Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2016-08-01T16:21:23Z No. of bitstreams: 1 Briceño-Zuluaga 2016 Tese.pdf: 9025569 bytes, checksum: 00c4eb9cee0d346d7a8681fdbb975f49 (MD5) / Made available in DSpace on 2016-08-01T16:21:23Z (GMT). No. of bitstreams: 1 Briceño-Zuluaga 2016 Tese.pdf: 9025569 bytes, checksum: 00c4eb9cee0d346d7a8681fdbb975f49 (MD5) / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geociências - Geoquímica. Niterói, RJ / Este trabalho apresenta o registro da distribuição granulométrica de sedimentos laminados recuperados na plataforma continental de Pisco (Peru), que é caracterizada pelos aportes fluviais regionais (relacionado com aumento das precipitações) e pelo aporte eólico local (relacionado com a intensidade do vento local). Esse registro vai desde a Anomalia Climática Medieval (ACM) até o Período de Aquecimento Moderno (PAM) passando pela Pequena Idade do Gelo (PIG) numa escala secular até subdecadal. As simulações da distribuição e trajetórias atmosféricas do material eólico durante eventos registrados de erosão por tempestades de areia na região realizadas em Hysplit4 são apresentadas. Os resultados dessas simulações suportam o fato de que a origem eólica das partículas grosseiras ocorre no sedimento marinho. Os componentes granulométricos identificados são discutidos a partir do modelo matemático de fraccionamento de GOMES et al., (1990). Este modelo assume que a composição mineral dos sedimentos está composta por uma assembléia de diferentes populações de partículas minerais com distribuições granulométricas logarítmicas normais. Foi utilizada uma rotina interativa de mínimos quadrados para ajustar a distribuição granulométrica em uma expressão matemática que permite quantificar e identificar os diferentes componentes litológicos para depois inferir os mecanismos de transporte envolvidos e a variação espacial e temporal. O objetivo deste estudo foi separar os padrões de sedimentação do material terrígeno (eólico e fluvial) assim como os processos mais importantes que controlam à entrada deste material para entender como esses processos refletem a variabilidade climática e atmosférica durante o ultimo milênio. Nossos resultados mostram um ativo transporte de partículas eólicas durante a segunda metade da ACM com uma rápida diminuição da ACM para a PIG. Durante a PIG a erosão eólica exibe uma diminuição na sua atividade e assim, um enfraquecimento na intensidade do vento, ao mesmo tempo um incremento na descarga fluvial é apresentada e, isto se relaciona com um incremento na precipitação continental. Durante o PAM o transporte eólico apresenta um rápido e progressivo incremento em relação com o ACM e a PIG, enquanto que a aporte fluvial apresenta uma diminuição. Neste trabalho as simulações da distribuição e trajetórias do material eólico durante os eventos de erosão é apresentado. Comparações com outros registros paleoambientais indicam que essas mudanças estão vinculadas à mudanças no deslocamento meridional da Zona de Convergência Intertropical (ZCIT) e Alta Subtropical do Pacífico Sul (ASPS) assim como a atividade da circulação da célula de Walker em escala de tempo secular. Finalmente a deposição eólica e em consequência a intensidade do vento e sua variabilidade dos últimos 100 anos é muito mais forte que durante a ACM sob condições similares na posição do sistema ZCIT-ASPS. Esta tendência sugere uma forçante adicional na intensificação da circulação atmosférica, consistente com o atual padrão da Oscilação multidecadal do Atlantico e a tendência de aquecimento climático. / In this work are present record of laminated sediments cores retrieved in the continental shelf of Pisco (Peru) that characterize fluvial regional discharge and the wind local aeolian transport (related with the wind intensity) from Medieval Climate Anomaly (MCA) to Little Ice Age (LIA) and the current warm period (CWP) at centennial to sub-decadal resolution. The particle grain size components are discussed using a mathematical model of fractionation. This model assumes that lithological composition of the sediment is an assembled of several log-normally distributed particle population. In this way, an interactive least square fitting routine is used to fit the particle grain size collected with the mathematical expression. This allows inferring the spatial and temporal variation of particles populations and thus transport mechanisms involved. The aim of the study is unmixing and reconstructs the patters of terrigenous (aeolian and fluvial) sedimentation as well as the most important processes that control the input of this material to understand how these components reflect atmospheric climate variability during the last millennium. Our results presented in this work showed active aeolian erosion during the second half of the MCA and rapid decrease from the MCA to the LIA. During the LIA the aeolian erosion exhibit a decreased activity and them a weak in the atmospheric circulation on the same time an increase of fluvial discharge is showed this is relate with an increase of continental precipitation. During the CWP the aeolian erosion transport, display a rapid and progressive increase in relation to MCA and LIA, whereas the fluvial discharge exhibited a decrease. In this work simulation of the aeolian distribution and their trajectories during erosion events are also presented. Comparison with others records indicate that those changes are linked to change in the meridional position of the Intertropical convergence zone (ITCZ) and South Pacific Subtropical High (SPSH) at the centennial time resolution. Finally the CWP show increase in the aeolian deposition and thus in the wind intensity over the past two centuries likely represents the result of the modern position of the ITCZ–SPSH system and the associated intensification of the local and regional winds. Nevertheless, the aeolian deposition and in consequence the wind intensity and variability of the last 100 yr are stronger than the second sequence of the MCA under similar position of the ITZC-SPSH system. This trend suggests an additional forcing in the intensification of the atmospheric circulation, consistent with the current pattern of climate change.

Abstract In this thesis, methods to process ultrafine ferritic (UFF) structures in steels, i.e. grain sizes below about 3 μm have been investigated. It is shown here, in accordance with the results in the literature, that a steel with a UFF grain size can be obtained by two methods, more or less convenient to mass production: deformation-induced ferrite transformation from fine-grained austenite (the DIF route) and the static recrystallization of various heavily cold-worked initial microstructures (the SRF/SRM route). In the present work, the influencing factors in the processing of UFF structure in the DIF route have been systematically studied in four low-carbon steels: one C-Mn steel and Nb, Nb-Ti and Nb-high Ti microalloyed steels. A high strain, a low deformation temperature close to Ar3 and a fine prior austenite grain size are beneficial to promote the formation of UFF grains. Especially by using complex pretreatments to refine the prior austenite grain size, cold rolling, repeating the low-temperature reheating cycle or using martensitic initial microstructure, a UFF grain size can be obtained in these steels at the strain of 1.2 (70% reduction) at 780 °C. By controlling the cooling rate, the type of the second phase can be adjusted. When using the static recrystallization route, it was found that UFF is difficult to obtain from a single-phase ferrite, but it is relatively readily obtained from deformed pearlite, bainite or martensite, especially in high-carbon steels with 0.3–0.8%C. In deformed pearlite, the cementite lamellae fragmented and spheroidised in the course of heavy deformation can provide numerous nucleation sites by the particle stimulated nucleation mechanism and retard the subgrain and recrystallized grain growth. Nucleation and retardation of grain growth are effective also in deformed bainite, martensite or high-carbon tempered martensite, as discussed in detail in the work. The thermal stability of UFF grained steels was tested and found to be generally excellent, but it varies depending on the processing method. The UFF structure obtained by the SRM route has a thermal stability somewhat weaker than that of the DIF route. For a given steel, UFF grains may show different grain growth modes, related to the dispersion of second phase particles. In the DIF structure, abnormal grain growth occurs at 700 °C after about 2.5 h, while in the SRM structure, normal grain growth takes place slowly at 600 °C. Carbides on the grain boundaries seem to play an important role in inhibiting grain coarsening. No coarse-grained zone was formed at the HAZ of electron beam or laser welded seams, as performed at low heat inputs (up to 1.5 kJ/cm) on thin strips. The hardness even increased from the base metal towards the HAZ and the weld metal in all seams as an indication that they were hardened during the rapid cooling.

Les modèles d'érosion et de transport couramment utilisés sont construits à partir de données empiriques obtenues avec des sédiments de granulométries quasi uniformes. Or, il y a beaucoup de situations pour lesquelles la granulométrie des sédiments n’est pas uniforme. Les expériences réalisées en laboratoire et dans les rivières montrent que l’érosion et le transport des sédiments dépendent de la dispersion du diamètre des grains. Cette observation est à l’origine de cette thèse qui a pour objectif l’étude de l’influence de la distribution du diamètre des grains sur le transport de sédiments. Cette influence est envisagée à partir du développement d’un modèle numérique. La prédiction de l’érosion et du transport de sédiments tient de la résolution de deux problèmes : le premier est lié à l’écoulement au dessus du lit, le second à la mise en mouvement du sédiment. Le modèle développé détermine explicitement le mouvement des grains dans le lit de sédiments lorsque sa face supérieure est soumise à un écoulement. Pour cela, il mobilise la Méthode des Eléments Discrets (DEM), développée par Cundall et Strack (1979). Afin de reproduire l’effet de la topographie du lit sur le champ de vitesse du fluide, le modèle DEM est couplé avec le modèle d’écoulement FLOWSTAR. Le modèle FLOWSTAR est proposé par Carruthers et al. (2004) pour déterminer l’écoulement moyen dans une couche limite turbulente atmosphérique au-dessus des collines de faible pente. Le modèle numérique développé est appliqué à différents types d’arrangements de grains. Il permet d’estimer l’évolution du débit de sédiments au cours du temps pour différentes vitesses de frottement. Les seuils d’érosion des lits et l’évolution des débits de sédiments en fonction de la vitesse de frottement sont conformes à l’expérience. L’utilisation de l’approche DEM permet par ailleurs de connaître le comportement des grains dans et à la surface du lit au cours du temps (profil vertical de la vitesse des grains à l’intérieur de l’arrangement par exemple) / The models for the erosion and transport of sediments that are currently used rely on empirical data obtained from experiments with sediments having a uniform or unimodal distribution. But there are many practical situations for which the size distribution is significantly different from this assumed distribution, and laboratory and field experiments have shown that the erosion threshold and the transport rate depend on the size distribution and the range of particle sizes. The aim of this study is therefore to investigate and explain the influence of size distribution on erosion and transport rates, using a numerical model that has been developed specifically to study this problem. The sediment bed is assumed to consist of individual, non-cohesive, spherical particles, and the physical interactions between the particles are modelled explicitly, using the Discrete Element Method developed by Cundall and Strack (1979). The flow above the bed is computed using the FLOWSTAR model (Carruthers et al 2000) which was originally developed to compute the flow in the atmospheric boundary layer above arbitrary topography. These two models are coupled, and the resulting numerical code has been used to investigate the temporal evolution of erosion and transport rates agree well with experimental measurements, and the DEM provides additional information concerning the temporal evolution of the particle size distribution within the bed.

In Canada, about 60% of contaminated sites involve petroleum hydrocarbon (PHC) contamination and most of these sites have been abandoned due to contamination. Among current technologies used for soil remediation, supercritical fluid extraction (SFE) is a relatively recent and potentially viable method. The main aim of this research was to investigate the application of SFE for removal of PHCs from contaminated soils. In the first phase, the effects of SFE operational parameters including fluid pressure, fluid temperature, time duration and mode of extraction on the removal efficiency of PHCs from a spiked sandy soil (with diesel fuel with a ratio of 5 wt%) were investigated. SFE experiments were performed at different pressures (15, 33 and 50 MPa) and temperatures (30, 75 and 120 °C). The combination of 10 min static mode followed by 10 min dynamic mode, repeated for 3 cycles (60 min in total) led to the highest PHC removal percentage. According to response surface methodology (RSM), the optimum pressure and temperature were found to be 50 MPa and 69.3 °C, respectively. According to experimental results, the optimum combination of pressure and temperature determined to be 33 MPa and 75 °C; which resulted in the extraction percentages of 99.2%, 91.7% and 86.1% for PHC F2, F3 and F4 fractions, respectively. In the second phase, the influence of several parameters including soil water content, soil pH and addition of modifier on PHCs removals from a field-contaminated sandy soil using SFE were experimentally investigated. SFE experiments were performed at 33 MPa pressure and temperatures of 45 and 75 °C. Three water content levels of 8%, 14% and 20% at two levels of pH 6.5 and 7.5 were investigated. The extraction of total petroleum hydrocarbon fractions (TPHF), the sum of F2, F3, and F4 fractions, decreased due to the increase in the water content from 8% to 20% at both pH 6.5 and 7.5. The difference of extractions of all PHC fractions at pH values of 6.5 and 7.5 were not statistically significant (at p < 0.05 confidence level) at all three water content levels and pH did not have a significant influence on the PHC removal efficiency. Addition of acetone as a modifier (33.7% TPHF removal) was more effective than hexanes (24.3% TPHF removal) to decrease the concentrations of PHCs for the field contaminated soil. In the third phase, the influence of soil texture and grain size on the extraction of PHC fractions was investigated. SFE experiments were performed at 33 MPa pressure and 75 °C temperature. Three types of soils (soil A, B and C) were spiked with diesel fuel with a ratio of 5 wt%. Soil A, B and C had different particle sizes and were categorized as sand, silt loam and clay, respectively. Soil A (sand) which had the largest particle size resulted in the highest TPHF removal percentage while soil C (clay) with the smallest particle size led to the lowest TPHF removal percentage. A higher clay content in soil C resulted in a lower extraction of PHCs. In the fourth phase, the effects of pressure and temperature on the extraction of PHC fractions from a clay soil spiked with diesel fuel with a ratio of 5 wt% were investigated. SFE experiments were performed at three pressures (15, 33 and 50 MPa) and temperatures (30, 75 and 120 °C). According to the statistical analysis including factorial design and RSM, the optimized combination of pressure and temperature was selected at 42.8 MPa and 120 °C; which resulted in the removal percentages of 74.9% and 65.6% for PHC F2 and F3 fractions, respectively. The optimum combination of pressure and temperature based on the experimental results was selected at 33 MPa and 120 °C that led to 70.3%, 58.4% and 32.6% removal of PHC F2, F3 and F4 fractions, respectively.

Abstract From the largest discontinuities to the smallest of the elements, various factors can threaten structural integrity. Susceptibility to these factors elevates with higher yield strengths. As-quenched low-carbon steels with a martensitic or martensitic-bainitic microstructure are modern ultra-high-strength structural steels. They can possess sufficient toughness, formability, and weldability, and are typically used in weight-critical and high-performance structures. Common problems with as-quenched steels with a yield strength of 900 MPa or more are that they do not obey the conventional correlation between the fracture toughness reference temperature T₀ and the impact toughness transition temperature T₂₈ᴊ used in many standards and structural integrity assessment procedures, and a lack of design rules in general. This thesis studies the relationship between the T₀ and T₂₈ᴊ to provide additional knowledge for future standardisation, the microstructural features governing the toughness at these temperatures on both global and local scale, and whether hydrogen embrittlement is present at subzero temperatures. It uses steels produced via laboratory rolling and quenching as well as from pilot-scale and full-scale industrial production, studying them with standardised toughness tests, microstructural characterisation, fractography, and cohesive zone modelling. As-quenched steels have a distinct correlation between T₀ and T₂₈ᴊ. An improved general T₀ – T₂₈ᴊ correlation applies to a wide range of steels. T₂₈ᴊ correlates closely with a dynamic reference toughness, which can be used together with the fraction of detrimental {100} cleavage planes near the main fracture plain to effectively estimate the transition temperatures. On a local scale, centreline segregation decreases the effective coarse grain size, which more than compensates for the harmful effects associated with the higher hardness and inclusion content of the centreline, resulting in increased fracture toughness. Hydrogen embrittlement causes a decrease in fracture toughness and local deformability, thereby increasing T₀ while leaving T₂₈ᴊ unaffected. Overall, the results show that high toughness demands good control of effective coarse grain size and hydrogen content. / Tiivistelmä Tekijät suurimmista epäjatkuvuuskohdista aina pienimpään alkuaineeseen voivat uhata rakenteellista eheyttä, minkä lisäksi alttius näille kasvaa materiaalin myötölujuuden kasvaessa. Modernit karkaistun tilan ultralujat matalahiiliset rakenneteräkset voivat silti omata riittävän sitkeyden, muovattavuuden ja hitsattavuuden. Tyypillisiä käyttökohteita näille ovat painon suhteen kriittiset ja korkean suorituskyvyn rakenteet. Yleinen ongelma myötölujuudeltaan noin ja yli 900 MPa karkaistun tilan teräksillä on se, että ne eivät noudata perinteistä murtumissitkeyden referenssilämpötilan T₀ ja iskusitkeyden transitiolämpötilan T₂₈ᴊ välistä korrelaatiota, jota käytetään useissa standardeissa ja suunnitteluohjeissa, jotka eivät myöskään vielä salli näin lujien terästen käyttöä. Tämä väitöstyö tutkii transitiolämpötilojen T₀ ja T₂₈ᴊ välistä suhdetta edistääkseen näiden terästen sisällyttämistä standardeihin, haurasmurtuma-sitkeyteen vaikuttavia mikrorakenteellisia tekijöitä sekä yleisellä että paikallisella tasolla, ja vetyhaurautta matalissa lämpötiloissa. Koeteräkset ovat laboratoriovalmisteisia, tuotantokokeita ja tuotantolaatuja. Niitä tutkitaan standardisoiduilla sitkeyskokeilla, mikrorakenteen karakterisoinnilla, fraktografialla ja koheesiovyöhykettä hyödyntävällä mallinnuksella. Tulokset osoittavat karkaistun tilan terästen omaavan erityisen korrelaation T₀ ja T₂₈ᴊ välillä. Muokattu, ultralujat teräkset huomioiva yleinen T₀ – T₂₈ᴊ -korrelaatio soveltuu laajalti eri terästyypeille. T₂₈ᴊ korreloi läheisesti dynaamisen referenssisitkeyden kanssa, jonka avulla yhdessä haitallisten {100} lohkomurtumatasojen osuuden kanssa voidaan estimoida joukko transitiolämpötiloja. Paikallisella tasolla keskilinjasuotauma pienentää efektiivistä karkeiden rakeiden kokoa, mikä suotauman suurista sulkeumista ja kovuudesta huolimatta parantaa murtumissitkeyttä. Vetyhauraus taas huonontaa sitkeyttä ja paikallista muodonmuutoskykyä myös matalissa lämpötiloissa nostaen T₀ lämpötiloja. Kokonaisuutena erinomainen transitiolämpötilasitkeys vaatii efektiivisen karkearaekoon ja vetypitoisuuden minimointia.

Ces travaux de thèse portent sur l’influence de l’état métallurgique sur les propriétés mécaniques et physico-chimiques des alliages électrodéposés nanostructurés de Ni-W pour lesquels la gamme de taille de grains peut être élargie à l’échelle nanométrique grâce à l’ajout de tungstène. Les alliages sont obtenus par électrodéposition en régime continu ou pulsé, à partir d’un bain citrate/ammonium. Une approche multi-échelle associant différentes techniques d’analyse (MEB, EBSD, MET, DRX, EDS, µFluo-X, SIMS et extraction à chaud) permet la caractérisation fine des paramètres métallurgiques. Nos résultats montrent que l’augmentation de la teneur en tungstène engendre un affinement de la taille de grains qui s’accompagne d’une évolution de la morphologie, de la texture cristallographique et de la contamination par les éléments légers (O, H, N, C). Afin de séparer l’influence des différents paramètres métallurgiques sur les propriétés, une démarche originale a été proposée, notamment en utilisant des recuits thermiques sous atmosphère contrôlée comme un moyen de faire varier la microstructure sans modifier la teneur en W et en prenant en compte l’influence de l’état de surface. En plus de l’effet classique de la taille de grains sur l’augmentation de la microdureté, la loi de Hall et Petch dépend fortement des solutés interstitiels et substitutionnels. En milieux acides et alcalins désaérés, le tungstène joue un rôle majeur aussi bien dans le domaine cathodique que dans le domaine anodique. Les autres paramètres métallurgiques comme la taille de grains interviennent plutôt au deuxième ordre. / The aim of this study is to understand the influence of the metallurgical state on the mechanical and anti-corrosion properties of electrodeposited nanostructured Ni-W alloys, in which the grain size can be extended towards nanometric scale by the tungsten addition. Citrate-ammonium baths were used to obtain the alloys by applying direct and pulse currents. A combination of several microstructural techniques at different scales (SEM, EBSD, TEM and XRD) has permitted the characterization of the morphology, the grain size, the crystallographic texture and the nature of grain boundaries. Concentrations of alloying element and contaminants were determined using several techniques such as EDX, GDOES, SIMS, µ-XRF and hot extraction analysis. The obtained results show that tungsten incorporation leads to grain refinement but also to other microstructural changes (morphology or crystallographic texture) and to different levels of contamination. In order to separate the influence of the different metallurgical parameters on the mechanical and corrosion properties, an innovative process was proposed using annealing treatments under controlled atmosphere to vary the microstructure without modifying the tungsten concentration. In addition to the influence of the grain size on the hardness evolution in alloys, the Hall-Petch relationship is also strongly dependent on the incorporation of light elements and tungsten. The study of the polarization curves in acidic and alkaline deaerated solutions revealed that the tungsten addition plays an important role on the electrochemical reactivity in both anodic and cathodic domains and that the other metallurgical parameters such as grain size intervene only at second order.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / In the last decades, several applications of niobium nitride thin films has been proposed or effectively implemented. In the cubic δ − NbN phase, the bulk material presents a Tc for the superconducting transition near 17 K, what is far larger than those found in other normal (BCS) superconductors and useful in, for example, Josephson tunnel junctions. More recently, other phases have been also focus of interest, like the hexagonal δ-NbN phase. The hardness and resistance to chemical corrosion make this material well fitted for mechanically improved surface. Thin film preparation or deposition of niobium nitrides by physical methods (PVD) is not a trivial task. Stoichiometry, crystal structure and morphology of the resulting films are strongly affected by the deposition conditions, and even a qualitative model for the growth mechanisms of niobioum nitride is still lacking. In this work we have studied the effect of some parameters on the structural and morphologic properties of NbN thin films. The samples have been produced by reactive magnetron sputtering for different nitrogen partial pressures, substrate temperatures, bias voltages and deposition times. The crystallographic structure, preferred orientations, grain sizes and surface roughness were stablished by XR diffraction and, for some samples, atomic force microscopy. The results have shown that without bias voltage cubic NbN thin films are obtained, with or without substrate heating, when the partial pressure of N2 in the reactive atmosphere is between 13 and 25 %. Films produced with 17 % N2 are preferentially oriented in the <200> direction and this texture is enhanced by substrate heating. The analysis of the results in two samples with different thickness clearly indicates that for cubib NbN, the growth is remarkable different in the <111> and <200> directions. A possible mechanism to explain this difference is presented. The main effect of the voltage bias was to induce a hexagonal δ - NbN structure even for voltages as low as -10 V. These films present larger densities values than those found in the films with cubic phase, being the highest density achieved with -70V bias. All samples deposited with bias present a compressive stress and small grain size. The connections between stress, grain size and density are presented and discussed. In summary, we have identified a group of key parameters that makes possible the deposition of NbN thin films by reactive magnetron sputtering, either for superconductivity or tribological applications. / Nas últimas décadas, têm sido propostas e implementadas muitas aplicações para filmes finos de nitreto de nióbio. Na fase cúbica δ − NbN, o material na sua forma bulk apresenta Tc de transição supercondutora próxima a 17 K, o qual é de longe muito maior do que os valores encontrados para outros supercondutores normais (BCS). E, proveitoso, por exemplo, para junções túnel Josephson. Mais recentemente, outras fases também têm sido foco de interesse, como a hexagonal δ0 − NbN. A dureza e resistência à corrosão química fazem deste material bem equipado para melhoramento mecânico de superfícies. A preparação de filmes finos de nitretos de nióbio por PVD não é uma tarefa trivial. Estequiometria, estrutura cristalina e morfologia dos filmes resultantes são fortemente afetadas pelas condições de deposição. E, mesmo um modelo qualitativo para os mecanismos de crescimento do nitreto de nióbio ainda está faltando. Neste trabalho estudamos o efeito de alguns parâmetros sobre as propriedades estruturais e morfológicas de filmes finos de NbN. As amostras foram produzidas por magnetron sputtering reativo com diferentes pressões parciais de nitrogênio, temperaturas do substrato, voltagem bias e tempos de deposição. Os resultados mostraram que sem bias aplicado são obtidos filmes finos de NbN na fase cúbica, com ou sem aquecimento do substrato, quando a pressão parcial de N2 na atmosfera reativa está entre 13 e 25%. Filmes produzidos com 17% de N2 estão preferencialmente orientados na direção (200) e sua textura é aumentada por aquecimento do substrato. A análise dos resultados em duas amostras com diferentes espessuras indicou claramente que, para NbN cúbico, o crescimento é notavelmente diferente nas direções (111) e (200). Um possível mecanismo capaz de explicar esta diferença é proposto neste trabalho. O efeito significativo da aplicação do bias foi induzir a estrutura hexagonal δ − NbN mesmo para voltagens pequenas como -10 V. Estes filmes apresentam valores de densidade maiores do que para os filmes com fase cúbica, sendo a maior densidade alcançada para -70 V de bias. Todas amostras depositadas com aplicação de bias apresentaram estresse compressivo e tamanho de grãos pequeno. As conexões entre estresse, tamanho de grão e densidade são apresentados e discutidos. Em resumo, identificamos um grupo de parâmetros chave que tornam possível a deposição de filmes finos de NbN por magnetron sputtering reativo, seja para supercondutividade seja para aplicações tribológicas.

Abstract In this thesis, the influence of reversion and recrystallization annealing on microstructure and mechanical properties was studied in metastable austenitic low-Ni high-Mn stainless steels, some alloyed with up to 0.45 wt.% Nb. Further, the effect of the various microstructures created by reversion and recrystallization on strain-induced martensite transformation in tensile testing was investigated. The aim was to achieve excellent combinations of strength and ductility in the steels and to improve understanding of the behaviour of ultrafine-grained austenitic stainless steels during deformation. All the steels were cold-rolled up to 60% thickness reduction producing up to 60% strain-induced &#945;’-martensite in the austenitic structure. Annealing was carried out using a Gleeble thermomechanical simulator between 450–1100 &#176;C for durations of 0.1–1000 s. The resultant microstructures were examined using different research equipment and methods. Regardless of the amount of Nb alloying, shear- and diffusion-controlled reversion could be completed by annealing at 700 &#176;C, although at this temperature no recrystallization of the untransformed cold-rolled austenite occurred. At 800 &#176;C, however, the cold-rolled austenite recrystallized, producing a non-uniform grain structure comprising ultrafine-grained areas formed via reversion and coarser ones formed by recrystallization of the retained austenite. At 900 &#176;C, a uniform fine austenite grain size of about 2 &#956;m was obtained. At higher annealing temperatures of 1000–1100 &#176;C, normal grain growth of fine grains took place during prolonged annealing in steel with no Nb. However, grain growth was effectively retarded by alloying with 0.28 wt.% Nb. The non-uniform structures consisting of reverted and retained austenite exhibited excellent combinations of yield strength and uniform elongation. The results also showed that tensile strain-induced martensite nucleation sites and &#945;’-martensite formation vary in a complex way depending on grain size. / Tiivistelmä Väitöstyössä tutkittiin reversiohehkutuksen vaikutusta metastabiilin 1% nikkeliä ja 9% mangaania sisältävien austeniittisten ruostumattomien terästen mikrorakenteeseen ja mekaanisiin ominaisuuksiin sekä austeniitin raekoon ja mikrorakenteen vaikutusta muokkausmartensiitin syntyyn vetokokeessa. Koeteräksistä osa oli lisäksi niobiseostettuja. Tavoitteena oli nostaa teräksien lujuutta ja ymmärtää ultrahienorakeisen austeniittisten ruostumattomien terästen käyttäytymistä muokkauksessa. Teräkset kylmämuokattiin 60% valssausreduktiolla, jolloin austeniittiseen rakenteeseen muodostui muokkausmartensiittia enimmillään 60%. Reversiohehkutukset tehtiin Gleeble termomekaanisella simulaattorilla lämpötiloissa 450–1100 &#176;C ja 0.1–1000 s pitoajoilla. Saatuja mikrorakenteita tutkittiin eri tutkimuslaitteistoilla ja -menetelmillä. 700 &#176;C hehkutuksessa leikkautumalla ja diffuusion välityksellä tapahtuva reversio oli nopea myös niobi-seostetuilla teräksillä, mutta rekristallisaatiota ei tapahtunut. 800 &#176;C hehkutuksessa muokkauksessa teräksiin jäänyt austeniitti rekristallisoitui, mutta raerakenne muodostui epätasaiseksi koostuen reversion tuottamasta ultrahienoista rakeista ja jäännösausteniitin rekristallisaation tuottamista karkeammista rakeista. Sitä vastoin hehkutus 900 &#176;C:ssa tuotti tasainen 2 &#956;m austeniitin raekoon. Pitkissä hehkutuksissa korkeammissa lämpötiloissa 1000–1100 &#176;C niobi-seostamattomissa teräksissä tapahtui hienojen rakeiden normaalia rakeenkasvua. Kuitenkin 0.28p-% niobi-seostuksen havaittiin oleva riittävä estämään rakeenkasvu. Reversion ja osittaisen rekristallisaation tuottamilla raerakenteilla saatiin erinomaiset myötölujuus-tasavenymäyhdistelmät. Vetokokeissa martensiitin ydintymispaikat ja -nopeus vaihtelivat monimutkaisella tavalla raekoosta riippuen.

The exceptional wear resistance and work hardenability, place Hadfield steel as one of themost important materials for manufacturing cast components used in the mining, crashing,drilling, and excavation industries. In all metallic alloys used for component casting, themechanical properties are highly influenced by the microstructure of the material. Castcomponents with finer microstructural characteristics are known to present bettermechanical properties and reduced risk of defects when compared with components witha coarser microstructure. A reduced grain size in Hadfield steel can increase the strengthof the material up to 30% and reduce the risk of porosity formation during solidification.The practice of adding selected compounds or alloying elements in a metal melt to modifyand refine the microstructure is called inoculation. It is currently one of the trendingmethods utilized in light-metal alloys and cast-iron components production but has not,yet, gained adequate acceptance in the steel casting industry because researchers have notbeen able to find proper inoculants.The main objective of this work is to investigate the qualitative and quantitativecharacteristics of the by-products of deoxidation of Hadfield steel that remain in thematerial after solidification and their positive or negative effect on the coarseness of thefinal as-cast microstructure. This type of research can help to identify the type of particlesor alloying elements that are most effective for refining the microstructure of austeniticsteels and pave the way for developing new or improving conventional deoxidation andinoculation processes that will, in turn, result in the improvement of the properties of thecomponent.The precipitation of particles and the as-cast grain size are studied in aluminum andtitanium deoxidized Hadfield steel samples acquired under pilot scale experimentalconditions. In the first part of this work, the qualitative and quantitative characteristics ofparticles such as type, morphology, composition amount and size are identified. Thesequence of precipitation is established. A model for predicting particle size and growth isdeveloped. The experimental results are compared against thermodynamic equilibriumcalculations and the precipitation mechanisms for each type of particles are described. Inthe second part, the as-cast grain size of samples with varying deoxidation treatments ismeasured. Then, the grain-size is correlated with certain particle characteristic and theparticles are ranked according to their ability to refine the microstructure. The particledisregistry with austenite is calculated and compared to the experimentally acquiredranking. / Hadfieldstålen exceptionella slitstyrkan och deformationshårdnande har gjort dessa till ettav de viktigaste materialen för tillverkning av gjutna komponenter som används inomgruv-, kross-, borr-och gruvindustrin. I alla metallegeringar som används för tillverkningav gjutna komponenter styrs de mekaniska egenskaperna av materialets mikrostruktur.Gjutna komponenter med fin mikrostruktur presentera bättre mekaniska egenskaper ochminskad risk för defekter jämfört med komponenter med grov mikrostruktur. En minskadkornstorlek i Hadfieldstål kan öka materialets hållfasthet upp till 30% och minska riskenför porositetsbildning vid stelning.Tillsatsning av spårämnen eller legeringselement i en metallsmälta för att modifiera ochförbättra mikrostrukturen kallas ympning. Denna metod används i lättmetaller och vidtillverkning av gjutjärnskomponenter, men har ännu inte fått acceptans i stålindustrineftersom forskningen inte har funnit effektiva kärnbildare att användas som ympmedel.Huvudsyftet med detta arbete är att undersöka kvalitativa och kvantitativa egenskaper hosde desoxideringsprodukter som skapas under tillverkningen av Hadfield stål och hur deunder och efter stelning påverkar mikrostrukturens grovlek. Arbetet syftar till att identifierapartikeltyper och legeringselement som är effektiva för att förfina den austenitiskamikrostrukturen och bana väg för utveckling nya och förbättra desoxiderings- ochympningsprocesser som i sin tur kommer att resultera i en förbättring av den gjutnakomponentens egenskaper.Partiklarnas utskiljning och materialet resulterande kornstorlek studerades i aluminiumochtitan-desoxidiserade Hadfieldstål, tillverkade i pilotskala. Den första delen av dettaarbete var att identifiera kvalitativa och kvantitativa egenskaper hosdesoxidationspartiklar, som typ, morfologi, sammansättning och storlek.Utskiljningssekvensen fastställdes. En modell för att förutsäga partikelstorlek och derastillväxt utvecklades. De experimentella resultaten jämfördes med termodynamiskajämviktberäkningar och utskiljningen för varje typ av partikel beskrevs. I den andra delenstuderades kornstorleken och hur denna varierade desoxideringsbehandlingen. Därefterkorrelerades kornstorleken med partikeltyp och dess karaktäristika och rangordnades efterderas förmåga att förfina mikrostrukturen. Partiklarnas kristallografiska missanpassningmot austenitens kristallstruktur beräknades och jämfördes med experimentellt fastställdarangordningen. / InDeGrainS I

Philosophiae Doctor - PhD / The results of the multivariate analyses suggest that most of the variation in the composition of the samples was of an intra-sample nature, illustrating large scale patchiness in foraminiferal distribution. There were, however, definite differences between communities around Robben Island and in St Helena Bay, and least variation was found between the control and pipeline sites, and between the stations of each site. When the trace metal concentrations and the percentage nitrogen increased, the richness, diversity and abundance of foraminifera tended to decrease. Sediment grain size positively affected abundance but negatively affected diversity and richness. In both areas mean grain size did not, however, appear to play a very large role in influencing diversity. Cadmium, copper, chromium, the percentage nitrogen and the mean grain size were identified as the most important variables influencing the community structure by the BIOENV BEST routine in PRIMER. The trace metals and percentage nitrogen only had negative effects on the diversity and abundance as well as on the abundance of the dominant genera, whereas the mean grain size had variable effects. / South Africa