Issue 78

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

sliding conditions [18]. Similarly, in [19] demonstrated that LSP significantly improves the wear resistance of Ti-6Al-4V alloy under boundary lubrication. Aluminum alloys also show a positive effect from LSP application. It is shown that treating 7075-T6 alloy leads to grain refinement to 32 µm, a 25% increase in microhardness, and the formation of CRS up to 227 MPa, which comprehensively improves tribological characteristics [20]. Under boundary lubrication, LSP-treated surfaces of aluminum alloys exhibit a more stable coefficient of friction and reduced susceptibility to scuffing. The tribological characteristics of structural and tool steels are investigated in [21]. It was shown that LSP of GCr15 steel allows for nanoscale grain refinement (~35 nm) and a significant reduction in wear rate under low loads. For AISI 9310 steel, work [22] demonstrated that femtosecond LSP reduces the wear rate by 61.7% and achieves a coefficient of friction of 0.47 due to gradient hardening and the formation of LIPSS. While most studies note improved wear resistance, in [23] reported a possible deterioration in the wear resistance of duplex stainless steel SAF 2205 after LSPwC under high loads, which is associated with thermal effects and strain localization at phase boundaries. In [24] LSP significantly improve the tribological properties of 55SiMoVA bearing steel. This was achieved through work-hardening, grain refinement, and the creation of a residual compressive stress layer, which reduced the friction coefficient, wear volume, and suppressed abrasive and delamination wear. The systematically investigation of the effects of LSP on the tribological properties of M50 steel at room (25°C) and elevated (300°C) temperatures was carried out in [25]. The results demonstrate that LSP significantly reduces friction and wear, particularly at 300°C, through a synergistic mechanism involving dislocation proliferation, work-hardening, grain refinement, and the formation of a deep CRS layer. The findings from the testing of LSP-treated materials under rolling and sliding friction conditions confirm the conclusions drawn in [26] based on mathematical modeling of the frictional interaction of elastic bodies, taking into account the presence of residual stresses in them. In particular, in [26], it was established that, compared to unprocessed materials, the creation of compressive residual stresses as a result of LSP processing leads to a decrease in the amplitude values of subsurface equivalent stresses arising under conditions of cyclic frictional interaction both under conditions of sliding friction and during rolling. A decrease in the amplitude values of equivalent stresses leads, in turn, to a slowdown in the rate of accumulation of fatigue damage in the subsurface layers of materials of interacting bodies and, thus, to a slowdown in their wear by the contact fatigue mechanism. The main contributing factors to the improvement of tribological characteristics of metal could be summarized as follow. LSP leads to creation of deep CRS and structural transformations at all hierarchical levels of the solid body. At nanoscale level LSP leads to increase in dislocation density, formation of nanoscale subgrains, twinning in materials with an FCC lattice. A dynamic recovery and polygonization, formation of a cellular dislocation structure, dynamic recrystallization are observed at microscale level. A mesoscale level is characterized by creation of a gradient structure with variable grain size, formation of deformation texture. Surface texturing can also have a significant positive effect on friction and wear conditions. Despite the promising results of LSP application in tribology, several problems remain unsolved for its successful industrial implementation. These include, for example, optimizing LSP parameters for specific friction pairs and loading conditions, the need to develop a detailed mathematical model of the process, separate study of behavior under dry and boundary lubrication, and insufficient understanding of the individual contribution of each factor (residual stresses, surface texture, hardness, microstructure) to the overall improvement of tribological characteristics. This work investigates and selects LSP parameters to enhance the tribological characteristics of friction pairs made of high-chromium bearing steel grade AISI 440-C (Russian equivalent 95 Х 18 Ш ). The specimens were divided into two groups: the first group served as a reference one and was not subjected to additional processing, while the surfaces of the second group specimens were modified by laser shock peening (LSP). Steel disks and counterbodies of thrust bearings made of bearing steel AISI 440-C (Russian equivalent 95 Х 18 Ш ) were used as counterbodies interacting with the disks during tribological tests. The selection of counterbodies is guided by the objective A M ATERIALS AND EXPERIMENTAL CONDITIONS group of disks made of high-chromium bearing steel grade AISI 440-C (Russian equivalent 95 Х 18 Ш ) (Fig. 1) were selected as specimens for laser shock treatment and subsequent tribological testing. The chemical composition of the steel is presented in Tab. 1. The steel was supplied in a hardened condition, achieving a bulk hardness of approximately 60-62 HRC. The choice of this material is determined by the widespread use of this steel in critical friction units requiring high wear resistance and resistance to contact fatigue. Disc specimens are intended for rolling friction testing.

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