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Solid Materials: Joining Processes
Published in Leo Alting, Geoffrey Boothroyd, Manufacturing Engineering Processes, 2020
In cold welding or cold pressure welding, coalescence is created by pressure alone. The pressure causes the workpiece to deform plastically, providing the necessary intimacy between the virgin metal structures. To obtain reasonably high strength welds, the surfaces must be cleaned, usually mechanically by wire brushing. The remaining oxide layers will be dispersed in the welding zone as islands and will decrease the strength of the weld. To obtain good welds, the surface expansion caused by plastic deformation must be in the range of 50– 90%. The cold-welding process is generally used to join relatively small parts (wires, rods, sheets, rings, etc.) as butt or lap (inclusive seam) welds. Materials most frequently cold-welded are aluminum, copper, lead, nickel, and zinc. A common example is the cold-welded electrical connection.
Sliding Bearings and Lubrication Mechanics
Published in Maurice L. Adams, Bearings, 2018
In dry friction sliding bearings, adhesive friction is the most probable of all unlubricated surface-to-surface rubbing phenomena. But even with unlubricated surfaces, naturally formed oxides become a dry lubricant. Significant adhesive friction is also possible to occur between boundary-lubricated rubbing surfaces, but at a reduced rate depending on the rubbing materials' strength properties and the boundary lubrication capability of the intervening lubricant. As well-known and universally used by engineers, the classical Coulomb friction coefficient is usually approximated as a “constant” independent of the sliding speed and independent of the normal force magnitude that pushes together the two bodies in relative sliding motion. Archard (1953) hypothesized adhesive friction and wear as illustrated in Figure 1.2, by postulating what might occur at the microscopic level between two surface asperities in rubbing contact. The two contacting asperities are postulated to momentarily form an adhesive bond called cold welding. In one possibility, this bond is simply broken as the two surface asperities each go unaltered their own way as illustrated. In the other possibility shown, the adhesive bond between the two asperities overcomes the yield strength of the weaker of the two asperities, creating a wear particle.
Operating Failure Contributors
Published in Maurice L. Adams, Power Plant Centrifugal Pumps, 2017
Adhesive wear is most probable in all unlubricated surface-to-surface rubbing contacts. But even in unlubricated surfaces, naturally formed oxides become a dry lubricant. Significant adhesive wear can also occur between lubricated rubbing surfaces, but at a reduced rate depending upon the rubbing materials’ strength properties and the boundary lubrication capability of the intervening lubricant. The classical Coulomb friction coefficient is often approximated as a “constant” independent of the normal force magnitude that pushes together the two bodies in relative sliding motion. Figure 3.16 hypothesizes what can occur at the microscopic level between two surface asperities in rubbing contact. Two contacting asperities are postulated to momentarily form an adhesive bond called cold welding. In one possibility, this bond is simply broken as the two surface asperities each go unaltered their own way as illustrated. In the other possibility, the adhesive bond between the two asperities overcomes the yield strength of the weaker of the two asperities, creating a wear particle as also illustrated.
Magnetic field edge-effect affecting joint macro-morphology in sheet electromagnetic pulse welding
Published in Materials and Manufacturing Processes, 2020
Chengxiang Li, Yan Zhou, Xin Shi, Zhigang Liao, Jian Du, Ting Shen, Chenguo Yao
In recent years, it has become a trend to adopt intelligent, efficient and environmentally friendly technologies in manufacturing process. As an advanced, clean, and smart material processing technology, electromagnetic pulse welding (EMPW) technology has attracted more and more attention.[1,2] It applies pulse power technology to material processing and production. The Lorentz force is induced in metal workpieces through strong pulse magetic field, which accelerates the workpiece and achieves metallurgical combination at a high-speed with the welded metal within few microseconds.[3] This technology makes the materials to be welded at the room temperature without heat affected zone (HAZ), so it is also called cold welding. During the welding process, the differences in material properties of different metals can be ignored, thus, it is considered as an ideal solution for welding the dissimilar metals and metal-composite materials, [4] which can be applied to the field of the multi-material mixing.[5-7] Thus, it presents a great application potential in aerospace, automobile industry, nuclear industry and power industry.[8-10]
ECAP process capability in producing a power transmission bimetallic rod
Published in Materials and Manufacturing Processes, 2018
M. Pourdavood, M. Sedighi, A. Asgari
The SEM images of bonding interface between steel core and Al before and after ECAP are shown in Fig. 10. According to the literature,[26] reducing the gap between steel and aluminum leads to increasing the number of cracks in the interface that creates a proper bonding properties. According to Fig. 10, after four passes ECAP, the gap between steel and Al has been reduced, significantly. After 4th pass, maximum value of this space has been reduced to less than 2 µm. Temperature and pressure are the dominant mechanisms for connecting the two metals, and this phenomenon is called cold welding.[27] Two metals are connected to each other when surface expansion due to the pressure has been increased in the interface of materials.[10,27] This bonding has been created between steel core and Al after four passes ECAP.
Progress in Developing Novel Double-Shell Metal Targets Via Magnetron Sputtering
Published in Fusion Science and Technology, 2018
H. Xu, H. Huang, J. Walker, C. Kong, N. G. Rice, M. P. Mauldin, J. D. Vocke, J. H. Bae, W. Sweet, F. H. Elsner, M. P. Farrell, Y. M. Wang, C. Alford, T. Cardenas, E. Loomis
Inner shells were constructed using the materials as listed in Table I which were found not to exhibit the cold-welding phenomenon discussed in Sec. II. W formed the basis for the high-Z inner shells but was combined with other nonsticking elements. It should be noted that all the nonsticking elements have reasonably low ductility. In general, higher-ductility metals, e.g., Al, Cu, and Au, were unusable unless alloyed due to this cold-welding phenomenon. It should be mentioned that this sticking issue is only a problem when fabricating spherical capsules but not for planar depositions.