Issue 78

M. Bronovets et alii, Frattura ed Integrità Strutturale, 78 (2026) 367-377; DOI: 10.3221/IGF-ESIS.78.21

insufficient and allows for the evaluation of the wear resistance of materials under extreme conditions. The second mode is boundary friction, which assumes the presence of a thin adsorption film of lubricant on the friction surfaces. For the boundary friction tests, a high-temperature lithium-based bearing grease was used. The lubricant has a base oil viscosity of approximately 120 cSt at 40°C, a dropping point of 180°C. Prior to each test, a thin, uniform layer of grease weighing 0.5 g was applied to the contact surfaces to ensure boundary lubrication conditions. In this mode, the properties of the lubricant, such as viscosity, adhesion, and the presence of antifriction additives, have a significant impact on the wear processes. Boundary friction testing is a method of assessing the efficacy of lubricants in minimizing wear and friction within specific tribological pairs. The utilization of dual lubrication modes facilitated a thorough evaluation of the tribological characteristics of the materials and coatings under investigation. Due to the exceptionally long duration of the tribological tests (up to 200 hours), each tribological condition (untreated/LSP, dry/boundary) was evaluated using two independent specimens (N=2). The experimental study was conducted under ambient conditions at a temperature T = (23 ± 1)° С and relative humidity of (30 ± 5) %. The surface topography of the specimen raceways was studied using a 3D non-contact profilometer with a 10x confocal lens. Stitching 1936 adjacent scans yielded a 45 x 45 mm sample surface topography image. Roughness parameters were assessed in accordance with ISO 25178, which allows for three-dimensional (area-based) determination of the height and parameters of hybrid relief using the device's software tools. A 20x confocal lens was used for a detailed analysis of the surface wear depth of the specimens and visualization of wear traces arising during tribological testing. To obtain the topography, measurements were taken on typically repeating areas of the specimen surface, reflecting the characteristic features of the microrelief and wear traces. To assess the roughness of each wear track, measurements were taken at a minimum of five randomly selected points located along the track. This spatial sampling allowed for possible local heterogeneity in the wear profile to be taken into account.

R ESULTS AND DISCUSSION

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Tribological tests ig. 5 shows the results of the tribological tests aimed at quantitatively assessing the rolling resistance moment for the studied steel disk samples after laser shock treatment and untreated ones. The rolling resistance moment is a key parameter characterizing the energy efficiency and service life of rolling bearings.

Figure 5: Dependence of the rolling resistance moment on the test time, where (A), (B) - steel samples without LSP, (C), (D) – after treatment; (A), (C) – tests under friction conditions without lubricant, and (B), (D) – boundary friction. A thorough analysis of the tribological test results revealed a substantial and consistent reduction in the rolling resistance moment for the samples subjected to LSP compared to the untreated ones. The lowest rolling resistance moment was recorded under boundary friction conditions during contact interaction with a steel disk after LSP; it is Ts = 0.18 Nm. On average, the LSP treatment has been shown to reduce rolling resistance by 30-40%, which is a significant improvement

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