Edgar Willenborg

Laser-based processing of materials has progressed from traditional applications such as macroscale cutting and welding, to sophisticated techniques, including ultrafast micromachining, additive manufacturing, and surface engineering at micro- and nano-metric scales. Innovations in laser source technology, particularly the advent of high-power and ultrashort-pulse lasers, have expanded the range of processable materials, enabled a plethora of manufacturing applications, and propelled groundbreaking research in optics, photonics, electronics, and biomedical domains. In this article, we provide a concise, yet broad review of the congruent evolution of lasers and materials processing, and highlight seminal developments in the field over the years, combined with a critical assessment of the state of the art. Finally, we also provide an outlook on emerging needs, as well as a roadmap of anticipated developments in laser technologies and materials platforms over the next 50 years. Graphic Abstract

Fine-grained Nb metal sheets were successively laser macro- and micro-polished for a potential use of the so-prepared materials in superconducting radiofrequency cavities in particle accelerators. The laser-treated Nb surfaces were investigated by a combination of white light interferometry, optical profilometry, electron microscopy with X-ray spectroscopy, and X-ray diffraction to study the influence of the conditions during the laser treatments on the resulting surface topography, the crystallographic structure, and the chemical composition of the material samples. For optimum polishing conditions, smooth, wavy surfaces with a minimum surface roughness could be achieved. However, local defects such as carbon contamination, as well as holes and cracks in the surface, were found. For the different prepared surfaces, the maximum acceleration field gradients, i.e., the onset fields for field emission (E_On), were determined, indicating that for smooth surface regions without defects, E_On may reach values of up to almost 1 GV/m, while for the pristine, rough surface and local defects such as particles and cracks, E_On is limited to values around 100 MV/m or less. The present study suggests that laser polishing should be considered as an alternative to conventional polishing strategies of niobium accelerator cavities.

Dual-phase (DP) steels are widely used in the automotive industry due to their exceptional performance. It offers excellent strength, ductility, formability, and weldability. However, there is a high risk of edge cracking, particularly in materials like DP1000 steel, caused by residual damage from blanking, such as microcracks and burrs, which needs further investigation. In this study, the transformative potential of laser-polishing on DP1000 steel was investigated. The goal was to reduce edge crack sensitivity and enhance edge formability. In this work, laser-polished samples produced by various pre-manufacturing techniques such as sawing, punching, and waterjet cutting were examined. Various evaluations were performed on laser-polished samples. Those included white-light-confocal microscopy, scanning electron microscopy, and Electron Backscatter Diffraction (EBSD) analysis. Those evaluations aimed to analyze the microstructural transformation, surface roughness, and micro grain size distribution resulting from laser-polishing. Laser-polishing is a process in which the edge of the sample is remelted locally. Hence, residual damage vanishes, and surface defects disappear, which should be beneficial for edge formability. On the other hand, the cooling rate during re-solidification is high, leading to high strength and reduced ductility compared to the initial DP steel. Therefore, hole expansion tests were conducted to evaluate the edge formability of the steel. The results indicated a significant improvement in the hole expansion ratio of the laser-polished samples compared to samples with conventional manufactured edges. These findings will help to assess the advantages and limitations of laser-polishing in sheet material manufacturing.

Laser remelting is being explored as a viable technique for obtaining a graphite-free, defect-free surface layer on cast iron EN GJS 400-15. The goal is to obtain a large remelted layer along with a low surface roughness to enable a subsequent manual high-gloss surface finish. The impact of the laser remelting process parameters is evaluated by using samples with three different cooling rates, resulting in different graphite microstructures. By utilizing four passes and a laser power of 300 W, the smallest roughness and largest remelting depth are achieved. The remelted layer is mostly devoid of graphite particles. Subsequent manual polishing is performed to evaluate the potential for achieving a high-gloss finish with a roughness of Sa < 0.05 µm. Laser remelting alone does not improve visual appearance or reduce roughness. However, after manual polishing, the roughness of the laser-remelted surfaces with Sa = 0.018 µm is one order of magnitude smaller than the manually polished initial state. Graphite removal during laser remelting therefore makes it possible to achieve a conventional and high-gloss polish, overcoming the previous limitations of GJS materials.