O processo HDDR tem-se mostrado de grande interesse para a produção de ímãs à base de terras raras e polímeros. Apresenta vantagens comerciais quando comparado com os ímãs sinterizados convencionais, por exemplo, pela facilidade e menores custos de produção. Com o desenvolvimento de pós anisotrópicos, utilizando praseodímio, as expectativas em relação a este processo aumentam e, também, a necessidade de se estudar novas composições e adições. Neste trabalho, foram investigadas as propriedades magnéticas de ímãs moldados com resina, preparados com pós de ligas magnéticas de PrFeB, usando o processo HDDR. A liga magnética padrão utilizada foi a Pr14FebalCo16B6Nb0,1. Adições de elementos de liga como fósforo, cobre, alumínio, gálio e gadolíneo foram realizadas com o objetivo de melhorar as propriedades magnéticas do material padrão. A caracterização microestrutural dos ímãs foi realizada por microscopia óptica e MEV. A complexidade da microestrutura influencia o comportamento eletroquímico das ligas magnéticas. A literatura sobre este assunto é escassa. Assim, a resistência à corrosão das diferentes ligas preparadas ao longo do trabalho foi avaliada por espectroscopia de impedância eletroquímica e curvas de polarização potenciodinâmica. Foi estabelecida uma correlação entre as características microestruturais e o comportamento eletroquímico das ligas. Os resultados indicaram que adições de fósforo e alumínio em teores de até 1,0%p têm um efeito benéfico sobre as propriedades magnéticas e resistência à corrosão da liga padrão. A presença de cobre, por outro lado, diminui sensivelmente as propriedades magnéticas da liga padrão. / HDDR process has attracted great interest for producing polymer- bonded rareearth based magnets. It presents commercial advantages when compared with conventional sintered magnets owing to easy and low cost manufacturing. With the development of anisotropic powders using praseodymium, the expectations about this process grow e also the need for studying new compositions and alloy additions. In this work the magnetic properties of polymer-bonded magnets prepared with PrFeB magnetic alloys using HDDR process have been studied. Pr14FebalCo16B6Nb0,1 was used as the reference alloy Phosphorus, copper, aluminium, galium and gadolynium additions have been performed to increase the magnetic properties of the reference alloy. The microstructural characterization of the magnets has been carried out through optical microscopy and SEM. The complex microsctructure influences the electrochemical behavior of the magnetic alloys. The literature about this subject is scarce. Thus, the corrosion resistance of the different alloys prepared during this work was evaluated using electrochemical impedance spectroscopy and potentiodynamic polarization curves. A correlation between the microstructural features and the electrochemical behavior of the alloys has been established. The results showed that phosphorus and aluminium additions up to 1.0wt% had a beneficial effect on the magnetic properties and corrosion resistance of the alloys. Copper additions, on the other hand, strongly diminished the magnetic properties of the reference alloy.

Neste trabalho foram obtidas barras da liga (Fe0,80Al0,20)97B3 por solidificação direcional (SD), nos diâmetros de 3 e 4 mm, com o objetivo de melhorar a magnetostricção desse material através da introdução de textura. As etapas de produção das barras envolveram a fabricação de lingotes da liga por fusão a arco L1, L2 e L6, seguida de usinagem (U) ou forjamento rotativo (F) a quente. O maior comprimento de barra obtido foi de 50 mm. Através de microscopia eletrônica de varredura e análise de composição por espectroscopia de energia dispersiva, detectou-se a presença de boro nas amostras pela visualização do microconstituinte eutético formado da fase ? e da fase Fe2B. Resultados obtidos por difração de raios X indicam que a amostra da liga L1 para o diâmetro de 4 mm apresentou orientação preferencial nas direções , o que causou uma diminução expressiva da magnetostricção se comparada a da amostra do mesmo lingote para o diâmetro de 3 mm. Medidas de magnetização em função do campo magnético aplicado (Ha) indicaram que a magnetização de saturação das amostras que têm boro são em média 181 Am2/kg, sugerindo que as amostras tem ~ 2% de B. A barras obtidas por SD, tratadas termicamente (CTT) a 1100°C por 6 h, alcançaram uma maior magnetostricção (? = ?l/l), comparada as amostras sem tratamento térmico (STT), no qual o maior valor foi de 73 ? 10-6 na direção longitudinal da barra L1 forjada no diâmetro de 3 mm (L1F3-CTT). O maior fator de sensibilidade d?/dH obtido em função do comprimento da barra L1F3 foi de d?/dH = 0,9 x 10-9 m/A para a razão de aspecto ? = 12. Valor da constante anisotrópica K1 calculada a partir dos resultados experimentais se comparadas com dados da literatura, sugerem que em algumas amostras ocorre ordenamento parcial da fase cúbica da matriz, havendo assim a coexistência das fases Fe3Al (D03) e ?. / In this work, bars of the alloy (Fe0,80Al0,20)97B3 were obtained by directional solidification (DS) in diameters of 3 and 4 mm, with the goal of improving the magnetostriction of the material through the introduction of texture. Production steps of the bars involved the manufacture of the alloy ingots, L1, L2, L6, by arc melting, then machining (M) or hot swaging (F). The greatest length that was achieved in a bar was 50 mm. The presence of boron in the samples was identified by scanning electron microscopy and energy dispersive spectroscopy, due to the presence of an eutectic microstructure that has dendrites and a microconstituent formed of phases ? and Fe2B. Results obtained by X-ray diffraction indicates that the bar L1 at the diameter of 4 mm showed preferential orientation in the directions , which caused a significant decrease of the magnetostriction compared to the same sample of the bar of diameter 3 mm. Magnetization measurements as a function of applied magnetic field (Ha) reveal that the saturation magnetization of the samples having boron is in average 181 Am2/kg, suggesting that the samples have ~ 2% of boron. The bars obtained by DS, thermally treated (CTT ) at 1100 ° C for 6 h, achieved higher magnetostrictions (? = ?l/l) compared to the samples without heat treatment.The highest value was 73 ? 10-6 was obtained in the longitudinal direction of the bar L1F in the diameter of 3 mm (L1F3-CTT). The maximum sensitivity factor d?/dH found as a function of the bars lengths was d?/dH = 0.9 x 10-9 m/A for an aspect ratio of ? = 12. Values of anisotropic constant K1, calculated using experimental results suggest that in some samples occur partial ordering of the cubic phase matrix , so there is the coexistence of phases Fe3Al ( D03 ) and ?.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

No description available.

No description available.

No description available.

No description available.

This is the first systematic report on the synthesis of mechanically alloyed Fe-Ni powders ball milled at liquid nitrogen temperature. Pure Fe-Ni samples were ball milled in a SPEX 8000 shaker mill at liquid nitrogen temperature. X-ray diffractometry was used to determine the phase fractions of the bcc and fcc phases in the alloys and to determine the lattice parameters and crystallite size. The main objective of this project is to study how the milling at low temperatures affects the region of two phase co-existence, phase structure and crystallite size. It was found that the composition ranges of the bcc and fcc single phase regions were extended well beyond the equilibrium ranges. The results obtained for the samples ball milled at liquid nitrogen temperature were compared to the previous samples ball milled at room temperature.

Afin d’enrayer le dérèglement climatique actuel dû à l’utilisation à grande échelle de combustibles fossiles comme source d’énergie, une transition vers des énergies non émettrices de dioxyde de carbone est nécessaire. L’hydrogène, vecteur d’énergie neutre en dioxyde de carbone, pourrait y jouer un rôle important. Cependant, ses propriétés thermodynamiques interdisent de le stocker pur à des pressions modérées dans un volume raisonnable pour alimenter un véhicule. Le stockage solide sous forme d’hydrure métallique semble être une solution prometteuse à ce problème. Les alliages de structure cubique centrée à base de vanadium étant légers comparés aux alliages à base de terres rares étudiés depuis les années 1970, cette thèse a pour objet l’étude des propriétés d’hydrogénation (pression d’équilibre et capacité d’absorption notamment) d’alliages du système Fe Ti–V. Les composés à étudier devant être de structure cubique centrée et la limite de solubilité du fer dans cette phase du système Fe–Ti–V n’étant pas documentée de manière fiable, la première partie du travail a consisté en l’approfondissement des connaissances sur le diagramme d’équilibre grâce notamment à la détermination des sections isothermes à 1000 °C et 1200 °C. Pour cela, des échantillons massifs ont été synthétisés par fusion en four à arc puis recuit en four résistif. Les relations de phases ont été systématiquement analysées par diffraction des rayons X sur poudre et microsonde électronique. Grâce à ces techniques, nous avons pu montrer qu’après recuit à 1000 °C, la limite de solubilité du fer dans un alliage Ti–V dépasse 15 at.% pour tout rapport Ti/V. Lorsque la température de recuit est portée à 1200 °C, cette limite de solubilité dépasse 20 at.% de fer quel que soit le rapport Ti/V < 1. Une réaction quasi-péritectique a également pu être mise en évidence à 1140 °C et une projection de la surface liquidus est proposée, basée sur l’analyse de la microstrucure des échantillons. La seconde partie de notre travail a consisté en l’étude sur banc manométrique des propriétés d’hydrogénation d’échantillons de structure cubique centrée. Il en ressort que la majorité des composés étudiés ont une capacité totale à température ambiante de 1,7H/M, soit 3,4 wt.%, ou 140 g_L-1, la capacité réversible s’élevant à 0,98H/M, soit 1,93 wt.%, ou 82,5 g_L-1 (densité supérieure à celle du dihydrogène liquide) pour l’échantillon de compositionTi10V88Fe2. La dépendance entre l’enthalpie d’hydrogénation et la compositiondes échantillons est linéaire et a été déterminée. On peut ainsi, en fonction de la composition choisie, obtenir des pressions d’équilibre allant de 0,1 bar à plus de 100 bar. Une étude structurale par diffraction des rayons X pour de faibles concentrations en hydrogène a mis en évidence la déformation de la maille cubique en maille quadratique lorsque la quantité d’hydrogène absorbé augmente. La cinétique d’absorption des échantillons de structure cubique centrée est par ailleurs très avantageuse, puisqu’une minute suffit pour que 90% de la capacité totale soit atteinte. En revanche, on observe un ralentissement de la cinétique en fonction du nombre de cycles appliqués. Toutefois, ce type d’alliage reste prometteur pour des applications de stockage de l’hydrogène / In order to stop the current climatic disturbance due to the large scale use of fossilfuels as a source of energy, a transition towards less carbon dioxide emitting energies is necessary. Hydrogen, a carbon dioxide neutral energy carrier, could play an important role. However, its thermodynamic properties prevent from storing it pure under moderate pressure in a reasonable volume in order to feed a vehicle. Metallic hydride storage seems to be a promising solution to this problem. Vanadium based body centered cubic alloys being light compared to rare earth based alloys used since the 1970s, the purpose of this work is the study of the hydrogenation properties (equilibrium pressure and absorption capacity in particular) of Fe–Ti–V system alloys.Since the compounds to be investigated have to take the body centered cubic structure, but the solubility limit of iron in this phase of the Fe–Ti–V system is not reliably documented, the first part of this work consisted in deepening the equilibrium diagram knowledge by determining the isothermal sections at 1000 °C and 1200 °C. With this aim in view, bulk samples were synthesized by arc melting followed by an annealing in a resistive furnace. The phase relations were systematically analysed by means of powder X-ray diffraction and electron probe microanalysis. Thanks to these techniques, we showed that after annealing at 1000 °C, the solubility limit of iron in a Ti–V alloy exceeds 15 at.% for any ratio Ti/V < 1. A quasi-peritectic reaction at 1140 °C could also be evidenced and a liquidus surface projection is proposed, based on microstructural analyses. The second part of this work consisted in the study of the hydrogenation properties of body centered cubic samples. The majority of the studied compounds showed a total capacity at ambient temperature of 1.7H/M, corresponding to 3.4 wt.%, or 140 g_L��1, and the reversible capacity of the sample of composition Ti10V88Fe2 amounts to 0.98H/M, corresponding to 1.93 wt.%, or 82,5 g_L��1 (density higher than that of liquid hydrogen). There is a linear relationship, which was determined, between the alloy compositions and the hydrogenation enthalpy. We can thus, depending on the chosen composition, obtain equilibrium pressures ranging from 0.1 bar to more than 100 bar. A structural study by meansof X-ray diffraction for low hydrogen concentrations pointed out the unit cell distortionfrom body centered cubic to body centered tetragonal by increasing hydrogen concentration. Furthermore, absorption kinetics of the body centered cubic samples is interesting, since 90% of the total capacity is absorbed within one minute. On the other hand, a slowing down of the kinetics is observed when a large number of hydriding – dehydriding cycles is applied. However, this kind of alloy remains promising for hydrogen storage applications

The research of Fe-Mn-Al-C K phase