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

国家科学基金会--化学与运输系统部门？颗粒和安培；多相工艺计划(1415)提案编号：0730143主要研究人员：张宇文隶属：密苏里大学哥伦比亚分校提议标题：金属微米和纳米颗粒的纳秒和飞秒激光烧结建模的集成方法本项目的目标是开发一种对金属微米和纳米颗粒的纳秒和飞秒(ns和fs)激光烧结建模的集成方法。在理论研究中，将首先模拟粉末颗粒和团聚体的堆积，然后对微米颗粒(直径远大于激光波长)和纳米颗粒(直径与激光波长相当或更小)进行激光-颗粒相互作用的建模。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表征过热、超快熔化、汽化或相爆炸、再结晶、过冷和粘结强度等性质。利用分子动力学模拟的性质，建立了飞秒激光烧结的半经典双温热力学耦合模型和ns激光烧结的简化经典热力学模型。在粉末床层/烧结区中远离激光的区域将被建模为连续介质。时间和长度尺度的几个数量级的模型将被集成在一起，以开发出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，可以制备出孔隙率和纳米孔隙率可变且可控的各种金属零件。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，该模型与实验的结合将为颗粒科学与技术领域以前所未有的多尺度模拟短脉冲激光烧结提供一个通用的解决方案。智能优点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中的气孔率。飞秒激光脉冲-粒子相互作用过程中电子和声子之间的非平衡将用分子动力学/双温混合模型来考虑。与大多数现有的将整个粉末床层视为一个连续体的模型不同，离散区域中每个颗粒的颗粒级模拟将使用耦合的半经典双温热力学模型。离散区域和连续区域之间的相互作用是通过在连续区域中靠近两个区域之间的界面放置一层颗粒层来考虑的，并利用颗粒层中颗粒的温度来连接离散区域和连续区域。开发的技术的应用包括制造具有渐变孔隙率的整形外科植入物、燃料电池电极和纳米孔表面。更广泛的影响所提出的模拟ns和fs激光烧结的综合方法将为能源、航空航天和生物工程中的应用提供孔隙率预测和控制的指导方针。该计划将把拟议研究的资料整合到数项现有和新的课程中，为机械工程教育奠定坚实的基础。PIS计划在MU工程周计划期间向初中生和高中生演示激光烧结实验和可视化计算结果，并在一年一度的女童子军工程日向女童子军开放他们的热制造实验室，以激发他们攻读工程学学位的兴趣。

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.