Multiscale Modeling of Laser-Induced Surface Nanostructuring of Metals

该奖项支持计算研究和教育，以开发和使用计算建模工具来理解非常快的激光脉冲如何以潜在的复杂和复杂的方式改变金属和半导体的结构和表面。快速激光脉冲在辐照材料表面的小区域沉积能量的能力，例如以热的形式，使得可以进行非常有选择性的表面修饰，并产生独特的表面形态，亚稳相和不寻常的晶体缺陷排列，构成微观结构。快速激光脉冲也为研究高能量电子、快速加热和冷却以及超快速机械变形等极端条件下的材料行为提供了独特的机会。该研究项目的目标是开发一种先进的计算模型，该模型包含跨越长度和时间尺度的基本物理过程的描述，并且能够真实地表示非常快的激光脉冲如何与从金属合金到有机化合物的各种材料制成的目标相互作用。通过使用具有许多并行操作的处理器的非常快的计算机，PI将应用该模型来研究控制激光修饰材料表面形态和微观结构的主要因素。虽然激光脉冲只持续很短的时间，但材料的响应时间要长得多。再加上被模拟材料样品的大小和物理过程的复杂性所激发的响应导致对计算机性能的高要求。研究材料对短脉冲激光辐照的反应，旨在深入了解材料在超快加热、冷却和变形速率的极端条件下，远离稳定平衡状态的特性。超快激光表面改性具有广泛的潜在应用，包括具有增强表面性能的材料制造，包括硬度，减少摩擦和减少磨损。学生参与高性能并行计算的各个方面，并与世界各地的实验和计算合作者密切互动，将在快速扩展的科学计算和激光材料相互作用领域创造一个肥沃的教育环境。一个教育网站包含了激光材料相互作用的基本概念，通过本项目制作的图像和动画来说明，将作为一个平台，向更广泛的受众传达计算材料研究的相关性和兴奋性。技术摘要：该奖项支持在短脉冲激光修饰材料表面形态方面的理论和计算研究以及教育。短脉冲激光辐照产生独特的表面形貌、亚稳相和不寻常的微观结构的能力已经在实验中得到证明，这通常归因于激光激发在照射目标中产生的强烈的电子、热、相和机械不平衡条件。然而，对激光能量沉积引起的快速非平衡过程与激光处理目标区域的结构和性能之间的关系的详细理解仍然缺乏，从而限制了激光技术向纳米材料加工和制造新领域的扩展。本研究项目的主要目的是通过先进的多尺度建模和理论分析，提供由短脉冲激光照射金属靶触发的快速非平衡结构和相变的机制和动力学的详细信息，并负责在纳米尺度和微尺度上产生复杂的层次表面形貌，以及不寻常的表面微观结构。该项目的一个关键组成部分是设计和验证一种新的多尺度计算方法，以协同的方式结合短脉冲激光激发下材料初始响应的大规模原子模拟，包括快速熔化、空化，以及在更高的激光影响下，过热液体的爆炸沸腾和相分解。用粗粒度模型模拟随后较慢的流体动力运动和熔化表面区域的凝固。新的计算模型将能够详细探索在不同时间和长度尺度上发生的激光诱导过程的复杂相互作用，并将揭示辐照条件、材料特性、多晶靶中晶粒的晶体取向以及激光照射产生的表面特征的微观结构之间的联系。对于快速能量沉积的材料响应的多尺度建模，新的柔性计算方法的出现可能会在计算材料科学的一般领域产生广泛的影响。该项目中开发的方法将广泛传播到研究界，并通过现有的和新的合作，应用于不同的材料系统，从金属合金到有机材料，以及各种激光加工条件，例如背景气体、液体环境或透明覆盖层的存在。由于被模拟材料体积大、模拟时间长、模型复杂等原因，需要进行高性能的计算模拟。学生参与高性能并行计算的各个方面，并与世界各地的实验和计算合作者密切互动，将在快速扩展的科学计算和激光材料相互作用领域创造一个肥沃的教育环境。一个教育网站包含了激光材料相互作用的基本概念，通过本项目制作的图像和动画来说明，将作为一个平台，向更广泛的受众传达计算材料研究的相关性和兴奋性。

NONTECHNICAL ABSTRACTThis award supports computational research and education to develop and use computational modeling tools to understand how very fast laser pulses can modify the structure and surfaces of metals and semiconductors in potentially complex and intricate ways. The ability of very fast laser pulses to deposit energy, for example in the form of heat, in small regions of irradiated material surfaces makes it possible to perform very selective surface modifications and produce unique surface morphologies, metastable phases and unusual arrangements of crystal defects which constitutes microstructure. Fast laser pulses also provide unique opportunities to investigate material behavior under extreme conditions of highly energetic electrons, rapid heating and cooling, and ultrafast mechanical deformation. The objective of this research project is to develop an advanced computational model that contains descriptions of essential physical processes across scales of length and time and is capable of realistic representation of how very fast laser pulses interact with targets made of a wide range of materials from metal alloys to organic compounds. Through the use of very fast computers with many processers that operate in parallel, the PI will apply this model to investigate the main factors that control the surface morphology and microstructure in laser-modified materials. While the laser pulse lasts for only a very short time, the time for the material to respond is much longer. Together with the size of the simulated material sample and complexity of the physical processes stimulated by the response leads to the need for high computer performance. The investigation of how materials respond to short-pulse laser irradiation is aimed to provide insights into the peculiarities of material behavior far from the steady state of equilibrium, under extreme conditions of ultrafast heating, cooling, and deformation rates. Ultrafast laser surface modification has a wide range of potential applications including materials fabrication with enhanced surface properties including hardness, reduced friction, and reduced wear. The involvement of students in all aspects of high-performance parallel computing and close interaction with experimental and computational collaborators worldwide will create a fertile educational environment in the quickly expanding areas of scientific computing and laser-materials interactions. An educational website containing an accessible presentation of basic concepts of laser-materials interactions illustrated by images and animations produced in this project will be developed as a platform for conveying the relevance and excitement of the computational materials research to broader audiences.TECHNICAL ABSTRACTThis award supports theoretical and computational research, and education in short pulse laser modification of material surface morphology. The ability of short pulse laser irradiation to produce unique surface morphologies, metastable phases and unusual microstructure has been demonstrated in experiments and is generally attributed to the conditions of strong electronic, thermal, phase, and mechanical nonequilibrium created in irradiated targets by the laser excitation. Detailed understanding of the relations between the fast nonequilibrium processes caused by the laser energy deposition and the resulting structure and properties of laser-treated regions of the targets, however, is still lacking, thus limiting the expansion of laser technologies into the new domains of nanoscale material processing and fabrication. The main objective of this research project is to provide, through advanced multiscale modeling and theoretical analysis, detailed information on the mechanisms and kinetics of fast nonequilibrium structural and phase transformations triggered by short pulse laser irradiation of metal targets and responsible for the generation of complex hierarchical surface morphology at the nanoscale and microscale, and unusual surface microstructure.A key component of this project is the design and verification of a novel multiscale computational approach combining, in a synergistic manner, large-scale atomistic simulations of the initial material response to short pulse laser excitation, including rapid melting, cavitation, and, at higher laser fluences, explosive boiling and phase decomposition of superheated liquid, with a coarse-grained modeling of the subsequent slower hydrodynamic motion and solidification of the melted surface region. The new computational model will enable a detailed exploration of the complex interplay of the totality of laser-induced processes occurring at different time- and length-scales and will reveal the connections between irradiation conditions, material properties, crystallographic orientation of grains in polycrystalline targets, and the microstructure of surface features generated by laser irradiation.The emergence of new flexible computational methodology for multiscale modeling of material response to a rapid energy deposition is likely to make a broad impact in the general area of computational materials science. The methods developed within this project will be broadly disseminated to the research community and applied, through existing and new collaborations, to different material systems, ranging from metal alloys to organic materials, and various laser processing conditions, for example the presence of a background gas, liquid environment, or a transparent overlayer. Owing to the size of the simulated material, the need for long simulation time, and the complexity of the model, high performance computing simulations are required.The involvement of students in all aspects of high-performance parallel computing and close interaction with experimental and computational collaborators worldwide will create a fertile educational environment in the quickly expanding areas of scientific computing and laser-materials interactions. An educational website containing an accessible presentation of basic concepts of laser-materials interactions illustrated by images and animations produced in this project will be developed as a platform for conveying the relevance and excitement of the computational materials research to broader audiences.