An Integrated Approach for Modeling Nano- and Femtosecond Laser Sintering of Metallic Micro- and Nanoparticles

美国国家科学基金会化学与运输系统分部？项目编号：0730143项目负责人：张玉文合作院校：密苏里大学哥伦比亚分校项目名称：金属微粒子和纳米粒子纳米和飞秒激光烧结综合建模方法该项目的目标是开发一种金属微粒子和纳米粒子纳米和飞秒激光烧结综合建模方法。在理论研究中，将首先模拟粉末颗粒和团聚体的堆积，然后模拟微颗粒（直径远大于激光波长）和纳米颗粒（直径与激光波长相当或小于激光波长）的激光-粒子相互作用。采用分子动力学和双温模型相结合的混合分子动力学模拟方法，对材料的过热、超快熔化、汽化或相爆炸、再凝固、过冷和结合强度等性能进行表征。利用分子动力学模拟的性质，建立了激光烧结的半经典双温度耦合热力学模型和激光烧结的简化经典热力学模型。粉末床/烧结区中远离激光束的区域将被建模为连续体。在时间和长度尺度上的几个数量级的模型将被整合在一起，以发展一个ns和fs激光烧结的连贯框架。在实验中，通过控制激光加工工艺和材料参数，制备出具有可变可控孔隙率和纳米孔层的各种金属零件。实验结果将用于验证所建立的多尺度激光烧结模型。如果成功，将为粒子科学与技术领域前所未有的多尺度短脉冲激光烧结模型提供一个通用的解决方案。在该领域首次提出通过控制激光脉冲宽度、重复频率、激光强度和扫描速度来利用和控制激光烧结最终产品的孔隙度。在激光脉冲与粒子相互作用过程中，电子和声子之间的不平衡将由一个混合分子动力学/双温度模型来考虑。与大多数将整个粉末床视为连续体的现有模型相反，离散区域中每个颗粒的颗粒级建模将使用耦合的半经典双温度热力学模型进行。通过在连续区和连续区的交界面附近放置一层粒子来考虑连续区和离散区之间的相互作用，并用粒子层中粒子的温度来架起连续区和离散区之间的桥梁。该技术的应用包括制造具有渐变孔隙度的骨科植入物、燃料电池电极和纳米多孔表面。所提出的综合方法建模ns和fs激光烧结将为预测和控制孔隙度提供指导，应用于能源，航空航天和生物工程。这些项目将整合拟议研究的材料到几个现有的和新的课程中，为机械工程教育奠定坚实的基础。pi计划开放他们的热制造实验室，在MU工程周计划期间向中学生和高中生展示激光烧结实验和可视化计算结果，并在年度女童子军工程日向女童子军展示，以激发她们攻读工程学位的兴趣。

National Science Foundation - Division of Chemical &Transport Systems ? Particulate & Multiphase Processes Program (1415)Proposal Number: 0730143Principal Investigators: Zhang, YuwenAffiliation: University of Missouri ColumbiaProposal Title: An Integrated Approach for Modeling Nano- and Femtosecond Laser Sintering of Metallic Micro- and NanoparticlesThe objective of this project is to develop an integrated approach for modeling nano- and femtosecond (ns and fs) laser sintering of metallic micro- and nanoparticles. In theoretical investigation, packing of powder particles and agglomerates will be simulated first, followed by modeling of laser-particle interaction for microparticles (diameters are much greater than the laser wavelength) and nanoparticles (diameters are comparable or smaller than the laser wavelength). A hybrid molecular dynamics simulation combining molecular dynamics and two-temperature model will be performed to characterize the properties of superheating, ultrafast melting, vaporization or phase explosion, resolidification, undercooling and bonding strength. With the properties from the molecular dynamic simulation, a coupled semi-classical two-temperature thermomechanical model for fs laser sintering and a reduced classical thermomechanical model for ns laser sintering will be developed for each particle in the region under the laser spot (discrete region). The region far from the laser beam in the powder bed/sintered region will be modeled as a continuum. The models ranging several orders of magnitude of temporal and length scales will be integrated to develop a coherent framework for ns and fs laser sintering. In experiments, various metallic parts with variable and controllable porosity and nanoporous layer will be fabricated by controlling the laser processing and material parameters. The experimental results will be used to validate the developed multiscale laser sintering model. If successful, the combined modeling and experiments will provide a general solution to model short-pulsed laser sintering in unprecedented multiscale in the field of particle science and technology. Intellectual Merit For the first time in the field, the PIs propose to utilize and control the porosity in the final product of laser sintering by controlling the laser pulse width, repetition rate, laser intensity, and scanning velocity. Nonequilibrium between electrons and phonons during fs laser pulse-particle interaction will be considered by a hybrid molecular dynamics/two-temperature model. In contrast to most existing models that treat the entire powder bed as a continuum, particle level modeling for each particle in the discrete region will be performed using a coupled semi-classical two-temperature thermomechanical model. The interaction between the discrete and continuum regions is considered by placing a layer of particles in the continuum region next to the interface between the two regions, and the temperatures of the particles in the particle layer are used to bridge the discrete and continuum regions. Applications of the developed technology include fabrication of orthopedic implants with graded porosity, electrodes for fuel cells, and nanoporous surfaces. Broader Impact The proposed integrated approach for modeling ns and fs laser sintering will provide guidelines on prediction and control of the porosity for applications in energy, aerospace, and bioengineering. The PIs will integrate materials from the proposed research into several existing and new courses to build a solid foundation for mechanical engineering education. The PIs plan to open their Thermal Manufacturing Lab to demonstrate laser sintering experiments and visualized computational results to middle- and high-school students during MU Engineering Week Program, as well as to Girl Scouts in the Annual Girl Scouts Engineering Day to stimulate their interests to pursue a degree in engineering.