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The Relationship of Microstructure to Fracture and Corrosion Behavior of a Directionally Solidified SuperalloyTrexler, Matthew David 18 December 2006 (has links)
SUMMARY
GTD-111 DS is a directionally solidified superalloy currently used in turbine engines.
To accurately predict the life of engine components it is essential to examine and characterize
the microstructural evolution of the material and its effects on material properties. The
as-cast microstructure of GTD-111 is highly inhomogeneous as a result of coring. The
current post-casting heat treatments do not effectively eliminate the inhomogeneity. This
inhomogeneity affects properties including tensile strength, fracture toughness, fracture
path, and corrosion behavior, primarily in terms of the number of grains per specimen. The
goal of this work was to link microstructural features to these properties.
Quantitative fractography was used to determine that the path of cracks during failure
of tensile specimens is influenced by the presence of carbides, which are located in the
interdendritic regions of the material as dictated by segregation. The solvus temperature
of the precipitate phase, Ni3(Al, Ti), was determined to be 1200C using traditional metallography,
differential thermal analysis, and dilatometry. A heat-treatment was designed
to homogenize the microstructure for tensile testing that isolates the carbide by dissolving
all of the eutectic Ni3(Al, Ti) precipitate phase, which is also found in the interdendritic
areas.
High temperature oxidation/sulfidation tests were conducted to investigate the corrosion
processes involved when GTD-111 DS is utilized in steam and gas combustion turbine
engines. The kinetics of corrosion in both oxidizing and sulfidizing atmospheres were determined
using thermogravimetric analysis. Additionally, metallography of these samples
after TGA revealed a correlation between the presence of grain boundaries and sulfur attack,
which led to catastrophic failure of the material under stress-free conditions in a sulfur
bearing environment. In summary, this work correlates the inhomogeneous microstructure
of GTD-111 DS to tensile fracture, and the corrosion process in turbine engines.
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Perchlorate reduction using electrochemically induced pitting corrosion of zero-valent titaniumLee, Chun Woo 15 May 2009 (has links)
Perchlorate is a threat to public health through water but also food. However,
there is no effective chemical treatment process which can destroy perchlorate found in
groundwater and surface water. Thus, there is growing interest in developing effective
technologies, especially chemical treatments, to completely destroy trace levels of
perchlorate present in drinking and groundwater.
The research on perchlorate reduction by zero-valent titanium (Ti(0)) showed
that perchlorate was effectively reduced to chloride using electrochemically developed
pitting corrosion on Ti(0). Perchlorate reduction was believed to be caused by an active
reductant (dissolved Ti(II)) during the pitting corrosion of Ti(0). The rate of perchlorate
reduction was independent on the imposed potential as long as the potential was
maintained above the pitting potential of Ti(0), but it was proportional to the applied
current. The perchlorate reduction on the pitting developed Ti(0) was inhibited by the
presence of chloride and bromide. Inhibition mechanism of perchlorate reduction inhibition was believed to be caused either by competitive adsorption of aggressive
anions on bare Ti(0) surface or Ti(II) consumption by electrochemically produced
chlorine. Kinetic models were developed based surface coverage of aggressive anions on
bare Ti(0) and Ti(II) oxidation by chlorine. These kinetic models supported the
perchlorate concentration change in the solution, but Ti(II) consumption model was not
able to predict chloride concentration due to insufficient information describing complex
nature of pitting on Ti(0).
These results shown in this research demonstrate that pitting corrosion developed
Ti(0) has the capability to chemically reduce perchlorate present in natural water and
engineered systems as well as possible problems associated with electric input. This
research may be a starting point for development of a new treatment process that applies
titanium or titanium metal ions as a chemical reductant to abate contaminants present in
natural and engineering systems. Further developments can be achieved by alloying
titanium metal with other metals such as iron and aluminum, and finding a methodology
producing stable Ti(II) in ambient conditions.
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High-strength stainless steels for corrosion mitigation in prestressed concrete: development and evaluationMoser, Robert David 16 May 2011 (has links)
The use of stainless steel alloys in reinforced concrete structures has shown great success in mitigating corrosion in even the most severe of exposures. However, the use of high-strength stainless steels (HSSSs) for corrosion mitigation in prestressed concrete (PSC) structures has received limited attention. To address these deficiencies in knowledge, an experimental study was conducted to investigate the feasibility of using HSSSs for corrosion mitigation in PSC. The study examined mechanical behavior, corrosion resistance, and techniques for the production of HSSS prestressing strands. Stainless steel grades 304, 316, 2101, 2205, 2304, and 17-7 along with a 1080 prestressing steel control were included in the study. Tensile strengths of 1250 to 1550 MPa (181 to 225 ksi) were achieved in the cold-drawn HSSSs. 1000 hr stress relaxation of all candidate HSSSs was predicted to be between 6 and 8 % based on the results of 200 hr tests conducted at 70 % of the ultimate tensile strength. Residual stresses due to the cold drawing had a significant influence on stress vs. strain behavior and stress relaxation. Electrochemical corrosion testing found that in solutions simulating alkaline concrete, all HSSSs showed exceptional corrosion resistance at chloride (Cl-) concentrations from zero to 0.25 M. However, when exposed to solutions simulating carbonated concrete, corrosion resistance was reduced and the only HSSSs with acceptable corrosion resistance were duplex grades 2205 and 2304, with 2205 resistant to corrosion initiation at Cl- concentrations up to 1.0 M (twice that in seawater). Based on these results, duplex grades 2205 and 2304 were identified as optimal HSSSs and were included in additional studies which found that: (1) 2304 is susceptible to corrosion when tested in a stranded geometry, (2) 2205 and 2304 are not susceptible to stress corrosion cracking, and (3) 2205 and 2304 are susceptible to hydrogen embrittlement. Efforts focused on the production of 2205 and 2304 prestressing strands showed that they could be produced as strands using existing ASTM A416 prestressing strand production facilities. Due to the ferromagnetic properties of 2205 and 2304, a low-relaxation heat treatment was found to be a viable option to reduce stress relaxation and improve mechanical properties. The overall conclusion of the study was that HSSSs, especially duplex grades 2205 and 2304, show excellent promise to mitigate corrosion if utilized as prestressing reinforcement in PSC structures exposed to severe marine environments.
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Comportement à la corrosion des alliages d'aluminium utilisés dans l'industrie automobile pour la fabrication de radiateur de chauffageDin-Stirbu, Elena Luminita Abrudeanu, Marioara Millet, Jean-Pierre. January 2006 (has links)
Thèse doctorat : Génie des Matériaux : Villeurbanne, INSA : 2005. Thèse doctorat : Génie des Matériaux : Université de Pitesti (Roumanie) : 2005. / Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Bibliogr. , 6 p.
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Etudes expérimentales et simulations des processus de corrosion aux interfaces matériaux métalliques-environnementMendy, Henri Joseph Chaussé, Annie. January 2008 (has links) (PDF)
Thèse de doctorat : Chimie : Evry-Val d'Essonne : 2008. / Titre provenant de l'écran-titre.
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Effects of Oxide Additions on the Corrosion Behaviour of Cr2O3 Based Ceramics in High Temperature Supercritical Water EnvironmentWang, Renfei Unknown Date
No description available.
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Early stages in the interaction of carbon monoxide with iron single crystal filmsRatliff, James Titus 08 1900 (has links)
No description available.
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Tarnishing of dental gold alloysVillastrigo, Aaron Collins 08 1900 (has links)
No description available.
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Effects of precipitation heat treatment on the microstructure, toughness and stress corrosion crack propagation resistance of aluminum alloy 2020Rinker, John George 12 1900 (has links)
No description available.
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Corrosion behavior of ion plated filmsPaul, George Doll 12 1900 (has links)
No description available.
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