Issues »  Volume 48, Issue 6

Stability of Physical and Mechanical Properties of Wear-Resistant Ultrafine-Grained Surface Friction Layers under Extreme Conditions of Thermal Effects during Operation of Sliding Bearings

V. V. Tykhonovych

G. V. Kurdyumov Institute for Metal Physics, N.A.S. of Ukraine, 36 Academician Vernadsky Blvd., UA-03142 Kyiv, Ukraine

Received: 19.05.2025; final version - 25.08.2025. Download: PDF

As established, the transition of the friction pair composed of steel 130Cr17 and steel 20Cr13 to a stationary operating mode with minimal wear and friction coefficient occurs due to the self-organization of the wear-resistant ultrafine-grained coatings on the contact surfaces of both solids. These coatings are formed from a qualitatively new ultradispersed and nanostructured material that can contain up to 25 at.% of oxygen and carbon. As shown, self-organizing wear-resistant coatings are composed of friction layers, each of which is the result of a separate act of layering a microvolume of metal on the working surfaces of the solids. Friction layers differ from the deformed original metal of steels in terms of their high hardness and elasticity. They prevent the formation of strong adhesive bonds between rubbing solids and facilitate the transition of the system to a stationary operating mode with a minimal coefficient of friction and wear. During operation, the material of the surface friction layers is subject to intense cyclic thermomechanical effects. Therefore, its ability to retain its unique physical and mechanical properties under extreme conditions of high temperature and pressure determines the behaviour and performance properties of friction units. To analyse the possible influence of external thermal effects on the physical and mechanical properties of the rubbing material, the samples obtained after friction tests are annealed in a vacuum of 0.01 MPa at temperatures of 620°C and 720°C for 1 hour. As established, these causes complete softening of the original metal that was deformed by friction. At the same time, the material of the friction layers retains high hardness and elasticity even after the samples have been annealed at 720°C. The maximal softening of the metal is observed at the beginning of the friction layers, where the structure is least fragmented, while the minimal softening is observed in the nanostructured material at the final part of the friction layers. As shown, during the formation of surface friction layers, the carbide phase dissolves and the metal is saturated with active chemical elements of the working environment. This enriches the grain boundaries of the surface friction layers with C and O atoms. Thermal treatment of samples after friction results in carbon atoms occupying octahedral interstitial sites of the b.c.c. iron–chromium alloy in the boundary regions of the grains of the surface friction layers, while oxygen atoms form a fine-dispersed oxide phase (α-Fe2O3). Their number at grain boundaries increases with the increased degree of metal fragmentation. The carbon atoms in the octahedral interstitial sites of the b.c.c. iron–chromium alloy form strong covalent bonds with the surrounding metal atoms. They reduce significantly the mobility of atoms and make the metal structure less sensitive to external thermomechanical influences. The presence of a fine-dispersed oxide phase at the grain boundaries also contributes to this one. This makes the physical and mechanical properties of the material of the surface friction layers significantly more resistant to external thermal influences compared to those of the deformed original metal.

Key words: sliding friction, wear resistance, nanostructured material, ultrafine-grained structure, plastic deformation, surface friction layers, physical and mechanical properties, recrystallization.

URL: https://mfint.imp.kiev.ua/en/abstract/v48/i06/0633.html

DOI: https://doi.org/10.15407/mfint.48.06.0633

PACS: 62.20.Qp, 62.23.St, 62.25.Mn, 68.37.Hk, 68.37.Lp, 81.65.Ps, 81.40.Np

Citation: V. V. Tykhonovych, Stability of Physical and Mechanical Properties of Wear-Resistant Ultrafine-Grained Surface Friction Layers under Extreme Conditions of Thermal Effects during Operation of Sliding Bearings, Metallofiz. Noveishie Tekhnol., 48, No. 6: 633–654 (2026)

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