Study on surface quality of laser cleaning of oxide film on nickel-base superalloy

In this paper, nanosecond pulsed laser was used to clean the oxide film on the surface of nickel-base superalloy. The evolution laws of surface morphology, roughness, oxygen content, and line profile of samples after cleaning with different laser energy density and scanning speed were studied. The microhardness of the cleaned samples was characterized. The results show that when the energy density is from 0.50 to 0.88 J/cm2 and the scanning speed is from 6000 to 7000 mm/s, the cleaning surface is gradually flat, the line contour is more smooth and uniform, and the oxygen content and roughness value are reduced. When the energy density is from 0.88 to 1.99 J/cm2 and the scanning speed is from 7000 to 10,000 mm/s, the surface cleaning quality decreases, the line profile height difference increases, and the roughness value and oxygen content increase. When the energy density is 0.88 J/cm2 and the scanning speed is 7000 mm/s, the surface is relatively flat, and the roughness reaches the lowest value in the experiment, which is 0.171 μm; The oxygen content was 2.42 wt%, which decreased by 66% compared with the unclean surface. The main reason for the increase in surface roughness is that there are sputtering particles, ring-shaped craters, and molten protrusions on the cleaned surface. In addition, the increase of energy density will aggravate the surface ring-shaped craters phenomenon, secondary oxidation on the cleaned surface, more obvious surface melting and ablation, and the microhardness of the sample will be improved accordingly. According to the thermodynamic theoretical model and analysis results, it is concluded that the laser removal mode of Superalloy oxide film is the mechanism of thermal expansion explosion and recoil pressure in the defect.