Made available in DSpace on 2014-12-17T14:06:59Z (GMT). No. of bitstreams: 1 NarayannaMF_DISSERT.PDF: 4537293 bytes, checksum: 5d2c22b8b17b69adbe02ea6e28e15de6 (MD5) Previous issue date: 2011-07-29 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Microalloyed steels constitute a specific class of steel with low amount of carbon and microalloying elements such as Vanadium (V), Niobium (Nb) and Titanium (Ti). The development and application of microalloyed steels and steels in general are limited to the handling of powders with particles of submicron or nanometer dimensions. Therefore, this work presents an alternative in order to construction of microalloyed steels utilizing the deposition by magnetron sputtering technique as a microalloying element addiction in which Ti nanoparticles are dispersed in an iron matrix. The advantage of that technique in relation to the conventional metallurgical processes is the possibility of uniformly disperse the microalloying elements in the iron matrix. It was carried out deposition of Ti onto Fe powder in high CH4, H2, Ar plasma atmosphere, with two deposition times. After the deposition, the iron powder with nanoparticles of Ti dispersed distributed, were compacted and sintered at 1120 ? C in resistive furnace. Characterization techniques utilized in the samples of powder before and after deposition of Ti were Granulometry, Scanning Electron Microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (DRX). In the case of sintered samples, it was carried out characterization by SEM and Vickers Microhardness assays. The results show which the deposition technique by magnetron sputtering is practicable in the dispersion of particles in iron matrix. The EDX microanalysis detected higher percentages of Ti when the deposition were carried out with the inert gas and when the deposition process was carried out with reactive gas. The presence of titanium in iron matrix was also evidenced by the results of X-ray diffraction peaks that showed shifts in the network matrix. Given these results it can be said that the technique of magnetron sputtering deposition is feasible in the dispersion of nanoparticles of iron matrix in Ti. / Os a?os microligados constituem uma classe espec?fica de a?o com baixos teores de carbono e elementos microligantes, como: van?dio (V), ni?bio (Nb) e tit?nio (Ti). O desenvolvimento e aplica??o dos a?os microligados, e de a?os em geral, est?o limitados ? manipula??o dos p?s com part?culas de dimens?es submicrom?tricas ou mesmo nanom?tricas. Mediante isto, este trabalho apresenta uma t?cnica alternativa para a fabrica??o de a?os microligado empregando a deposi??o por magnetron sputtering, como fonte de adi??o de elemento microligante na forma de nanopart?culas de tit?nio dispersa em matriz de ferro. A vantagem dessa t?cnica em rela??o aos processos metal?rgicos convencionais ? a possibilidade de dispersar uniformemente o elemento microligante na matriz de ferro. Foram realizadas deposi??es de Ti sobre p? de ferro em atmosfera de CH4, H2, Ar, com dois tempos de deposi??o diferentes. Ap?s as deposi??es, o p? de ferro com nanopart?culas de Ti dispersamente distribu?das, foram compactados e sinterizados a 1120?C em forno resistivo. As t?cnicas de caracteriza??o utilizadas nas amostras de p? de ferro antes e ap?s a deposi??o de Ti foram granulometria, microscopia eletr?nica de varredura (MEV), energia dispersiva de raios X (EDX) e difra??o de raios X (DRX). Para as amostras sinterizadas utilizou-se a caracteriza??o por microscopia eletr?nica de varredura (MEV) e ensaio de microdureza Vickers. A microan?lise por EDX detectou percentuais maiores de Ti para as deposi??es em atmosfera de g?s inerte em rela??o ?s deposi??es em atmosfera de g?s reativo. A presen?a de tit?nio na matriz de ferro tamb?m foi evidenciada pelos resultados da difra??o de raios-X que apresentaram deslocamentos nos picos da rede da matriz. Diante desses resultados pode-se afirmar que a t?cnica de deposi??o por magnetron sputtering ? vi?vel na dispers?o de nanopart?culas de Ti em matriz de ferro.

Dans cette thèse, l’étude des interactions entre des particules ultrafines émises par les pots d’échappement et l’écoulement de sillage créé par le véhicule émetteur a été réalisée principalement selon une approche numérique. Une campagne expérimentale a été conduite à des fins de validation. L’objet de la thèse vise à comprendre l’impact des particules issues des pots d’échappement sur l’environnement proche tant du côté piéton que du côté des passagers des véhicules suiveurs. Pour cela, l’écoulement du fluide a été traité avec une approche eulérienne type URANS (Unsteady Reynolds Average Navier-Stokes) combinée à un suivi lagrangien pour les nanoparticules. En effet, cette thèse est conduite en parallèle d’un projet collaboratif financé par l’ADEME (CAPTIHV) dont le but est d’évaluer la qualité de l’air des habitacles des véhicules automobiles, et en particulier de l’infiltration des particules ultrafines issues du trafic environnant. L’étude de la dispersion des particules fines en écoulements turbulents nécessite une analyse fine des structures turbulentes qui s’y développent. Notre étude numérique a donc consisté, en premier lieu, à analyser cette dispersion dans le cas d’un écoulement de sillage classique à l’aval d’un cylindre. Cela nous a permis de caractériser la dynamique d’interactions de nanoparticules solides de carbone avec les structures tourbillonnaires en considérant l’impact de la turbulence et de la diffusion brownienne. Cela a permis d’évaluer l’influence des principaux mécanismes influençant la dispersion. Les résultats de ces simulations nous ont permis de sélectionner les mécanismes/forces importants pouvant influencer la dispersion de telles particules dans le sillage d’un véhicule automobile ; Cela nous a facilité la mise en place et l’analyse des simulations relativement plus complexes de l’aérodynamique du corps d’Ahmed à culot droit en présence des nanoparticules simulant les suies des gaz d’échappement. Les interactions des particules ultrafines avec les structures tourbillonnaires se créant dans le sillage des véhicules ont été évaluées à partir de profils de concentrations et les coefficients de dispersions transversales. La dernière étape a consisté en une campagne d’essais en soufflerie qui nous a permis de caractériser les champs de vitesses moyens et turbulents ainsi que les champs de concentrations particulaires à l’aval du véhicule pour valider les résultats numériques / In this thesis, the study of the interactions between ultrafine particles emitted by the exhaust pipes and the wake flow generated by the emitting vehicle was carried out mainly using a numerical approach. An experimental campaign was conducted for validation purpose. The goal of the thesis is to understand the impact of exhaust particles on the surrounding environment on both the pedestrian and the passengers of the following vehicles. For this purpose, the fluid flow was resolved with an Eulerian type URANS model (Unsteady Reynolds Average Navier-Stokes) combined to the Lagrangian approach for the nanoparticles trajectories calculation. This thesis is conducted simultaneously with a collaborative project funded by ADEME (CAPTIHV) whose purpose is to assess the air quality of automotive car cabins, and particulate infiltration from the surrounding traffic in particular of ultrafine particles. The study of the dispersion of fine particles in turbulent flows requires a fine analysis of the turbulent structures that develop in such flows. Our numerical study therefore consisted, first, in analyzing this dispersion in the case of a classic wake flow downstream of a cylinder. This enabled us to characterize the interaction of solid carbon nanoparticles with vortical structures evaluating at the same time the impact of turbulence and Brownian diffusion. This allowed determining the influence of the main mechanisms influencing nanoparticles dispersion. In a second step, we replaced the cylinder configuration by a simplified geometry of a motor vehicle, Ahmed body configuration. Therefore, simulations with and without of particles presence have been conducted and have allowed to highlight the swirls structures and to characterize the particles dispersion through particle concentration profiles and the particles dispersion coefficients. The results of these simulations allowed us determining the important mechanisms / forces that can influence the dispersion of such particles in the wake of a ground vehicle; this facilitated the implementation and analysis of relatively more complex simulations of the aerodynamics of the square back Ahmed body in the presence of nanoparticles simulating soot from the exhaust gases. The interactions of ultrafine particles with vortical structures appearing in the wake of vehicles were evaluated from concentration profiles and transverse dispersion coefficients. The final step was a wind tunnel experimental campaign that allowed us to characterize the average and turbulent velocity fields as well as the particle concentration fields downstream of the vehicle to validate the numerical results