Date of Award

Summer 8-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular Science and Nanotechnology

First Advisor

Collin Wick

Abstract

The objective of this research was to investigate the deformation behavior of metal/ceramic interfaces under external loadings in a multi-scale framework including first principles density functional theory (DFT) and molecular dynamics (MD) simulations. The mechanical properties of the metal/ceramic interfaces are dominated by defects on a length scale that first principles computations cannot access. Since the DFT calculations become computationally expensive for such large sized systems, therefore, MD simulations are required to deal with such systems. For MD simulations, second nearest neighbor modified embedded atom method (MEAM) potentials were developed to study metal/ceramic interfaces involving Cr, Ti, Al, and N.


The effect of misfit dislocation networks (MDNs) on the stability and shear strength of Cr/TiN was investigated using the newly developed potential. Good agreement with a combination of experimental and DFT results was achieved. The interfacial energy was lowest when the MDN was located in the Cr layer adjacent to the chemical interface, which also had the largest dislocation core width. This was consistent with generalized stacking fault energies, which had lower energy barriers between the first and second Cr layers next to the chemical interface. For all positions of MDNs, shear failure occurred in the ceramic, between the first and the second TiN layers next to the chemical interface. The lowest shear strength was found for the system with the MDN in the first Cr layer with respect to the chemical interface. Only for this particular configuration was there a significant plastic deformation present.


The impact of Al doping on the stability and shear strength of Ti/TiN metal/ceramic interface was also investigated. The model was parameterized to the interfacial properties of pure Al, TiAl and AlN binaries as well as TiAlN ternary systems. A Monte Carlo scheme was developed to find the most likely doping configuration of Al atoms in Ti/TiN. The doping was increased up to 25 mol % Al concentration after which the enthalpy of mixing started to increase. There was a drastic increase in the maximum shear stress from about 200 MPa in case of the undoped system to almost 1 GPa for the 25 mol % Al doped Ti/TiN. This study would be particularly useful in materials-based engineering of metal/ceramic interfaces and will have a significant impact on applications of ceramic coating/substrate systems in material engineering.

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