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Williams, Katherine E. (Katherine Edith). "An examination of Maya metallurgy, 1150 to 1544 A.D." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/32576.
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Morris, Brian 1974. "Microstructural characteristics and processing parameters affecting hydrogen permeation through polycrystalline materials." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21314.
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An electrochemical permeation cell has been used to test the influence of microstructural characteristics of metal specimens and electrochemical processing parameters on electrochemical hydrogen diffusion. The affect of intercrystalline volume, entry surface roughness, cathodic charging current density and different cold working conditions on hydrogen diffusion through polycrystalline metals was tested. Nanocrystalline specimens of pure nickel and of 80%-Nickel 20%-Iron were tested to determine the affect of intercrystalline volume on hydrogen breakthrough diffusion. Specimens of pure palladium were tested to determine the influence of entry surface roughness, cathodic charging current density, different cold working and texture conditions on hydrogen permeation. A series of permeation tests performed on nanocrystalline nickel were used to optimize the measurement conditions. Experiments performed on 80/20 Ni-Fe thin foils determined that the hydrogen breakthrough diffusion coefficient drops dramatically with increasing grain size in the range of 20--40 nanometers. Above 40 nanometers, the breakthrough diffusion coefficient reaches a steady-state level. This decrease in breakthrough diffusion coefficient is thought to be due to a decrease in intercrystalline volume. Tests performed on palladium showed that the hydrogen effective diffusion coefficient increased logarithmically with increasing cathodic charging current density. These experiments also demonstrated that the optimum charging current density for palladium is 0.1 mA/cm2. Other tests on palladium determined that the surface roughness, on the entry side of the specimens, had no influence on the effective diffusion coefficient, processing efficiency or hydrogen subsurface entry concentration. Experiments on cold rolled palladium sheets determined that cold working dramatically lowers both the hydrogen subsurface entry concentration and effective diffusion coefficient. The lowering of the effective diffusio
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Saarimäki, Jonas. "Effect of Dwell-times on Crack Propagation in Superalloys." Licentiate thesis, Linköpings universitet, Konstruktionsmaterial, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-123306.
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Gas turbines are widely used in industry for power generation and as a power source at "hard to reach" locations where other possibilities for electrical supply are insufficient. There is a strong need for greener energy, considering the effect that pollution has had on global warming, and we need to come up with ways of producing cleaner electricity. A way to achieve this is by increasing the combustion temperature in gas turbines. This increases the demand on the high temperature performance of the materials used e.g. superalloys in the turbine. These high combustion temperatures can lead to detrimental degradation of critical components. These components are commonly subjected to cyclic loading of different types e.g. combined with dwell-times and overloads at elevated temperatures, which influence the crack growth. Dwell-times have shown to accelerate crack growth and change the cracking behaviour in both Inconel 718 and Haynes 282. Overloads at the beginning of the dwell-time cycle have shown to retard the dwell time effect on crack growth in Inconel 718. To understand these effects more microstructural investigations are needed. The work presented in this licentiate thesis was conducted under the umbrella of the research program Turbo Power; "High temperature fatigue crack propagation in nickel-based superalloys", concentrating on fatigue crack growth mechanisms in superalloys during dwell-times, which have shown to have a devastating effect on the crack propagation behaviour. Mechanical testing was performed under operation-like conditions in order to achieve representative microstructures and material data for the subsequent microstructural work. The microstructures were microscopically investigated in a scanning electron microscope (SEM) using electron channeling contrast imaging (ECCI) as well as using light optical microscopy. The outcome of this work has shown that there is a significant increase in crack growth rate when dwell-times are introduced at the maximum load (0% overload) in the fatigue cycle. With the introduction of a dwell-time there is also a shift from transgranular to intergranular crack growth for both Inconel 718 and Haynes 282. When an overload is applied prior to the dwell-time, the crack growth rate decreases with increasing overload levels in Inconel 718. At high temperature crack growth in Inconel 718 took place as intergranular crack growth along grain boundaries due to oxidation and the creation of nanometric voids. Another observed growth mechanism was crack advance along phase boundaries with subsequent severe oxidation of the phase. This thesis comprises two parts. The first giving an introduction to the field of superalloys and the acting microstructural mechanisms that influence fatigue during dwell times. The second part consists of two appended papers, which report the work completed so far in the project.
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Rolinska, Monika. "Extraction Replicas of Common Engineering Alloys for Analysis of Small Precipitates." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291204.
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Characterization of small precipitates is important for development of new alloys. One inherent difficulty in characterisation of small precipitates with electron microscopy techniques while the particles are embedded in the matrix, is that the surrounding bulk material will contribute to the analysed signal- limiting, for example, the quantification of the composition of particles. In order to avoid the matrix contribution, the extraction replica technique was developed in the 1950's. Extraction replicas are made by extracting only the particles from a material onto a thin film for further analysis by scanning or transmission electron microscopy. Different types of particles can be examined by this technique, including various carbides, nitrides, oxides and borides, as well as many intermetallic phases. In this work, direct replication techniques were compared to two-stage replication for low-alloyed steel, concluding that both are suitable for qualitative analysis, but direct replication is preferred for quantitative analysis. Successful replication of the zirconium-based Zirlo and the stainless steel 254 SMO was performed, where the precipitated phases were isolated and the composition quantified. Particle extraction was successful also for the zirconium-based Zircaloy-2 and two types of aluminium alloys, but no quantification of composition could be made due to different problems associated with etching of each alloy, showing that properchoice of etchant is crucial for the quality of the replicas.Karaktärisering av små utskiljningar är viktigt för utveckling av nya legeringar. En svårighet vid karaktärisering av små utskiljningar med elektronmikroskopi när partiklarna sitter kvar i matrisen är att matrisen kommer ge ett bidrag till den analyserade signalen, därför är t.ex. möjligheterna för kvantifiering av sammansättning begränsade. För att undvika bidraget från matrisen utvecklades extraktionsrepliker på 1950-talet. Extraktionsrepliker tillverkas genom att extrahera partiklar från ett material till en tunn film som sedan kan analyseras med hjälp av svep- eller transmissionselektronmikroskopi. Olika sorters partiklar kan undersökas med hjälp av denna metod. Dessa inkluderar olika typer av karbider, nitrider, borider, oxider och många olika sorters intermetalliska partiklar. I detta arbete jämfördes direkta metoder med tvåstegsrepliker på låglegerat stål. Slutsatsen blev att båda metoderna lämpar sig för kvalitativ analys av små partiklar, men direkta metoder är att föredra för kvantitativ analys. Lyckade repliker tillverkades även av zirkoniumlegeringen Zirlo och det rostfria stålet 254 SMO, där utskiljningarna kunde isoleras och sammansättningen kvantifieras. Extraktion av partiklar var lyckad även för zirkoniumlegeringen Zircaloy-2 samt två typer av aluminiumlegeringar, men ingen kvantifiering av sammansättningen kunde göras på grund av olika problem relaterade till den valda etsmetoden för varje legering, vilket visar att valet av etsmedel ar avgörande för kvaliteten av replikerna.
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Lu, Jian 1964. "Computer modeling of intergranular fracture in textured materials." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39950.
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An integrated computer simulation employing the Embedded-atom method (EAM), Molecular dynamics (MD), and Markov Chain Fracture models has been constructed and applied to study the intergranular fracture of brittle polycrystalline materials at both the atomistic and microscopic levels. At the atomistic level, the computer model is capable of treating bicrystals under the influence of external load and temperature with dynamic periodic boundary conditions along the grain boundary plane and a dynamic boundary condition perpendicular to the grain boundary plane. At the microscopic level, the computer model is capable of treating the sample with microstructure defined by the grain boundary character distribution under the influence of an external load to predict the intergranular fracture propagation under stress.The fracture behavior of many $ Sigma$ grain boundaries has been investigated at the atomistic level for Cu, Ni, and Ni$ sb3$Al, and the fracture resistance of the grain boundary was predicted. It has been found that grain boundary energy and fracture resistance greatly depend on the grain boundary structure. Symmetrical $ Sigma$3 twin boundaries and low angle $ Sigma1$ boundaries are particularly strong in resisting intergranular fracture, while some other low $ Sigma$ boundaries are also strong, but grain boundaries with high energies are not at all fracture resistant. The calculated correlation between fracture resistance and misorientation of grain boundaries is in accordance with the experimental data. The calculated fracture resistances of the grain boundaries for Ni$ sb3$Al alloy are not significantly different from those for pure Ni. This suggests that the tendency to intergranular fracture is not due merely to the poor fracture resistance of grain boundaries. One must also consider the overall grain boundary character distribution.
In order to find the role of grain boundary character distribution on the intergranular fracture in brittle polycrystalline materials, the crack path, crack arrest distance, and fracture toughness have been investigated at the microscopic level with the different fraction of low-energy grain boundaries, grain boundary fracture resistance, orientation distribution of grain boundary planes, and grain shape factor. The simulations have indicated that with an increase in the fraction of low energy grain boundaries, the fracture toughness increases while the crack arrest distance decreases. With an increase in the number of low energy grain boundaries which are aligned parallel to the stress axis, one observes an increase in the fracture toughness and a decrease in the crack arrest distance. By increasing the grain shape factor, the fracture toughness decreases while the crack arrest distance increases.
If five grain diameter is defined as the critical length, and more than 25% of grain boundaries are of low-energy with the highest fracture resistance, such as $ Sigma$3 twin grain boundaries, the intergranular crack formed initially cannot propagate further due to the presence of fewer random boundaries, and the polycrystalline materials will show high ductility. The improvement in fracture toughness of Ni$ sb3$Al brittle polycrystal is due to the introduction of a high frequency of low energy grain boundaries (up to 70% by experimental treatments). Grain boundary design and control achieved by manipulating the grain boundary character distribution (GBCD) are important to fracture toughness improvement of the brittle polycrystal materials.
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Halilovic, Selma. "Evaluation of new powder grade for furnace control pieces in sintering process." Thesis, Uppsala universitet, Tillämpad materialvetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-448371.
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To be able to supervise the quality of a sintering process, furnace control pieces are therefore used. The current furnace control piece is not sensitive enough small variations during insert production. The goal of the project was to find and evaluate a new suitable cemented carbide grade, which better captures temperature variations during sintering process, likewise, evaluate the alternative placing in the production furnace and methods to supervise and follow the status of the sintering process. The cemented carbide grade 592, which is a DQ-grade, captured larger temperature variations during the sintering compared to the current furnace control piece. The process charge for 592 that captured the largest variations also had the highest charge weight, which indicates that the new grade is also sensitive to the charge weight. The purpose of the project was fulfilled when a more suitable cemented carbide grade, 592, was evaluated for both sintering temperatures 1410 ℃ and 1450 ℃.
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Webster, Rhiannon Alys. "Passive materials for high frequency piezocomposite ultrasonic transducers." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/1311/.
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High frequency ultrasound is receiving increased attention for medical imaging in areas such as ophthalmology and dermatology. Recent advances in the manufacture of fine scale piezocomposite materials mean there is great potential for commercial transducers far superior to conventional devices currently in clinical use. This Thesis reports the fabrication and characterisation of passive materials suitable for use in high frequency piezocomposite transducer devices. Epoxy composites have been fabricated using tungsten and alumina as filler material with volume fractions up to 0.4. Acoustic impedance and attenuation has been determined for different filler volume fractions to provide data for modelling to aid transducer design and also determine the filler volume fraction required to provide optimal results. Acoustic impedance values of 3-15MRayl were measured for the materials made in this work and the influence of filler particle size and shape is also discussed. Piezocomposite transducers have been constructed using material developed in this work and compared to devices made with more conventional passive materials. In addition to the fabrication of the composite samples for characterisation a process for incorporating material into transducers is described showing how the fabrication can be a part of the transducer construction resulting in an efficient and neat package.
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Almebäck, Julia Linnea Hildur, Amanda Edberg, and Rafa Shah. "Corrosion in Pulp Mills : Material Selection for an Evaporation Plant." Thesis, KTH, Materialvetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-277877.
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Corrosion is a global problem which leads to both economicalct on the environment as well as other negative social and ethical aspects. Sodra Cell Monsteras, one of the largest producer of pulp in the world, suffers from corrosion problems in their evaporation plant. Problems with corrosion can be handled with an effective material selection process, where suitable materials for specific conditions is discovered. The purpose with this report is to investigate the evaporation plant at Sodra Cell and its specific conditions, including environment and temperature. Also to investigate different types of corrosions common in pulp mills and how these can be prevented, as well as how materials behave under corrosive circumstances. The information is later to be used in a detailed material selection process, which is handled in this report but also should work as a foundation for Sodra Cell Monsteras for future material selections. The material selection process in this report is performed according to Ashby's method, with CES Edupack as a supporting tool. The duplex steels, especially EN 1.4485 and EN 1.4362, showed to be the best suitable materials. However, to do a fair judgment and to choose one material, one should do a complete cost efficiency analysis, as well as decide a specific required pitting resistance equivalent number (PREN).Korrosion ar ett globalt problem som leder till både ekonomiska förluster, negativ miljöpåverkan samt andra negativa sociala och etiska aspekter. Södra Cell Mönsterås, en av världens största producenter av pappersmassa, har problem med korrosion i sin indunstningsanläggning. Korrosionsproblem kan lösas genom att ha en effektiv materialvalsprocess där rätt material för specifika förhållanden och ändamål används. Syftet med den här rapporten är att undersöka vilka specifika förhållanden som råder i Södra Cells indunstningsanläggning, däribland miljö och temperatur. Men även att undersöka vilka olika korrosionstyper som vanligen förekommer i massaindustrin, hur dessa kan förhindras samt hur olika material beter sig under korrosiva förhållanden. Informationen ska kunna användas som underlag i en utförlig materialvalsprocess, som även hanteras i denna rapport men kan även fungera som en grund för Södra Cell Mönsterås framtida materialval. Materialvalsprocessen i denna rapport är utförd enligt Ashbys metod, med CES Edupack som ett hjälpmedel. Det visar sig att Duplexa stål, speciellt EN 1.4485 samt EN 1.4362 är material som lämpar sig bäst för användning i den korrosiva miljön i indunstningsanläggningen. För att kunna göra en rättvis bedömning och välja ut ett av dessa material, bör en fullständig kostnadsanalys utföras, samt att det bör klargöras vilket specifikt värde för "pitting resistance equivalence number" (PREN) som krävs.
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Yi, Xiaodong. "Rapidly solidified magnesium : nickel alloys as hydrogen storage materials." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5174/.
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Due to high hydrogen capacity, good reversibility and low cost, magnesium hydride is one of the most promising hydrogen storage materials. However, the high desorption temperature and slow hydriding kinetics hinder the application of magnesium hydrides. To improve the hydrogen storage characteristics of magnesium hydrides, many effective treatments have been developed and applied, such as ball milling, melt spinning, alloying with other metals, adding catalysts and using thin film technique. In this work, melt spinning and alloying with Ni were the main sample modification methods used to improve hydrogen storage properties for magnesium hydrides. At the beginning of this project, it was found that it was difficult to repeat the methodology of sample preparation in the literature. Therefore, sample synthesis method was developed after numerous preliminary trials and a series of Mg-Ni alloys were melt-spun successfully. The structural characterization and analysis of hydrogen storage property were performed on the melt-spun Mg-Ni samples in a range of compositions. It was found that a nanocrystalline / amorphous structure was produced by melt spinning, and a metastable intermediate phase, Mg\(_6\)Ni, was discovered in the melt-spun materials. The melt-spun Mg-Ni ribbons exhibited fast kinetics of both absorption and desorption at 300 °C, with a high capacity. Moreover, they exhibited low temperature and even room temperature hydrogen sorption, with slow kinetics.\(\gamma\)-MgH\(_2\) phase, which forms usually under high pressure, has been found in the samples, which probably caused the ambient hydrogen absorption.
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Muscat, Daniel. "Silicon nitridesilicon nitride whisker-reinforced composites." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60102.
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One of the major setbacks of ceramic materials is their inherent brittle nature which often leads to catastrophic failure, especially under impact and tensile stress conditions. Whisker-reinforcement of ceramic matrices has been shown to be an effective way of increasing toughness. However, the hot-pressing techniques being used at present are expensive. Si$ sb3$N$ sb4$ is a major contender for high temperature application, mainly due to its excellent mechanical, chemical and thermal properties.In this work Si$ sb3$N$ sb4$ whiskers have been incorporated into a Si$ sb3$N$ sb4$ matrix and densified using pressureless sintering. An isotropic distribution of whiskers in the starting powder was seen to inhibit shrinkage of the bulk material as a result of whisker bridging.
An extrusion process was developed to align the whiskers such that they do not impinge on one another. This was done using a water soluble, cellulose based plasticizer. The process was sensitive to water content and mixing. Entrapped air caused problems in the extrudate, resulting in misaligned areas in the microstructure. Relative densities of 94.5% were obtained for composites having 15% whiskers. The toughness of this material was measured to be 13.5MPa.m$ sp{1/2}$ in the direction perpendicular to the direction of extrusion.
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Baczynski, Jerzy 1958. "Torsion textures produced by deformation and by dynamic recrystallization in a-iron and two IF steels." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40311.
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The textures of two IF steels and a high purity $ alpha$-iron were determined after deformation in torsion over the temperature range 20-840$ sp circ$C. The three characteristic bcc torsion fibres are described in detail and the locations of some important ideal orientations are identified on the $ {110 }$ pole figure. At room temperature, these are the F(110)(001), J1 (011) (211), J2 (110) (112), D1 (112) (111), D2 (112) (111), E1 (011) (111) and E2 (011) (111). At elevated temperatures, the conditions were chosen so that dynamic recrystallization (DRX) took place in the ferrite and that static recrystallization was avoided during cooling after deformation. The DRX textures differ from those observed at room temperature and are dominated by the D2 (112) (111), D1 (112) (111) and E2 (011) (111) components. The D2 becomes increasingly important as the strain is increased, which leads to weakening of the D1 and disappearance of the E2 at large strains.Deformation textures were simulated using the rate sensitive theory of crystal plasticity. These called for lengthening to take place, in agreement with the measured length changes. The simulated and experimentally observed 'tilt' phenomena are similar to those commonly reported in the literature for fcc materials. The explanation of this phenomenon developed for the latter materials is extended to bcc metals. The development of torsion textures is discussed in terms of the rotation rate vector R, the divergence-convergence properties of orientation flow, and the stability parameter S.
DRX textures were simulated using a model based on sequential deformation, nucleation and growth steps. The types of oriented nucleation and selective growth required to reproduce the experimentally observed textures are discussed. The simulations indicate that the low energy nucleation mechanism plays a dominant role in the formation of bcc DRX textures. The results are also interpreted in terms of the continuous (in situ) and discontinuous mechanisms of dynamic recrystallization.
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Cardoso, Geraldo I. S. L. "The influence of microstructure on the hot ductility of four low carbon steels with respect to transverse crack formation in continuously cast slabs /." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59567.
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The influence of Al, Mn and Ti on the hot ductility of four low C steels has been examined.Ductility troughs were exhibited by all the steels. These could be related to the austenite-to-ferrite phase transformation and grain boundary precipitation behavior. When no precipitation took place at the austenite grain boundaries, the trough occurred by intergranular failure. Fracture surfaces revealed microvoid coalescence, with voids associated with MnS inclusions.
Increasing the Mn in the steels lowers the $ gamma to alpha$ transformation temperature, causing the trough to be moved to lower temperatures. It also decreases the volume fraction of MnS inclusions within the ferrite film. Increasing the Al level caused AlN to be precipitated at the austenite grain boundaries, extending the trough to higher temperatures into the single phase austenite region.
The addition of Ti results in a fine austenite grain size after the solution treatment and impedes AlN precipitation. This leads to improved ductility in the austenite region.
When austenite recrystallization occurs during deformation, any voids which have initiated at the boundaries are trapped within the newly recrystallized grains. Intergranular failure cannot progress and the ductility is high.
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Roucoules, Christine. "Dynamic and metadynamic recrystallization in HSLA steels." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39794.
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A Mo, a Nb and a Ti steel were tested in torsion to study the characteristics of dynamic and postdynamic recrystallization. To characterize dynamic recrystallization, continuous torsion tests were carried out between 850 and 1050$ sp circ$C at strain rates of 0.02, 0.2 and 2s$ sp{-1}.$ Quenches were performed to investigate the grain refinement produced by dynamic recrystallization. Interrupted torsion tests were performed between 850 and 1050$ sp circ$C and at strain rates between 0.02 and 2s$ sp{-1}$ to study the characteristics of postdynamic recrystallization. Quenches were performed after increasing holding times to follow the evolution of the postdynamic microstructure. The evolution of the grain size distribution as a function of holding time shows that the growth of dynamically recrystallized grains is the first change that takes place. Then metadynamically recrystallized grains appear and contribute to the softening of the material. The rate of metadynamic recrystallization increases with strain rate and temperature and is observed to be independent of strain, in contrast to the observations for static recrystallization. The dependence of the metadynamically recrystallized grain size on the Zener-Hollomon parameter was established and is shown to differ from static recrystallization dependence. Simple torsion simulations were carried out using constant interpass times to study the conditions under which dynamic, metadynamic or static recrystallization takes place. Dynamic recrystallization controlled rolling (DRCR) is shown to require such short interpass times that they are not attainable in hot strip mills. A new concept, metadynamic recrystallization controlled rolling (MDRCR), is introduced to describe the case where there is 20 to 80% softening by metadynamic recrystallization. The occurrence of dynamic and metadynamic recrystallization causes the load to increase less rapidly than in the case of pure strain accumulation.
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Barnett, Matthew R. "Influence of warm rolling temperature on ferrite recrystallization in low C and IF steels." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41976.
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Experiments involving single pass laboratory rolling and isothermal salt bath annealing were carried out; three steels were studied: a titanium stabilized interstitial free grade and two low carbon grades, one of which contained a particularly low level of manganese ($ sim$0.009wt.%). The two low carbon grades were produced such that any complication from AlN precipitation was avoided. X-ray, neutron diffraction, optical metallography and mechanical testing measurements were carried out on the samples before and after annealing. The main aim of this work was to further the understanding of the metallurgy of recrystallization after ferrite rolling at temperatures between room temperature and 700$ sp circ$C.Deformation textures, recrystallization kinetics, final grain sizes and recrystallization textures were quantified for all the samples and experimental conditions. A major conclusion based on these data is that the influence of rolling temperature is far greater in the low carbon samples than in the IF grade. Indeed, the IF results alter only marginally with increasing temperature. In the low carbon grades, however, the rolling texture sharpens, recrystallization slows, the final grain size coarsens, and the recrystallization texture changes when the rolling temperature is increased.
This distinct difference between the two steel types is explained in terms of their contrasting deformation behaviors. Solute carbon and nitrogen in the low carbon grades interact with dislocations causing high stored energy levels after low temperature rolling (due to dynamic strain aging) and high strain rate sensitivities during high temperature rolling (due to the solute drag of dislocations in the transition region between DSA and DRC). Nucleation during subsequent recrystallization is strongly influenced by both the stored energy and the strain rate sensitivity. The latter affects the occurrence of the flow localisations that enhance nucleation.
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Saxena, Pawan. "Slip casting of silicon nitride." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=56974.
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Slip casting is a well established technique for the manufacture of traditional ceramic bodies, such as clays and whitewares. It combines complex shaping with high green densities, resulting in low shrinkage and good densification behaviour.This method, however, has received little attention in the field of engineering ceramics especially with regard to silicon nitride. Commercial fabrication of silicon nitride, a major contender for high temperature applications due to its excellent thermomechanical properties, has been confined to hot pressing. This is an expensive process and has geometrical limitations.
Slip casting, followed by sintering, has been identified as a potentially economical alternative fabrication method, however a number of parameters have to be optimized before a good slip cast silicon nitride body can be made. The aim of the present work is to control parameters such as pH, viscosity and deflocculation in order to form dense, homogeneous, slip cast silicon nitride bodies.
A detailed investigation of the rheological properties of Si$ sb3$N$ sb4$ and careful control of processing parameters, made it possible to produce slip cast Si$ sb3$N$ sb4$ bodies having up to 97% TD on sintering. Mechanical strength values obtained by slip casting were compared with those obtained by die-pressing. Strength values of the slip cast material was limited by iron inclusions entrained in processing.
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Li, Dongyang. "Texture formation in iron electrodeposits." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29076.
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The texture of electrodeposits has attracted increasing interest, as it is recognized that it is a possible to benefit from the texture and to improve the various properties of electrodeposits or electrolytic coatings. For example, the corrosion resistance of materials is affected by texture. If appropriate textures are introduced in electrodeposited coatings, their corrosion resistance would be enhanced and the coatings will therefore have a longer service time. Texture development during electrodeposition is still poorly understood, and this makes it difficult to control the texture formation during the electrodeposition processes. In order to better understand the texture formation during electrodeposition, extensive theoretical and experimental investigation are undertaken in this thesis.A computer model was proposed to describe texture development. In this model, the microstructure of deposit was represented using a two dimensional triangle lattice. The deposit growth was modelled as previously empty lattice sites are being occupied based on fundamental physical rules. The author proposed that the main driving force for the development of microstructure and texture is the minimization of the system's free energy. This results in texture development, and the minimization of the free energy includes deposit's surface energy and occasionally the magnetic energy. Based on this hypothesis, the texture formation during iron electrodeposition and its variation with the deposition condition were simulated. It was demonstrated that the crystallographic anisotropy of deposit's surface energy plays an important role in the formation of the deposit's fibre texture. The study also indicated that the surface-energy anisotropy could be modified by hydrogen co-deposition and the deposit's texture can be modified by varying the current density, temperature, or pH value of the bath. In addition, the study illustrated that the magnetization energy also plays an important role in texture development during electrodeposition of magnetic materials. When external magnetic fields of sufficient strength are applied during the deposition of magnetic materials, the magnetic fields align grains in such a way that the deposits' fibre textures may transform to non-fibre textures.
In order to further justify the minimum-energy texturing mechanism proposed in the model, and to obtain a clear physical picture of the texture formation during electrodeposition, the process of texture development was analyzed using classical thermodynamics. Various experiments were conducted to verify the computer simulation. A positive correlation between the results of the simulation and the experiments were found.
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Debray, Bruno. "Microstructure and mechanical properties of an as-hot rolled carbon manganese ferrite-bainite sheet steel." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69713.
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By means of torsion testing, the microstructures and mechanical properties produced in a 0.14%C-1.18%Mn steel were investigated over a wide range of hot rolling conditions, cooling rates and coiling temperatures. The reheating temperature was varied between 800$ sp circ$C and 1050$ sp circ$C, and strains between 0 and 0.8 were applied. This led to austenite grain sizes ranging from 10 to 150$ mu$m. Two cooling rates, 55$ sp circ$C/s and 90$ sp circ$C/s, were applied and cooling was interrupted at coiling temperatures ranging from 550$ sp circ$C to 300$ sp circ$C.Optical microscopy and TEM were used to study the microstructures. The mechanical properties were studied by means of tensile testing. A method developed by IRSID for deducing the transformation kinetics from the cooling data was adapted to the present context and used successfully to interpret the observed influence of the process parameters. (Abstract shortened by UMI.)
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Zarandi, Faramarz MH. "The effect of high temperature deformation on the hot ductility of Nb-microalloyed steel /." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85109.
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Low hot ductility at the straightening stage of the steel continuous casting process, where the surface temperature ranges from 600 to 1200°C, is associated with transverse cracking on the billet surface. This is attributed to various microalloying elements, which are essential for the mechanical characteristics of the final products. Thermomechanical processing is a new approach to alleviate this problem. In this work, two grades of Nb-containing steel, one modified with B, were examined. In order to simulate the key parameters of continuous casting, specimens were melted in situ and subjected to thermal conditions similar to that occurring in a continuous casting mill. They were also deformed at different stages of the thermal schedule. Finally, the hot ductility was evaluated at the end of the thermal schedule, corresponding to the straightening stage in continuous casting at which the hot ductility problem occurs in the continuous casting process.The results showed that the presence of B is noticeably beneficial to the hot ductility. Failure mode analysis was performed and the mechanism of fracture was elaborated. As well, the potential mechanisms under which B can improve the hot ductility were proposed.
Deformation during solidification (i.e. in the liquid + solid two phase region) led to a significant loss of hot ductility in both steels. By contrast, deformation in the delta-ferrite region, after solidification, was either detrimental or beneficial depending on the deformation start temperature.
The hot ductility was considerably improved in the steel without B when deformation was applied during the delta → gamma transformation. The effect of such deformation on the other steel grade was not significant. Examination of the microstructure revealed that such improvement is related to a grain refinement in austenite. Therefore, the effect of deformation parameters was studied in detail and the optimum condition leading to the greatest improvement in the hot ductility was determined.
Finally, some solutions to the industrial problem in the continuous casting process were proposed.
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Hassani, Farideddin. "Mechanical behaviour of steel near the incipient melting temperature." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69719.
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A new method of incipient melting temperature (IMT) detection, continuous heating and fracture (CHF) method, has been developed in which a constant strain rate tensile or torsion deformation is applied to a specimen whose temperature is simultaneously increased. The IMT is determined in a single test and any phase transformations before the IMT will also be detected by the effects on the stress vs. strain behavior in the same experiment. This method also provides information about the effect of phase transformation and temperature on the mechanical behaviour of steel near the incipient melting temperature.By means of such tests, the incipient melting behaviour of a series of steels with carbon levels from 0.031 to 0.45 wt% was examined. For the steels containing 0.08-0.097%C and about 1.5%Mn, it was found that incipient melting occurs in the two phase ($ gamma$+$ delta$) region in the temperature range from 1470-1480$ sp circ$C, and is significantly influenced by microalloying elements. In the ultra-low carbon steel (0.031%C), the IMT is in the single phase $ delta$ region at 1495 $ sp circ$C, and for the medium carbon steels containing 0.3-0.42%C (hyper-peritectic) it is in the $ gamma$ single phase in the temperature range of 1401-1414$ sp circ$C. Comparison between the IMT obtained from CHF testing and the solidus temperature calculated from K-O model showed that these two values are extremely close. Since there is no nucleation barrier for melting, it seems that the CHF testing can delineate the solidus temperature in steel. (Abstract shortened by UMI.)
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Jiang, Lan 1970. "Effect of silicon on the interaction between recrystallization and precipitation in niobium microalloyed steels." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79236.
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The effect of Si addition on the interaction between recrystallization and precipitation during multipass deformation has been investigated in terms of the no-recrystallization temperature (Tnr), the minimum temperature at which recrystallization can be completed. The Tnr was measured in three Nb microalloyed steels with Si concentrations ranging from 0.01 to 0.48wt.%. Continuous cooling conditions were employed, with interpass times of 20--200s and strains of 0.2 and 0.35 applied at a strain rate of 2s -1.It was observed that for similar Nb contents, the Tnr increased with Si level, but appeared to saturate at long interpass times. In addition, high strains also reduced the influence of Si on the Tnr. This behaviour can be attributed to the acceleration of the Nb(C,N) precipitation kinetics by the addition of Si. With increasing interpass time or strain, the precipitates start to coarsen and, in consequence, the pinning effect due to precipitation is reduced. Therefore, under these conditions, the effectiveness of Si addition in raising the Tnr is diminished.
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Elalem, Kaled. "Application of heat pipe technology in permanent mold casting of nonferrous alloys." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=85067.
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The issue of mold cooling is one, which presents a foundry with a dilemma. On the one hand; the use of air for cooling is safe and practical, however, it is not very effective and high cost. On the other hand, water-cooling can be very effective but it raises serious concerns about safety, especially with a metal such as magnesium. An alternative option that is being developed at McGill University uses heat pipe technology to carry out the cooling.The experimental program consisted of designing a permanent mold to produce AZ91E magnesium alloy and A356 aluminum alloy castings with shrinkage defects. Heat pipes were then used to reduce these defects. The heat pipes used in this work are novel and are patent pending. They are referred to as McGill Heat Pipes.
Computer modeling was used extensively in designing the mold and the heat pipes. Final designs for the mold and the heat pipes were chosen based on the modeling results.
Laboratory tests of the heat pipe were performed before conducting the actual experimental plan. The laboratory testing results verified the excellent performance of the heat pipes as anticipated by the model.
An industrial mold made of H13 tool steel was constructed to cast nonferrous alloys. The heat pipes were installed and initial testing and actual industrial trials were conducted. This is the first time where a McGill heat pipe was used in an industrial permanent mold casting process for nonferrous alloys.
The effects of cooling using heat pipes on AZ91E and A356 were evaluated using computer modeling and experimental trials. Microstructural analyses were conducted to measure the secondary dendrite arm spacing, SDAS, and the grain size to evaluate the cooling effects on the castings. The modeling and the experimental results agreed quite well. The metallurgical differences between AZ91E and A356 were investigated using modeling and experimental results. Selected results from modeling, laboratory and industrial trials are presented. The results show a promising future for heat pipe technology in cooling permanent molds for the casting of nonferrous alloys.
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Akbarzadeh, Abbas. "Effect of thermomechanical processing on microstructure, texture, and anisotropy in two Nb microalloyed steels." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq29871.pdf.
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Zhang, Bin. "Fatigue behavior in an aluminum casting alloy (A356.2): Effects of some defects, SDAS, Hipping and strontium modification." Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/280228.
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Effects of pore, secondary dendrite arm spacings (SDAS ), hot isostatic pressing (Hipping), and strontium-modification on fatigue behavior were studied in an aluminum casting alloy (A356.2). Microstructures were revealed by X-ray radiography, light microscopy and scanning electron microscopy. Small-cracks were monitored by taking replicas of the surfaces with which the cracks intersected. As the SDAS increases from 15 to 55 μm, fatigue life decreases by a factor of 3 in low-cycle fatigue, and 100 in high-cycle fatigue. When SDAS is less than 30 mum, the pore size is below a critical size of ∼80 μm and large eutectic constituents initiate cracks; and the initiation life is as high as 70% of the fatigue life. As the SDAS increases beyond 30 μm, pores are the main crack-initiation sites; the initiation life is as low as 5% of the fatigue life. Near-surface oxides initiate the fatigue crack regardless of SDAS. When crack initiated at pore and oxides, fatigue life is well correlated with the size of the initiation site and the effect of SDAS is overshadowed by the effect of pore. Non-hipped A356.2 without Sr shows better fatigue life and the deleterious effect of pores overshadowed the beneficial effect that Sr-modification might have had. Hipping significantly increased the initiation life and small-crack propagation life of A356.2 with Sr as a result of the elimination of the porosity. However, hipping did not significantly improve the fatigue life of A356.2 without Sr. After hipping, Sr-modification is beneficial in improving the crack initiation life, and increasing both small-crack and long-crack propagation lives. Fracture mechanics models (Newman-Raju, and Trantina-Barishpolsky models) yielded similar results on the crack-propagation rate against the effective stress-intensity factor range. In the micro-mechanics model, the theory of continuously distributed dislocations was applied to represent crack and crack-tip plastic zone, and the propagation rate was related to the length of the crack-tip plastic zone. When the grain size is used as the characteristic length of the microstructures, the model predicts the oscillations of the propagation rates and the predicted rates agreed reasonably well with those from experiments.
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Moats, Michael Scott 1970. "Electrochemical characterization of anode passivation mechanisms in copper electrorefining." Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/282777.
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Anode passivation can decrease productivity and quality while increasing costs in modern copper electrorefineries. This investigation utilized electrochemical techniques to characterize the passivation behavior of anode samples from ten different operating companies. It is believed that this collection of anodes is the most diverse set ever to be assembled to study the effect of anode composition on passivation. Chronopotentiometry was the main electrochemical technique, employing a current density of 3820 A m⁻². From statistical analysis of the passivation characteristics, increasing selenium, tellurium, silver, lead and nickel were shown to accelerate passivation. Arsenic was the only anode impurity that inhibited passivation. Oxygen was shown to accelerate passivation when increased from 500 to 1500 ppm, but further increases did not adversely affect passivation. Nine electrolyte variables were also examined. Increasing the copper, sulfuric acid or sulfate concentration of the electrolyte accelerated passivation. Arsenic in the electrolyte had no effect on passivation. Chloride and optimal concentrations of thiourea and glue delayed passivation. Linear sweep voltammetry, cyclic voltammetry, and impedance spectroscopy provided complementary information. Analysis of the electrochemical results led to the development of a unified passivation mechanism. Anode passivation results from the formation of inhibiting films. Careful examination of the potential details, especially those found in the oscillations just prior to passivation, demonstrated the importance of slimes, copper sulfate and copper oxide. Slimes confine dissolution to their pores and inhibit diffusion. This can lead to copper sulfate precipitation, which blocks more of the surface area. Copper oxide forms because of the resulting increase in potential at the interface between the copper sulfate and anode. Ultimate passivation occurs when the anode potential is high enough to stabilize the oxide film in the bulk electrolyte. The effect of anode impurities or electrolyte concentrations can be related to the formation of one of these films. Reactions occurring after passivation have also been examined. Post-passivation reactions are believed to include silver dissolution, transformation of lead sulfate to lead oxide, and oxygen evolution. Following the sharp potential increase caused by the passivation, silver that has accumulated on the anode surface will dissolve into the electrolyte at a potential between 1.0 and 1.3 V. After the silver has dissolved, the potential increases again at which point the oxidation of lead sulfate to lead oxide occurs. The formation of lead oxide provides a surface with a lower oxygen evolution overpotential. The presence of kupferglimmer also results in a stable lower oxygen evolution potential occurring at approximately 2.0 V.
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Cherne, Frank Joseph. "Calculation of transport properties of liquid metals and their alloys via molecular dynamics." Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284305.
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The advanced casting modeler requires accurate viscosity and diffusivity data of liquid metals and their alloys. The present work discusses the use of equilibrium and non-equilibrium molecular dynamics techniques to obtain such data without having to rely on oversimplified phenomenological expressions or difficult and expensive experiments. Utilizing the embedded atom method (EAM), the viscosities and diffusivities for a series of equilibrium and non-equilibrium molecular dynamics simulations of nickel, aluminum, and nickel-aluminum alloys are presented. A critical comparison between the equilibrium and non-equilibrium methods is presented. Besides the transport properties, structural data for the liquids are also evaluated. EAM does a poor job of describing the transport properties of nickel-aluminum alloys, particularly near the equiatomic concentration. It has been suggested that charge transfer between nickel and aluminum atoms is responsible for the discrepancy between numerical calculations and available experimental data. A modified electronic distribution function has been developed to simulate the charge transfer associated with compound formation. The effects of such a "charge transfer" modification to the embedded atom method are evaluated. The results of these simulations indicate that the embedded atom method combined with molecular dynamics may be used as a method to predict reasonably the transport properties.
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Apprill, Jon M. 1974. "Process control of GASAR porous metals." Thesis, The University of Arizona, 1998. http://hdl.handle.net/10150/291491.
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GASAR porous metals are produced by melting under a partial pressure of hydrogen and then casting into a mold that ensures directional solidification. Hydrogen is driven out of solution and grows as cylindrical pores normal to the solidification front. Experiments have been performed to produce GASARs from pure Ni and Inconel 718, a nickel-base superalloy. The processing variables studied in these experiments included the pressure of H₂(g), total pressure, superheat, and solidification rate. An analysis that considers heterogeneous bubble nucleation was developed that identifies processing conditions in which H₂(g) bubbles are stable in the liquid before solidification. It is hypothesized that these conditions lead to low porosity because the bubbles float out of the melt and are not incorporated into the final porosity. Experimental data are shown to support this hypothesis.
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Frueh, Christian 1969. "The effect of silica-containing binders on the titanium/face coat reaction." Thesis, The University of Arizona, 1995. http://hdl.handle.net/10150/291718.
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The interactions of CP-Ti and Ti-6Al-4V with investment molds with alumina/silica and yttria/silica face coat systems, and yttria crucibles were studied. It was found that the thickness of the reaction layer (alpha case) was the same, whether a yttria/silica or alumina/silica face coat was used, indicating that it is the silica binder truly which reacts with the titanium. Furthermore, it was found that only the yttria crucible was inert to reacting with titanium when it was used as a mold. When titanium was heated in yttria crucibles, however, and held just above the liquidus for 15 s and 30 s, oxygen and yttrium were found in the resulting samples. This indicates that commercial castings requiring longer solidification times might not be free of the alpha case even when produced in a 100% yttria mold system.
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Tedds, Steven Paul. "Microporous materials for hydrogen storage." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/1765/.
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Microporous materials (with pores of less than 2 nm in diameter) have attracted considerable attention due to the variety of applications such as gas storage. Physisorption of molecular hydrogen offers several advantages over chemical absorption, namely, fast kinetics and complete reversibility. The overall aim of this work was to investigate the potential of microporous materials for hydrogen storage, with particular attention given to a relatively new class of material: Polymers of Intrinsic Microporosity (PIMs). Generally the PIMs were seen to adhere to Chahine’s rule, which predicts a linear correlation of hydrogen adsorption capacity, at 77 K, with surface area (1 wt.% per 500 m\(^2\) g\(^{-1}\)). IRMOF 1 and Cu-BTC exhibited the largest gravimetric storage capacities of 4.86 and 4.50 wt.% at 77 K and 15 bar, respectively. The largest for a microporous polymer was 3.26 wt.% at 77 K and 15 bar, for the methyl triptycene-based PIM. Two empirical equations, Sips and Tóth, were used in addition to a multi-parameter Virial type thermal equation to fit hydrogen adsorption curves over a range of temperatures (77 to 137 K), in order to calculate the enthalpy of adsorption for all materials as a function of hydrogen adsorption. The findings in this investigation suggest that there is a trade-off between gas sorption capacity and enthalpy of adsorption where dispersive van der Waals interactions dominate adsorption. It is unlikely that the optimal enthalpy of adsorption (of ca. 20 kJ mol\(^{-1}\)) will be achieved by simply reducing the pore size of the material.
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Ranalli, Juan Manuel. "Relationship between microstructure and corrosion of pressure vessel cladding materials." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8333/.
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Type 347L and Type 309L stainless steels used as weld cladding materials of nuclear reactor pressure vessels were investigated under realistic conditions of fabrication and service. Electron backscatter diffraction and metallographic observations were used in combination with double loop electrochemical potentiokinetic reactivation (DLEPR) test and ASTM-262-A test to determine the precipitation behaviour and its influence on intergranular corrosion (IGC) resistance as a function of post welding heat treatment (PWHT) time at 600 oC and after simulated service ageing at 425 °C. It was shown that during the first stage of PWHT, M23C6 carbides precipitate in both alloys as a result of δ ferrite decomposition. This increased sensitization of the materials is due to the creation of a chromium-depleted zone, which was found to be replenished after 40 h of treatment, recovering the resistance of the materials to IGC. After combined treatment of PWHT + simulated service, 309L was shown to be re-sensitized whereas 347L remained resistant. Sigma phase was found to precipitate during the last stages of PWHT with a higher tendency on 309L. Two characteristic reactivation potentials were found for both materials. A specific split-cycle DLEPR was applied to show that this technique can be further developed to identify deleterious phases in austenitic stainless steel welds. Micro hardness and Charpy impact tests showed an increase in hardness and a decrease in absorbed energy of materials without PWHT after ageing at 425 oC.
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Chen, Ke. "The Origin of Coarse Grain Structure in Friction-Stir Welded AA5083 after Heat Treatment." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1244047069.
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Welk, Brian A. "Microstructural and Property Relationships in β-Titanium Alloy Ti-5553." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1262191957.
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May, Katelun. "Small Scale Tensile Testing of Titanium Alloys." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1282099780.
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Caron, Jeremy Leonard. "Weldability Evaluation of Naval Steels." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1285050450.
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Zhong, Wei. "Measurement of Diffusion Coefficients of Nine Elements in Magnesium and Establishment of a Comprehensive Mobility Database for Lightweight Magnesium Alloys." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1557147025847122.
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Sliwinski, Peter R. "Powder painting of aluminium." Thesis, Aston University, 1985. http://publications.aston.ac.uk/14478/.
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The mechanisms involved in the production of chromate-phosphate conversion coatings on aluminium have been investigated. A sequence of coating nucleation and growth has been outlined and the principle roles of the constituent ingredients of the chromate-phosphate solution have been shown. The effect of dissolved aluminium has been studied and its role in producing sound conversion coatings has been shown. Metallic contamination has been found to have a dramatic influence on chromate-phosphate coatings when particular levels have been exceeded. Coating formation was seen to be affected in proportion to the level of contaminaton; no evidence of sudden failure was noted. The influence of substrate and the effect of an acidic cleaner prior to conversion coating have been studied and explained. It was found that the cleaner ages rapidly and that this must .be allowed for when attempting to reproduce industrial conditions in the laboratory. A study was carried out on the flowing characteristics of polyester powders of various size distributions as they melt using the hot-stage microscopy techniques developed at Aston. It was found that the condition of the substrate (ie extent of pretreatment), had a significant effect on particle flow. This was explained by considering the topography of the substrate surface. A number of 'low-bake' polyester powders were developed and tested for mechanical, physical and chemical resistance. The best formulation had overall properties which were as good as the standard polyester in many respects. However chemical resistance was found to be slightly lower. The charging characteristics of powder paints during application by means of electrostatic spraying was studied by measuring the charge per unit mass and relating this to the surface area. A high degree of correlation was found between charge carried and surface area, and the charge retained was related to the powder's formulation.
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Johnston, Cameron L. "Structure and properties of arc sprayed steel coatings." Thesis, Aston University, 1985. http://publications.aston.ac.uk/14479/.
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Cooney, Elizabeth Myers. "Bronze metallurgy in Iron Age central Europe : a metallurgical study of Early Iron Age bronzes from Stična, Slovenia." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39480.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (v. 2, p. 375-377).
The Early Iron Age (750-450 BCE) marks a time in the European Alpine Region in which cultural ideologies surrounding bronze objects and bronze production were changing. Iron was becoming the preferred material from which to make many utilitarian objects such as weapons and agricultural tools; this change can be clearly seen in the different treatments of bronze object deposits from the Late Bronze Age to the Early Iron Age. The Early Iron Age hillfort settlement of Sticna in what is now southeastern Slovenia was one of the first incipient commercial centers to take advantage of the new importance placed on iron, conducting trade with Italy, Greece, the Balkans, and northern Europe. This metallurgical study of bronze funerary objects from Sticna identifies construction techniques, use patterns, and bronze metallurgical technologies from the ancient region of Lower Carniola. This information is then used to explore the cultural importance of bronze at Early Iron Age Sticna and to compare the bronze work of Lower Carniola with that of other regions in central Europe and Italy from this time of great change in Iron Age Europe.
S.M.
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Crisan, Ioan Adrian. "Vortex matter, dynamics and pinning in superconducting materials." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4091/.
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The enclosed body of work represents a compilation of published papers coveringwork carried out in the Universities of Birmingham, Bath and Southampton, UK, in theSecond University of Rome “Tor Vergata”, Italy, in the Nanoelectronics Research Institute (former Electrotechnical Laboratory) of AIST Tsukuba, Japan, and in the National Institute of Materials Physics (former Institute of Physics and Technology of Materials), Bucharest, Romania, during my research career over more than twenty years. The thesis comprises mainly research work on science and technology of high temperature superconducting cuprates of various compositions (Y-based, Bi-based, Tl-based, Hg-based, (Cu,C)-based) and morphologies (polycrystalline, single crystals, thin films, tapes, artificial superconducting superlattices). The major theme common to most of the research done on the abovementioned materials is the study of vortex matter, dynamics, and pinning, which determine a large number of superconducting properties for various applications. The submitted work presents the results of experimental and fundamental studies of superconducting materials in six main areas. These comprise: (i) synthesis and characterization (current-voltage characteristics, dissipation mechanisms, interaction between inter-and intra-grain vortices) of Y- and Bi-based superconducting ceramics; (ii) experimental and theoretical studies of current-induced unbinding of thermally-created vortex-antivortex pairs; (iii) fabrication and characterization of artificial superconducting superlattices; (iv) fabrication and characterization of anomalous superconductors, two- and multi-component superconductors, and exotic vortex matter; (v) study of vortex matter and dynamics by Scanning Hall Probe Microscopy; and (vi) science and technology of vortex pinning, including through self-assembling nanotechnology of pinning centres. There are a small number of publications that do not fall in the above-mentioned areas, but they are also in the larger field of science and technology of superconducting materials. The papers are presented essentially chronologically, with no attempt to group them into separate research areas, since the common philosophy and approach to the investigation of various superconducting materials is to determine how vortex matter, dynamics and pinning influence their physical properties.
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Demmons, Alan C. "Superalloy Metallurgy a Gleeble Study of Environmental Fracture in Inconel 601." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1595.
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At temperatures above 0.5 Tm and in aggressive atmospheres predicting alloy performance is particularly challenging. Nickel alloys used in regimes where microstructure and properties are altered dynamically present unique requirements. Exposure may alter properties with unexpected early failure. The Gleeble is a valuable tool for investigation and simulation of thermo-mechanical properties of an alloy in various regimes up to the threshold of melting. In this study, four regimes of temperature and strain rate were simulated in an argon atmosphere to both investigate and document normal and abnormal failure modes. Commercial Inconel 601 was tested in selected regimes and in two treatments (as received and strain aged). Next two exposed conditions (TEOS and Hydride) were tested. Slow strain-rate and high temperature produced brittle intergranular fracture. Exposure at elevated temperature to process gases reduced both strength and ductility in both TEOS and Hydride. TEOS exposure reduced reduction in area in the alloy significantly more than the Hydride exposure.
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Mickelsson, Sandra. "Kartläggning av AOD-konverterns ingångsförhållanden och dess påverkan på färskningstiden." Thesis, Luleå tekniska universitet, Industriell miljö- och processteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-70230.
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Sandvik Materials Technology tillverkar varje år cirka 230 000 ton stål varav en stor del är rostfritt stål. För att sänka kolhalten i stålet används en AOD-konverter där en kombination av syrgas och inertgas blåses in stålet för att avlägsna kol som kolmonoxid. Vissa duplexa rostfria stålsorter är trögfärskade vilket lätt leder till att konvertern blir flaskhalsen i stålverket. Syftet med arbetet är att undersöka och kartlägga parametrar som påverkar färskningstiden för trögfärskade duplexa stålsorter. Tiden i konvertern kan variera kraftigt mellan olika charger och det finns därför en ekonomisk drivkraft i att förkorta färskningstiden. Kolfärskningen i AOD-konvertern bygger på drivkraften hos kol att reagera med syre. Genom att använda blåssteg med ökande andel inertgas kan partialtrycket av CO-gas i stålet sänkas vilket gynnar oxidationen av kol. Vid färskning av rostfria stål som innehåller höga halter krom oxideras både kol och krom på grund av hög affinitet för syre. En liten slaggvolym kan anses som gynnsamt för färskningen då en mindre mängd kromspineller kan bindas till slaggen. Parametrarna har undersökts genom statistik från historiska charger samt genom ytterligare provtagningar under färskningsförloppet. De parametrar som undersökts är ståltemperatur, tid i överföringsskänk, mängd justeringar, antal dysor och gasflöde, operatör, stålsammansättning och slaggens inverkan. Det är ett stort antal parametrar som påverkar färskningen och det är svårt att avgöra vilken eller vilka som påverkar mest. Utifrån resultatet kan det ses att de undersökta parametrarna påverkar resultatet på olika sätt; en hög temperatur in i konvertern är gynnsam lika som en kort tid i överföringsskänken och en stålsammansättning nära riktvärdet. Många av parametrarna är dessutom beroende av varandra så som att stålsammansättningen påverkas av justeringarna och temperaturen påverkas av tiden i överföringsskänken. Slaggens inverkan på färskningen studerades utifrån typen och mängden slaggbildare. Resultaten visar att kromspineller bildas i slaggen oberoende av vilken slaggbildare som används. För chargen med slaggbildare 1 var det tydligt att det fanns fri kalciumoxid i slaggen vilket tyder på att slaggen är mättad på kalciumoxid. En mättad slagg kan leda till bildandet av en större mängd spineller vilket kan leda till en längre färskningstid. När slaggbildartillsatsen förändrades och tillsattes under steg 2 visar resultatet att 5/10 charger når en kolhalt under riktvärdet vid prov 54. Slutsatser som kan dras är att det är viktigt att fokusera på de parametrar som har en stor påverkan på färskningstiden men samtidigt är möjliga att påverka. Det kan vara att använda fler dysor och på så sätt öka gasflödet, minska slaggvolymen eller undvika att stålet förvaras långa tider i överföringsskänken.
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Wang, Ye. "Self-assembled nanorods and nanowires from oxide functional materials grown by pulsed laser deposition." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5231/.
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In this study, ZnO, MgO, In2O3, SnO2, iron oxide nanowires and nanorods were successfully produced by using Pulsed Laser Deposition. It was observed that the parameters, such as gold nanodots, number of pulses on the targets, temperature, oxygen pressure and substrate, contribute to various results. Different metal catalyst or substrate results in different morphology. Controlling oxygen pressure and substrate temperature was found to be crucial for the ZnO, In2O3 and iron oxide nanowires growth using this technique. The morphology of ZnO nanowires is highly influenced by plasma plume. Increasing the shots on gold target would increase the width of MgO nanorods, but by increasing the number of gold pulses, the distribution of the sizes and dimensions of ZnO nanorods become smaller. However, in the case of In2O3, retaining the total number of gold shots between 5 shots and 25 shots is critical. The variation of the number of laser pulses on oxide target mainly affects the length of nanowires in the case of MgO. However, in regards to In2O3, it does affect both the width and length of the nanowires.
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Johnson, Luke N. "Analysis of Microstructure and Macrosegregation for Directional Solidification of Al-7 wt% Si Alloy with a Cross-Section Change at Growth Speeds of 10 and 29.1 μm/s." Cleveland State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=csu1372067962.
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Zhang, Jing Zavaliangos Antonios. "Numerical simulation of thermoelectric phenomena in field activated sintering /." Philadelphia, Pa. : Drexel University, 2004. http://dspace.library.drexel.edu/handle/1860/407.
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Kannan, Manigandan. "A Study of Microstructure, Quasi-Static Response, Fatigue, Deformation and Fracture Behavior of High Strength Alloy Steels." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1417552570.
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Lan, Song. "High Temperature Nitridation of Powder and Nanocomposite Iron-based Magnetic Alloys." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1527853642053372.
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Wang, Tianxue. "DYNAMIC BEHAVIOR OF COMMERCIAL PURITY POLYCRYSTALLINE MAGNESIUM AT ELEVATED TEMPERATURES AND HIGH STRAIN-RATES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case156233794566219.
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Bourassa, Louis. "Improving the fatigue strength of Ti-6Al-4V by surface thermomechanical processing." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=26376.
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Surface thermomechanical processing was explored as a way to improve the fatigue strength of Ti-6Al-4V load bearing orthopaedic prosthesis. In this study, the surface of an implant is microknurled to provide a "textured" surface that allows for mechanical fixation by bone ingrowth. The microknurling is essentialIty an indentation technique and thus generates plastic deformation which is limited to the surface. This in turn can be used to produce localized surface recrystallization, thus permitting the modification of the surface microstructure.The microstructure of Ti-6Al-4V can be controlled through thermomechanical processing to produce fine equiaxed morphologies which are known to be effective against crack initiation. Conversely, lamellar microstructures can be produced through heat treatment alone. This study deals with the production of a "dual microstructure" having a fine equiaxed microstructure surface layer and an inner coarse lamellar microstructure.
Indentation tests using a servo-hydraulic/load frame system were first run at room temperatures. These tests showed that deformation could be concentrated to produce localized recrystallization. Later, high temperature (800$ sp circ$C) indentation tests were run and it was found that localized recrystallization could also be obtained at higher temperatures. High temperature microknurling was then proposed as a potential method to alleviate surface cracking problems encountered when using the current room temperature microknurling process.
The dual microstructure was optimized under the present experimental limitations, and fatigue tests using microknurled specimens were run to determine the effect on fatigue strength The dual microstructures showed improved fatigue strength over the single homogeneous microstructures. It was also found that microknurling alone (without any heat treatment subsequent to the microknurling) imparts residual compressive stresses that can improve the fatigue strength to levels superior to the dual microstructure. However, it was concluded that a crack free dual microstructure may still have superior fatigue strength to a non-heat-treated microknurled specimen. (Abstract shortened by UMI.)
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Megharief, Jihad Dokali. "Behavior of composite castellated beams." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ37273.pdf.
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Varano, Rocco. "Structure-property investigation of Co-Cr-Mo alloys used in metal-metal total hip replacements." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0025/MQ50669.pdf.
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Sivasundaram, Mathumathi. "Glass ceramics from pulp and paper waste ash." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0032/MQ64248.pdf.
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