Key Engineering Materials Vol. 887

Abstract: The melting parameters (melting point, specific heat of fusion) of copper samples with different volume structure (fine-grained, submicrocrystalline) and dispersivity (fine powder) were explored using differential thermal analysis. It was found that change in the metal structure from bulk coarse-grained to submicrocrystalline, and to submicron powders led to depression of melting point by ~18 °C and of specific heat of fusion by ~45 % relative to the standard values. It was shown that the high-energy impact on the starting coarse-grained metal used to obtain the samples with modified structure and dispersivity (severe plastic deformation, electric explosion of thin wires) caused changes in the composition of the material. An explanation for the observed influence of structure and dispersion factors on the melting parameters has been proposed on the basis of X-ray diffraction data, electron microscopy, and model calculations.

Abstract: The oxidation processes for compact and powdery samples of titanium, copper, and molybdenum with different volume structure and dispersivity were studied using thermal analysis, electron microscopy, and X-ray diffraction. It is established that producing of metals with a modified structure under conditions of high-energy impact (severe plastic deformation, electric explosion of a thin wire) in accordance with intermediate annealing leads to an increase in the content of oxygen in the form of solid solutions and oxides; the oxide component’s share, form and localization within the material depend on physicochemical properties of both metal and oxide . It is shown that the structural-phase transformations of the oxide component during heating of fine-grained metals and powders have a significant effect on the parameters of the oxidation process of such materials. The thermally induced effects in the oxygen-containing components might play a critical role for the structure stability during long-term use of such materials under cyclic thermomechanical impacts.

Abstract: The article presents the developed method of channel angular pressing of the annular billets and gives the examples of hardening annular aluminum billet by channel angular pressing. The channel angular pressing is shown to result in aluminum hardening by 1.4 to 1.5 times. This increases the diameter of the annular billet.

Abstract: X-ray spectroscopic microanalysis was used to determine the concentration of titanium on the surface of the wear spot of a silicon carbide crystal during micro-scratching and the concentration of silicon on the treated surface after grinding by a wheel of silicon carbide. The wear resistance and grinding coefficient of titanium alloys under micro-scratching with single crystals and grinding with wheels made of corundum, silicon carbide, cubic boron nitride and diamond were determined. The morphology of the treated surface and the regularities of changes in the indicators of the grinding process of titanium alloys with circles of various characteristics were studied. The features of the process of grinding titanium alloys using various lubricants and coolants are shown. The influence of the characteristics of the abrasive tool and grinding modes on low-cycle fatigue on the operation of flat and round grinding of samples made of titanium alloys VT9 and VT22 was studied. The influence of abrasive material, grinding speed, feed and sparkout during finishing on low-cycle fatigue was analyzed. Based on the research, recommendations were given for choosing a rational characteristic of the abrasive tool and processing modes.

Abstract: The paper presents the results of studying the microstructure of samples obtained with laser processing of AK4-1 aluminum alloy powder. It has been found that increasing the initial temperature of the substrate to 100...150 °C allows to use this powder material in directed energy deposition (DED) additive process to create stiffening elements on the surface of thin-walled aluminum parts. When the specified temperature condition is satisfied, the crystallization rate decreases, allowing to obtain samples with almost no internal cracks. The results of comparing the microstructure and the microhardness of commercial AK4-1 wrought alloy and the samples obtained with DED process are presented. The structure of the samples prepared with laser cladding is more disperse in comparison with wrought alloy. The microhardness of the sample prepared at pre-heated substrate is comparable with wrought alloy. The conceptual architecture of the decision support software for laser powder cladding processes is presented. Its information and software components are briefly described.

Abstract: Analytical and experimental studies have been carried out, which made it possible to propose new technological modes of combined rolling-extruding for the production of rods from alloy 01417 for the further drawing of wire for electrical purposes. The force parameters on the rolls and the die are calculated when extruding a rod with a diameter of 5 mm on the laboratory unit CRE-200 and the industrial unit CRE-400. The obtained values of the forces on the rolls and the die do not exceed the permissible values of the power load of the units. Therefore the selected parameters are suitable for conducting experiments on the manufacture of prototypes of rods. To verify the conclusions made, experimental studies were carried out on the CRE-200 unit at a temperature of 320 oC and a drawing coefficient μ = 12.1. The results of experimental studies in comparison with the calculated data showed that the deviation of the calculated data does not exceed 15%.

Abstract: Additive manufacturing is a new approach to solving the problems of creating high-performance instrument components. This article is devoted to the solution of the narrowly directed problem of surfacing metal powder 321L using the LENS method on the solenoid valve core. The core is made of electrical steel, in which a complex groove is machined. The difficulty of this work was to accurately perform the geometry of the melt layer that is not standard for this method. As a result, the product was obtained according to a completely new approach to its design, which subsequently gave increased operational characteristics of the final product. The article presents the problems that can be encountered when performing complex crevice surfacing on a complex groove. The structure of the deposited layer is considered, defects characteristic of this method in the form of interlayer pores, unalloyed powder particles are identified and described. The LENS process control modes are presented in order to reduce defects and improve the development of surfacing geometry.

Abstract: The present study describes the impact of various protective process agents on chip forming processes. The research was conducted on NiCr20TiAl and 34NiCrMoV14-5 nickel-chromium alloys. New lubricant-cooling process agents with carbon nanopowder additives are studied. The optimal composition of the nanopowder additive and its effect during alloy cutting is examined. Experiments reveal the dependence of shrinkage ratio on cutting speed and various protective process agents. The values of H50 microhardness are also defined when cutting these alloys using protective process agents. Experimental studies found the positive effect of developed agents with nanopowder additives on the processes of NiCr20TiAl and 34NiCrMoV14-5 alloys chip formation.

Abstract: The kinetic features of electrodeposition process of a wear-and corrosion-resistant composite electrochemical nickel-cobalt-aluminum oxide coating were investigated. Potentiodynamic studies showed that in the process of the CEC formation at the cathode the electrode polarization decreases, and the value of the limiting current density increases by more than twice. Consequently, the rate of the CEC electrodeposition process increases and the range of operating current densities expand in comparison with the control coating with the Ni-Co alloy. Temperature-kinetic, chronopotentiometric methods, values of the temperature coefficient of the reaction rate and the diffusion coefficients of nickel ions were used to determine the mechanism of CEC electrodeposition. As the result of determining the nature of limiting stage of the electrodeposition process of CEC nickel-cobalt-aluminum oxide, it was found that it is caused by such two coupled processes proceeding at comparable rates, as electrophoretic transfer of electroactive particles to the cathode and overgrowing of dispersed particles adsorbed on the cathode surface with electrodeposited metals.

Abstract: Plasma electrolytic oxidation (PEO) method allows obtaining multifunctional ceramic-like coatings with unique properties. This article examines the relevant problem of the electrolyte effect on the chemical composition of PEO coating. The corrosion resistance of titanium alloy various PEO coatings in corrosive liquids has been studied: 1N sodium hydroxide solution, concentrated sulphuric acid (80%), 1N sulphuric acid solution, concentrated hydrochloric acid (30%), 1N hydrochloric acid solution. Comparative analysis of the VT-1 titanium alloy chemical resistance showed that the most resistant to the effects of corrosive substances were samples with PEO coating formed in a hydrophosphate electrolyte Na₂HPO₄.