Effect of Oxide Film Thickness on the Parameters of Laser-Induced Stress Waves in Carbon Steel

This study experimentally investigates the effect of oxide film thickness on the amplitude of laser-induced stress waves in AISI W1-7 carbon steel. Oxide layers of approximately 0.045 μm (straw-yellow) and 0.07 μm (blue) were synthesized via controlled heating using a free-running YAG:Nd3+ laser. The work used a Q-switched ruby laser (λ = 0.69 μm; FWHM = 25–30 ns; E up to 1.5 J) to generate intense stress waves. The displacement of the sample’s free surface was recorded using a Michelson interferometer with a probing He–Ne laser (λ = 0.6328 μm), which was used to construct the “pressure–time” relationship. It has been established that oxide films with thicknesses of 0.045 and 0.07 μm increase the wave amplitude by 1.15 and 1.4 times, respectively, relative to pure steel, which is associated with enhanced optical absorption and thin-film interference at the laser pump wavelength. Furthermore, the quasi-linear dependence of the stress wave amplitude on the laser pulse energy (0.7–1.5 J) indicates the absence of plasma shielding within this energy range. These findings suggest that controlled thermal oxidation can serve as an effective, clean absorptive coating to optimize laser shock peening (LSP) processes.