Insights into room- and elevated-temperature micro-mechanisms of laser shock peened M50 steel with superior tribological performance

Abstract

M50 steel, commonly utilized in aircraft engine bearings, is susceptible to friction-induced failures, particularly in high-temperature service conditions. To address this issue, various strategies have been proposed, with laser shock peening (LSP) garnering significant attention due to its deeper residual stress penetration and excellent surface integrity, whereas the underlying strengthening mechanisms have not yet been fully elucidated. In this study, we systematically investigate the impact of LSP treatment on the tribological properties of M50 steel at temperatures of 25 and 300 °C, alongside elucidating the relevant micro-mechanisms. Microstructural analysis reveals that laser impact strengthening primarily arises from dislocation proliferation, resulting in a surface hardness increase of approximately 14 % and the formation of a substantial compressive stress layer reaching a maximum value of about 1200 MPa, with a depth of around 2 mm. Friction test results demonstrate reduced coefficients of friction and wear rates following LSP treatment at both temperatures. Notably, a more pronounced reduction is observed at 300 °C, with values decreasing by 41.4 % and 55.8 %, respectively. The enhanced performance is attributed to the synergistic interplay of compressive residual stresses, work-hardening layers, increased density of dislocations, and substantial microstructure refinement.