Direct laser interference patterning (DLIP) has emerged as a versatile tool for producing well-defined microstructures that mimic natural surfaces with the aim of obtaining functionalized surfaces on relevant technological materials. On the other hand, the fabrication of surface patterns with micro- and submicron resolution features necessitates of advanced monitoring and setup strategies in order to ensure repeatability as well as quality control. In addition, the monitoring systems also allow inline capabilities to enable a closed-loop control approach. A possible strategy, that has been already applied to different laser processes, is the utilization of the sound pressure generated by the laser beam hitting the surface and producing ablation that can be detected and analyzed using commercially available microphones. In this frame, this work focuses on the analysis of the acoustic information extracted from the audio signal for determining process-inherent characteristics in DLIP, allowing the calculation of interference volume using stainless steel and titanium as reference materials. The results show that the acoustic emission measured at the ablation spot can be correlated to the interference volume shape and thus allowing to approximate the size of the interference spot. The possible utilization of this approach as an auto-focus and auto-setup method during DLIP is discussed.
Medical implants, such as dental screws or hip stems, are made of biocompatible materials so that they can be well integrated into living organisms. For instance, titanium and its alloys offer high biocompatibility and osseointegration, making these materials very common in such applications. Furthermore, the new advancements in additive manufacturing allow to customize the fabrication of implants which are tailored to the patients’ individual needs. Furthermore, it is known that the structural elements with feature sizes in the micrometer range on the implants’ surface play a significant role in the attachment and proliferation of cells. These elements can be fabricated through laser-based texturing methods that offer high flexibility and high throughput. In this work, we explore the potential of fabricating surface microstructures on additive manufactured near-beta titanium alloy parts (Ti-13Nb-13Zr), using the Direct Laser Interference Patterning (DLIP) technique. Hereby, a single laser beam is split into two sub-beams that are subsequently recombined on the substrate surface where they form a line-like interference pattern with a defined spatial period. We combine DLIP with a picosecond-pulsed laser source and investigate the morphologies and surface features that can be created. Thereby, different laser wavelengths were employed, including 355 nm, 532 nm and 1064 nm. The resulting surface textures are analyzed using scanning electron microscopy (SEM) and confocal microscopy (CM), showing different types of laserinduced periodic surface structures (LIPSS), of which the geometry and size depended on the used process parameters.
Surfaces with well-defined features (e.g. periodic structures) have shown to exhibit outstanding properties. The design of these textured surfaces often follows a biomimetic approach motivated by living organisms which developed over time through natural selection and evolution. The efficient production of these versatile patterns still represents one of the greatest technical challenges today in the development of new customized surface functionalities. Direct Laser Interference Patterning (DLIP) has been identified as an outstanding technology for the efficient fabrication of tailored surface structures. This method can show impressive processing speeds (up to 1 m²/min) as well as a superior flexibility in producing extremely versatile surface structures. This work gives an overview about recent developments of the DLIP technology by focusing on the topics: structure flexibility, process productivity, technical implementations and recent examples of achieved surface functionalities.
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