Graining and Texturing of Metal Surfaces by Picosecond Laser Treatment

Abstract

Different approaches have been proposed to control the tribological behavior of materials under different conformal and non-conformal contact conditions with influenced surface texturing. The ever-increasing demand to improve material friction, erosion wear, and adhesion bond strength of coatings is a major concern for the contact interface of surfaces. Laser texturing is considered a promising approach to tuning materials' tribological properties. The latter are strongly influenced by the texture density and shape imprinted on the engineered materials and vary in dry or lubricating conditions. In this work, the physicochemical properties of picosecond laser-textured surfaces of metallic materials have been systematically analyzed. Specifically, the wettability character of laser-textured materials was correlated with their morphological/compositional features.

Keywords: laser scribing; roughness; surface texturing; wettability.

Figure 1

Contact angle images and corresponding values of the solvent drops on brass foils. The standard deviation of CA values is less than 2° in all cases.

Figure 2

Contact angle values as a function of the laser scan speed using water, diiodomethane and mineral oil as solvents. Dashed lines correspond to CA values for the untextured surfaces.

Figure 3

Surface energy (SE) vs. texturing scan speeds for all the studied metal foils. The dispersive (squares) and polar (circles) SE components are shown together with the total surface energy (triangles). Dashed lines correspond to SE values for the untextured surfaces.

Figure 4

Root mean square roughness vs. texturing scan speeds for all the studied metals. Dashed lines correspond to Rq values for the untextured surfaces. The bottom right panel reports the texturing depth as a function of the scan speed evaluated from acquired profiles (in the inset see the example for brass textured at 50 mm/s).

Figure 5

CA vs. Rq for all the considered textured material surfaces. Star symbols correspond to the values for the untextured foil; dashed lines are guides for the eye.

Figure 6

SEM images at different magnifications of nickel (a–c) and molybdenum (d–f) samples textured at scan speeds of 50, 500 and 2500 mm/s. The insets of panels (d–f) show a higher magnification of molybdenum surfaces to highlight LIPSS formation. The reported distance is the laser wavelength.

Figure 7

SEM images at different magnifications of stainless steel samples untextured (a) and textured at scan speeds of 50 (b), 500 (c–e) and 2500 (f) mm/s.

Figure 8

SEM images at different magnification of brass samples untextured and textured (a) at scan speeds of 50 (b,c) and 500 (d) mm/s.

Figure 9

SEM images at different magnifications of copper samples untextured (a) and textured at scan speeds of 50 (b,c) and 500 (d) mm/s.

Figure 10

Oxygen percentage content evaluated by EDX and XPS analyses.