An Incompressible Smoothed Particle Hydrodynamics (ISPH) Model of Direct Laser Interference Patterning

Cornelius Demuth,Andrés Fabián Lasagni

doi:10.3390/computation8010009

Abstract

Functional surfaces characterised by periodic microstructures are sought in numerous technological applications. Direct laser interference patterning (DLIP) is a technique that allows the fabrication of microscopic periodic features on different materials, e.g., metals. The mechanisms effective during nanosecond pulsed DLIP of metal surfaces are not yet fully understood. In the present investigation, the heat transfer and fluid flow occurring in the metal substrate during the DLIP process are simulated using a smoothed particle hydrodynamics (SPH) methodology. The melt pool convection, driven by surface tension gradients constituting shear stresses according to the Marangoni boundary condition, is solved by an incompressible SPH (ISPH) method. The DLIP simulations reveal a distinct behaviour of the considered substrate materials stainless steel and high-purity aluminium. In particular, the aluminium substrate exhibits a considerably deeper melt pool and remarkable velocity magnitudes of the thermocapillary flow during the patterning process. On the other hand, convection is less pronounced in the processing of stainless steel, whereas the surface temperature is consistently higher. Marangoni convection is therefore a conceivable effective mechanism in the structuring of aluminium at moderate fluences. The different character of the melt pool flow during DLIP of stainless steel and aluminium is confirmed by experimental observations.

Highlights

Microscopic periodic features provide surfaces with superior functionalities
The melt pool width and depth obtained from the smoothed particle hydrodynamics (SPH) computations are presented in Figure 4a,b, respectively, for Direct laser interference patterning (DLIP) of stainless steel in the considered range of energy densities
The results of DLIP simulations performed by SPH for the high-purity aluminium substrate and energy densities ranging from 0.6 J/cm2 to 1.2 J/cm2 are outlined in the following

Summary

Introduction

Microscopic periodic features provide surfaces with superior functionalities. In biological and medical applications, repetitive surface textures improve the biocompatibility of bone implants [1], guide directional cell growth [2] and inhibit bacterial adhesion and biofilm formation [3]. Further advantages of periodic structured surfaces include enhanced light absorption [4], reduced friction [5,6] and anisotropic wetting [7]. Direct laser interference patterning (DLIP) is a novel method that allows the production of periodic surface structures with feature sizes in the submicron to micron range in a single processing step. For this purpose, the primary beam of a pulsed laser with wavelength λ is split into two or more partial beams

Results

Discussion

Conclusion