Self-organization of vortex filament structures generated in pulsed-laser melting of rough metal surfaces

Abstract

Abstract Laser melting of rough metal surfaces, in particular in those containing parallel scratch lines of micron and submicron size, differs from melting of smooth planar surfaces. It is associated with the reach of the spectra of self-organized structures, which consist of vortex filaments as basic entities. Self-organized structures of vortex filaments on rough metal surfaces were generated by short laser pulses and studied by optical and scanning electron microscopy. Their formation starts with melting of the surface that generates a shear layer with radially oriented flow in the laser spot. Parallel scratch lines represent the flow perturbation which is spanwise, streamwise or oblique in different zones of the spot giving rise to the self-organized flow structures. The flow structures are permanently frozen by ultra-fast cooling after laser pulse termination, thus enabling a posteriori analysis. Long vortex filaments organized into very complex structures ranging from parallel Kelvin-Helmholtz rolle...