Advanced design of hierarchical topographies in metallic surfaces by combining micro-coining and laser interference patterning

Abstract

A new process idea to create hierarchical surface structures is based on the combination of micro-coining and laser interference patterning. Micro-coining already proved to be a high precision cold bulk metal forging process which allows for the production of small surface structures in the range of 20-200 μm while fulfilling high requirements related to the geometrical accuracy of those structures. In addition to that, laser interference patterning utilizes interfering laser beams from a pulsed solid state Nd: YAG laser to generate precisely defined surface topographies with a long-range order on the micron-scale. For the first time, initial results of a process combination consisting of micro-coining and laser interference metallurgy to induce hierarchical surface structures will be presented. The results highlight the advantages of the sequence micro-coining prior to laser interference patterning due to smaller defects in contrast to the inverted process cycle. Additionally, process limitations such as shadowing which may result from steep flank angles of the coined structures and surface roughness effects are discussed by the use of finite element simulations within this research work. The tailoring of surface properties requires a method being able to access structural sizes ranging from sub μm up to some 100 μm or even more. So far, several mechanical techniques such as embossing, cast moulding, or lithography based methods are needed to create the necessary structures on different scales. Therefore, a new technology combination is studied within this work on aluminum surfaces. The idea is based upon the combination of laser interference metallurgy for the advanced design of topographies and microstructures with micro-coining leading to superior hierarchical surface textures. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.