This diploma thesis studies the machining of group S materials. In the theoretical part of this thesis these materials were divided into groups and subsequently analyzed. These materials were also analyzed in terms of their impaired machinability. In the practical part of this thesis experimental tests were conducted to determine tool life, tool wear and in the case of testing titanium alloy surface roughness too.

No description available.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 170-176).

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / O uso de componentes revestidos por ligas de nÃquel do sistema Ni-Cr-Mo em equipamentos da indÃstria do petrÃleo pode vir a ser mais freqÃente, pois os aumentos no Ãndice de acidez naftÃnica e no peso molecular do petrÃleo nacional requerem materiais mais resistentes à corrosÃo, temperatura e pressÃo. Desta forma, como parte de um estudo sistemÃtico, este trabalho pretende definir faixas operacionais para revestir de forma adequada aÃo estrutural com o eletrodo ERNiCrMo-3, atravÃs da soldagem MIG/MAG, e avaliar caracterÃsticas microestruturais e propriedades mecÃnicas de revestimentos na condiÃÃo como soldados e envelhecidos. Para atingir o objetivo, foram realizadas soldagens automÃticas com utilizaÃÃo de robà industrial, fonte eletrÃnica e argÃnio puro como gÃs de proteÃÃo. Para definiÃÃo das faixas operacionais, as soldagens foram em simples deposiÃÃo, com avaliaÃÃo de aspecto superficial, geometria e diluiÃÃo da solda. Nesta etapa, foi constatado que a solda apresenta alta convexidade em corrente eficaz abaixo de 200 A e a variaÃÃo da corrente, para o cÃlculo da energia, influencia de forma mais significativa na convexidade e na diluiÃÃo da solda, em comparaÃÃo com a variaÃÃo da velocidade de soldagem, para o cÃlculo das mesmas energias. AtravÃs dos testes preliminares, foi selecionada a corrente de 290 A em duas energias de soldagem (10 e 14 kJ/cm). O revestimento foi em Ãnica camada aplicada em aÃo ASTM A516 g60 de 12,7 mm de espessura, com sobreposiÃÃo acima de 40 % e temperatura de interpasse abaixo de 100 oC. A diluiÃÃo em ambas as energias ficou em torno de 15 %. O envelhecimento foi na temperatura de 600 oC por tempos de 100 e 300 horas. Para caracterizaÃÃo metalÃrgica foram utilizados: perfis de microdureza, microscopia Ãtica (MO) e eletrÃnica de varredura (MEV), energia dispersiva de raio X (EDX), difraÃÃo de raio X, energia de elÃtrons retro-espalhados (EBSD) e ensaio de arrancamento, segundo norma ASTM A 265-03. Os perfis de microdureza e estruturas observadas foram semelhantes para ambas as energias de soldagem utilizadas. ApÃs envelhecimento foi observado uma descarbonetaÃÃo da ZAC-GG onde as ferritas passaram a nÃo possuir segundas fases (carbonetos). A estrutura dendrÃtica do revestimento apresentou microfases do tipo MC e Laves na condiÃÃo como soldada. ApÃs o envelhecimento, houve formaÃÃo de carbonetos secundÃrios, dissoluÃÃo de carbonetos primÃrios e formaÃÃo de fase gamaââ. Os perfis de dureza indicaram que na condiÃÃo como soldada a dureza do revestimento foi de 240 HV e da ZAC-GG de 190 HV, com o envelhecimento a dureza na ZAC-GG caiu para 120 HV, e a do revestimento cresceu para 290 HV em 100 h e 310 HV em 300 h. Na interface foram observadas, somente apÃs o envelhecimento, regiÃes duras da ordem de 800 HV, devido a grande concentraÃÃo de carbonetos e envelhecimento da zona parcialmente diluÃda, com teor elevado de ferro, que atua na formaÃÃo de gamaââ. Apesar das elevadas diferenÃas de dureza entre o revestimento, metal base e interface nÃo foram identificadas trincas nas anÃlises metalogrÃficas. A carga mÃxima no ensaio de arrancamento foi superior a da norma (140 MPa) nas condiÃÃes analisadas. O perfil de penetraÃÃo dos cordÃes (tipo taÃa) favoreceu esse resultado, e o envelhecimento provocou um aumento gradativo de resistÃncia ao cisalhamento. / The use of nickel alloy cladding components could be more frequently in petroleum industry. The crescent naphthenic corrosion and high molecular weight of national petroleum contribute for needs of materials with more resistance to corrosion, to temperature and to pressure. At this way, how part of systematic study, this work pretends to define operational range for adequate ERNiCrMo-3 weld overlay in structural steel with application of GMAW process, and to evaluate microstructural characteristics and mechanical properties in as welded and aging conditions. To realize the objective, were used an industrial robot, an electronic power source and an argon shielding gas for automated welding. To define the operational range, simple deposit welds and evaluation of superficial aspect, geometry and dilution were conducted. This step indicated that the welds in efficient current below 200 A showed high convexity and the variation of current for the calc of heat input is more significant for convexity and dilution of the weld than the variation of welding speed for the calc of same heat input. It was selected 290 A as welding current in two heat inputs (10 and 14 kJ/cm). The overlay at ASTM A 516 g60 steel was in simple layer, had overlap up to 40 pct between passes and had about 15 pct of dilution at the two heat inputs. The aging temperature employed was 600 oC for times of 100 and 300 hours. To metallurgical characterization was used: microhardness measures, optical microscope, scanning electron microscope, composition variations (EDAX), x-ray diffraction, electron backscatter diffraction and shear tests according ASTM A 265-03 standard specification. The microhardness and structures observed were, approximately, the same for the two heat inputs. Post aging HAZ showed absence of carbides. The dendritic structure had MC and Laves micro-phases in as welded condition and the aging provoked formation of secondary carbides, dissolution of primary carbides and formation of gamaââ. As welded overlay microhardness was 240 HV and as welded HAZ was 190 HV. Aging HAZ was 120 HV and aging overlay was 290 HV for 100 h and 310 HV for 300 h. Only for aging conditions, were observed hard zones (800 HV) in interface of overlay, due to carbide concentration and aging of partially dilution zone, where the Fe favored the formation of gamaââ. Despite the hardness differences of overlay, base metal and interface, were identified no cracks in metallographic analyses. The maximum shear strength was above of the specification requirement (140 MPa) in all conditions employed, the penetration shape (like finger) favored this result, and the aging provoked a gradual grow up in shear resistance.

O NbAl3 e algumas ligas intermetálicas do sistema Nb-Ni-AI foram sintetizadas por combustão a partir dos pós de seus elementos constituintes. O efeito de variáveis de processo, como o tamanho de partícula dos pós, a composição química, a pressão de compactação, o tratamento de desgaseificação e a taxa de aquecimento, foram investigados na síntese do NbAl3 na forma de pastilhas cilíndricas. A síntese de ligas do sistema Nb-Ni-AI foi realizada a partir de misturas com as composições Nb10Ni70AI, Nb20Ni65AI e Nb30Ni60AI. A microestrutura das amostras reagidas foi caracterizada por microscopia óptica, microscopia eletrônica de varredura, EDS e difração de raios-X (método de Rietveld). Foram obtidas pastilhas de NbAl3 com 98,5 % da densidade teórica, superior ao valor encontrado na literatura (95%), mediante o controle de variáveis de processo. Nas pastilhas contendo níquel, a combustão ocorreu nas pastilhas de todas as composições. Fases metaestáveis, presentes na microestrutura das pastilhas baitas de reação, foram transformadas após tratamento térmico, originando ligas trifásicas com diferentes concentrações de fases (NbAl3, NiAI e NbNiAI), conforme a composição inicial do compactado. Algumas propriedades mecânicas de amostras brutas de reação e tratadas termicamente foram determinadas pela técnica da impressão (microdureza e tenacidade). Os resultados obtidos são comparáveis aos da literatura, salvo algumas discrepâncias atribuídas a processos de fabricação distintos. As etapas de reação da síntese do NbAl3 e de ligas Nb-Ni-AI foram posteriormente investigadas mediante interrupção da reação durante sua propagação ao longo de barras paralelepipédicas compactadas. Verificou-se que a síntese do NbAl3 ocorre pela dissolução de nióbio no alumínio fundido, seguida da precipitação do NbAl3. Nas amostras contendo níquel, a síntese ocorre em dois estágios: no primeiro estágio formam-se o Ni2Al3 ou o NiAl3, em quantidades relativas dependentes da composição geral. As reações deste primeiro estágio podem disparar as reações do segundo estágio, referentes à síntese do NbAl3. / NbAl3 and Nb-Ni-AI intermetallic alloys have been obtained by pressureless combustion synthesis from elemental powders. The effects of process variables as powder particle size, composition, compaction pressure (green density), degassing treatment and heating rate on the combustion (thermal explosion mode) of NbAl3 cylindrical pellets were studied. Combustion synthesis of Nb-Ni-AI alloys was performed on powder mixtures with nominal compositions Nb10Ni70AI, Nb20Ni65AI and Nb30NI60AI. The microstructure of reacted samples was characterized by optical microscopy, scanning electron microscopy, EDS and X-ray diffraction (Rietveld method). It was shown that careful control of the processing conditions allowed near full (98,5%) dense pellets of NbAl3. In the nickel containing pellets, reaction occurred for all the compositions investigated. Metastable phases were seen to be present in the as reacted pellets, which were transformed after a heat treatment, producing a three phase alloy (NbAl3, NiAI and NbNiAI) with different phase concentrations, depending on the initial compact composition. Some mechanical properties, like microhardness and tenacity were measured by microidentation technique on the as reacted and heat-treated samples. The results are comparable with the literature, excepted for some discrepancies caused by different fabrication processes. The reaction sequence for both cases (NbAl3 and Nb-Ni-AI alloys) was further investigated by DSC analysis and also by interrupting the reaction during its propagation along compacted parallelopipedal bars. It was found that the NbAl3 synthesis occurs through niobium dissolution in molten aluminum and precipitation of NbAl3. In the nickel containing samples, synthesis occurs as two-stage reaction: Ni2Al3 or NiAl3 are formed in the first stage, with relative amounts depending on the general composition. This first stage reaction can trigger the second one, related to the formation of NbAl3.

A model was created to predict the thermo-mechanical fatigue crack growth rates under typical engine spectrum loading conditions. This model serves as both a crack growth analysis tool to determine residual lifetime of ageing turbine components and as a design tool to assess the effects of temperature and loading variables on crack propagation. The material used in the development of this model was a polycrystalline superalloy, Inconel 100 (IN-100). The first step in creating a reliable model was to define the first order effects that influence TMF crack growth in a typical engine spectrum. Load interaction effects were determined to be major contributors to lifetime estimates by influencing crack growth rates based upon previous load histories. A yield zone model was modified to include temperature dependent properties that controlled the effects of crack growth retardation and acceleration based upon overloads and underloads, respectively. Multiple overload effects were included in the model to create enhanced retardation compared to single overload tests. Temperature interaction effects were also considered very important due to the wide temperature ranges of turbine engine components. Oxidation and changing temperature effects were accounted for by accelerating crack growth in regions that had been affected by higher temperatures. Constant amplitude crack growth rates were used as a baseline, upon which load and temperature interaction effects were applied. Experimental data of isolated first order effects was used to calibrate and verify the model. Experimental data provided the means to verify that the model was a good fit to experimental results. The load interaction effects were described by a yield zone model, which included temperature dependent properties. These properties were determined experimentally and were essential in the model's development to include load and temperature contributions. Other interesting factors became apparent through testing. It was seen that specific combinations of strain rate and temperature would lead to serrated yielding, discovered to be the Portevin-Le Chatelier effect. This effect manifested itself as enhanced hardening, leading to unstable strain bursts in specimens that cyclically yielded while changing temperature.

Microstructural features at different scales affect the constitutive stress-strain response and the fatigue crack initiation life in Ni-base superalloys. While numerous efforts have been made in the past to experimentally characterize the effects of these features on the stress-strain response and/or the crack initiation life, there is a significant variability in the data with sometimes contradictory conclusions, in addition to the substantial costs involved in experimental testing. Computational techniques can be useful tools to better understand these effects since they are relatively inexpensive and are not restricted by the limitations in processing techniques. The effect of microstructure on the stress-strain response and the variability in fatigue life were analyzed using two Ni-base superalloys; DS GTD111 which is a directionally solidified Ni-base superalloy, and IN100 which is a polycrystalline Ni-base superalloy. Physically-based constitutive models were formulated and implemented as user material subroutines in ABAQUS using the single crystal plasticity framework which can predict the material stress-strain response with the microstructure-dependence embedded into them. The model parameters were calibrated using experimental cyclic stress-strain histories. A computational exercise was employed to quantify the influence of idealized microstructural variables on the fatigue crack initiation life. Understanding was sought regarding the most significant microstructure features using explicit modeling of the microstructure with the aim to predict the variability in fatigue crack initiation life and to guide material design for fatigue resistant microstructures. Lastly, it is noted that crystal plasticity models are often too computationally intensive if the objective is to model the macroscopic behavior of a textured or randomly oriented 3-D polycrystal in an engineering component. Homogenized constitutive models were formulated and implemented as user material subroutines in ABAQUS, which can capture the macroscale stress-strain response in both DS GTD111 and IN100. Even though the study was conducted on two specific Ni-base superalloys; DS GTD111 and IN100, the objective was to develop generic frameworks which should also be applicable to other alloy systems.

科学研究費補助金 研究種目:基盤研究(C)(2) 課題番号:08650815 研究代表者:村田 純教 研究期間:1996-1997 年度

The surface of a dense Ni-YSZ anode was modified with a thin-film coating of niobium oxide (Nb2O5) in order to understand the mechanism of sulfur tolerance and the behavior of carbon deposition. Results suggest that the niobium oxide was reduced to NbO2 under operating conditions, which has high electrical conductivity. The NbOx coated dense Ni-YSZ showed sulfur tolerance when exposed to 50 ppm H2S at 700°C over 12 h. Raman spectroscopy and XRD analysis suggest that different phases of NbSx formed on the surface. Further, the DOS (density of state) analysis of NbO2, NbS, and NbS2 indicates that niobium sulfides can be considered as active surface phases in the H2S containing fuels. It was demonstrated that carbon formation was also suppressed with niobium oxide coating on dense Ni-YSZ in humidified CH4 (3% H2O) at 850ºC. In particular, under active operating conditions, there was no observable surface carbon as revealed using Raman spectroscopy due probably to electrochemical oxidation of carbon. Stable performances of functional cells consisting of Pt/YSZ/Nb2O5 coated dense Ni-YSZ in the fuel were achieved; there was no observable degradation in performance due to carbon formation. The results suggest that a niobium oxide coating has prevented carbon from formation on the surface probably by electrochemically oxidation of carbon on niobium oxide coated Ni-YSZ. On the other hand, computational results suggest that, among the metals studied, Mo seems to be a good candidate for Ni surface modification. Ni-based anodes were modified with Mo using wet-impregnation techniques, and tested in 50 ppm H2S-contaminated fuels. It was found that the Ni-Mo/CeO2 anodes have better sulfur tolerance than Ni, showing a current transient with slow recovery rather than slow degradation in 50 ppm H2S balanced with H2 at 700°C.

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