Doctor of Engineering (DEng)
Quantitative assessment of the adhesion strength of ceramic hard coatings on substrates is a subject of great technological importance as well as current scientific relevance. Achievement of reliable and quantitative measurements of interfacial strength has proven difficult over the past two decades. In this dissertation, how the deformation and fracture behavior of ceramic/metal/substrate interfacial regions under shear and tensile loading is influenced by the structure and chemical composition of the interfacial region were observed and discussed. Interfacial shear failure experiments were carried out on focused ion beam fabricated micro pillars containing interfacial regions of ceramic/metal/substrate systems. Detailed characterization was carried out, using X-ray diffraction (XRD), instrumented nanoindentation, Ga+ focus ion beam (FIB) scanning electron microscopy (FIB/SEM), and transmission electron microscopy (TEM). Additional insights on interfacial failure mechanisms were offered through results of accompanying density functional theory (DFT) calculations, molecular dynamics (MD) and crystal plasticity finite element analysis (CPFEA) simulations. Tensile testing was conducted on CrN/Cu/CrN/Si micro-pillar specimens with varying Cu layer thickness. The interlayer plasticity and the critical tensile fracture stress were observed to display a significant dependence on the Cu interlayer thickness. To yield mechanical response data on metal/ceramic interfaces with better defined structural characteristics, growth of Cu thin films at varying temperatures were conducted onto single crystal TiN(001) thin film templates and structure of the Cu thin films were examined. A new Cu-TiN orientation relationship with Cu(110)//TiN(001) was found for the first time. The influence of nanoscale twinning and lattice strain on structure and interfacial energetics of Cu/TiN bi-crystals was discussed and augmented through MD simulations. Axial shear and tensile testing were performed on such TiN/Cu/TiN interfacial regions. All experimental results described in this dissertation are new and exemplify effective experimentation protocols for quantitatively assessing the interfacial mechanical integrity of metal/ceramic interfacial regions, as well as providing a start point for further investigations on mechanical response of other solid-solid interfaces.
Zhang, Xiaoman, "Mechanical Failure of Metal/Ceramic Interfacial Regions under Shear and Tensile Loading" (2021). LSU Doctoral Dissertations. 5571.
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