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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Deformation and recrystallisation of Cu-2%Fe

Chan, Hang-ting., 陳杏婷. January 2000 (has links)
published_or_final_version / Mechanical Engineering / Master / Master of Philosophy
32

Origins of recrystallisation textures in intersitial: free steels

謝尤優, Tse, Yau-yau. January 2001 (has links)
published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy
33

Grain refinement and texture development of cast bi90sb10 alloy via severe plastic deformation

Im, Jae-taek 15 May 2009 (has links)
The purpose of this work was to study learn about grain refinement mechanisms and texture development in cast n-type Bi90Sb10 alloy caused by severe plastic deformation. The practical objective is to produce a fine grained and textured microstructure in Bi90Sb10 alloy with enhanced thermoelectric performance and mechanical strength. In the study, twelve millimeter diameter cast bars of Bi90Sb10 alloy were encapsulated in square cross section aluminum 6061 alloy containers. The composite bars were equal channel angular (ECAE) extruded through a 90 degree angle die at high homologous temperature. Various extrusion conditions were studied including punch speed (0.1, 0.3 and 0.6 in/min), extrusion temperature (220, 235 and 250oC), number of extrusion passes (1, 2 and 4), route (A, BC and C), and exit channel area reduction ratio (half and quarter area of inlet channel). The affect of an intermediate long term heat treatment (for 100 hours at 250oC under 10-3 torr vacuum) was explored. Processed materials were characterized by optical microscopy, x-ray diffraction, energy dispersive spectroscopy, wavelength dispersive spectroscopy and scanning electron microscopy. Texture was analyzed using the {006} reflection plane to identify the orientation of the basal poles in processed materials. The cast grains were irregularly shaped, had a grain size of hundreds-of-microns to millimeters, and showed inhomogeneous chemical composition. Severe plastic deformation refines the cast grains through dynamic recrystallization and causes the development of a bimodal microstructure consisting of fine grains (5-30 micron) and coarse grains (50-300 micron). ECAE processing of homogenizied Bi-Sb alloy causes grain refinement and produces a more uniform microstructure. Texture results show that ECAE route C processing gives a similar or slightly stronger texture than ECAE route A processing. In both cases, the basal-plane poles become aligned with the shear direction. Reduction area exit channel extrusion is more effective for both grain refinement and texture enhancement than simple ECAE processing.
34

Thermal stability of submicron grain structure in an Al-Sc alloy.

Bommareddy, Aravinda Reddy, Materials Science & Engineering, Faculty of Science, UNSW January 2008 (has links)
Severe plastic deformation (SPD) has been used over the past few decades for producing submicron grain (SMG) structures in range of metals and alloys. Equal channel angular pressing (ECAP) is a useful process for producing these types of structures whereby the material is deformed to very high plastic strains by passing a billet several times through the ECAP die. This process has an added advantage maintaining the initial dimensions of the billet. SMG materials produced by ECAP and related routes are useful as they usually exhibit excellent properties including high strength and hardness, and excellent superplastic formability: these and other properties make SMG materials useful for industrial and aerospace applications. In this thesis, a binary aluminium alloy containing a very low concentration of scandium (0.1 wt. %) Sc alloy was investigated and compared with higher Sc-containing alloys. The material was deformed by ECAP in the solution treated condition to an equivalent von Mises strain of 9.2 then pre-aged at 250 0C to generate a submicron grained material containing a relatively uniform dispersion of nanosized Al3Sc dispersiods. The thermal stability of this pre-aged microstructure was investigated by annealing at temperatures up to 450 0C resulted in continuous grain coarsening by the process of continuous recrystallization whereby the initial microstructure evolves gradually with no marked change in the grain size distribution, texture and grain boundary character. However, extended annealing (> 1h) at 4500 C resulted in discontinuous grain coarsening (often termed recrystallization) whereby a few grains grow rapidly to eventually produce a coarse-grained final microstructure. Throughout annealing, there was a good correlation between the dispersion parameter, (f/d) where f and d is the volume fraction and the mean diameter of Al3Sc particles in the alloy, respectively, and both the mean grain size (D ) and D /D max where max D is the maximum grain diameter observed in the microstructure. The grain structure was found to undergo moderate coarsening at the high f/d-values but converted to a coarsegrained structure for f/d ~<0.5/μm, and this change occurred when the mean grain diameter was ~ 3-4μm. Hence, the critical value of the dispersion parameter for the transition from continuous to discontinuous coarsening falls between the theoretical value for submicron grain size alloys (f/d ~ 1.5/μm) and the value found for conventionally-deformed alloys (f/d ~ 0.1/μm). This behaviour is the result of the alloy no longer being ultra-fine grained at the onset of discontinuous coarsening.
35

Microstructural evolution and recrystallization modeling in AA6013 and compositional variants of 6013

Thanaboonsombut, Buncha 12 1900 (has links)
No description available.
36

Effect of stress relaxation on the kinetics of recovery and recrystallization in hot worked ETP copper

Vazquez Brisen̄o, Lucio. January 1980 (has links)
No description available.
37

Effect of aluminum on recrystallization and precipitation of Nb HSLA steels

Wang, Ganlin. January 1986 (has links)
No description available.
38

Scanning electron microscopy applied to studies of recrystallization in cubic metals

Pease, Nicolas Clive January 1979 (has links)
No description available.
39

Synthesis of Nitrogen-Containing Carbohydrate Derivatives and Their Use Toward Inhibiting Ice Recrystallization and Gas Hydrate Formation

Doshi, Malay January 2016 (has links)
Ice recrystallization during cryopreservation results in cell death and decreased cell viabilities due to cellular damage. This is a significant problem particularly in regenerative medicine where decreased cell viabilities post-thaw affect the success of the therapy. Given the success of these therapies to treat various diseases, the development of novel cryprotectants which have the ability to inhibit ice recrystallization during freezing and thawing are urgently required. Current cryoprotectant such as dimethyl sulfoxide, is associated with cytotoxicity in the clinical settings and thus are not optimal cryoprotectants. Our laboratory is interested in the rational synthesis of non-cytotoxic small molecules which possess the property of ice recrystallization inhibition (IRI) activity. Previously, the Ben laboratory has demonstrated that simple monosaccharides possess moderate ice recrystallization inhibition activity and that this activity is linked to hydration. The “compatibility” of the carbohydrate within the three-dimensional hydrogen bonded network of water is inversely proportional to its IRI activity. Hydration has previously been directly linked to the stereochemical relationship of individual hydroxyl groups on the carbohydrate. Additionally, it has been proposed that intramolecular hydrogen bond formation and hydrogen bonding cooperativity has a large effect on the water structure thus impacting hydration. Structure-function work has suggested that the presence of an amine as a hydrogen donor at the endocyclic position within the pyranose ring maybe beneficial to IRI activity. Thus, the first part of this thesis describes the synthesis and IRI activity of D-glucose and D-galactose based azasugars and its analogues. These azasugars have replaced the endocyclic ring oxygen with an amine. These azasugars and their analogues were found to possess moderate to potent IRI activity suggesting that hydrogen bond donation may be important for hydration and thus, IRI activity at the endocyclic ring oxygen. During the development of these azasugars, the Ben laboratory developed carbohydrate-based surfactants and hydrogelators possessing unprecedented IRI activity. A potential use of molecules possessing IRI activity is towards the inhibition of gas hydrate formation. Gas hydrates are ice-like solids containing gases within a highly ordered network of water molecules. These gas hydrates tend to accumulate in oil and gas pipelines posing significant dangers as the build-up of solid material leads to blockages in the pipeline reducing flow. Previous work had demonstrated the use of antifreeze proteins possessing potent IRI activity in inhibiting gas hydrate formation. However, their complex structure limits commercial use. Thus, the second part of the thesis describes the use of the azasugars, carbohydrate-based surfactants and hydrogelators in inhibiting gas hydrate formation. The effectiveness of the small molecules is compared to a commercial inhibitor PVP 10. Some of these small molecules were significantly better inhibitors of gas hydrate formation than the currently utilized inhibitor PVP 10. The low molecular weights of these small molecules, easy synthesis and potency make them excellent alternatives to PVP 10. However it was found that while some of the structural features in the small molecules may be amenable to both activities, it seems that the ability to inhibit ice recrystallization is not a good indicator of a compounds ability to inhibit gas hydrate formation. In a continuing effort to develop novel small molecule IRIs, the Ben laboratory has develop three classes of compounds. These include: carbohydrate-based surfactants and hydrogelators, lysine-based surfactants and truncated C-linked glycopeptides. Structure-function work utilizing these compounds revealed that presence of long alkyl chains, an amide linkage and the presence of an open-alditol chain are all important to IRI activity. However, the surfactant-like nature limits their use in cryopreservation and thus prompted the discovery of phenoxyglycosides as IRI active molecules. The structural features of these recently developed small molecules were combined to generate novel small molecule IRIs which do not resemble surfactants. These novel small molecules included “disaccharides” which possessed an aryl group at the anomeric position of a pyranose ring and an open-alditol chain linked via an amide bond. Additionally, N-cycloalkyl-D-aldonamides and N-phenyl-D-aldonamides were also synthesized. Of these novel small molecules, two very potent IRI active molecules were discovered: a “disaccharide” possessing an aryl group at the anomeric position with the open-alditol chain of D-galactose linked via an amide bond at C3 and N-phenyl-D-arbonamide. Both of these small molecules were assessed for their ability to cryopreserve hematopoietic stem cells. Unfortunately, the additional of these compounds failed to improved percent cell viabilities as compared to DMSO.
40

Elaboração e estudos de recristalização de ligas alumínio-magnésio-tório e alumínio-magnésio-nióbio

ALMEIDA FILHO, AMERICO de 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:50:54Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:07Z (GMT). No. of bitstreams: 1 11108.pdf: 32426138 bytes, checksum: e0fd60a0b29703462d6537e5ea445860 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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