Influence of Sulphur Content on Structuring Dynamics during Nanosecond Pulsed Direct Laser Interference Patterning

Area of Science:

• Materials Science
• Surface Engineering
• Laser Processing

Background:

• Melt formation and spreading are critical in high-temperature processes like laser welding and cutting.
• Surface-active elements, such as sulfur, significantly influence melt pool dynamics by altering surface tension gradients.

Purpose of the Study:

• To investigate the application of direct laser interference patterning (DLIP) for structuring steel surfaces.
• To analyze the effect of varying sulfur concentrations on melt convection patterns and pool shapes during DLIP.
• To correlate laser fluence with topographic features and sulfur content.

Main Methods:

• Direct laser interference patterning (DLIP) was used to structure steel surfaces with varying sulfur content.
• Laser fluence was systematically varied to study the resulting topographic features.
• Numerical simulations using a smoothed particle hydrodynamics (SPH) model were employed to understand melt pool convection.

Main Results:

• Steel substrates with sulfur content below 300 ppm formed single peak geometries.
• Steels with higher sulfur content (>300 ppm) exhibited split peak structures.
• The observed peak formations were explained by thermocapillary convection principles in weld pools.

Conclusions:

• Sulfur concentration is a key factor in determining the microstructural topography generated by DLIP on steel.
• DLIP offers a method to control surface structuring based on material composition.
• SPH simulations provide insights into the influence of sulfur on melt pool convection during pulsed laser processing.