Simulating the solid-state sintering of nanoparticles in a powder bed configuration



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This document presents an approach to modelling the sintering of nanoparticles for applications in solid-state diffusion micro–Additive Manufacturing processes like the novel Microscale Selective Laser Sintering process. The simulations presented here use the Discrete Element Method and Phase Field Modelling approach to model the sintering of nanoparticles. There are currently no simulations of solid-state sintering for nanoparticles in a powder bed. These simulations are important to understand the kinetics on the particle scale, the phenomenon driving sintering and how the nanoparticles fuse together with input energy. Understanding this allows for a better control of the actual fabrication process. In this dissertation, the steps taken to build this simulation package are detailed. Additional simulation tools are created for analysis of the resulting sintered simulation beds. Scripts for visualizing the particles are used to depict the sintering process and are qualitatively compared to Scanning Electron Microscopy images of actual nanoparticles after solid-state sintering. These qualitative results show good agreement between the simulation results and the experimental results. To provide quantitative metrics to test the simulation, packages are developed to measure the amount of densification in the sintered powder beds as well as the electrical resistance as the densification of the bed increases. These metrics are used for calibration as well as validation of the sintering simulation. Several experiments are performed for the purposes of calibrating the simulations to physical parameters, as well as validating the simulation results. The details of these experiments are also presented in this document as well as the resulting findings. Prior to this, there is yet to be any publicly available data from experiments of this kind, measuring the densification of copper nanoparticles as functions of temperature and time, as well as the electrical resistivity as a function of densification. The simulation results are compared to experimental results and show that the simulations can be accurately used to make predictions for the electrical resistance properties expected during solid-state sintering of the copper nanoparticles used in this study.


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