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Orientador: Paulo Roberto Mei / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T13:15:12Z (GMT). No. of bitstreams: 1 Cunha_AdiltoPereiraAndrade_D.pdf: 32849719 bytes, checksum: a54b97b2dde32f5f0d6b96ee877e51fb (MD5) Previous issue date: 2013 / Resumo: Neste trabalho foi estudada a influência da adição de molibdênio e nióbio na microestrutura e propriedades mecânicas de aços com 0,5 e 0,6 %C, utilizado na fabricação de rodas ferroviárias. A deformação dos aços foi aplicada através da laminação, em escala de laboratório, simulando o forjamento no processo real de fabricação. As amostras foram aquecidas a 1250 °C para solubilização do nióbio, sendo então laminadas em 4 passes, a partir de 1200 °C, sofrendo uma deformação total (redução em altura) de 67%, seguida de resfriamento ao ar. Posteriormente, os aços C5 e C5Nb foram submetidos a um tratamento térmico de têmpera e revenimento. Foram analisadas amostras dos aços por microscopia óptica, eletrônica de varredura e transmissão e também foram realizados ensaios mecânicos em todas as condições. Após a laminação entre 1200 e 1120 °C, observou-se que a adição de molibdênio e nióbio promoveu um aumento da resistência mecânica em 171 e 119 MPa no limite de escoamento e 61 e 66 MPa no limite de resistência à tração, nos aços C5Nb e C6Nb, respectivamente, devido à precipitação de carbonetos de nióbio, mantendo a mesma ductilidade e tenacidade para o aço C5Nb, mas houve uma queda dessas propriedades para os aço C6Nb. Após a laminação com posterior têmpera e revenimento a 500°C, simulando o mesmo tratamento feito na roda ferroviária, o aço C5 apresentou dureza, resistência mecânica e alongamento iguais à do aço da MWL, porém com redução de área e energia absorvida maiores que o aço da MWL. O aço C5Nb apresentou maiores valores de resistência mecânica, ductilidade e tenacidade que o aço da MWL, o que demonstra seu potencial para melhorar a qualidade das rodas ferroviárias atualmente produzidas / Abstract: The influence of molybdenum and niobium addition on the microstructure and mechanical properties of 0,5 and 0,6 %C steels used in railway wheels was studied. The deformation was applied by rolling, in a thermo mechanical processing laboratory, simulating the forging in the real process of manufacture. The samples were heated to 1250 °C to ensure dissolution of niobium and hot rolled in four passes, starting at 1200 °C, undergoing a total reduction of 67%, followed by air cooling. Steels were water quenched and tempered (heat treatment). Steel samples, before and after rolling and heat treated were analyzed by optical and scanning electron microscopy. Mechanical tests were performed on the all conditions. After rolling between 1200 and 1120 ° C, it was found that the addition of molybdenum and niobium resulted in an increase of mechanical strength at 171 and 119 MPa in yield strength and 61 and 66 MPa in tensile strength, respect due to precipitation of niobium carbides, while maintaining the same ductility and toughness for C5Nb steel, but there was a decrease of these properties for C6Nb. After rolling with subsequent quenching and tempering at 500 ° C, simulating the same treatment done in the railway wheel, steel C5 showed the same toughness, strength and elongation in comparison with MWL rail wheels steel, but with reduced area and absorbed energy greater than the MWL steel. C5Nb steel showed higher strength, ductility and toughness than MWL steel, which demonstrates its potential to improve the quality of railway wheels currently produced / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

The aim of the present work is to study the formation of the cubic carbide phase (gamma phase) free gradient zone and the gamma cone structure at the edges of gradient sintered cemented carbides. Four types of cemented carbides; WCTi(C,N)-Co, WC-Ti(C,N)-Ni, WC-Ti(C,N)-Fe, WC-(Ti,Ta,NB)(C,N)-Co were gradient sintered and the thicknesses of the gradients were measured. Formation of the gradients is simulated and the simulations results are compared with experimental data. For all of the one-dimensional simulations, the DICTRA [1] software is used. The two-dimensional simulations are carried out by using a new simulation tool which is called “YAPFI”. The YAPFI software is a tool for simulation of diffffusion in multiphase systems along one, two, or three spatial coordinates. Various numerical parameters have been studied by running less computationally demanding one-dimensional simulations. The optimized parameters are used to setup the two-dimensional simulations. Two different kinetic databases were used in the simulations. The effect of different so-called labyrinth factors were studied systematically. The simulation results are in close agreement with the experimental observations, although some anomalies are present in the results. Results of the two-dimensional simulations show the formation of the gamma cone at the edges of the insert.

The catalytic conversion of biomass-derived oxygenates into valuable fuels and chemicals is a promising route to address the current energy and environmental issues. The low-temperature catalytic conversion is particularly promising in that it does not require intense energy input and can yield a variety of value-added products. In this approach, the hydrodeoxygenation reaction removes excess oxygen in biomass-derived oxygenates to convert them into value-added fuels and chemicals. There are two promising conversion pathways under this category: the conversion of lignocellulosic biomass and the biodiesel production from waste cooking oils. In the first approach, furfural is an important platform chemical that can be further upgraded into value-added products. Transition metal carbide catalysts have been demonstrated to be highly active and selective in cleaving the aliphatic C-O bond to form 2-methylfuran from furfural. However, the stability of these catalysts needs further improvement. In the second approach of biodiesel production, glycerol is a major by-product. The upgrading of glycerol via the selective hydrodeoxygenation reaction is especially economically promising. Different numbers of C-O bonds of glycerol can be cleaved to form value-added compounds, such as allyl alcohol, propanal, and acetol. Mo₂C has previously been shown as a selective catalyst for C-O bond scission, but its interaction with oxygen is so strong that all the C-O bonds in glycerol are cleaved. In order to selectively break certain numbers of C-O bonds while preserving others, the Mo2C catalyst needs to be modified. In this dissertation, the strategies for modifying the Mo₂C surface to achieve enhanced stability for furfural conversion and tunable selectivity for glycerol upgrading are demonstrated. With the addition of cobalt, the interaction between the surface and the oxygen atom in furfural is lowered to a proper extent and therefore the stability of Mo₂C is enhanced. By using different coverages of copper to modify Mo₂C, the number of C-O bonds cleaved in glycerol can be controlled. The subsequent chapters then compare the reactions of glycerol over the corresponding transition metal nitride, Mo₂N, as well as the C-O bond scission over a modified transition metal oxide, WOx/Pt(111), surface. It is shown that while Mo₂C and Mo₂N both break all C-O bonds of glycerol to produce propylene, Mo₂N also selectively cleaves two C-O bonds of glycerol to form allyl alcohol and propanal, a phenomenon only observed on the Cu/Mo₂C interface. DFT calculations reveal that the surface nitrogen atoms in Mo₂N block some Mo sites, and therefore promote the selective C-O bond scission. In the case of C-O bond scission of isopropanol over WOₓ/Pt(111), it is shown that surface hydroxyl groups on WOx sites catalyze the reaction. DFT results also demonstrate the synergistic effect between WOx and Pt and predict the energetics of in situ acid sites formation, which are very useful for the optimization of relevant metal oxide/metal catalysts. Overall, this dissertation compares the similarities and differences regarding the active sites and reaction mechanisms of C-O/C=O bond scission of biomass-derived oxygenates over transition metal carbide, nitride, and oxide surfaces, which should in turn provide useful guidelines for the rational catalyst design for biomass upgrading reactions.

The usage of cobalt (Co) as binder phase material in cemented carbides has been questioned becauseof the potential health hazards associated with cobalt particle inhalation. Cobalt is used because ofits excellent adhesive and wetting properties, combined with adequate mechanical properties. Thepurpose of this work is to investigate the mechanical properties of Fe-Ni bulk alloys and WC-Cocemented carbides using Integrated Computational Materials Engineering (ICME) methods com-bined with FEM data. The report investigates the mechanical properties of several bulk alloys inthe Fe-Ni system as a function of void size and fraction. FEM indentation and FEM fracture datais interpolated and used to model the hardnessHand fracture toughnessKIc. A precipitationhardening model based on the Ashby-Orowan’s equation is implemented to predict the e↵ect on theyield strength from precipitated particles. A model for solid solution hardening is also implemented.Existing models are used to simulate the properties of WC-Co cemented carbides together with thesolid solution hardening model. Results show that the simulated properties of the Fe-Ni bulk alloysare comparable to those of cobalt. However, the results could not be confirmed due to a lack ofexperimental data. The properties of WC-Co cemented carbides are in reasonable agreement withexisting experimental data, with an average deviation of the hardness by 11.5% and of the fracturetoughness by 24.8%. The conclusions are that experimental data for di↵erent Fe-Ni bulk alloys isneeded to verify the presented models and that it is possible to accurately model the properties ofcemented carbides. / Anv¨andandet av kobolt (Co) som bindefas-material i h°ardmetall har blivit ifr°agasatt som en f¨oljdav av de potentiella h¨alsoriskerna associerade med inhalering av koboltpartiklar. Kobolt anv¨ands p°agrund av dess utm¨arkta vidh¨aftande och v¨atande egenskaper, kombinerat med tillr¨ackliga mekaniskaegenskaper. Syftet med detta arbete ¨ar att unders¨oka de mekaniska egenskaperna hos Fe-Ni bulklegeringarochWC-Co h°ardmetall genom att anv¨anda Integrated Computational Materials Engineering(ICME) metoder kombinerat med FEM-data. Rapporten unders¨oker de mekaniska egenskapernahos flera bulklegeringar i Fe-Ni systemet. FEM-indentering och FEM-fraktur data interpoleras ochanv¨ands f¨or att modellera h°ardheten H och brottsegheten KIc. En modell f¨or utskiljningsh¨ardningbaserad p°a Ashby-Orowans ekvation implementeras f¨or att f¨oruts¨aga e↵ekten p°a brottgr¨ansen av utskiljdapartiklar. ¨Aven en modell f¨or l¨osningsh¨ardning implementeras. Existerande modeller anv¨andsf¨or att simulera egenskaperna hos WC-Co h°ardmetall tillsammans med modellen f¨or l¨osningsh¨ardning.Resultaten visar att de simulerade egenskaperna hos Fe-Ni bulklegeringar ¨ar j¨amf¨orbara medde f¨or kobolt. Dock kan de inte bekr¨aftas p°a grund av avsaknad av experimentell data. Egenskapernahos WC-Co h°ardmetall st¨ammer rimligt ¨overens med existerande experimentell data, meden genomsnittlig avvikelse av h°ardheten med 11.5% och av brottsegheten med 24.8%. Slutsatserna¨ar att det beh¨ovs experimentell data f¨or Fe-Ni bulklegeringar f¨or att kunna verifiera modellernasnoggrannhet och att det ¨ar m¨ojligt att f¨oruts¨aga egenskaperna hos h°ardmetall.