National Science Foundation - Division of Chemical &Transport Systems ? Particulate & Multiphase Processes Program (1415)
Proposal Number: 0730143 Principal Investigators: Zhang, Yuwen Affiliation: University of Missouri Columbia Proposal Title: An Integrated Approach for Modeling Nano- and Femtosecond Laser Sintering of Metallic Micro- and Nanoparticles
The 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.
