No description available.

There is growing interest in using additive manufacturing for various alloy systems and industrial applications. However, existing process development and part qualification techniques, both involve extensive experimentation-based procedures which are expensive and time-consuming. Recent developments in understanding the process control show promise toward the efforts to address these challenges. The current research uses the process mapping approach to achieve control of melt pool geometry and microstructure in different alloy systems, in addition to location specific control of microstructure in an additively manufactured part. Specifically, results demonstrate three levels of microstructure control, starting with the prior beta grain size control in Ti-6Al-4V, followed by cell (solidification structure) spacing control in AlSi10Mg, and ending with texture control in Inconel 718. Additionally, a prediction framework has been presented, that can be used to enable a preliminary understanding of melt pool geometry for different materials and process conditions with minimal experimentation. Overall, the work presented in this thesis has the potential to reduce the process development and part qualification time, enabling the wider adoption and use of additive manufacturing in industry.

Aus der Einleitung: "Das selektive Elektronenstrahlschmelzen (engl. Electron Beam Melting (EBM®)) ist ein pulverbettbasiertes additives Fertigungsverfahren, mit dessen Hilfe metallische Bauteile schichtweise hergestellt werden können. Der schematische Aufbau einer entsprechenden Anlage ist in Abbildung 4 dargestellt. Dabei erfolgt die Strahlerzeugung im Bereich 1 (die Kathode besteht entweder aus Wolfram oder bei den neuesten Systemen aus einkristallinem LaB6). Die Strahlablenkung durch ein elektromagnetisches Linsensystem erfolgt im Bereich 2. Der Bereich 3 ist die eigentliche Baukammer, in der sich unter anderem die Vorratsbehälter für das Pulver, das Rakelsystem sowie die Komponenten des Bauraums (Käfig mit Hitzeschild, Bauplattform mit Startplatte) befinden. ..."

Additive manufacturing is revolutionizing the way of production and use of materials. The clear tendency for shifting from mass production to individual production of net-shape components has encouraged using selective laser melting (SLM) or electron beam melting (EBM). In this thesis, austenitic, duplex and martensitic stainless steel parts were fabricated by laser melting technique using fixed laser scanning parameters. The fabricated steel parts were characterised using XRD, SEM, TEM/STEM, SADP and EBSD techniques. Mechanical properties of the fabricated steel parts were also measured. The mechanism of the evolution of microstructure during laser melting as well as the mechanism of the effect of developed microstructure on the mechanical properties was investigated. It was found that the intense localized heating, non-uniform and asymmetric temperature gradients and subsequently fast cooling introduces unique high level structural hierarchies and microstructure heterogeneities in laser melted steel parts. A unique structural hierarchy from the millimetre scale melt pools down to the sub-micron/nano scale cellular sub-grains was observed. The cellular sub-grains were 0.5-1μm with Molybdenum enriched at the sub-grain boundaries in SLM 316L. The Mo enriched cell boundaries affected the chemical and microstructure stability of the post heat treated samples. Well dispersed and large concentration of dislocations around the cell boundaries and well distributed oxide nano inclusions, imposed large strengthening and hardening effect that led to relatively superior tensile strength (700 MPa), yield strength (456 MPa), and microhardness (325Hv) compared to those of HIP 316L steel. The in-situ formation of oxide nano inclusions provided a unique way for preparation of oxide dispersion-strengthened (ODS) steel in a single process. The formation of oxide nano inclusions in the very low oxygen partial pressure of laser chamber was thermodynamically explained. High concentration of nano size dislocation loops, formation of nitride phases along with nitrogen enriched islands and oxide nano inclusions lead to strong dislocation pinning effect which strengthened the laser melted duplex stainless steel with a total tensile strength of 1321 MPa, yield strength of 1214 MPa and microhardness of 450HV. The grade 420 stainless steel was laser melted in Ar and N2 atmosphere which also showed a two level hierarchy with nanometric martensite lathes embedded in parental austenite cellular grains. The Ar treated sample had relatively higher retained austenite, lower YS (680-790 MPa) and UTS (1120-1200 MPa) compared to those treated in N2 (YS= 770-1100 MPa, UTS=1520-1560 MPa). The mechanism of the effect of atmosphere on phase transformation was explained. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.</p>

Dealing with the issue of spring flood events is primarily based on their causes. It is therefore important to study the processes of snow accumulation and snowmelt especially in mountain areas where the development of snow water equivalent (SWE) is primarily observed. The snow water equivalent indicates amount of the water in the snow and thus represents a runoff volume during the spring melting period and demonstrates the flood risk potential. In this thesis the lumped modelling approach of the rainfall-runoff model HEC- HMS was used. The model was applied in the Bystřice River basin in the Ore Mountains where the field measurements of the snow cover and SWE is carried out. Applied temperature-index method is the well-developed method because it takes into account both the melting during precipitation and melting in the period without any precipitation and aims to capture snow energy balance by means of air temperature. Three winter periods (2006, 2008 and 2009) were simulated. The evolution of the snow water equivalent was observed and the agreement between observed and simulated hydrographs was assessed in the closure profile Ostrov. Published results show the influence of winter course and character on the model capability to simulate the snow water equivalent and runoff. The observed and...

Reverse-flow combustors have been used in heavy land-based gas turbines for many decades. A sheath is typically installed to provide cooling at an expense of large pressure losses, through small jet impingement cooling and strong forced convention channel flow. With the modern advancement in metallurgy and thermal-barrier coating technologies, it may become possible to remove this sheath to recover the pressure losses without melting the combustor chamber. However, without the sheath, the flow inside the dump diffuser may exert nonuniform cooling on the combustion chamber. Therefore, the objective of this project is to investigate the flow pattern, pressure drop, and heat transfer in the dump-diffuser reverse-flow combustor with and without sheath to determine if the sheath could be removed. The investigation was conducted through both experimental and computational simulation. The results show that 3.3% pressure losses could be recovered and the highest wall temperature will increase 18% without the sheath.

O objetivo do presente trabalho consistiu no desenvolvimento de fios de liga de cobre-cromo-zircônio (CuCrZr) em uma composição estabelecida em Cu-0,7%Cr- 0,1%Zr (em massa). Nas etapas desenvolvidas, foram feitos botões de cobrecromo (CuCr) e cobre-zircônio (CuZr) em um forno a arco elétrico de eletrodo não consumível, sendo esses botões, posteriormente, fundidos junto com cargas de cobre em um cadinho de alumina (Al2O3) inserido no interior de um vaso de aço inoxidável, que serviu como suporte. Após a fusão dos botões e cargas, o banho foi vazado em uma coquilha de cobre, obtendo-se os tarugos da liga de cobre. Dos tarugos em estado bruto de fusão, foram retiradas amostras para ensaios de dureza Vickers. Nesses tarugos foi feito um tratamento térmico de homogeneização a 910 °C por 2 h. Os tarugos foram posteriormente trabalhados mecanicamente a frio por forjamento rotativo seguido de trefilação, para obtenção final dos fios no calibre de 2,174 mm. Os fios passaram por dois tratamentos térmicos de recristalização, um a 510 °C por 1 h e outro de 480 °C por 5 h. Os fios foram caracterizados mecanicamente por ensaios de tração e de dureza e os resultados foram comparados com dados experimentais da literatura. / The objective of this work is the development of copper alloy wire-chromiumzirconium (CuCrZr) in a chemical composition Cu-0,7% Cr-0,1% Zr (weight). The main steps were, buttons were made of copper-chromium (CuCr) and copperzirconium (CuZr) in an electric arc furnace, these buttons were later melted with copper charge in a alumina crucible, placed inside a stainless steel can which served as a support. After melting buttons and charge, the bath was poured into a copper chill mold obtaining copper alloy billets. From the as cast cooper alloy billets, small samples were cut for Vickers hardness and then, a homogenizing heat treatment at 910 °C for 2 h was performed. The billets were then mechanically cold worked by swaging followed by drawing to obtain the wires with a diameter of 2,174 mm. The wires are mechanically characterized using tensile and hardness testing after recrystallization heat treatment at 510 °C for 1 h and at 480 °C for 5 h and the results were compared with experimental data from literature.

Thesis advisor: Seth C. Kruckenberg / The Potters Pond migmatite domain (PPMD) is a heterogeneous zone of migmatites located ~10 km southwest of Cascade, Idaho within the western Idaho shear zone (WISZ). The PPMD is the only known exposure of migmatites within the WISZ over its ~300 km length, occurring where the shear zone orientation changes from 020° south to 000° north of the migmatite domain. Structural mapping within the PPMD has identified multiple generations of migmatite with varied structural fabrics. Leucosome layers were sampled from distinct migmatite localities and morphologies (e.g., metatexite, diatexite) to determine the timing and duration of partial melting in the PPMD. U-Pb age determinations of zircon by means of LA-ICP-MS document two periods of protracted migmatite crystallization during the Early and Late Cretaceous. Early Cretaceous (ca. 145 to 128 Ma) migmatite crystallization ages are coeval with the collision and suturing of oceanic terranes of the Blue Mountains province with North America, and the formation of the Salmon River suture zone (SRSZ). Migmatite crystallization ages from ca. 104 to 90 Ma are associated with Late Cretaceous dextral transpression in the WISZ. Field observations and geochronology of cross cutting leucosome relationships are interpreted to record deep crustal deformation and anatexis associated with formation of the SRSZ, subsequently overprinted by solid-state deformation and renewed anatexis during the evolution of the WISZ. These data are the first direct evidence of the synmetamorphic fabric related to the SRSZ east of the initial Sr 0.706 isopleth, and that the WISZ is a temporally distinct overprinting structure. / Thesis (MS) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

O anfibolito Cafelândia faz parte da Sequência Serra da Malacacheta, Complexo Barro Alto, GO. Por ser rocha com bandamento composicional bem definido, o anfibolito tem sido interpretado como produto de metamorfismo de gabro acamadado. Entretando, uma das feições que esse bandamento composicional apresenta é a presença de veios de leucossoma paralelos à foliação da rocha. O contato transicional entre o anfibolito e alguns dos veios de leucossoma indicam que os veios foram formados por fusão in situ. O objetivo do presente trabalho é investigar o processo de fusão que afetou a rocha, utilizando descrições macroscópicas, microscópicas e análises químicas de minerais em diversos contextos texturais. O bandamento composicional é definido pela variação na proporção modal de hornblenda, plagioclásio, titanita, clinopiroxênio, granada e quartzo. Veios de leucossoma com porfiroblastos de hornblenda, concordantes ou discordantes da foliação são observados reforçando o bandamento. No topo estrutural do anfibolito ocorrem camadas com mais de 70% de hornblenda e outras dominadas por clinopiroxênio e granada. Ortopiroxênio é raro e não é possível ter certeza se os grãos presentes são reliquiares do protolito ígneo ou se são metamórficos. As camadas ricas em granada e clinopiroxênio não ultrapassam espessuras maiores que 5 a 10 cm. Na porção basal do anfibolito a proporção de hornblenda é menor e a proporção de clinopiroxênio e granada maior, ocorrendo ortopiroxênio em alguns afloramentos. Os porfiroblastos de hornblenda do leucossoma são substituídos por clinopiroxênio e rara granada. Diferenças sutis nas composições dos grãos de hornblenda e clinopiroxênio do anfibolito Cafelândia e do leucossoma ocorrem, mas são mascaradas pela influência da composição da banda na composição dos minerais. De modo geral, a hornblenda no leucossoma é mais rica em Si e Mg do que os grãos da matriz, enquanto o clinopiroxênio do leucossoma é mais rico em Al. Micro-exsoluções no clinopiroxênio do leucossoma também impedem a comparação da sua composição real com os grãos da matriz da rocha. Cálculos termobarométricos foram feitos em amostras do topo e da base estrutural do anfibolito utilizando o termômetro granada-clinopiroxênio e o barômetro granada-clinopiroxênio-plagioclásio-quartzo, além do programa THERMOCALC. A termobarometria convencional fornece valores P-T menores para temperatura e similares de pressão aqueles calculados com o THERMOCALC e não são muito diferentes dos que já foram calculados previamente, com valores para o topo de 870 ºC e 10,9 kbar e para a base de 881 ºC e 9,8 kbar. Se quartzo não é usado nos cálculos P-T, acréscimo de 2 a 3 kbar ocorre nos resultados. Os dados P-T calculados são compatíveis ou algo inferiores aos resultados experimentais de fusão de rochas máficas contendo hornblenda, produção de líquido tonalítico e resíduo contendo clinopiroxênio e granada. A presença de hornblenda dentro do leucossoma do topo da unidade pode estar associada com influxo de H2O no sistema durante a fusão, diferente do que ocorre na base do corpo. É possível que o líquido que se encontrava na porção basal esvai em direção as porções superiores do anfibolito, reidratando a rocha e formando porfiroblastos de hornblenda dentro do leucossoma do topo. Uma conclusão importante tirada aqui é que o protolito do anfibolito Cafelândia pode ser o anfibolito da base da sequência Juscelândia, sobreposta, e que o bandamento composicional foi gerado por metamorfismo, fusão e segregação/perda do liquido e não por metamorfismo de gabro acamadado. / The Cafelândia amphibolite is part of the Serra da Malacacheta sequence, Barro Alto Complex, GO. As it is a rock with well-defined compositional banding, the amphibolite has been interpreted as a product of metamorphism of layered gabbro. However, a feature that reinforces the banding is the presence of leucosome veins, which are mainly parallel to the rock foliation. The transitional contact between amphibolite and some of the veins of leucosome indicate that the veins were formed by in situ melting. The purpose of this study is to investigate the melting process that affected the rock using macroscopic and microscopic descriptions, as well as chemical analysis of minerals in various textural contexts. The compositional banding is defined by variation in modal proportion of hornblende, plagioclase, titanite, clinopyroxene, garnet and quartz. Veins of leucosome with porphyroblasts of hornblende, concordant or discordant to foliation are observed, reinforcing the banding. At the structural top, layers of amphibolite occur with more than 70% of hornblende and others are dominated by clinopyroxene and garnet. Orthopyroxene is rare and its metamorphic origin cannot be assured, being possible that these grains are relicts of the igneous protolith. The garnet and clinopyroxene rich layers do not exceeding thicknesses greater than 5 to 10 cm. In the basal portion hornblende proportion is much smaller, but clinopyroxene and garnet are larger. Orthopyroxene occurs in some outcrops. The porphyroblasts of hornblende from the leucosome are replaced by clinopyroxene and rare garnet. Subtle differences in the composition of the of hornblende and clinopyroxene grains in the Cafelândia amphibolite and leucosome occur, but are masked by the influence of the bulk composition of each band in the composition of minerals. In general, the hornblende in the leucosome is richer in Si and Mg than the matrix grains, whereas the leucosome clinopyroxene is richer in Al. Micro-exsolutions in clinopyroxene in the leucosome also hampers the comparison of its \"real\" composition with the grains of the rock matrix. Thermobarometric calculations were done on samples from the structural top and bottom of amphibolite, using the garnet-clinopyroxene thermometer and garnetclinopyroxene- plagioclase-quartz barometer, besides the THERMOCALC. The conventional thermobarometry provides lower P-T values for temperature and similar pressure to those calculated with the THERMOCALC, and results are not very different from those that have been previously calculated. Results for the top are 870 ºC and 10.9 kbar and for the basis 881 ºC and 9.8 kbar. If quartz is not used in the P-T calculations, raise of 2 to 3 kbar occurs in the results. The calculated P-T data are compatible or something lower than the results of experiments for melting of hornblende-bearing mafic rocks with production tonalitic liquid and clinopyroxene and garnet residue. The hornblende-bearing leucosome of the top of the unit may be associated with influx of H2O in the system during melting, unlike what occurs at the base of the body. It is also possible that the liquid formed in basal portion oozes toward the upper portions of amphibolite, rehydrating it to form the hornblende porphyroblasts within the leucosome. An important conclusion drawn here is that the protolith of amphibolite Cafelândia can be bottom amphibolite of the Juscelândia sequence, which overly the Cafelândia amphibolite, and that the banding was generated by metamorphism, melting and segregation / loss of melt and not by metamorphism of layered gabbro.

[pt] Este estudo estabelece uma modelagem para o processo de análise de fusões e aquisições de empresas e ativos. O modelo é composto por seis fases, que englobam desde as reais motivações para aquisição de uma empresa até o desenvolvimento de um plano de take over que deverá ser implementado para gerir a empresa após a concretização da transação. À luz da proposta apresentada, é analisado o processo de aquisição da Agip do Brasil pela Petrobras. Procura-se verificar a aderência do processo ocorrido com a metodologia proposta, identificando as possíveis conseqüências advindas das diferenças encontradas. A proposta contribui para a manutenção da racionalidade econômica na Companhia na medida em que auxilia o processo de tomada de decisão, tornando-o mais transparente e agregando maior valor aos seus acionistas. / [en] The study establishes a proposal of modeling the assets mergers and acquisition process analysis. The model is composed of six phases, in witch is defined all the steps from the motivation to the acquisition in the beginning process, to the take over plan that will run after the deal. Based on the presented methodology, the case analyzes the acquisition process of Agip do Brasil by Petrobras. The study compares the real process to the proposed methodology, looking for consequences that might appear from the differences found. The proposal contributes to the economic rationality in the company, since it discloses and assists the decision making process, adding value to its shareholders.