Frontier Materials & Technologies

The application of a circuit with a common pulse current source for surfacing with two electrode wires increases the energy efficiency of the arc process and the welding arc technological properties, but requires a more detailed study of the influence of the mode parameters on its stability. In this regard, this paper focuses on studying the dynamics of formation and transfer of metal drops under various modes of pulsed power supply of the welding arc. Using high-speed video filming of the welding arc and synchronized recording of current and voltage signals, a mode was set (average current value was 250 A, maximum current value in pulse was 600 A, arc voltage was ~30 V), which ensured a stable process of transfer of electrode metal by a drop common to two wires without short circuits. It was found that the common drop under the action of electrodynamic forces acquires centripetal acceleration, which contributes to its directed transfer to the weld pool and allows minimizing the amount of spatter on the surface of the base metal. Using mathematical modeling, the nature of the interaction of welding arcs on two wires was confirmed and it was found that even at the stage of the current pulse “hot” phase (600 A, t=0.8 s), the arc pressure on the plate surface is less than when welding with one wire at direct current. The identified effect is associated with a change in the direction of the plasma flow to perpendicular to the wire axis due to an increase in the electrodynamic attractive force of the magnetic fields around the two wire conductors. Together with a decrease in the arc temperature and pressure on the plate surface during the “heat input control” phase of the current pulse (180 A, t=1.4 s), this should help to reduce the heat input and the depth of penetration of the base metal, and, consequently, reduce the degree of dilution of the deposited alloy by the substrate metal. The latter is especially relevant when solving problems of creating a technology for surfacing of relatively thin layers of corrosion-resistant alloys, in particular, on the surface of petrochemical equipment products.

The research status on such functional properties, as bending capability, wrapping capability and ductility of conductive Al–Fe and Al–Fe–Cu alloys wires is uncertain. Bending and wrapping capability is determined by the industrial standards while no attempts were made to study the relation between them and ductility of the Al alloys wires, paying even less attention to the ultrafine-grained Al-based wires, produced by electromagnetic casting and equal-channel angular pressing. In this study alloys with two different chemical compositions (Al–0.5 wt. % Fe and Al–0.5 wt. % Fe–0.3 wt. % Cu) and two different casting methods (casting into electromagnetic mold and continuous casting and rolling) were used. Part of the wires for the study was prepared by cold drawing (CD), the other part – by the combination of the equal-channel angular pressing by the Conform scheme and cold drawing (ECAP-C+CD) to obtain coarse grained (CG) and ultrafine grained (UFG) structures, respectively. Annealing at 230 °C for 1 h was carried out to evaluate the thermal stability of the wires. It was shown that the correlation between ductility (elongation to failure), number of wraps and number of bends (both before the first crack and before complete failure of the specimen) may differ depending on the deformation value, deformation scheme, and amount of alloying elements of the alloy wire, as well as ability to form solid solutions.

The wide application of amorphous alloys is complicated by a narrow range of their thermal stability, embrittlement at elevated temperatures, difficult machinability, and low tensile plasticity. Ultrasonic treatment is an innovative method for solving these problems. Integration of ultrasonic technology into the technological chain can contribute to the improvement of the operational property of amorphous alloys, the manufacture of parts from them at different scale levels, and high-quality joining with other materials. The effect of ultrasonic vibrations on structural transformations and mechanical behaviour of amorphous alloys is not completely understood. The lack of an integrated scientific basis for the physical processes and accompanying effects in amorphous alloys under ultrasonic excitation prevents the development of the corresponding technology and optimization of its modes. Over the past decade, researchers have proposed various methods of ultrasonic treatment of amorphous alloys to improve their formability, achieve a balance of plasticity and strength, and consolidate with each other and with metals. In addition, certain ideas have been developed about their structure rejuvenation and the possibilities of transformation them to a partially nanocrystalline state under the action of ultrasound. To summarise these developments, the systematic discussion on features, parameters, and modes of ultrasonic treatment applied to ribbon and bulk amorphous alloys to improve their structure-sensitive properties are provided in this review. On this basis, the limitations of current study are discussed. The most promising applications of ultrasonic technologies for rapidly melt-quenched alloys in the near future include: their additive manufacturing, creation of hybrid composites by ultrasonic welding, ultrasonic forming for manufacturing products of complex shapes and geometries, complex multi-stage processing to obtain a unique combination of properties (e.g., melt quenching → laser irradiation → ultrasonic stimulation). This review enhances the existing knowledge on ultrasonic control of the properties and structure of amorphous alloys and facilitates a fast references on this topic for researchers.

This paper deals with the study of the influence of nanosized diamonds produced by the cavitational synthesis method on the tribological properties of a commercial water-oil-based cooling lubricant. The study is aimed at assessing the prospects for application of this type of nanodiamonds as an antifriction and antiwear additive. Tribological tests were carried out using the “indenter on a disk” friction scheme at a constant load and sliding speed. High-speed P18 steel for the indenter and 30HGSA steel for the rotating counterbody (disk) were used as friction couple materials. The studies were carried out for the base lubricant and two variants of its composition modifications using colloidal dispersion (distilled water with dispersed nanodiamonds) with a final additive concentration of 0.5 and 2.5 %. It was experimentally found that both variants of modification of the base water-oil emulsion resulted in increase of the bearing capacity of lubricating layers, decreasing the total linear wear of friction couple elements by 1.8–2.4 times. The presence of nanodiamonds in the composition enhanced as well the shielding effect of the cutting coolant. A decrease in visible damage to friction surfaces was recorded using optical microscopy. Analysis of profile diagrams of worn areas in the transverse direction showed a decrease in the size of a groove on the counterbody against the background of a decrease in roughness from Ra=0.49 μm in the basic variant to Ra=0.29–0.34 μm. Evaluation of the loss in counterbody weight for nanodiamond concentrations of 0.5 and 2.5 % showed a decrease in their value by 1.3 and 1.9 times, respectively; for the indenter, the decrease in this parameter was 1.2 and 1.5 times. Thus, the use of cavitational synthesis nanodiamonds as an additive may become a promising direction for increasing the antiwear properties of water-oil-based cooling lubricants.