Crack healing in quartz has been investigated by optical microscopy and interferometry of rhombohedral ( 1 1 10 ) cracks in polished Brazilian quartz prisms that were annealed hydrothermally at temperatures of 250°C and 400°C for 2.4 to 240 hours, fluid pressure Pf = Pc = 41 MPa, and varying pOH- (from 5.4 to 1.2 at 250°C for fluids consisting of distilled water and NaOH solutions with molalities up to 1). Crack morphologies before and after annealing were recorded for each sample in plane light digital images. Crack apertures were determined from interference fringes recorded using transmitted monochromatic light (l = 598 nm). As documented in previous studies, crack healing is driven by reductions in surface energy and healing rates are governed by diffusional transport; sharply defined crack tips become blunted and split into fluid- filled tubes and inclusions. A rich variety of fluid inclusion geometries are also observed with nonequilibrium shapes that depend on initial surface roughness. Crack healing is significant at T=400°C. Crack healing is also observed at T=250°C for smooth cracks with apertures <0.6 mm or cracks subject to low pOH-. The extent of crack healing is sensitive to crack aperture and to hackles formed by fine-scale crack branching during earlier crack growth. Crack apertures appear to be controlled by hackles and debris, which prop the crack surfaces open. Upon annealing, crack apertures are reduced, and these reduced crack apertures govern the kinetics of diffusional crack healing that follows. Hackles are sites of either enhanced or reduced loss of fluid-solid interface, depending on slight mismatches and sense of twist on opposing crack surfaces. Hackles are replaced either by healed curvilinear quartz bridges and river patterns surrounded by open fluid-filled crack, or by fluid- filled tubes surrounded by regions of healed quartz. For a given temperature, aperture and anneal time, crack healing is enhanced at low pOH- ( £ 1.2) either because of changes in the hydroxylated quartz- fluid interface that enhance reaction rates or because of increased rates of diffusional net transport of silica at high silica concentrations.

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La durabilité des verres, leur réactivité ou leur fonctionnalisation peuvent être optimisées en modifiant leur état de surface, ouvrant ainsi la voie à de nouvelles applications. L'objectif de cette thèse est de mieux appréhender les modifications induites à la surface et à la sub-surface des verres d'oxydes, ainsi que l'évolution des micro-défauts existant à leur surface au cours de traitements thermiques. Ces traitements sont réalisés autour de la température de transition vitreuse, mais à des températures où le verre ne se déforme pas. Cette étude met en évidence l'influence cruciale de l'atmosphère de traitement. Elle porte principalement sur le cas du verre « float », en distinguant les faces « air » et « étain ».En s'appuyant sur les spectroscopies SIMS et Infrarouge, l'étude montre que les modifications de la sub-surface du verre dépendent de la teneur en eau de l'atmosphère du four. Alors que la sub-surface, initialement hydratée, est peu modifiée lorsque le taux d'humidité est élevé, les changements les plus significatifs sont observés sous atmosphère sèche. La déshydratation de la sub-surface du verre induit en effet la création d'une couche enrichie en silice par appauvrissement en ions modificateurs.Pour caractériser l'influence de ces modifications sur l'évolution de la morphologie des micro-défauts de surface au cours des traitements thermiques, des micro-fissures sont générées par indentation Vickers puis analysées par microscopies optique et électronique. Deux mécanismes sont mis en évidence : soit une fermeture des fissures dans les premiers instants du traitement sous l'effet de la relaxation des contraintes, soit une sphéroïdisation des fissures par flux visqueux induit par les forces tensions capillaires. Ces mécanismes sont en compétition et dépendent de l'état initial de la sub-surface du verre. En effet, la viscosité de cette sub-surface est fortement dépendante de son taux d'hydratation et peut varier très significativement au cours du traitement thermique. Dans le cas de la face « étain » du verre float, l'influence du caractère oxydant de l'atmosphère est également mis en évidence. / The glass durability, its reactivity or its functionalization can be optimized by surface modification, allowing development of new applications. The aim of this thesis is to better understand the changes induced at the oxide glass surface and sub-surface and the evolution of surface micro-flaws during thermal treatment.These treatments are performed around glass transition temperature, but at temperatures at which the samples are not deformed. The key role of the atmosphere of treatment is especially highlighted. Analyses focused on the float glass both on the “air side” and “tin side”.Based on SIMS and infrared spectroscopies, results show that the sub-surface changes depend on the water content of the furnace atmosphere. While the sub-surface, initially hydrated, is not strongly modified when the humidity level is high, significant changes are induced under dry atmosphere. The dehydration of the sub-surface induces indeed the formation of a silica enriched layer by impoverishment of modified ions.In order to characterize the influence of these changes on the evolution of micro-flaws morphology during thermal treatments, micro-cracks are generated by Vickers indentation and analyzed by optical and electronic microcopies. Two main behaviors are evidenced: either a direct crack closure during the first step of the thermal treatment due to stress relaxation or a crack spheroidization caused by viscous flow driven by capillarity forces. Both mechanisms are in competition and depend on the initial state of the glass sub-surface. The viscosity of this layer is highly dependent on the hydration level and can vary significantly during the treatment. In case of “tin side” of float glass, the effect of oxidant atmosphere is also evidenced.

The current US fleet of nuclear reactors has been in service for three decades. Over this period, existing welds in stainless steel (SS) shrouds have sustained stress corrosion cracking (SCC) and are in need of repair. Additionally, helium has formed interstitially as a byproduct of proton bombardment. Current repair technology, such as TIG welding, puts extreme amounts of heat into the material and allows for interstitial helium atoms to aggregate and form bubbles/voids at grain boundaries. This significantly weakens the material, proving to be a very counterproductive and ineffective repair technique. Much study has been done on friction stir processing (FSP), but none has explored it as an enabling repair technology for use in nuclear applications. Because of its relatively low energy input as a solid state joining technology, it is proposed that FSP could effectively heal SCCs in these existing welds without the negative side effect of helium bubble formation. A spread of speeds and feeds were initially tested using a PCBN-W-Re tool on 304L SS. Six of these parameter sets were selected as representations of high, medium, and low temperature-per-power outputs for this research: 2 IPM-80 RPM, 2 IPM-150 RPM, 4 IPM-150 RPM, 4 IPM-250 RPM, 6 IPM-125 RPM, and 6 IPM-175 RPM. These varied parameter sets were tested for their tensile, micro-hardness, and corrosion resistant properties. In general, the lower IPM and RPM values resulted in higher ultimate tensile strengths (UTS). Higher IPM and RPM values resulted in tunnel, pin hole, and surface void defects. These defects caused premature failure in tensile tests and could often be identified through microscopy. Micro-hardness testing demonstrated a strong correlation per the Hall-Petch relationship – finer grain sizes resulted in higher yield strength (hardness values) of the material. The tool temperature during FSP was a good indicator of the expected hardness – lower temperatures resulted in higher hardness values. Corrosion testing was performed with a 1000-hour alternate immersion test in a room temperature 3.5% NaCl solution. With these testing parameters, the results demonstrated that FSP had no effect on the corrosion resistance of 304L SS under these conditions.

Continuing an investigation on using FSP to heal stress corrosion cracks (SCC) in welds on nuclear reactors, this study seeks to use AM in addition to FSP to aid crack repair. Previous studies address that current repair technology on nuclear reactors involves the use of TIG welding which can allow helium atoms to aggregate and form voids at the grain boundaries. This weakens the material and renders the repair ineffective. Another previous study evaluated the effectiveness of FSP alone in repairing SCC which did have defects depending on the parameters used during FSP. This study evaluated the use of AM in addition to FSP. Literature is available on FSP and AM separately and literature is available on technologies that used both them together. However, the current processes that are available that use both AM and FSP can be expensive and may be impractical for some purposes. This study shows a new process that is both less expensive and more practical in SCC repair. Initial proof of concept trials was performed on 1018 mild steel using both wire fed additive and insert additive technologies. A slot would be removed and filled in with an additive process and processed using FSP. Because of poor repeatability, substantial distortion, and voids present this study went forward using insert technologies in further experiments rather than wire wed additive technologies. In addition, the depth and width of the insert or area where the added material would be placed was varied in initial trails. Tensile testing was performed on initial steel trials and the stainless steel experiments and it demonstrated a correlation between depth of the added material and the tensile strength. Micro-hardness mapping performed on initial steel trials also showed hardening in the FSP stir zone. Three-point bend tests were performed to show that an existing crack underneath the FSP zone would not propagate through the nugget. All evaluations supported a substantial increase in yield strength increased after FSP.

To minimize global carbon emissions, having efficient jet engines and internal combustion engines necessitates utilizing lightweight alloys such as Al, Ti, and Mg-based alloys. Because of their remarkable strength/weight ratio, these alloys have received a lot of attention. Nonetheless, they have very poor tribological behavior, particularly at elevated temperatures beyond 200 °C, when most liquid lubricants begin to fail in lubrication. Over the last two decades, there has been a lot of interest in protecting Al, and Ti-based alloys by developing multiphase solid lubricants with a hard sublayer that provide mechanical strength and maintain the part's integrity while providing lubricity. The development of novel coatings with superior lubricity, high toughness, and high-temperature tolerance remains a challenging and hot topic to research and provide new engineered solutions for. To address and provide solutions to protect light-weight, i.e., Al, and Ti alloys at high-temperature and bestow superior tribological properties to such alloys, three types of adaptive lubricious coatings have been studied in this thesis: Nb-Ag-O self-healing lubricious ternary oxide, PEO-chameleon a self-adaptive multi-phase coating, and Sb2O3-MSH-C lubricious adaptive coatings to address this challenge. The development of the Nb-Ag-O ternary resulted in a coefficient of friction as low as 0.2 at 600 °C and crack healing at 900 °C. PEO-chameleon coatings demonstrated a remarkably low COF, as low as 0.07 at 300 °C and 1.4 GPa applied pressure. Finally, the Sb2O3-MSH-C multi-phase lubricious solid lubricant revealed superlubricity, with a CoF of 0.008 at 300 °C, providing a potentially promising contender for high-temperature, high-load applications.