Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 242 for “"nanocrystalline"”.
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Nanocrystalline copper-tantalum composites
This research investigated the physical metallurgy, high temperatures coarsening, and processing/structure relationships for Cu$\sb{\rm 1-x}$Ta$\sb{\rm x}$ (x = $\sim$5 to 20 atomic percent) alloys. These metastable alloys were produced using a plasma assisted physical vapor deposition (PAPVD) …
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Processing and characterization of nanocrystalline ceria
… and cosmetics. The use of high surface area, nanocrystalline CeO₂ powder could benefit all of these applications. This is particularly true for processing dense components, since the high melting point (2400⁰) of pure CeO₂ makes it difficult to sinter. In this dissertation, a semi-batch …
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Design of a stable nanocrystalline alloy
Nanocrystalline materials are inherently unstable due to their high material fraction of grain boundaries, preventing their improved properties from being used in application. To stabilize the nanoscale grain size against rampant growth, past literature has proposed lowering the grain boundary …
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Densification and Mechanical Properties of Nanocrystalline FeAl
Impression creep measurements were performed on nanocrystalline FeAl specimens sinterforged to full density. The tests were conducted over the temperature range of 500--600°C, and using punches with diameters of 0.5 and 0.2 mm. For specimens sinterforged at 500°C, a decrease in creep rate …
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The thermal stability of bulk nanocrystalline steels
Nanocrystalline bainite, commonly known as “superbainite”, is a novel class of steel that utilises careful alloy design to reduce the bainite transformation temperature to below 300℃. This results in grains that are tens of nanometres in width, which make steel strong and tough. The structure can …
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Customisable Magnetic Components Using Nanocrystalline Flake Ribbon
… power electronics. In this thesis, a novel nanocrystalline flake ribbon (NFR) is proposed to customise high-performance magnetic components for power electronics in a cost-effective way without high-energy equipment. Conventional nanocrystalline alloys do offer much higher saturation flux …
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Residual stress in nanocrystalline nickel tungsten electrodeposits
Characterizing the residual stress of thick nanocrystalline electrodeposits poses several unique challenges due to their fine grain structure, thickness distribution, and matte surface. We employ a three-dimensional profilometry-based approach that addresses each of these complicating factors and …
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Synthesis, processing, and properties of nanocrystalline nitrides
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997.
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Synthesis, Processing And Characterization Of Nanocrystalline Titanium Dioxide
… on the synthesis and characterization of the nanocrystalline TiO2 ceramic in details. The study selected a simple sol-gel synthesis process, which can be easily controlled and reproduced. Titanium tetraisopropoxide, isopropanol and deionized water were used as starting materials. By careful …
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Continuum models of deformation mechanisms in nanocrystalline metals
Nanocrystalline metals are polycrystalline metals with grain sizes in the nanometer range. They have attracted significant interest in recent years due to their unique mechanical and electrical properties. The main objective of this thesis is to develop continuum-scale descriptions of nanoscale …
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Nanocrystalline perovskites for catalytic combustion and oxygen separation
Nanocrystalline perovskites (Lal-xAMnl-yByO3) were successfully synthesized with higher surface area and smaller grain size by chemical co-precipitation compared to solid-state and complexation/combustion synthesis routes. The choice of solvent, base and suspension pH in co-precipitation was found …
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Controlling microstructure of nanocrystalline thermoelectrics through powder processing
… When processed via mechanical alloying to obtain nanocrystalline structures, their efficiency is increased dramatically, due to enhanced phonon scattering at grain boundaries. However, the excess free energy of these interfaces renders them inherently susceptible to grain growth, therefore there …
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Nanocrystalline Transition Metal Ferrites Synthesis, Characterization and Surface Functionalization
In this thesis, a new synthetic methodology for the high yield synthesis of spineltype transition metal ferrite nanoparticles has been developed. This approach is based on the complexation of the first-row transition metal cations with diethylene glycol (DEG) followed by the hydrolysis of the …
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Nanocrystalline Fe-Pt alloys: phase transformations, structure and magnetism
… structure of ordered and partially ordered nanocrystalline Fe-Pt alloys. It has been shown that the magnetic moment of Fe atoms in L10-type Fe Pt alloys is sensitive to the compositional order. The results are compared to density functional calculations.
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Isotropic nanocrystalline (Nd,Pr)(Fe,Co)B permanent magnets
Nanokristalline Permanentmagnete zeigen ungewöhnliche magnetische Eigenschaften aufgrund von Oberflächen- und Grenzflächeneffekten, die verschieden von denen massiver oder mikrokristalliner Materialien sind. Diese Arbeit zeigt Ergebnisse einer systematischen Untersuchung der Beziehung zwischen …
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Microstructural Heterogeneity and the Mechanical Behavior of Nanocrystalline Metals
… heterogeneity and size in ultrafine grained and nanocrystalline metals leads to unusual mechanical behavior. In the first part of the study, we have shown that (a) nanocrystalline metals, unlike their coarse grained counterparts, recover a substantial fraction (50 to 100%) of their plastic …
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Nanostructure stabilization and mechanical behavior of binary nanocrystalline alloys
The unique mechanical behavior of nanocrystalline metals has become of great interest in recent years, owing to both their remarkable strength and the emergence of new deformation physics at the nanoscale. Of particular interest has been the breakdown in Hall-Petch strength scaling, which is …
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Evaluating the Thermal Stability of Nanocrystalline Ag-Cu Alloys
Nanocrystalline alloys offer multitudinous advantages over their larger-grained counterparts including increased strength, hardness, resistance to fatigue, and more. However a significant barrier to their implementation is their low thermal stability—they are prone to coarsening at very low …
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