Investigation of ultrashort pulse laser material processing of low- and high-entropy alloys using an ultrafast temperature and density sensor

激光材料加工是目前现代激光系统最常见的应用领域，其次是电信、医学和基础研究。特别是各种制造工艺对材料的可自由设计加工，使激光成为不可缺少的柔性工具。由于其高精度和广泛的应用，金属及其合金的超短脉冲激光材料加工在工业4.0中具有巨大的潜力。在质量、能源和资源效率方面优化工艺参数是至关重要的。然而，由于材料性质和激光系统参数的差异很大，迄今为止还没有开发出通用的工艺窗口。特别是对于新型合金，如高熵合金，由于技术要求的提高，它变得越来越重要。该项目的目标是研究一个定量的、实验验证的超短脉冲激光材料加工各种含铁和含镍的三维过渡金属合金的模型，范围从传统的不锈钢到现代的高熵合金。因此，通过使用实验验证的模型，将开发对过程动力学的透彻理解。这只能通过理论和实验的密切相互作用来完成。利用超快时间分辨椭偏和干涉泵-探针实验，以及理论从头算模型，将可以得出热力学状态变量瞬态变化的定量结论。实验验证的模型应该能够预测瞬态反射、吸收和表面膨胀等随时间变化的观测值，以及烧蚀阈值和效率等最终状态观测值。所开发的方法被称为“超快温度和密度传感器”，其结果有望对现代合金的超短脉冲激光材料加工的整体定量理解做出重大贡献。此外，对这些合金在异国状态下的材料参数有了新的认识，这是以前未被探索过的。

Laser materials processing is currently the most common application for modern laser systems, followed by telecommunications, medicine, and basic research. Especially the freely designable processing of materials with a variety of manufacturing processes has made the laser an indispensable flexible tool. Because of its high precision and broad range of applications, ultrashort pulse laser material processing of metals and their alloys has enormous potential for Industry 4.0. The optimization of process parameters in terms of quality, energy and resource efficiency is crucial. However, due to widely varying material properties and laser system parameters, no universal process window has been developed so far. Particularly for novel alloys such as high-entropy alloys, which are becoming progressively important due to rising technical demands. The project's goal is to investigate a quantitative, experimentally validated model of ultrashort pulse laser material processing of various iron and nickel-containing alloys of 3d transition metals, ranging from conventional stainless steels to modern high-entropy alloys. As a result, a thorough understanding of the process dynamics will be developed through the use of an experimentally validated model. This can solely be accomplished through the close interplay of theory and experiments. Utilizing ultrafast time-resolved ellipsometric and interferometric pump-probe experiments, as well as theoretical ab-initio modeling, will allow quantitative conclusions on the transient change of thermodynamic state variables to be drawn. The experimentally validated model should be able to predict both time-dependent observables like transient reflection, absorption, and surface bulging as well as final state observables like ablation thresholds and efficiencies. The developed methodology, referred to as an "ultrafast temperature and density sensor” and the resulting findings are expected to contribute significantly to the overall quantitative understanding of ultrashort pulse laser material processing of modern alloys. Furthermore, novel insights into the material parameters of these alloys in exotic states, which have previously been unexplored, are expected.