Issue 78

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

steel disks surfaces after tribological tests under the conditions of friction without lubricant and boundary friction, respectively. An analysis of the worn surface profiles facilitates the evaluation of the intensity and the character of wear, as well as the identification of the effect of laser shock treatment on the tribological characteristics of the samples under study. A comparison of the profilograms of the disks before and after LSP reveals a substantial discrepancy in the character and extent of the surface damage. Under friction conditions of unlubricated surfaces (Fig. 7), a significant degree of wear is evident in the untreated samples. The profilograms show the presence of deep scratches and burrs, indicating intensive material removal from the friction surface. The wear mechanism in this case is caused by direct contact between the roughness of the contacting surfaces, which leads to plastic deformation and the detachment of the material microparticles. The measurements showed that the friction track on the reference sample has an average width of 2.2 ± 0.3 mm and a depth of 13 ± 2 µm over a test duration of 10 hours, confirming high wear intensity. To enable a fair comparison across different test durations, wear was evaluated in terms of the specific wear rate (Ih = V / F·L), where V is wear volume (mm 3 ), F is normal load (N), and L is test distance (m). Which is a standard approach in tribology based on Archard's wear equation [27]. The wear volume was calculated by approximating the wear track cross-section as a parabolic segment. The specific wear rate for the untreated samples under dry friction was 3.16×10 -8 mm 3 /(N·m), whereas for the LSP-treated samples (tested for 200 hours) it drastically decreased to to 1.70×10 -10 mm³/(N·m). In contrast, the samples subjected to LSP exhibit a significantly lower wear rate. The friction track width on the sample with LSP was only 0.9 mm, and the depth was 1.4 µm, which indicates a significant reduction in wear intensity. Under boundary friction conditions (Fig. 8), the character of wear differs from friction of unlubricated surfaces, but the general tendency to maintain the advantages of LSP remains. For the untreated samples, wear is also observed, but its intensity is somewhat lower than under friction conditions of unlubricated surfaces, which is due to the lubricating effect of a thin film of lubricant. The friction track width for the untreated sample was 1.7 ± 0.15 mm, and its depth was 7 ± 1.2 µm over a test duration of 30 hours. Under these boundary lubrication conditions, the specific wear rate decreased from 6.58×10 -9 mm³/(N·m) for the untreated samples to 1.18×10 -10 mm³/(N·m) for the LSP-treated ones (tested for 200 hours). The samples treated with LSP also showed a substantially reduced degree of wear in this case: the friction track width was 0.9 mm and the depth was 1.2 µm.

(A) (B) Figure 7: Surface topography of steel disks after tribological tests under friction conditions of unlubricated surfaces before (A) and after (B) LSP treatment.

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