PSI - Issue 59

Olha Maksymiv et al. / Procedia Structural Integrity 59 (2024) 378–384 Olha Maksymiv et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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The concentration of hydrogen and oxygen in the surface strengthened layer with NCS after MPT in air is the lowest (Fig. 6a, c), and the concentration of carbon is sufficiently increased and is similar to that in the initial state (Fig. 6b). The concentration of hydrogen in the surface metal layer after MPT in the aqueous TF is higher than that after the treatment in the industrial oil (Nykyforchyn et al. (2015b)), which accelerates the failure of the NCS layer during contact durability tests. Gorskiy (1989) and Tychonovych (2015) showed that the saturation of the border zones by the atoms of carbon is due to the dissolution of the fine-dispersed carbide phase during deformation. During the attrition in an aqueous environment, deformation of the surface layers is accompanied by the saturation of the surface structural fragments by atoms of carbon and oxygen penetrating into the metal from an environment due to mechanical-thermal decomposition of water molecules in the friction contact zone. It resulted in the formation of metastable atomic clusters Fe – O – C as described by Gorskiy (1989) and Tychonovych (2015), being the octahedral pore of the bcc-Fe in the structure. The oxygen atom is in the centre of the octahedral pore with two iron atoms replaced by carbon. These clusters and iron atoms of the lattice separate the regions with lowered electron density arising due to the reduction of the electron density s - and p -electrons and the growth of three-dimensional localization of valence d -electrons on iron atoms surrounded by oxygen and carbon atoms. It limits the contribution of the valence electrons in bounding formation between iron atoms of the lattice and atoms of clusters, and relatively easy their destruction during shifting the structural components along the boundaries created by clusters. The concentrations of hydrogen (Fig. 6a) and oxygen (Fig. 6c) in the surface metal layer after the contact fatigue test in an aqueous environment are slightly higher than that in oil for all types of used TF for the MPT. The concentration of carbon in the surface metal layer after testing in oil is somewhat higher than that after testing in tap water. It should be emphasized that saturation of the surface layers by components of TF occurs during MPT and their redistribution during contact fatigue tests due to high-pressure action in the frictional zone. However, TF used during MPT has a more significant effect and the most effective is treatment in air used as a reference environment. In this case, the lowest concentrations of oxygen and hydrogen are in the surface-strengthened metal layer, which negatively influences the serviceability of components with the surface NCS. However, MPT in air reduces the strengthening tool's durability and worsens the roughness of the strengthened surface, and it is, therefore, technologically unsuitable. The best option to improve the working capacity of components working under high loads is MPT in oil TF. The negative impact of water as a working environment during drilling should be minimized by sealing parts of the drilling bit, namely legs and milling cutters in the position of their joint. 4. Conclusions The contact fatigue durability of the alloy structural steel with surface NCS was improved in comparison with that of the steel after cementation with further quenching and low tempering. It is mainly influenced by the type of technological fluid used during MPT and the test environment; it is significantly higher in the oil test environment compared with tap water. The elements of technological and test environments (hydrogen, carbon, oxygen), which saturate surface layers during MPT and contact durability tests, influence on contact fatigue resistance of the steel, as well. References Babak, V.P., Fialko, N.M., Shchepetov, V.V., Kharchenko, S.D., Hladkyi, Ya.M., Bys, S.S., 2023. Self-lubricating glass composite nanocoatings. Materials Science 59(1), 33 – 39. Berezhnitskaya, M., Paustovskii, A., Kirilenko, S., Gubin, Y., 2003. Determination of residual stresses in electric-spark deposited coatings. Strength of Materials 35(6), 633 – 637. Beynon, J., Garnham, J., Sawley, K., 1996. Rolling contact fatigue of three pearlitic rail steels. Wear 192(1 – 2), 94 – 111. Glikman, E., Bruver, R., 1972. Equilibrium segregation on grain boundaries and intercrystalline cold brittleness of solid solutions. Metallofizika, 43, 42 – 63. Gorskiy, V., 1989. Formation of oxygen-alloyed melts Me – Me – O in the contact zone of metals in friction. TrenieiIznos 10(3), 452 – 460. Gurey, V., Maruschak, P., Hurey, I., Dzyura, V., Hurey, T., Wojtowicz, W., 2023. Dynamic analysis of the thermo-deformation treatment process of flat surfaces of machine parts. Journal of Manufacturing and Materials Processing 7(3), 101. Hutsaylyuk, V., Student, M., Posuvailo, V., Student, O., Hvozdets'kyi, V., Zakiev, V., 2021. The role of hydrogen in the formation of oxide ceramic layers on aluminum alloys during their plasma-electrolytic oxidation. Journal of Materials Research and Technology 14, 1682 – 1696.