Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 86-89). Also available on the Internet.

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Thesis (M.App.Sc.) - Carleton University, 2005. / Includes bibliographical references (p.138-143 ). Also available in electronic format on the Internet.

Thesis (M.S.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains xi, 94 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 88-89).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1968. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Changes in pretreated 5182, 6061 and 7075 aluminum surfaces on exposure to moisture for short times was studied. The pretreatment used was the standard ASTM method for FPL etching of aluminum. The moisture treatment used was either immersion in water at 81° C or exposure to water vapor at 81° C. The experimental techniques used to analyze the pretreated aluminum surfaces before and after exposure to moisture were ESCA or XPS, AES, high resolution SEM, and specular reflectance FTIR. There was a change in the surface topography on exposure of the aluminum surfaces to water as determined using high resolution SEM. Stoichiometric calculations based on XPS analysis were made to estimate the amount of excess water present on the surface. Water was present on the surface before exposure to moisture, for all three alloys. The amount of water present on the surface was found to decrease with increasing times of exposure to water for all three alloys. This result was consistent with the model that pseudoboehmite formed on the surface was being converted into boehmite at longer times of exposure to water. The thickness of the oxide layer was found to increase with time of exposure to water based on ESCA results. The same conclusion was reached by depth profiling the oxide layer using AES. The rate of increase in the concentration of pseudoboehmite on the surfaces as calculated from FTIR data went in the order 7075 < 5182 < 6061. The activation energy for the third step (transport of soluble species to the surface) in the conversion of surface Al₂O₃ to AlOOH was calculated from FTIR results to be 3.5 kcal mol⁻¹. / Master of Science

The effects of variations in composition on the decomposition process in Al-Zn-Mg-Cu alloys (i.e. – 7xxx-series aluminum alloy) were studied emphasizing their effect on mechanical properties. Several experimental quaternary alloys were studied to compare their behavior with commercial 7xxx-series alloys. The investigation included studies on the effects of natural aging, artificial aging, quench sensitivity, precipitate free zone formation, and homogenization. Additionally, “true aging” curves (i.e. – hardness/strength vs. conductivity) were presented in order to visualize and quantify the entire precipitation process. It is obvious that fluctuations in the main alloying elements/processing parameters can alter the precipitation process, but the purpose of this work was to quantify those changes using standard industrial techniques. It was found that natural aging was detrimental for strength in the T6 temper for alloys containing more than 1.0 wt.% Cu, and was shown to alter the coarsening kinetics in the over-aged condition (T7). Conversely, for alloys with Cu contents less than 0.5% natural aging was shown to be beneficial for strength. Altering the Zn:Mg ratio was also shown to effect natural aging response of an alloy in addition to introducing additional precipitation processes (T-phase). Therefore, this work is a blueprint for advanced alloy manufacturing that allows for the rapid production of new alloys and tempers by narrowing the research focus depending on an alloy’s composition.

Approved for Public Release; Distribution is Unlimited / Friction Stir Processing (FSP), although relatively simple in concept, results in an extremely complex thermomechanical treatment to the material being processed. Previous studies of FSP have shown that the process results in extremely high strain, strain rates and temperatures as well as gradients in strain, strain rate and temperature within a small volume of material. This thesis will study the effect of varying FSP parameters during the processing of Nickel-Aluminum-Bronze (NAB) propeller material. The modeling program CTH was used to define the relationship between tool rotation speed, traversing speed and the total power input to the material. The tool's mechanical power and the power generated by deformation of the material has been investigated. The modeling experiments were designed to gain an understanding of the relationship of process parameters, microstructure and mechanical properties, and to enhance our understanding of the flow patterns and thermal histories of the NAB material in the stir zone. / Lieutenant, United States Navy

A thermally grown oxide (TGO) such as the alumina scale formed on a bondcoat enhances the oxidation and corrosion resistance of thermal barrier coating (TBC)- bondcoat-superalloy substrate systems. As the external alumina scale lies between the thermal barrier coating and bondcoat, its first spallation and subsequent TBC delamination become critical. Once the external alumina scale spalls, it will spall together with the TBC, leaving the system with no temperature barrier protection. Operational factors such as thermal cycling conditions, water vapour in the oxidation atmosphere, and alloying elements comprising the bondcoat system affect alumina scale adherence. Another problem that arises for the majority of bondcoat systems, β (Ni,Pt)Al and MCrAlY (M=Metal), are rich in aluminium. This causes aluminium to diffuse into the substrate, enriching it with aluminium during service, transforming phases in the substrate alloying system. The purpose of this study was to develop bondcoat materials that promote formation of a strongly adherent TGO, but have an aluminium content near the substrate composition. Cyclic oxidation experiments were performed with Ni-Al, Ni-Pt-Al, and Ni-Pt-Al-Ir alloys in dry air and air-12%H2O. Thermal cycles of 1 hr at 1200OC and 10 minutes at 80OC were carried out in flowing gases at a total pressure of 1 atm. Experiments in N2- 12%H2O were performed only on Ni-Al binary alloys. Binary Ni-Al cast alloys were tested for fundamental study purposes, while Ni-Pt-Al and Ni-Pt-Al-Ir cast alloys were intended to be models for aluminide coatings, with attention focused on γ+γ' -Ni-(20 to 23)Al. Comparisons were made with β-Ni-50Al, as it forms an external alumina scale and was found to have the smallest weight loss rate during testing of binary alloys. Assessments of Pt and Pt-Ir additions, with and without hafnium, to the γ+γ' binary alloy were made. Compared to binary alloys, platinum was found to reduce the total weight loss caused by scale spallation. Experiments in air-12%H2O led to more rapid weight loss than in dry air. This was due to enhanced spallation. However, the degradation rate was slower than in platinum-free alloys exposed to the same atmosphere. Partial replacement of platinum with iridium was found to improve alloy scale adherence during exposure in both dry and wet air. Addition of 1wt% hafnium was found to reduce oxide thickness and increase the oxide adherence simultaneously. The hafnium addition was essential in order to reduce spallation rate in wet air. Water vapour in the presence of oxygen generally increased the spallation rate. It weakened the oxide metal interface, causing subsequent spallation to be increased, but only if the gas had access to the alloy-scale interface. Water vapour did not affect the spallation rate of the strongly adherent oxide grown on Ni-22Al-30Pt+1wt%Hf and Ni- 20Al-15Pt-10Ir+1wt%Hf.

The miniaturization of Microtechnology-based Energy, Chemical and Biological Systems (MECS) is made possible by the use of high aspect ratio microchannel arrays to increase the surface-area-to-volume ratio of the flow conduits within the devices, resulting in an improvement in the heat and mass transfer performance of the devices. However, advantages of the MECS concept cannot be applied to high-temperature applications (above 650��C) due to lack of high-temperature MECS devices; therefore, the development of high-temperature MECS devices is necessary to overcome this bottleneck. This dissertation involves the development of high-temperature MECS devices from a high-temperature material, nickel aluminide (NiAl). NiAl foil was synthesized from elemental nickel (Ni) and aluminum (Al) foils through a two step process--tack bonding and reactive diffusion. The elemental foils were tack bonded at 500��C, 3.9 MPa for 15 minutes. The reactive diffusion process was then performed through a heat treatment at 1000��C for a period of time corresponding to the thickness of the composite foil. The synthesized NiAl foil showed an atomic ratio of Al to Ni up to 0.96. The foil also showed a decent flatness and surface roughness. This dissertation proposes a reactive diffusion bonding as a joining technique of nickel aluminides. An investigation of bonding parameter effects on the warpage of nickel aluminide fins in the reactive diffusion bonding process was performed. Results showed that bonding time and temperature had significant effects on warpage of the fin. The fin warpage increased with the increase of bonding time and bonding temperature. Results also suggested that the bonding pressure had an effect on the fin warpage. However, chemical compositions of the fin were not significant to the warpage. This research also proposes a new fabrication procedure for producing NiAl MECS devices. NiAl foils were used as the starting material, and the reactive diffusion bonding technique was employed as the joining technique. The research outcome indicated the viability of the proposed method in fabricating NiAl MECS devices. This method achieved leak-tight devices with a reasonable fin flatness. / Graduation date: 2003