Doctor of Philosophy (PhD)
In this study, air or atmospheric plasma spraying (APS), one of thermal spraying processes, was used to produce alumina coatings and single splats. Nanoindentation technique was used to measure the mechanical properties, such as hardness and elastic modulus, of APS alumina coatings and single splats. The detailed procedures to calculate elastic modulus and hardness, and testing parameters for nanoindentation have been provided. This study revealed that the phase combination of α-Al2O3 and γ-Al2O3 played an important role in the scattering distribution of nanoindentation results on APS alumina coatings. In addition, nanoindentation technique was used to predict the phase information of the APS coatings in this study by elastic modulus comparison. Nanoindentation result confirmed disc-shaped alumina splats were γ phase, which was also consistent with the XRD result that the bottom surface of APS alumina coating was almost pure γ-Al2O3. An analytical model of nanoindentation on multilayered thin films was provided. Then, this analytical model was used to study nanoindentation response with APS alumina coatings. The analytical results were compared with experimental data and used to guide nanoindentation experimental parameters setup. Reactive Al/Ni multilayered thin films were deposited by DC magnetron sputtering. Reactive Al/Ni multilayer foils can be used as local heat sources to melt solder or braze layers and thus bond different components. Performance of reactive Al/Ni multilayered thin films was studied under 1D, 2D and 3D configurations using multiphysics based numerical simulations. Temperature evolution during the reaction process was simulated. The simulation result showed both localized heating and rapid cooling during reaction. Alumina thin films were fabricated by DC reactive magnetron sputtering. The hysteresis experiment has been carried out to find the suitable oxygen flow rate. The XRD analyses showed that the deposited aluminum oxide thin films were amorphous since no reflections of crystallized oxide could be observed. The stoichiometry of the aluminum oxide thin films was measured by XPS. The XPS analyses gave the O/Al ratio of 1.59, while the exact ratio is 1.50 corresponding to the stoichiometric Al2O3.
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Liu, Ranran, "Fabrication and property study of plasma sprayed alumina coatings and magnetron sputtered multilayers" (2011). LSU Doctoral Dissertations. 3341.