Ukrainian Journal of Mechanical Engineering and Materials Science
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Item Prediction of tribological properties of structural steels using artificial neural networks(Видавництво Львівської політехніки, 2019-03-20) Uvarov, Viktor; Bespalov, Serhii; G. V. Kurdyumov Institute for Metal Physics of the NAS of Ukraine; Presidium of NAS of Ukraine; Technical Center of NAS of UkraineThe effect of quenching temperature on wear resistance of 40Kh steel after tempering has been investigated. It was found that compared to standard heat treatment, quenching from 1050 °С and high temperature tempering increase its tribological characteristics. The character of fracture of the contacting surfaces was studied. It was shown that in the specimens quenched from 860 °С and tempered, the fracture of the contact surface occurs by the mechanisms of smooth splitting and delamination with plastic deformation. Increasing the quenching temperature to 1050 °С along with high temperature tempering changes the character of the contact surface destruction. The areas with a distinctive microstructure appear on the surface exhibiting substantially higher wear resistance during friction as compared to the surrounding volume. The structural-geometrical parameters characterizing the roughness and bearing capacity of the contact interaction surface were analyzed. It was found that increasing the quenching temperature to 1050 °С allows to reduce the surface roughness and increase the bearing capacity. Using the methods of optical and transmission electron microscopy, the peculiarities of forming the microstructure of the investigated steel were studied, depending on the temperature conditions of the thermal treatment. It was shown that raising the quenching temperature to 1050 °С increases the austenitic grain size, enhances non-uniformity of carbon distribution, which leads to the formation of large needle-shaped crystals of lath martensite with microtwin boundaries inside. This, in turn, promotesthe formation at high tempering of non-uniformly distributed aggregates of coarse carbides at these microtwin boundaries. The aggregates form areas of microstructure with increased resistance to plastic deformation processes. That is, the morphology of the carbide phase is one of the main factors that determine the tribological characteristics of steel, namely roughness, structural-geometrical parameters and bearing capacity of the surface. The expediency of using artificial neural networks for prediction of tribological properties of structural steels was shown. According to the results of modeling the structural-geometrical parameters of the surface and the roughness characteristics, the bearing capacity of the 40Kh steel surface during friction was predicted.Item Structure and wear resistance of aluminium alloys coated with surface layer laser-modified by silicon carbide(Lviv Politechnic Publishing House, 2018-01-29) Student, Mykhaylo; Pokhmurska, Hanna; Zadorozhna, Khrystyna; Dzyubyk, Andrii; Khomych, Ivan; Karpenko Physico-Mechanical institute of the NAS of Ukraine; Lviv Polytechnic National UniversityModern approaches to ensuring the necessary characteristics of surface of a material with the aim to improve economic and technological characteristics of the structures are considered in this paper. It is shown that aluminium alloys gain wide application in industry. Nevertheless, surface characteristics of materials are insufficiently good for their use in structures which operate under abrasive wearing and boundary friction. The use of the method of surface modification by a concentrated light-beam of energy is of prospect. Analysis of literature data indicates that in the course of laser-modification of surface of an aluminium alloy it is possible to form a material whose operational characteristics are higher than those of the material in its initial state. However, herewith it is important to quantitively estimate properties of the obtained composite layer on the surface of the article as well as to estimate the distinction between the layer and the main metal. The microstructure of laser-modified composite layers of aluminium alloys which had been formed by means of direct blow-in of SiC powder into the melted by laser radiation zone of surface has been investigated. Laser reinforcement of surfaces of aluminium alloys by SiC particles causes pronounced inhomogeneity of structure of surface layers of alloys. It has been shown that preliminary heating of specimens in the course of their laser-treatment increases the depth of the modified layer over the whole zone of treatment and improves the uniformity of distribution of reinforcing SiC particles; however, because of turbulence in the melt there is observed some non-uniformity of distribution of SiC particles in the modified layer. It is found that in the interaction of Al melt with SiC particles there forms plates of Al4C3 carbide at the interface, these plates grow mainly co-axially to the orientations of SiC crystals in the direction to the melt. Besides, in the matrix there takes place partial dissolution of SiC with formation of needle-shaped Al4C3 carbides. During the modification of surfaces of these alloys, in the case of increased concentration of silicium in the melt there is also observed inclusion of pure silicium. Besides, there is also possible the diffusion of aluminium into thin near-surface layer of silicium carbide, the layer separates from SiC crystal (phenomenon of ply separation) when the concentration of aluminium reaches a value of 3–5 %. It is established that the abrasive wear resistance of the non-modified AD35 alloy, which is determined according to the method of rigid abrasive wheel, is by 30–45 % higher than that of B95 alloy. In this case, the deterioration (wear-and-tear) proceeds according to the following two mechanisms: (1) by cutting and (2) by adhesive grafting between the abrasive wheel and the aluminium alloy by tearing out alloy particles from the surface. Optimal regimes of laser reinforcement of surfaces of aluminium alloy by means of fine SiC particles have been determined in this paper; this enabled us to increase 40–70 times the wear resistance of aluminium alloys in comparison with non-modified alloys when they are subjected to friction by rigidly fixed abrasive particles. The same reinforcement almost two times increases the wear resistance in dry reversive friction, and it increases the wear resistance only by 10–25 % in wearing by loose abrasive particles.Item Regulation of the phase-structural composition and metastability of austenite by alloying elements and parameters of tempering for increase wear-resistance of Fe-Cr-Mn deposited steel(Lviv Politechnic Publishing House, 2018-01-29) Cheylyakh, Yan; SHEI "Pryazovskyi State Technical University"It is shown that under the influence of alloying (Cr, Mn, C, Si, Ti, N, V) during electric arc hardfacing with a flux cored wire, as well as technological tempering parameters at temperatures of 300–700 °C, the phase-structural composition of the cost-saving alloyed deposited steel (from 0 to 75 % quenching martensite and austenite), the degree of metastability of austenite are regulated. At optimal parameters of alloying and tempering, an increased wear resistance is achieved due to the development of the deformation induced martensite γ→α' transformation of austenite during the wear process, which causes the effect of self-strengthening during testing and operation. This is an important advantage of the developed metastable deposited steel before the deformation-stable metal.