Orientadores: Julio Cesar Hadler Neto, Peter Christian Hackspacher / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T05:57:37Z (GMT). No. of bitstreams: 1 Palissari_Rosane_D.pdf: 15939989 bytes, checksum: f455fc1254ec2dd67bb39d1df46cce88 (MD5) Previous issue date: 2007 / Resumo: O Método dos Traços de Fissão (MTF)é uma das técnicas mais poderosas usadas para descrever as histórias térmicas de rochas presentes na camada da superfície terrestre,sob condições de baixa temperatura.Se a rocha hospedeira teve a temperatura elevada em um dado período,os traços de fissão que se formaram desde então,são encurtados irreversivelmente ou apagados (os traços sofrem annealing ),como conseqüência de um processo de difusão termicamente ativada. Os minerais mais comumente utilizados no MTF são a apatita e o zircão,sendo este último o objetivo deste trabalho.O zircão é sensível ao annealing térmico sob temperaturas mais altas que a temperatura de fechamento da apatita,que é aproximadamente 120 o C . As características do annealing dos traços de fissão em zircão têm sido obtidas utilizando-se dados de experimentos de laboratório,que são executados em tempos menores que 1 ano,e comumente em tempos ainda menores.Estes dados são usados para calibrar modelos de annealing empíricos,que descrevem a dependência do encurtamento dos traços com o tempo e a temperatura.No entanto,um problema de ordem prática é a incerteza introduzida na extrapolação para tempos geológicos (10 6 ¿ 10 8 anos),através dos modelos calibrados pelos dados de laboratório (<1 ano). Um dos objetivos deste estudo é fornecer condições de contorno adicionais para a faixa de tempo-temperatura da zona de annealing do zircão,através de dados de zircões de poços, cujas amostras foram expostas a temperaturas estáveis por ~1 milhão de anos.Desta forma, o problema da extrapolação é abordado explicitamente ajustando-se os modelos a dados geológicos. Vários modelos de annealing foram propostos na literatura de traços de fissão.A formulação básica destes modelos baseia-se na equação de Arrhenius e foi apresentada por Laslett et al.(1987).Existem outros modelos de annealing que são baseados no mesmo princípio:Crowley et al.(1991);Laslett e Galbraith (1996);Rahn et al.(2004)e Yamada et al. (2007).Estes modelos têm sido usados preferencialmente,uma vez que inúmeros fenômenos, desde a formação dos traços até o ataque químico,não são bem entendidos ainda.orém,dois outros modelos calibrados no presente trabalho (Carlson,1990;Guedes et al.,2005a), procuram estabelecer uma correlação direta entre seus parâmetros e os fenômenos envolvidos.Os ajustes dos vários modelos foram comparados entre si,levando-se em conta considerações estatísticas. Além das calibrações efetuadas ajustando-se os modelos a dados geológicos, foram abordadas comparações de previsões dos modelos (relacionadas com as fronteiras da Zona de Annealing Parcial)com outros dados geológicos baseados em densidades de traços de fissão / Abstract: Fission-track (FT)analysis has developed into one of the most useful technique used to constrain the low-temperature thermal history of rocks in the upper part of the Earth's crust.If a host rock is subjected to elevated temperatures,fission tracks that have formed up to that point in time are shortened irreversibly or annealed,as a consequence of a thermally activated diffusion process. The most commonly analysed minerals are apatite and zircon and the latter is the focus of this work,since this mineral is sensitive to thermal annealing at higher temperatures,while the close temperature for apatite is around 120 o C. Short-term annealing characteristics of FT in zircon are generally based on laboratory experiments which are performed on timescales of less than 1 year,and typically much less. These data have been used to calibrate annealing empirical models,that describe the temperature and time dependence of fission track shortening.However,a practical problem is the uncertainty introduced through the extrapolation of laboratory calibrated models (<1 year)to geological timescales (10 6 ¿ 10 8 years). One of the purpose of this study is to give further constraints on the temperature range of the zircon annealing zone over a geological time scale using zircons data from boreholes,which samples have been exposed to a stable temperature for ~1 Ma.In this way,the extrapolation problem is explicity adressed by fit the zircon annealing models with geological timescale data. Several empirical models formulations have been proposed to perform these calibrations and have been compared in this work.The basic formulation is an Arrhenius-type model and is given by Laslett et al.(1987).There are other annealing models which are based on the same general formulation:Crowley et al.(1991);Laslett and Galbraith (1996);Rahn et al.(2004)and Yamada et al.(2007).These models equations have been preferred due to the great number of fenomena from track formation to chemical etching that are not well understood.However,two other calibrated models in this work (Carlson,1990;Guedes et al.,2005a)try to stablish a direct correlation between their parameters and the related fenomena.Several model fits are compared by themselves,considering statistical data. Besides calibrating annealing models with geological timescale data,model predictions (related with Parcial Annealing Zone boundaries)were compared with another geological data / Doutorado / Geofísica Nuclear / Doutor em Ciências

Hot strip mills (HSM) are used to roll cast slabs down from their initial size to plate or sheet, which is then used to manufacture a wide variety of goods for many industrial markets. The working rolls that contact and deform the strip are arguably the primary element of the hot strip mills. The work rolls must have sufficient strength to apply the mechanical force to the strip, while still resisting the wear and thermal stresses inherent to the process. The history of the development of these work rolls spans more than a hundred years. The more recent advancement in work roll technology was the development of High Speed Steel (HSS) work rolls during the 1990's. The HSS rolls utilise a variety of carbide forming elements to improve the wear resistance. The South African Roll Company (SARCO) is an established roll producer and the only one in South Africa with a well-established international client base. SARCO is currently developing a range of high quality HSS rolls and has developed an initial HSS grade, which has shown competitive performance and durability in service compared to established HSS alloys from other roll manufacturers. Although the initial trials show great promise, significant potential for development and associated improvements are available. It has been documented that an additional annealing treatment prior to the regular heat treatment will refine the microstructure of HSS rolls, which should improve mechanical properties and performance. However, although pre-annealing has been documented, the degree of mechanical property improvement associated with the pre-annealing has not been studied and the annealing step does not appear to be commonly applied by roll producers. The first aim of this research project was to investigate the properties of the HSS material currently produced by SARCO to elucidate the source of the combination of high wear resistance and durability. The roll material identified for characterisation consisted of four sets of samples. These were subjected to intensive characterisation, which included chemical analysis, ferrite scope measurements, metallography, hardness testing, Scanning Electron Microscopy (SEM) analysis, X-Ray Diffraction (XRD) analysis and Simultaneous Thermal Analysis (STA). The good combination of performance and durability appears to be the product of the Ni additions, W:Mo ratio, high carbon content, high austenitising temperatures and balanced carbide-former additions. The second objective was to investigate the effect of annealing prior to the typical solution, "soft" quench and tempering heat treatment, on the structure and mechanical properties of the HSS material used for the outer shell of mill rolls. As-cast material was used for the analysis, which was subjected to similar intensive characterisation. High Chromium (HC) used in roll material appears to be more sensitive to both temperature and time variations in heat treatment than HSS. No grain refinement of the HSS material was achieved by the pre-annealing. Higher peak hardness and more gradual reduction in hardness beyond the peak was not found under simulated conditions, indicating that a desired increase in hardness will not be achieved in practice. It was evident that the industrial heat treatment condition cannot be sufficiently simulated by shorter time laboratory tests. The effects of pre-annealing should be researched on lower alloy bainitic HSS material if feasible and the improved wear resistance and toughness benefits of pre-annealing could be quantified by performing industrial trials and fracture toughness testing respectively. / Dissertation (MEng)--University of Pretoria, 2017. / Materials Science and Metallurgical Engineering / MEng / Unrestricted

Recrystallisation annealing, a repeated heat treatment between different stages of cold rolling of martensitic chromium steel strip, is successful when neither high rolling forces nor wear of the working rolls occur during the subsequent cold rolling. Mechanical properties as tensile strength, yield, elongation or hardness have been, by tradition, the criteria that described the quality of the annealing process. In recent years, the development of the measurement equipment in the rolling mills and of the instruments for material investigations has accentuated more and more the role played by the microstructural properties in the evaluation of the heat treatment. Two microstructural characteristics of the degree of annealing are, firstly and most important, the recrystallisation degree, and, secondly, the secondary carbide density. The sample manufacturing and heat treatment, modelling and microstructure investigations by light optical- (LOM) and scanning electron microscopy (SEM) described in this article were carried out at Sandvik Materials Technology’s R&amp;D Department and Bell Furnace Line in Sandviken, Sweden, while microstructure investigations and evaluation by scanning electron microscopy with field emission gun (FEG-SEM) and electron back scatter diffraction (EBSD) were done at the Corrosion and Metals Research Institute (KIMAB) in Stockholm, Sweden. The first part of this work shows that, in contrast to the traditional methods LOM and SEM, that use chemical etching for the preparation of the samples, EBSD can successfully characterise recrystallised structures in annealed martensitic chromium steels. Unlike conventional microscopy with LOM and SEM, EBSD is able to reveal the grain geometry, as well as to separate and identify the different phases in this kind of steels (ferrite, M23-, M6-carbides). Important parameters such as grain size, particle size and recrystallised fraction can be measured with high accuracy. This information can be used to understand, evaluate, control and even predict the recrystallisation annealing of martensitic chromium steel. The second part of this work presents how the results from microstructure description by EBSD can be directly used in relatively simple empirical models for determination of recrystallisation degree as function of the annealing parameters and the deformation history. EBSD was applied to evaluate the degree of recrystallisation in a series of annealing tests, with the purpose to model recrystallisation temperature in two types of martensitic chromium steel strip, a traditional one and one alloyed with molybdenum, cold rolled with different amounts of reduction and annealed with different temperatures, soaking times and heating rates. The empirical quadratic models were built with Umetrics’ software for experimental design, MODDEÒ 8.0 and they defined the recrystallisation degree (limits for LAGB and HAGB were set to 1.5° and 7.5° for the first grade and 2.5° and 10° for second one) and the secondary carbides density as functions of annealing temperature, soaking time and cold reduction (the factor heating rate was removed as nonsignificant). To be observed that these empirical models were fit much better for the recrystallisation degree than for the secondary carbides density. The modelling work described above, together with the implementation of online physical temperature models in the bell annealers may lead to an increased productivity in the production plant by shortening the annealing cycle and minimising scrap and thus to an economical gain of ca 1,5 MSEK per year at Sandvik Materials Technology.

Abstract Nuclear Medicine (NM) images inherently suffer from large amounts of noise and blur. The purpose of this research is to reduce the noise and blur while maintaining image integrity for improved diagnosis. The proposal is to further improve image quality after the standard pre- and post-processing undertaken by a gamma camera system. Mean Field Annealing (MFA), the image processing technique used in this research is a well known image processing approach. The MFA algorithm uses two techniques to achieve image restoration. Gradient descent is used as the minimisation technique, while a deterministic approximation to Simulated Annealing (SA) is used for optimisation. The algorithm anisotropically diffuses an image, iteratively smoothing regions that are considered non-edges and still preserving edge integrity until a global minimum is obtained. A known advantage of MFA is that it is able to minimise to this global minimum, skipping over local minima while still providing comparable results to SA with significantly less computational effort. Image blur is measured using either a point or line source. Both allow for the derivation of a Point Spread Function (PSF) that is used to de-blur the image. The noise variance can be measured using a flood source. The noise is due to the random fluctuations in the environment as well as other contributors. Noisy blurred NM images can be difficult to diagnose particularly at regions with steep intensity gradients and for this reason MFA is considered suitable for image restoration. From the literature it is evident that MFA can be applied successfully to digital phantom images providing improved performance over Wiener filters. In this paper MFA is shown to yield image enhancement of planar NM images by implementing a sharpening filter as a post MFA processing technique.

Virginia Tech\'s Computational Bioinformatics and Bio-imaging Laboratory (CBIL) is exploring integrative network analysis techniques to identify subnetworks or genetic pathways that contribute to various cancers. Chen et. al. developed a bagging Markov random field (BMRF)-based approach which examines gene expression data with prior biological information to reliably identify significant genes and proteins. Using random resampling with replacement (bootstrapping or bagging) is essential to confident results but is computationally demanding as multiple iterations of the network identification (by simulated annealing) is required. The MATLAB implementation is computationally demanding, employs limited concurrency, and thus time prohibitive. Using strong software development discipline we optimize BMRF using algorithmic, compiler, and concurrency techniques (including Nvidia GPUs) to alleviate the wall clock time needed for analysis of large-scale genomic data. Particularly, we decompose the BMRF algorithm into functional blocks, implement the algorithm in C/C++ and further explore the C/C++ implementation with concurrency optimization. Experiments are conducted with simulation and real data to demonstrate that a significant speedup of BMRF can be achieved by exploiting concurrency opportunities. We believe that the experience gained by this research shall help pave the way for us to develop computationally efficient algorithms leveraging concurrency, enabling researchers to efficiently analyze larger-scale data sets essential for furthering cancer research. / Master of Science

Long time annealing of semicrystalline PEEK above the glass transition results in the observation of several time dependent phenomena - &quot;physical aging&quot;, &quot;secondary crystallization&quot;, &quot;multiple melting&quot; of lamellae with different thermal stability etc. Their interrelation - common origin and kinetics of development, is characterized extensively for the first time in this study. The evolution of the crystallinity during the secondary crystallization process was monitored by DSC and density measurements. Crystallinity was characterized according to the standard two-phase model of semicrystalline polymers and analyzed with respect to the failure of the model to adequately describe the physical state of the polymer. A discrepancy was observed between DSC and density crystallinity values and their respective rates of development during the secondary crystallization stage. WAXS reveals that the crystal density is not a physical constant, but depends on the crystallization and/or annealing temperature. Furthermore, the crystalline lamellae densify with time during crystallization and/or annealing. This observation leads to the conclusion that there is no one-to-one correspondence between density and crystallinity and necessitates the application of a revised equation for density crystallinity which accounts for the dynamics of crystal densification. The characteristics of the low temperature endothermic peak in the DSC scan of PEEK (peak maximum, transition enthalpy etc.) were found to evolve with annealing time and temperature during the secondary crystallization process in a way similar to the kinetics of development of the enthalpy relaxation process in amorphous polymeric glasses. This study reports for the first time in the literature the observation of &quot;physical aging&quot; above the glass transition in the case of PEEK (according to the definition of this term given by Struik). An extensive investigation of the &quot;double melting&quot;/&quot;multiple melting&quot; phenomenon, which is observed as a result of isothermal treatment of the polymer above Tg, was performed and several new observations reported. After the end of the primary crystallization process, the semicrystalline polymer is a nonequilibrium system due to the fact that crystallinity is less than unity. The system's continuing approach to equilibrium and its response to mechanical perturbations follow kinetics similar to that of segmental relaxation below the glass transition. / Ph. D.

Part A of two Project Reports; Part B can be found at: http://hdl.handle.net/11375/17691 / <p>The annealing behaviour of 15N implanted, aluminum doped-SiC has been studied by measuring the differential capacitance as a function of applied bias. The samples were doubly implanted at 450°c with 45 Kev and 25 Kev ions, for a dose of 10^16/cm^2 at each energy.</p> <p> An n-i-p structure with a thick insulator region was found after annealing at 1000°c. The thickness of this i region could be substantially reduced with additional annealing at higher temperatures, and a fairly good n-p junction was obtained after 1480°c anneal.</p> <p> About 20-30% of the implanted nitrogen ions were found to be electrically active.</p> <p> The C-V behaviour was found to have large variations with the a.c. measuring frequency.</p> / Thesis / Master of Engineering (MEngr)

Automotive magnesium sheets typically exhibit poor room temperature ductility which makes them unsuitable for room temperature sheet stamping applications. This research involved aspects of re-processing and forming of AZ31 automotive magnesium sheet to improve its room temperature ductility and bendability (and, more generally, formability). The sheet re-processing studies for formability improvement were carried out by two different methods, (i) cyclic bending-unbending and annealing (or CBUA) and (ii) wire brushing and annealing (or WBA). These two processing methods led to a complex stress and strain distribution through the thickness and a multi-layered microstructure after annealing. The grain structure, micro-texture, and micro-hardness of each of the layers were studied by optical microscopy, electron back-scattered diffraction (EBSD) and indentation measurements, respectively. The through-thickness grain structure study indicated grain refinement and texture randomization in the surface layers for both CBUA and WBA processed materials. In addition, the as-received (and fully annealed) sheet as well as processed materials were subsequently deformed in uniaxial tension and bending by a process referred to in the literature as pre-strain annealing (or PSA). The PSA process was studied as a single step as well as multi-step process to assess its effect on formability improvement, underlying changes in microstructural and mechanical behavior, and to explore practical limitations and advantages of the process. The results from single-step PSA process were also used to develop a microstructure-based constitutive material model to capture and predict the observed mechanical and microstructural response of AZ31 sheet to PSA variables. This model explicitly considered the effect of recovery on recrystallization kinetics, and non-constant nucleation and growth rate. The model was extended to predict the grain size at the end of recrystallization and within the grain growth stage as well as post-PSA yield and work hardening characteristics. The mechanical property prediction was based on considering the microstructure as a composite of un-recrystallized, recrystallized and coarsened grain structure and by employing a rule of mixture. The processing and forming methods led to significantly increased cumulative uniaxial tensile ductility and plane strain cumulative bendability of AZ31 sheet at room temperature depending upon PSA process parameters. The experimental and modeling studies collectively helped correlate mechanical properties from various processing conditions and forming methods with microstructural parameters, and to explain the improvement in room temperature formability based on microstructural and textural considerations. / Dissertation / Doctor of Philosophy (PhD)

Stronger and higher strength steels are continuously being demanded by industry. A stronger steel enables less material to be used to meet structural requirements, allowing for both cost and weight savings. Through collaboration with Stelco, CanmetMATERIALS, and McMaster University, this project focused on the development of a Grade 80 (550MPa YS and 600MPa UTS) steel with elongation at fracture of 16%. The design space for the creation of the steel was limited to high-strength low-alloy and low-carbon steels that are compatible with batch-annealing processes. To achieve this goal, two main strengthening methods were explored. The first method employed the use of precipitation hardening through microalloying additions of Mo, Nb, Ti, and V to form various metal carbide precipitates. The second method was based upon dislocation strengthening using recovery annealing and Ti to delay recrystallization. Multi-scale characterization was used to quantify the strengthening mechanisms and to explain how the microstructural changes, features, and evolution affected the properties of the steel. Uniaxial tensile testing was performed to determine key mechanical properties, namely the yield strength, tensile strength, and elongation at fracture. Optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, electron backscatter diffraction, transmission electron microscopy, and atom probe tomography were utilized extensively for microstructural analysis to further quantify the steels. The precipitation hardened steel reached a yield strength of 605MPa with 15.4% elongation at fracture for a 50mm gauge length. This was achieved using a cold rolling reduction of 66% followed by a heat treatment at 670°C for 24 hours. The recovery-annealed steel obtained even better properties. It achieved a yield strength of 610MPa with a 19.6% elongation at fracture for a 25.4mm gauge length. A cold rolling reduction of 60% was used followed by a heat treatment at 550°C for 36 hours. The strengthening mechanism for this steel is novel, and involves the slowing of recrystallization without Zener pinning nor solute decoration of dislocations. This thesis will hopefully bring upon new research into this mechanism. Furthermore, the properties of this recovery-annealed steel shows great promise for use in industry due to its high strength, good elongation, and low materials cost. Consequently, this steel could be the subject of substantial research in the near future. / Thesis / Master of Applied Science (MASc)

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