Issue 78

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

I NTRODUCTION

I

n order to enhance the service life and reliability of rolling bearings, methods of hardening the raceways are of key importance. The most common and proven industrial methods are surface hardening (carburizing, nitriding). Methods of surface plastic deformation (in particular, shot peening) are also being developed [1-3]. Carburizing involves saturating the surface layer of a component with carbon, followed by quenching, which creates a combination of a highly hard, wear-resistant surface layer and a tough, impact-resistant core. This is the optimal method for bearings operating under high impact and contact loads. Nitriding (and its variant, nitrocarburizing) forms hard iron nitrides on the surface, significantly increasing wear resistance, corrosion resistance, and fatigue strength with less deformation than carburizing. An exemplary method of processing that has garnered significant attention is shot peening. During the work hardening process, the material surface is bombarded with a stream of fine shot, which causes plastic deformation and creates residual compressive stresses in the surface layer. These stresses are instrumental in preventing the initiation and development of fatigue microcracks, thereby significantly extending the service life of the bearing. However, these conventional technologies exhibit a number of substantial disadvantages. Carburizing is a complex, multi stage, and energy-intensive treatment, accompanied by the risk of significant thermal deformations and the need for subsequent expensive mechanical processing. Nitriding, although carried out at lower temperatures, is an extremely lengthy process (tens of hours) and can lead to the formation of a brittle surface layer susceptible to chipping. Despite its effectiveness in increasing fatigue strength, shot peening has limitations in terms of process control and reproducibility of results. Key output parameters such as the depth and homogeneity of the hardened layer show significant dependence on the operational wear of the shot material, the geometric configuration of the workpiece, and the variability of the particle impact angle. In addition, this method is associated with the potential occurrence of surface microdefects and an increase in roughness, which can negatively affect the functional characteristics of the surface. Laser shock peening (LSP) is a fundamentally novel and highly promising method for solving these problems. LSP represents a promising surface modification technology that utilizes high-intensity laser pulses to generate weak shock (elastoplastic) waves. These waves induce compressive residual stresses (CRS) and modify the microstructure in the near surface layer of metallic structural components. The development of LSP began in the 1960s and evolved concurrently through the efforts of Soviet and American researchers. The concept of LSP was likely first proposed in 1962 at the P.N. Lebedev Physical Institute of the Russian Academy of Sciences following the discovery of the effect of anomalously high pressure under laser irradiation. This effect was confirmed two years later at the NASA Ames Research Center. Subsequently, in 1968, N.C. Anderholm at Sandia Laboratories proposed a scheme for generating shock waves by laser radiation that is close to the modern prototype of the LSP technology, including the possibility of amplifying shock waves using transparent confining layers. In 1970, Mirkin's work at Lomonosov Moscow State University was among the first to investigate changes in material structure resulting from the impact of laser-induced shock waves. Around the same time, similar research was conducted at the U.S. Naval Research Laboratory. The foundation for the development of the technology itself was laid at the Battelle Memorial Institute with the installation of a Gènèrale Electrique VD-640 laser and the systematic study of changes in the mechanical properties of materials due to laser irradiation [4]. Comprehensive reviews dedicated to the development and modifications of LSP for enhancing fatigue durability have recently appeared, for example, [5]. Despite this, scientific research on LSP continues actively worldwide [6-8]. LSP is used in the aerospace industry to improve fatigue strength and retard fatigue crack growth in various materials [9–13], employing pulses with a wide range of durations, including femtosecond pulses [14]. In recent years, a new scientific direction has begun to emerge, focusing on the application of LSP to improve the tribological characteristics of materials. Specialized reviews, such as [15, 16], systematically analyze the potential of LSP for controlling friction and wear. Numerous experimental studies examined in these reviews demonstrate the promise of applying LSP to a wide range of materials—from titanium alloys used in biomedical implants to tool steels in highly loaded friction assemblies. Analysis of the works presented in the review [17] indicates that in 89% of cases, LSP leads to a statistically significant improvement in tribological characteristics. It is often noted that LSP creates a complex effect capable of substantially increasing wear resistance and reducing the coefficient of friction under conditions of dry and boundary lubrication. To date, the application of LSP for enhancing tribological properties has been investigated for titanium alloys (e.g., Ti 6Al-4V), aluminum alloys (e.g., 7075-T6) and steels (e.g., AISI 9310, SAF 2205, 55SiMoVA, GCr15, M50). It is shown that multiple LSPwC of Ti-6Al-4V alloy leads to the generation of CRS up to 550 MPa and an increase in microhardness to 395 HV, which reduces wear volume by 17–30% under both room temperature and 300 °C in dry

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