, break only, and make & break (M&B) operation modes individually to differentiate the effects of making and breaking processes on contact dynamic welding. The typical dynamic force and electrical waveforms of contact making and breaking processes are obtained and the statistical results of welding force are presented. The roles of bounce arc and molten bridge in welding force are interpreted explicitly by using the variations in electrical parameters such as bounce energy, contact resistance, molten bridge energy, break arc energy, and surface substructure morphologies. It is determined that the bounce arc plays a crucial role in the formation of weld nugget and strength, and the strongest welding occurs in the M&B operation mode.

Thin, sensitive skin electronics The properties of the human sense of touch, including high sensitivity to differences in temperature, pressure, or surface roughness, are challenging to replicate in robotics because skin materials must be highly conductive, stretchable, and thin. Jung et al . developed a process to assemble nanomaterials as a monolayer that is partially embedded in an ultrathin elastomer. The process works by depositing a mixed solvent containing nanostructured silver and/or gold, along with elastomer, onto deionized water. This results in a layer of nanoparticles residing at the interface coating with elastomer, which is further densified by the addition of surfactant. The process is scalable, and the resulting elastomer membranes can be transferred to other substrates. —MSL

Glass-forming ability is a long-standing concern in the field of metallic glasses (MGs), which greatly limits their maximum casting size and extensive applications. In this work, we report an ultrasonic-assisted rapid cold welding of bulk MGs without using any additives. MGs with various compositions are welded together under a 20,000-Hz high-frequency ultrasonic vibration without losing their amorphous nature. The ultrasonic technology offers the advantages of rapid bonding (< 1 s) at low temperature (near room temperature) and low stress (< 1 MPa). According to the phenomenon observed in the experiment, the activated fresh atoms diffuse through the broken channel port under continuous rupture of the oxide layer, and the ultrasonic vibration accelerates the atomic-diffusion process. Finally, stable bonding of the MG interface is realized. This universal ultrasonic-assisted welding process can realize the composition design of dissimilar MGs as well as tuning of new materials with new performance.

Cold welding technique at room temperature is the preferred option in nano-assembly and nano-jointing. In this study, the cold welding behavior and mechanical strength of Cu50Zr50 metallic glass nanowires (MGNWs) in head-to-head contact are investigated by molecular dynamics simulation based on the embedded atom method potential. Effects of welding velocity, operating temperature, and size of nanowires are discussed with the consideration of stress, shear strain, atomic deformation processes, and weld quality. Our simulation results demonstrate that a desirable weld quality can be obtained at room temperature. With an increase in welding velocity, the shear deformation zones of the welded MGNWs increase, leading to a decrease in mechanical strength. However, the effect of temperature on the weld quality is not pronounced. Besides, the elongation ability of the welded MGNWs increases with increasing diameters of nanowires. Smaller diameter results in better weld quality due to the size effect of metallic glass. For a pair of MGNWs with different diameters, the necking and fracture of the welded MGNWs occur in the regions of the nanowire with a relatively smaller diameter. This study carries major implications for the fabrication and structural assembly of metallic glass-based nanomaterials.

Characteristics of organosilicon sealant of VGO-1 brand, which is employed in the preparation of glue-welded joints through contact welding are considered. Preparation conditions of glue-welded joints are given and it is determined that there is a decrease in the magnitude of welding current and an increase in the time of welding and electrode contact pressure upon welding of steel specimens of 08kp brand by the VGO-1 sealant. Structural studies of the sealant after exposure at various temperatures show that the sealant possesses high frost resistance at –30°C in the air and a satisfactory frost resistance at –50°C in the liquid. The swelling degree of the sealant after 20 days of exposure in medical ethyl alcohol is less than 4.5%.

Space Debris is a major problem posing a great threat to all the future space travels as well as to all the satellites which are orbiting around the earth. According to a definition by the Inter-Agency Debris Coordination Committee (IADC) “space debris are all man-made objects including fragments and elements thereof, in Earth orbit or re-entering the atmosphere, that are non-functional” [1]. According to J. C. Liou, even if we stop all the space launches the amount of space debris will remain constant up to 50 years but will increase later due to collisions among them [3], [4]. Till December 16, 2019 a total of 20047 objects are on orbit out of which 5370 objects are payloads and 14677 are debris, this means about 73% of the objects in orbit constitutes debris. [2] The rate at which the debris is generated is much greater than the rate at which this debris deaccelerates, leaves the earth orbit and re-enters the earth atmosphere. We can protect the future space missions from huge debris particles that are traceable but the small debris elements pose a major threat. In this paper we propose a technique to remove the small debris particles from Lower earth orbits based on cold welding. Cold welding is the process in which two similar metals stick to each other when there is a metal to metal contact in space. This happens because on the ground these metals have layers of oxides thus, two pure metals never come in contact but in space, due to wear and tear, this layer of oxides get removed irreversibly and as a result, pure metals come in contact and the adhesive forces cause the metals to join. The debris is orbiting around the earth at a speed of 17500 mph [10]. For our system we use a composite material made up of a combination of elements that usually orbit the earth. Since, in relative frames they are stationary by increasing the velocity with controlled amount we can control the impact during contact. We will propel this composite material with the same speed around the earth as the debris, so that in their relative frames it appears stationary. By bringing the debris particles into contact with the composite material, cold welding will take place between them and then, we will send the system to international space station where the captured debris particles are removed from the composite material. By repeating this process, we can remove most of the small debris particles of size less than 10cm which are orbiting around the earth in lower earth orbit.

Friction stir welding is a contact welding process that uses the heat generated by friction to fuse two different materials. This work is focused on the development of micro-friction stir welding which is carried out for very thin sectioned materials of thickness 1000[Formula: see text][Formula: see text]m or less. Friction welded butt-joints were successfully produced for 0.8[Formula: see text]mm thin AA6061 and SS304 sheets on a semi-automated vertical milling machine using a zero-pin length tool. A mild steel backing plate is used as fixture mechanism to hold the welding sheets on machine. Tool-rotational speed and Tool-travel speed are the weld-parameters examined on mechanical responses such as tensile behavior, micro-hardness and surface-roughness across the nugget-weld zone interface. The maximum tensile strength is obtained at lower weld-parameters. Tensile strength properties of AA6061-T6/SS304 joints were approximately found to be 25% lower than that of the AA6061-T6 alloy base metal. Maximum hardness value of 93HV and minimum roughness value of 2.808[Formula: see text][Formula: see text]m are observed for higher tool speeds at nugget-weld zone interface due to the formation of intermetallic phases. Microstructural behavior is studied on weld-parameters using scanning electron microscope and energy dispersive X-ray analyzer. Very thin intermetallic layers (consisting of Fe2Al5, FeAl3 and FeAl2 phases) were observed in stainless steel/aluminum interface.

The results of tests aimed at estimating the microhardness of a cast nugget and the heat-affected zone are provided. It is established that dot welding along a layer of glue is attended by nonlinear changes in microhardness along the diameter of the cast nugget. In glueless contact welding, the microhardness level along the entire cast nugget is higher than with the application of glue. The greatest reduction in microhardness is observed in the middle of the cast nugget and reaches 15%. The procedure of applying similarity criteria in estimating adhesive and weldbonded joints for microhardness is exposed. The similarity coefficient values are determined, and it is shown that they are effective for use in trying out production procedures in case of replacing welding modes or used material, for example, with a different glue compound.

The features of the welded joint formation of palladium foil with stainless steel by using nickel foil as an intermediate layer at resistance welding are considered. It is shown that through the ch...

This research presents a high energy ball milling method for producing supersaturated solutions of the Ti100-xMgx (x = 10, 15, 20) composite powders containing a process control agent (PCA) under an argon atmosphere at an ambient temperature. The microstructure of the Ti–Mg solid solution during milling was analyzed by scanning electron microscope, and an X-Ray diffraction. A particle size analyzer was employed to investigate the average particle size at different milling times (12 h, 20 h, 32 h). After milling for 32 h of Ti100-xMgx (x = 10, 15, 20) composite powders, the solid solubility of the Mg in Ti reached about 0.5 wt.%, 1.14 wt.%, and 1.92 wt.%, respectively. It was found that the crystallite size of the milled powder decreased by increasing the milling time and reached the value of 4–11 nm after 32 h of milling. Moreover, the addition of the process control agent after 12 h and 20 h significantly reduced the agglomeration by cold welding. As a result, the average particle size of the dispersed composite powder Ti100-xMgx (x = 10, 15, 20) was refined to about 1 μm which indicated that the Ti controlled the final size as being a major alloying element. The maximum value of the density of green compacts was found to be 2.69 g/cm3 for Ti–10Mg.

Welding production forms the basis of assembly production in many branches of industry. Welding equipment is the most numerous in the environment of assembly of transport engineering units. This equipment is used both at the initial stage of assembly operations and at the final stage. The most common machines are single-point and multi-point welding with pneumatic drive. Traditional disadvantage of welding machines using pneumatic drives is the presence of intense acoustic flows at the outlet of the energy carrier, the operating sound level of which significantly exceeds the established sanitary norms and worsens personnel working conditions. Among the sources of aerodynamic flows in contact welding machines, the most relevant noise is during technological release of energy from the pneumatic mechanisms of the welding machines control systems, including the existing fleet of contact welding machines. Standard noise mufflers in the contact welding machines, the acoustic elements of which are made in the form of porous metal bushings or pots, are working efficiently for a short period of time up to 200 hours, both domestic and foreign companies Festo, Camozzi, Pneumax. The reason is that when pulsed, technological release of compressed air containing oil particles, in the presence of external dust sources, the channels of porous sound-absorbing elements are clogged with a suspension of oil with the above specified particles and condensate. This leads to an increase in the hydraulic resistance of the muffler path, an increase in the back pressure in the silencing chamber, and, as a result, to the destruction of the acoustic element, which requires frequent replacement of the muffler. The results are presented concerning the development of new chamber mufflers for contact welding machines, which efficiently reduce noise, operate without maintenance for more than fifteen years without requiring replacement. They are recommended for various branches of industries operating pneumatic systems for various purposes.

There are extensive study on nano composites because of its outstanding mechanical properties when compared with the monolithic materials. The manufacturing of nano particles presents an increasing interest. There are two basic strategy for the synthesis of nano particles, they are bottom up and top down approach. Nano particles are built atom by atom in the bottom up approach. In the synthesis of nano particles, top down approach is most applied one. In this approach, bulk materials are broken down gradually into smaller sizes until they reach nano size. Ball milling is most widely used method for the top down approch. Ball milling process involves milling of constituent powders in a vial where mechanical deformation and chemical reactions takes place between the powders to form new phase. In the present study, constituent powder mixture of Al (1.845 μm) and MnO2 (0.75 μm) are subjected to high energy planetary ball milling to form new phase which is of nano alumina (Al2O3). Initially, Al and MnO2 powder mixture are taken in the ratio of 1:2.416 by weight for different milling duration of 120 min, 240 min and 360 min. The constant speed of the mill was maintained at 300 rpm. The powder mixture inside the mill subjected to impact force between ball to ball and between ball to wall of the container undergo cyclic deformation, cold welding and fracture ensures the generation of nano alumina particles in the range of 50 nm to 560 nm. The effect of mechanical alloying on the microstructure of the powder mixture have been studied by scanning electron microscope (SEM), X-ray diffraction (XRD) and EDS. Toluene was used during milling appears effective process control agent to avoid severe agglomeration and to enhance milling effect.

Using lighter materials like Aluminium(Al) is also a common practice for producing prosthetic devices. This method not only provides less weight but also gives freedom to the designer to design customized devices. But Al can not be used in its pure form as it lacks strength, toughness, rigidity. A common way to overcome these issues is the use of composite materials. In this paper, we have studied how mechanical milling can be used to disperse hard ceramic particles and Carbon nanotube homogenously in Al matrix. We have also demonstrated how changes in different process parameters affect the properties of this composite and how a uniform dispersion can be achieved by the use of the specialized technique. In this paper, we have also suggested methods to avoid clustering and cold welding of reinforcements.

The purpose of this work is to develop a methodology for determination of the total level of multifrequency magnetic field (MF) at the working area of welder by studying the dependences of the magnetizing force of its individual harmonic components to the electrical characteristics of the MF source and welding modes. The study was carried out at a wide frequency range of the MF action for the researching of dependences to MF technological parameters of the contact welding machine and the distance to it. An induction magnetic field sensor and a digital recording oscilloscope with a fast Fourier transform function were used for experimental studies of MF magnetizing force and their spectral ranges. Based on the analysis of the obtained MF oscillograms and spectrograms, the shape and magnitude of the MF magnetizing force signals in different frequency ranges were established. Since it is impossible to quantify the overall level for a multifrequency MF with taking into account all the harmonic components of the MF simultaneously, the generalized magnetic field level indicator (MFI) was proposed, which became the basis for its use as a methodology for the assessment of MF impact on human body. The use of the proposed methodology allowed to establish that it is generated MF with harmonic components in the frequency ranges 5-50 and 50-1000 Hz at working area under contact spot welding, which may exceed their maximum allowed levels, leading to the respective increase of MFI level. It was established that any changes in the mode of contact spot welding, compared to the mode of welding with one batch of full-phase pulses of welding current, lead to the increase in MFI with exceeding of maximum allowed level at a distance of 800-1000 mm from the axis of contact welding machine electrodes; modelling of the front and trailing edges of the pulse lead to the reduction of MFI level, while increasing the angle of phase control of the heating mode leads to the increase of MFI level. The proposed methodology can be applied as universal both for hygienic assessment of the electromagnetic environment during arc welding and for other electrical equipment. The developed methodology gives possibility to assess the overall impact of multifrequency MF on human body. It is based on the known laws of electrodynamics using a new generalized indicator - magnetic field level indicator MFI.

The high entropy alloy (HEA) coatings are potential candidates for advanced application in the protection of steel and other traditional alloys due to their excellent physical and mechanical performance. The AlCoCrFeNi alloy series were favorably studied due to comparably low cost and stable performance. In this research, the AlCoCrFeNi coatings were prepared through surface mechanical abrasion treatment (SMAT). The process implied the comprehensive effect of cold welding and friction. The submicron-size SiC particles were added into the raw materials in different amounts. For SMAT, a high-energy ball milling method was adopted to promote the alloying of metals, disperse SiCp, and combine the powder to the carbon steel substrate. Afterward, the phase composition, microstructure of coatings, and distribution of reinforcement were detected through XRD and SEM analysis, separately, and the effect of SiC particles content on the properties of the coatings was analyzed. The results show that the addition of submicron-sized SiC significantly improved the density and stiffness of the HEA coating and diminished defects and surface roughness. Сoatings containing SiC display enhanced adhesion force and wear resistance. The proposed mechanism is that the submicron SiC particles promoted mechanical alloying of pure metal and intensified the adherence and cold welding of the coating. Especially, herein, the addition of 15 wt.% SiC granted the best comprehensive properties of the coating. Excessive SiC content led to the deterioration of coating plasticity and the growth of cracks.

The concept of creating electrical insulating ceramic materialsproducts from powder systems representing oxide and nonoxide chemical compounds was formed; a program document for materials science and technological logistics of physical and chemical transformation of technogenic mineral raw materials into electrical materials-products of various scientific, practical and specific technological purposes was created and implemented. The principal theoretical approach and its appliedpractical aspects of the development - research - creation of thermo- and chemically resistant structural electrical insulation materials - products for various scientific and practical purposes: automatic contact welding of tubular bimetals (for example, copper - aluminum), electron beam welding in vacuum of thickwalled large-sized structures made of high-strength aluminum alloys, high-temperature (1050 oC) hardening of drilling tools in vacuum furnaces in the medium of dissociated acetylene are considered, in electric transmissions of brake installations of quarry dump trucks (k/s) BelAZ.

Objective The aim of this study was to determine the effect of insertion torque and angulation on the push-out strength of screws in Atraumatic Rigid Fixation (ARIX) system. Materials and Methods In vitro mechanical tests of the ARIX system were conducted. Screw plate constructs (n = 120) were tested using five different insertion torques at four different angles relative to the perpendicular axis of the plate. Before the push-out test, screws were locked into the plates, and the push-out force of the screw was measured by applying a load parallel to the screw axis. Results Implant failure was observed at 0.8 Nm at an insertion angle of 15 degrees, and at 1 Nm at 0 degree, 5 degrees and 10 degrees. Two types of failures were observed: cold welding and plate deformation. An insertion torque of 0.8 Nm produced a significantly higher push-out force compared with 0.2 Nm. Non-angled specimens with 0.8 Nm insertion torque exhibited significantly higher screw push-out forces compared with other tested specimens and insertion angles. Insertion angle did not affect screw push-out force at insertion torques of 0, 0.2, 0.4 and 0.6 Nm. Conclusion The ARIX locking system is much more sensitive to insertion torque than angle. An effect of insertion angle was observed only at an insertion torque of 0.8 Nm, under which all angles significantly decreased push-out force relative to zero degrees of angulation. In addition, low insertion torques can result in screws loosening over time, while greater insertion torques than 1 Nm can result in screw head stripping and plate hole deformation.

Stable isotopes are a powerful tool for tracking biogenic carbon in bio-fuel petroleum co-processing. High-precision determination of δ13C and δ15N values in bio-oils and co-processed bio-fuels by ...

In this paper, we present a calculation for settling times of grains falling under the action of the gravitational field inside a Jupiter mass protoplanet formed via disk instability, where the grains are assumed to be grown by the process of cold welding. As the energy equation, we have considered the conductive-radiative case of heat transport. In our calculation, we have not used any density model, rather, we have estimated the distribution of physical variables inside the protoplanet. With the obtained distribution of the physical variables, we have investigated the growth of the grains having different initial radii (5 × 10−3- 10−1cm) and hence calculated their sedimentation times. The results are found to be in good agreement with those obtained in other investigations.

Modularity in total hip arthroplasty allows a surgeon to have intraoperative versatility, allowing for fine adjustments of the femoral offset, leg length, and version. However, modularity can be a source of multiple complications. This case report describes a novel intraoperative solution for the problem of cold welding of a neck-stem junction using sterile ice to cryogenically disengage the modular components.

Problem of generation of local hardened areas in weld metal d ing rails welding in production of continuous welded rails is solved by using local heat treatment of weld joint. As a result, appearance of quenching structures is excluded. However, new zones of thermal influence with reduced hardness may appear. During operation, such rails are characterized by increased wear of the rolling surface in these areas and collapse of the head at welded joint. It is the main reason for removing rails from the track earlier than time guaranteed. Application of new technology based on dependences of dispersion degree of the structural components (primarily perlite and carbide particles formed during obtaining welded butt joints of rails) on steel composition and rails cooling conditions is proposed. Cooling rate has a decisive influence on the degree of dispersion of ferritic-cementite structure formed during decomposition of austenite. When welding rails in a butt weld, generation of granular perlite is possible in the areas with temperature between Ac 1 and Ac m points. To determine these critical temperatures, thermodynamic calculations were performed using Thermo-Calc ® software (TCFE database) taking into account chemical composition of the samples obtained by spectrometry. Fe – C state diagrams for 76KhSF rail steel were modeled with the minimum and maximum content of alloying elements according to the state standard GOST R 51685 – 2013. To obtain minimal volume of sections with reduced hardness, it is possible to conduct rails welding in hard conditions by electrocontact method using pulsating reflowing. To prevent formation of defective sections with quenching structure, it is possible to control cooling of welded joint using contact heating. Measurement of the temperature distribution during welding according to the given modes and controlled cooling confirms theoretical conclusions.

This work focuses on the synthesize of nanostructured (Fe65Co35)100-x (Pr6O11)x (x = 0, 5) powders using high energy ball milling. The influence of Pr6O11 on structural, morphological and magnetic properties of Fe65Co35 nanoparticles were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) with a dispersive energy analyzer (EDS), vibratory sample magnetometer (VSM) and differential scanning calorimetry (DSC). Results show that the praseodymium oxide addition increased the decrement rate of the crystallite size with milling time of about 27 % and decreased the increment rate of the internal micro-strain of 50 %. Moreover, because of its high grain fragmentation tendency, Pr6O11 increases the hardness and brittleness of Fe-Co powders. Moreover, it minimized the cold welding between Fe-Co ductile particles leading to a significant decrease in the average particle size (~1µm). The magnetic measurements conducted at room temperature show that the saturation magnetisation (Ms) and the coercivity (Hc) increased with milling time in both compositions. A low Ms and high Hc values were detected in (Fe65Co35)95 (Pr6O11)5 nanoparticles. The results demonstrated a soft ferromagnetic nature in all of the synthesized nanoparticles with Ms in the range 207 – 216 emu/g and Hc is found to be 113 Oe.

The dislocation model of welding joint formation during the process of cold welding is proposed. The relations were obtained and the estimated grade of tendency of a number of metals to cold welding was performed on the grounds of the hypothesis of active centers limiting sizes. Relations for the estimated grade of the required for cold welding plastic deformation are obtained.

The specific features of the procedures for heat-exchanging tubes assembly and fixation in the tube sheets of the power equipment heat-exchanging sections are set out, disadvantages of the existing procedure and the problems of joint quality control due to contact welding are noted. The approaches to assess the pressed joint quality are proposed. The calculation dependences to determine the joint tension considering the fixation procedure features.

In the present investigation, an axisymmetric spiral extrusion was used for fabrication of bimetallic Al/Cu composite rods. In this process, a cylindrical bimetallic sample was extruded through an extrusion die having engraved spiral grooves to produce near net shaped composite part. After preparation of composite rods, the bonding strength was evaluated by applying shear stress on Al/Cu interface using compression test. Also the bonding interface was examined by optical metallography and scanning electron microscopy. The results showed that the bond strength increased in Al/Cu composite rods after spiral extrusion and the bonded interface was free of intermetallic layer. The stress imposed on interface region during spiral extrusion broke the work hardened layer in the mating surfaces, and consequently, the cold weld was established between virgin Al and Cu in the contact area. The obtained results showed a feasibility of spiral extrusion processing for production of Al/Cu bimetallic composite rods.

Mechanical alloying is a powder processing technique in which repeated cold welding and fracturing of powder particles was done in high energy ball mill to produce a homogenous material. In this work, Brass matrix composites with different weight percentages of aluminium nitride (AlN) was synthesized through MA. The necessary amount of powders was milled to capitulate different compositions such as Brass-0 wt.% AlN, Brass-4 wt.% AlN, Brass-8 wt.% AlN and Brass- 12 wt.% AlN composites. The SEM and EDAX tests were conducted on the milled composite powders to investigate about their characterization. The SEM analysis established the homogeneous sharing of AlN in the Brass matrix. The green compacts were prepared and were sintered using electric muffle furnace under controlled atmosphere for a time period of 3 hr. The SEM images of the sintered composite samples ensured the uniform distribution of AlN in the matrix exclusive of pores. The outcome exposed that the adding together of AlN with the Brass matrix improved the mechanical properties of the brass matrix composites

In order to obtain high-quality composite powder for vacuum hot pressing sintering and TiAl alloy with good microstructure and properties, the effect of ball milling speed on the morphology of composite powder and the effect of sintering temperature on the microstructure and mechanical properties of the alloy were studied. The research results show that lower ball mill speed is beneficial to achieve the effect of uniform mixing of powder, excessive rotation speed of ball mill will lead to agglomeration and cold welding of composite powder. Three sintering temperatures give three typical structures of TiAl alloy, the matrix phase content of γ-TiAl and α2-Ti3Al changes with the sintering temperature, the increase in sintering temperature makes the alloy structure more uniform and the density also increases. When the sintering temperature rises to 1300℃, the density of the alloy reaches 4.419g/cm3, the hardness value of the hot-pressed alloy at 2h/1240℃ is the highest, and the value of hardness is 527.14HV.

The features of the formation of microconnections in electronic modules on an aluminum-polyimide basis by the method of ultrasonic welding, which allows to obtain reliable mounting joints of different thickness aluminum without preliminary removal of oxide films where the use of contact welding and soldering are practically difficult or impossible, are investigated. The influence of technological modes (power of an ultrasonic generator, oscillation amplitude of a welding tip (tool), welding force and welding time) on the reliability of mounting microconnections is considered

The article addresses the issue related to the disposal of dust from steel industry as a reinforcing filler for epoxy composites. The polymer composition of "cold welding" that has been developed and studied includes epoxy dian oligomer, amine hardener and the filler – finely dispersed waste of metals. Polyethylene polyamine was used as a hardener in order to improve heat resistance and strength characteristics. Manganese triacetate was used in order to decrease the temperature and reduce the time of curing. The possibility was established to dispose of finely dispersed metal-containing waste from metallurgical production to be used a filler for epoxy composites of cold curing. It was revealed that the optimal content of dusts from foundries in the composite is at the level of 45–60 %. At this content, there is the highest impact resistance at the level of 40–50 MPa and a softening temperature in the range of 170–190 °С. It was established that at an increase in the amount of a filler from 40 % to 70 %, the cross-linking degree increases by 88 % to 98 %, respectively. However, at the content of the filler less than 45 % or exceeding 60 %, the impact resistance of the resulting composites decreases. At the content of a filler in the composite less than 45 %, the cause of low values of impact resistance and softening temperature could be the low cross-linking degree, less than 90 %. A decrease in these properties of composites at the content of the filler exceeding 60 % could be associated with the formation of a heterogeneous structure of filler. In the compositions with the highest performance characteristics, there is an optimized content of the filler and catalyst. Using a hardener and a curing catalyst in quantities of 3–3.5 and 1.5–2 %, respectively, makes it possible to shorten curing time by up to 2 hours. In general, the resulting epoxy composites are superior in their performance to known cold-curing analogs. The dependences of impact resistance, softening temperature, and cross-linking degree on the content of waste in the composite were derived, which make it possible to calculate the optimal formulation for composites depending on the required properties. Стаття присвячена проблемi утилiзацiї пилу металургiйної промисловостi як армуючого наповнювача епоксидних композитiв. Розроблена i дослiджена полiмерна композицiя "холодної зварки", що включає епоксидний дiановий олiгомер, амiнний затверджувач i наповнювач – дрiбнодисперснi вiдходи металiв. З метою пiдвищення теплостiйкостi i мiцнiстних характеристик в якостi затверджувача використовувався полiетиленполамiн. Для зниження температури i скорочення часу затвердiння в якостi прискорювача використовувався триацетат марганцю. Встановлена можливiсть утилiзацiї дрiбнодисперсних металовмiсних вiдходiв металургiйних виробництв в якостi наповнювача епоксидних композитiв холодного затвердiння. Виявлено, що оптимальний вмiст пилу ливарних виробництв в композитi знаходиться на рiвнi 45–60 %. При цьому вмiстi спостерiгається найвища ударна мiцнiсть на рiвнi 40–50 МПа i температура розм'якшення в iнтервалi 170–190 oС. Встановлено, що iз збiльшенням кiлькостi наповнювача вiд 40 % до 70 % ступiнь зшивання зростає вiд 88 % до 98 % вiдповiдно. Проте, при вмiстi наповнювача менше 45 % або бiльше 60 % знижується ударна мiцнiсть одержаних композитiв. Застосування затверджувача i прискорювача затвердiння в кiлькостях 3–3,5 i 1,5–2 % вiдповiдно дозволяє знизити час затвердiння до 2 годин. При вмiстi наповнювача в композитi менше 45 % причиною низьких значень ударної мiцностi i температури розм'якшення може бути низький ступiнь зшивання менше 90 %. Зниження вказаних властивостей композитiв при вмiстi наповнювача бiльше 60 % може бути пов'язано з утворенням неоднорiдної структури наповнювача. У композицiях з найвищими експлуатацiйними характеристиками спостерiгається оптимiзований вмiст наповнювача i прискорювача. В цiлому, одержанi епоксиднi композити за своїми експлуатацiйними характеристиками перевершують вiдомi аналоги холодного затвердiння. Встановленi залежностi ударної мiцностi, температури розм'якшення i ступеня зшивання вiд вмiсту вiдходiв в композитi, що дозволяють розраховувати оптимальний склад композитiв залежно вiд необхiдних властивостей.

In order to analyze the making arc characteristics of AgSnO2 contact, experiments were carried out with a self-developed experimental equipment. It was found that contact resistance had no obvious change with the increase of the number of experiments.In the later stage of the experiment, the contact bounces occurred during the contact closing process, which not only prolonged the making arc duration, but also increased making arc energy. When the contact was eroded to a certain extent by arc, making welding occurs.

Tensile and creep properties of dissimilar cold weld joints (Al (metal)–Cu50Zr50 (metallic glass)) are investigated using molecular dynamics simulations. Embedded atom method potential is used to m...

—A short-cut method of synthesis of a hard-magnetic material made of a spherical powder of the 25Cr–15Co–Al–Nb alloy obtained by spraying a melt with a stream of gas was proposed. It was established experimentally that uniaxial pressing of the powder in the initial state did not allow obtaining compacts without defects despite of the split die and pressing pressure up to 600 MPa. Application of powder annealing in hydrogen at 800°C decreases the hardness of the material particles. However, when compacting, the similar separation of compacts is observed as with the original powder. The use of a plasticizer gives a positive effect for improved compactibility, but it reduces the values of magnetic hysteresis characteristics. It is shown that the mechanical activation of spherical powder in a planetary mill allows obtaining the high-quality compacts and sintered specimens with high values of magnetic characteristics. The changes in the morphology of the powder particles during processing are revealed. Enlargement of powders due to cold welding is observed; the shape of particles changes dramatically as compared to the original powder. The particles size spread is substantially smaller in comparison with the original spheres; a heteraxial character is observed. Application of balls of larger diameter for grinding leads to better results. The magnetic hysteresis characteristics of hard-magnetic material synthesized from an alloy powder mechanically activated for 80 min are at a high level which ensures its technical application: residual induction Br = 1.18 T; coercive force НсВ = 43.1 kA/m; maximum magnetic product (ВН)max = 31.8 kJ/m3.

Cu–(20 wt %)Cr alloys with a layered structure are synthesized by liquid phase impregnation of chromium powder with copper melt. In synthesizing the alloys, the corresponding composites are subjected to pre-crystallization vibrational treatment. The layers of composites are enriched in chromium to different extents (from ~2 to 90 vol %). The layer composition and structure are shown to depend on the temperature and duration of vibrational treatment, as well as on the degree of pre-synthesis compaction of chromium powder. We study the phase composition of prepared alloys, the element composition of phases, and their microhardness. Our experiments show for the first time the formation of Cr core–(Cr + Cu) shell structures on the basis of chromium particles. These structures have a gradient distribution of the elements in the shell and form at the initial stages of interaction between Cu and Cr. At advanced stages of interaction, chromium particles are permeated with copper completely. In electron microscopy images in backscattered electrons, these formations appear as being greatly blurred and shapeless. In this way, precursors to crystallization of chromium dendrites are formed. The dendrite crystallization takes place in upper layers of the melt provided copper is present at the necessary and sufficient concentration (or at considerable superheating). The morphology of dendrites in which crystallization from precursors was incomplete is studied. The contact area of α-Cu is anticipated to be greatly reduced by the precursors that spread in the copper matrix during arcing. At the same time, contact welding will be considerably reduced, compared to similar composites with purely copper matrices (e.g., Cu–W).

Algorithms for current stabilization in the control of contact welding are considered. The proposed method for specifying and maintaining the welding current permits correction of the thyristor firing angle by means of an approximate formula taking account of the measured current-pulse parameters in phase regulation. The proposed method simplifies the equipment and increases the efficiency of regulation.

The effect of milling time on the microstructural evolution and magnetic properties of Ti50Fe50 alloys prepared by mechanical alloying were investigated. The results showed that the powder size was decreased sharply and then stabilized. Correspondingly, the milled powders experienced a transition from the lamellar shape to the spherical shape due to severe plastic deformation as well as the competition of cold welding and fracturing when the milling time was increased. Compared with the detailed composition primary powder (composed of Ti and α-Fe phases), the nanocrystalline Ti and α-Fe phase gradually disappeared and the amorphous phase were formed in the Ti50Fe50 alloys after milling for 40 h. When the milling time was increased to 60–90 h, the nanocrystalline disappeared and the complete amorphization of the milled Ti50Fe50 alloys occurred. However, a small amount of the nanocrystalline TiFe was formed except for a large of amorphous phase in Ti50Fe50 alloys for 100 h. Meanwhile, the formation of paramagnetic amorphous/nanocrystalline Ti and TiFe phase resulted in the saturation magnetization and coercive of the milled Ti50Fe50 alloys were decreased. Therefore, they exhibited excellent soft magnetic (0–90 h) and paramagnetic properties (100 h). Keywords: Mechanical alloying, Amorphous, Nanocrystalline, Microstructure, Magnetism

The increased diversity of microstructure of nanoporous materials can be expected to greatly expand their functional application in more industries. By incorporating nanoporous metals into cold-welding technology, we report an approach to directly forming the nanoporous materials with various microstructure inside. Nanoporous gold (Au) with ideal bi-continuous nanoporous structures was modeled using spinodal decomposition. Understanding the mechanical properties is the primary step to improve the reliability on the operational performance of nanoporous structures. After the process of cold-welding manufacture, the well-interconnected nanoporous Au was successfully fabricated and the mechanical properties of cold-welded structures were studied. Molecular dynamic simulations on samples with ligament diameter ranging from 3.264 to 6.528 nm and relative density ranging from 0.30 to 0.45 were also carried out to study how these factors affect the assembly process. These results are believed to facilitate the bottom-up nanofabrication and nanoassembly of composite structures for better mechanical performance.

The article considers and substantiates the method of calculating metal panels with tubular channels, as new heat exchangers made of thin steel sheets, which used in thermal equipment at catering establishments. Today, the majorities of steam jackets of technological devices in the food industry arerepresentedby open slotted space and work under pressure, which leads to a thickening of the walls of heat exchangers, and therefore increases the specific quantity of metal. Plate-to-channel heat exchangers, unlike ordinary shirts, are made of thin metal sheets. Panel channel heat exchangers are a structure, which composed of two metal sheets, that are interconnected by contact welding. Heating steam channels are formed between the sheets. The design of sheet-channel heat exchangers can significantly reduce the wall thickness, and thus reduce the metal consumption and reduce the thermal inertia of the equipment. This article describes methods that allow calculating the area of steam channels and obtaining the optimal dimensions of inter-channel sections for sheet-channel heat exchangers of thermal devices of catering enterprises. A method for calculating the heat transfer coefficient based on an experimental study is also given. In order to reduce the thickness of the walls of the panels, it is proposed to maximize the area of inter-channel sections without reducing the heat flux, which the panel transmits to the heated medium. This problem is solved with the help of a calculation method based on the use of the coefficient of efficiency of the thermal edge.

The main advantages of the М2а-Magnum modular system pair are the presence of a group of metals metal with wear of the large head, which is the maximum value that makes it possible to increase the range of motion in the hip joint by more than 160 with virtually no risk of dislocation [1]. This allows you to freely conduct active work and sports. However, the system is not without drawbacks. First of all, this is the unrevealed danger of damage to metal ions in the blood, as well as the problem of the development of a pseudotumor lymphoid reaction [2,3], leading to extensive osteolysis, an increased risk of periprosthetic fractures, and, accordingly, an increase in the frequency of endoprosthesis destabilization. Currently, the use of constructions is practically suspended, but there are more than 1 million patients in the world [4] with implanted large "metals - metal pairs". In revision surgery with M2a-Magnum implants, the main problem is often the inability to remove the femoral head adapter component from the neck taper. fretting corrosion is observed, leading to the effect of cold welding. The latter is typical for the connection of titanium surfaces (adapter of the head module and the neck of the femoral component). It turns out that it should be noted that the M2a-38 system does not have a titanium adapter made of a cobalt-chromium alloy and devoid of this problem [4].

In-situ synthesis of Al2O3/TiAl composite was carried out by mechanical milling of the pre-alloy Ti-45Al-7Nb-0.3W and TiO2 powder mixture and subsequent sintering by spark plasma sintering (SPS) technique. The mixed powders experienced the initial destructive breakage stage, cold welding package stage and breaking up of boulders stage during mechanical milling. The particle size obviously declined with the mechanical milling time increasing. The number-average diameter (D(1,0)) of as-milled powders rapidly reduced from 75.0 μm to about 15.5 μm, and its distribution uniformity (U) decreased to 0.55 when milling time increased to 20 h. Nano Al2O3 particles had been formed during milling. The as-SPSed compacts were mainly composed of γ-TiAl phases, α2-Ti3Al phases and nano-Al2O3 particles that tended to disperse both on the grain boundaries and inside the lamellar microstructure of the matrix. The contents of A12O3 increased from 4.3% to 8.9 vol% as the milling time increased from 10 to 20 h. The increasing concentration led to the increase in Vickers hardness of Al2O3/TiAl composites, and a maximum value of 6.2 GPa was achieved. A corrected mixture rule was constructed which can predict the hardness of the composites accurately. The ultimate compression strength (UCS) increased firstly and then decreased with prolonging milling time. The highest value of 1848 MPa was obtained when the mixed powders milled for 15 h, i.e., the fraction of Al2O3 in the TiAl matrix was 7.6 vol%.

Magnesium diboride, MgB2, is known to be an important high-temperature superconductor material. High-energy ball milling with subsequent low-temperature sintering remains an attractive solid-state method for its synthesis. One main optimization parameter of this method is to ensure a balance between cold welding and fracturing at the milling stages. Therefore, in many cases, the use of a process control agent at the milling stage is considered to be the preferred solution in the prevention of particle size enlargement. The aim of this paper is to determine the effect of dry and toluene-assisted milling on the magnetic and surface topology properties of obtained MgB2. The calculated critical current density of 2.89 × 105 A/cm2 at 10 K 0.3 T for a toluene-assisted sample, compared with the 2.37 × 105 A/cm2 for a dry-milled sample as well as the relatively higher mean surface roughness, clearly indicated a notable positive contribution of surfactant use on the true alloying of MgB2 by mechanical activation.

The purpose of the proposed course is to enhance students’ knowledge, engineering skills and understanding in the field of electrical contacts power engineering – the currents of contact welding. The main goal for students is to acquire brief skills concerning measurements of certain parameters using static layout: currents that cause contact welding, clamping force of contacts joints and breaking force. Moreover, students are encouraged to obtain soft skills like confidence in the mentioned field and creativity. Student work during the exercise is evaluated on the basis of report from laboratory work and test. Essential aspect is safety training while working with HV and MV switchgears – that is another obligatory feature which participants will obtain from this course. Course results were evaluated as significant on the basis of concluded statistical analysis and comparison to previous formula employed during the classes.

The paper describes an advanced discrete-element based mechanical model, which allows modelling contact interaction of ductile materials with taking into account fracture and surface adhesion by the cold welding mechanism. The model describes these competitive processes from a unified standpoint and uses plastic work of deformation as a criterion of both local fracture and chemical bonding of surfaces in contact spots. Using this model, we carried out a preliminary study of the formation of wear particles and wedges during the friction of rough metal surfaces and the influence of the type of forming third body (interfacial) elements on the dynamics of the friction coefficient. The qualitative difference of friction dynamics in the areas of the contact zone characterized by different degrees of mechanical confinement is shown.

A combination of atomistic simulations and vacuum tribometry allows atomic-scale insights into the chemical structure of superlubricious hydrogenated diamond-like carbon (a-C:H) interfaces in vacuum. Quantum molecular dynamics shearing simulations provide a structure-property map of the friction regimes that characterize the dry sliding of a-C:H. Shear stresses and structural properties at the sliding interfaces are crucially determined by the hydrogen content CH in the shear zone of the a-C:H coating. Extremely small CH&nbsp, (below 3 at.%) cause cold welding, mechanical mixing and high friction. At intermediate CH (ranging approximately from 3 to 20 at.%), cold welding in combination with mechanical mixing remains the dominant sliding mode, but some a-C:H samples undergo aromatization, resulting in a superlubricious sliding interface. A further increase in CH (above 20 at.%) prevents cold welding completely and changes the superlubricity mechanism from aromatic to hydrogen passivation. The hydrogen-passivated surfaces are composed of short hydrocarbon chains hinting at a tribo-induced oligomerization reaction. In the absence of cold welding, friction strongly correlates with nanoscale roughness, measured by the overlap of colliding protrusions at the sliding interface. Finally, the atomistic friction map is related to reciprocating friction experiments in ultrahigh vacuum. Accompanying X-ray photoelectron and Auger electron spectroscopy (XPS, XAES) analyses elucidate structural changes during vacuum sliding of a hydrogen-rich a-C:H with 36 at.% hydrogen. Initially, the a-C:H is covered by a nanometer-thick hydrogen-depleted surface layer. After a short running-in phase that results in hydrogen accumulation, superlubricity is established. XPS and XAES indicate a non-aromatic 1–2-nm-thick surface layer with polyethylene-like composition in agreement with our simulations.