Publication Date

2025

Document Type

Dissertation/Thesis

First Advisor

Salehinia, Iman

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Mechanical Engineering

Abstract

This thesis presents a molecular dynamics (MD) simulation study of femtosecond laser-induced melting and heat transfer in multiple Cu–Al core–shell nanoparticle systems. The research builds upon previous single-particle studies and extends the investigation to multiple interacting nanoparticles to better understand nanoscale thermal transport and melting behavior under ultrafast laser irradiation. Understanding this process is essential for improving laser-based additive manufacturing and sintering of metal matrix nanocomposites (MMNCs), where precise control of heat flow and particle bonding determines the final material quality. The simulations were performed using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) integrated with the Modified Two-Temperature Model (MTTM). This approach allows the coupling of the electronic and lattice subsystems, accurately representing the nonequilibrium energy exchange that occurs during femtosecond laser heating. The Cu–Al core–shell configuration was selected because Aluminum absorbs laser energy efficiently while copper provides high thermal conductivity, enabling the study of localized melting and rapid heat conduction between particles. A Gaussian femtosecond laser pulse with a duration of 50 femtoseconds was applied to one nanoparticle to initiate melting, and the subsequent heat propagation to neighboring particles was analysed. The results show that the femtosecond laser pulse causes rapid electron excitation in the Aluminum shell, leading to surface melting within a few picoseconds, while the copper core remains relatively stable. As the electron–phonon coupling progresses, heat transfers efficiently to the lattice and spreads to adjacent particles. The rate of heat transfer was found to depend strongly on the spacing, alignment, and material composition of the nanoparticles. Visualization using OVITO confirmed the onset of melting through changes in crystal structure, atomic displacement, and temperature distribution. Overall, this study provides a detailed understanding of ultrafast thermal transport and localized melting in metallic core–shell nanoparticles. The findings contribute to the broader goal of optimizing femtosecond laser processing for the fabrication of MMNCs, enabling improved control of microstructure formation and interparticle bonding at the nanoscale.

Extent

86 pages

Language

en

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

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