Os produtos feitos de ferro puro contendo Ni expandiram enormemente as aplicaÃÃes de produtos sinterizados, incluindo a fabricaÃÃo de peÃas que suportam altas cargas em automÃveis tais como transmissÃes. O diagrama de equilÃbrio de ligas Fe-Ni demonstram a presenÃa de fases α e FeNi3, porÃm as transformaÃÃes de fases necessitam de uma satisfatÃria homogeneizaÃÃo quÃmica, obtidas por processos convencionais de fabricaÃÃo de ligas por elevaÃÃo dos componentes ao estado lÃquido. Jà a sinterizaÃÃo por fase sÃlida facilita a formaÃÃo de clusters, uma vez que as partÃculas se unem sem mudanÃa de estado, o que implica em regiÃes cuja composiÃÃo quÃmica difere bastante da composiÃÃo global. Deste modo, este trabalho pretende contribuir com um estudo direcionado a identificaÃÃo de fases em ligas Fe-Ni e Fe-Ni-Mo sinterizadas a temperatura de 1100ÂC e processadas por moagem de alta energia (MAE), de forma a avaliar: a interface dissimilar formada entre os elementos, analisar os fenÃmenos encontrados na mesma e identificar caracterÃsticas metalÃrgicas apÃs a sinterizaÃÃo que contribuam para aumento da dureza, microdureza, limite de resistÃncia a traÃÃo e mÃdulo de elasticidade. O estudo apresentarà a determinaÃÃo do diagrama de equilÃbrio atravÃs do software ThermoCalc, tÃcnicas de difraÃÃo por raios X e espectrometria de raios X por energia dispersiva (EDS), alÃm de anÃlises de microscopia optica e microscopia eletrÃnica de varredura (MEV). Os resultados mostraram a presenÃa das fases estÃveis como α(CCC) e fase metaestÃveis como FeNi (CFC Austenita). As anÃlises microscÃpicas demonstram tambÃm uma heterogeneidade com diferentes percentuais de NÃquel e Ferro ao longo das amostras. / The products made of pure iron containing Ni greatly expanded the applications of sintered products , including the manufacture of parts that withstand high loads such as transmissions in cars . The equilibrium diagram of Fe-Ni alloys demonstrate the presence of α and FeNi3 phase , but the phase transformations require a satisfactory chemical homogenization obtained by conventional processes for production of alloys by elevation of the liquid components .The solid-phase sintering facilitates the formation of clusters , since the particles together without change of state, which implies regions whose chemical composition differs significantly from the overall composition . Thus , this paper aims to contribute to a study aimed at identifying phases in alloys Fe - Ni and Fe - Ni - Mo sintered at temperature of 1100  C and processed by high energy ball milling ( RBM ) in order to assess the following: interface formed between dissimilar elements , analyze the phenomena found in it and identify metallurgical characteristics after sintering contributing to increased hardness, microhardness , ultimate tensile strength and modulus of elasticity . The study shall determine the equilibrium diagram through Thermocalc software , diffraction , X-ray spectrometry and X-ray energy dispersive ( EDS ) , and the analysis of optical microscopy and scanning electron microscopy (SEM ) . The results showed the presence of stable phases as α (CCC) and metastable phase as FeNi (CFC austenite). The microscopic analysis also demonstrated heterogeneity with different percentages of Nickel and Iron along the samples.

Thesis (Ph. D. (Physics)) -- University of Limpopo, 2013 / A combination of ball milling experiments and ab initio calculations in this study successfully yielded results that shed light into understanding the fundamental basis for immiscibility and the concept of mechanical alloying in Ti-Mg system. In addition, the conditions for achieving extended solid solubility in elements that usually do not dissolve in each other under thermodynamic equilibrium conditions have been predicted using ultrasoft (US) and norm-conserving (NC) pseudopotentials. Hydostatic pressures required to stabilize ordered phases were determined. Our new systematic representation of martensitic transformation (MT) paths as a result of dislocation necessary to induce α→FCC, α→BCC and α→ω phase transitions led to, for the first time, a direct determination of CRSS and tensile strength for Ti and Mg HCP metals. Furthermore, a new ω phase which is less stable than α phase at 0 GPa is proposed. Based on this phase, α→ω deformation path which yielded the onset of uniaxial transition pressure of 4.167 GPa is reported. Attempts of synthesizing Ti-Mg solid solutions by means of Simoloyer high energy ball mill were not successful; however, nanocrystalline Mg-TiH2-x composites were instead formed. These results were attributed to quick formation of metastable Ti hydrides or cold welding at early stages of BM prior to alloying, thus serving as possible obstacles to forming such solid solutions. The deformed Ti crystals adsorbed H+ from the stearic acid leading to formation of metastable orthorhombic TiH2-x phase which later transformed to a tetragonal TiH2-x or even cubic TiH2 when stoichiometric amount of H2 had been adsorbed. Although the yield was significantly lower, the product of milling a mixture of coarse Mg and fine Ti particles was comprised of Ti particles adhering around ductile Mg particles in a core shell manner. The adhesion of the fine hard titanium particles on the surface of the large ductile magnesium particles impeded the further plastic deformation of the titanium particles, thus suppressing the formation of the faults necessary for mechanical alloying. Nanocrystalline Ti powder of about 40 nm was produced by 30h ball milling. During BM of Ti powder, solid-state transformation from HCP to FCC occurred in the presence of PCA with lattice parameters of 4.242 and 4.240 Å after 24 and 30 h, respectively, v due to protonation. When Ti powder was milled in the absence of PCA, no phase transformation was observed for both uninterrupted and interrupted milling cycles. In addition, nanocrystalline Mg powder with crystallite size varying between 60 and below 40 nm was produced by ball milling. However, no solid-state transformation took place even if the powder was milled for 90 h. Therefore, we evidently report for the first time that the interstitial H+ is the driving force for α → FCC phase transformation in ball milled Ti powder. Our theoretical results predicted the ω phase to be the ground-state structure of Ti at 0K and P=0 GPa, in support of other previously reported calculations. We noticed that the stability of the α phase was surpassed by that of the FCC lattice at ~ 100 GPa, corresponding with sudden sharp rise in c/a ratio, hence attributed to α → FCC phase transition. Similar results were obtained for Mg at 50 GPa, although in this case the crossing of lattice energies coincided with minimum c/a. However, using our proposed HCP→BCC MT path mechanism for Mg, it is evident that the minimum c/a at 50 GPa corresponds to a change in the preferred deformation slip from basal (below 10 GPa) to prismatic rather than phase transition. Nonetheless, the proposed MT model predicts that both elemental Ti and Mg prefer to deform via prismatic slip as indicated by lower shear stress as well as CRSS values compared to those calculated for basal slip. Theoretical findings from ab initio calculations on hypothetical ordered Ti-Mg phases indicated absence of intermetallic phases at equilibrium conditions, in agreement with experimental data. However, the formation becomes possible at 80 GPa and above with respect to c/a ratio but requires at least 200 GPa with respect to stable lattices. Using calculated heats of formation, elasticity and DOS, it has been possible to show that L12 TiMg3 could not form even at high pressure as 250 GPa. Nonetheless, both approaches indicate that forming an intermetallic compound between Ti and Mg requires a crystal structure change, α→FCC for Ti and HCP→BCC for Mg. Proposed DFT-based solid solution model for predicting phase stability and elastic properties of binary random alloys, with Mg-Li system serving as a test case, successfully yielded reliable results comparable to experimental data. This method was successfully applied to study an immiscible Ti-Mg system and the solubility limit vi was for the first time theoretically established. Based on formation energy of Ti-Mg solid solutions, our calculations predicted for the first time that the solubility of up to 60 and 100 at.% Mg into Ti with the use of USP and NCP, respectively, to be thermodynamically favourable with necessary lattice kinetics being the main challenge. Nonetheless, NCP proved to be reliable in predicting structural and elastic properties of disordered alloys.

Mechanical milling (alloying) is one of the non-equilibrium techniques used to prepare alloys with exceptional properties. This technique was employed in this research to develop a new class of Al- and Mg-based nanocomposite alloys using SPEX high energy milling. These nanocomposites are characterized by the dispersion of nanocrystals in an amorphous matrix. Zirconium was added to the Al-Mg alloys for the purpose of promoting glass formability. As-milled samples were annealed at 400°C for 1 hour to investigate the thermal stability of the nanostructure. The phase evolution of the resulting alloys was studied using XRD and TEM/EDS, which showed a strong dependence of the resulting metastable phases on the starting alloys compositions. / The nanocomposite structure was developed at Zr concentrations of 20 and 35 at.% regardless of the Al/Mg ratio and with some traces of oxidation. However, the amount of amorphous phase was varied in each case depending on the Al concentration into the alloy, since in low Al-containing alloys the amount of amorphous phase was less pronounced. It was found that higher Zr concentrations will lead to greater refinement of the nanostructure. These nanocomposites showed improved mechanical properties, in terms of higher hardness values, in addition to improved thermal stability. The improvement in thermal stability was attributed to the presence of Al3Zr which proved to contribute significantly to retarding grain growth via grain boundary pinning. / Additionally, the employment of mechanical alloying was beneficial in producing Al3Zr in the cubic L12 ordered structure which improves the ductility of the alloy. Moreover, the homogeneity ranges of gamma-Al 12Mg17 and Al3Zr were extended significantly due to the nature of the non-equilibrium processing. In this research, the alloy with the maximum hardness was Al40Mg25Zr35, which has an average hardness value close to 780 HV and average crystallite size of about 10 nm. A common observation in the alloys that showed a higher hardness values combined with improved thermal stability, is that they contain higher Al and Zr concentrations. / Le broyage mécanique est une technique hors équilibre qui permet la fabricationde nouveaux alliages avec des propriétés exceptionnelles. Lors de cette recherche, unbroyeur SPEX 8000 a été utilisé pour développer une nouvelle classe denanocomposites à base d'aluminium et de magnésium. Ces nanocomposites tirent leurspécificité de leur dispersion de nanocrystaux dans une matrice amorphe. Duzirconium a été ajouté aux alliages d'aluminium et de magnésium pour promouvoirl'amorphisation. Les échantillons de poudres broyées ont été recuits à 400°C pour 1heure pour évaluer la stabilité thermique des différentes phases. Leur évolution a étécaractérisée par diffraction par rayon-X et par MEBIEDS. TI fut démontré que lesphases métastables obtenues dépendent fortement de la composition des alliages dedépart.

Thesis (Ph. D.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references (leaf 111-114).

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Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-10-17T13:44:45Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Full Version Text of Masters Dissertation (FINAL).pdf: 2248443 bytes, checksum: a736d9499830c375c8774936a8f7f8b6 (MD5) / Made available in DSpace on 2016-10-17T13:44:45Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Full Version Text of Masters Dissertation (FINAL).pdf: 2248443 bytes, checksum: a736d9499830c375c8774936a8f7f8b6 (MD5) Previous issue date: 2016-07-29 / The quasicrystalline alloy which contains the element aluminum present dispersion of particles in nanometric scale that exhibit high values of mechanical strength at room temperatures and high temperatures. The quasicrystalline solids have no crystallographic conventional symmetrical structures; but they are constituted by a unit cell with periodic repetition in space and ordination mode, intermediate between periodic phases and crystalline phases amorphous non-crystalline. The process of Mechanical alloying, a technique of powder metallurgy developed in the 60's, it was established as a viable processing method in the solid state to produce various quasicrystalline phases metastable and stable. The interest in obtaining this material is due to its good structural, electronic and magnetic properties, and the interactions between the properties. In general, the quasicrystalline alloy show resistant to friction and wear, good electrical and thermal insulators, are hard, used in photonic sensors and some formations of quasicrystals are good hydrogen storers. In this work, researched he used the Mechanical alloying to obtain the icosahedral and decagonal phases Al65Mn22Cu13 and Al67,6Cr23,3Fe9,1 in order to study the magnetic properties. Samples of quasicrystalline alloys were obtained by high energy milling with balls mass ratio of 20: 1 with rotation of 200rpm, at time intervals ranging from 1 hour to 40 hours a planetary ball mill Pulverisette 5 Frittsch. Evaluations of physical characterizations were made by scanning electron microscopy showed a microstructure with nonuniform and large nodules symmetries. The X-ray diffraction provides information about identification of phases resulting from Al65Mn22Cu13 Al67,6Cr23,3Fe9,1 and alloys, the formation of icosahedral phases, intermetallic and decagonal and the presence of typical diffraction pattern peaks of their crystallographic network. The magnetic measurements were performed as a function of temperature M (T), and also due to the applied field F (M). It can be concluded that the formation of quasicrystalline phases is possible as grinding time and speed for Al65Mn22Cu13 Al67,6Cr23,3Fe9,1 and alloys obtained by Mechanical alloying process. / As ligas quasicristalinas que contém o elemento o alumínio, apresentam dispersão de partículas em escala nanométrica que apresentam valores elevados de resistência mecânica em temperaturas ambientes e em altas temperaturas. Os sólidos quasicristalinos possuem estruturas simetricas não cristalográfica convencional; mas são constituídos por uma célula unitária com repetição periódica no espaço e ordenação, de modo, intermediário entre as fases cristalinas periódicas e as fases não-cristalinas amofas. O processo de mecanossíntese, uma técnica da metalurgia do pó desenvolvida nos anos 60, foi estabelecido como um método viável de processamento no estado sólido para a produção de várias fases quasicristalinas metaestáveis e estáveis. O interesse de obtenção desse material é devido as suas boas propriedades estruturais, eletrônicas e magnéticas, e a interações entre as propriedades. Em geral, as ligas quasicristalinas mostram resistentes á fricção e ao desgaste, bons isolantes elétricos e térmicos, são duros, utilizados em sensores fotônicos e algumas formações de quasicristais são bons armazenadores de hidrogênio. Neste trabalho, pesquisou o usou da mecanossíntese para a obtenção das fases icosaedral e decagonal Al65Mn22Cu13 and Al67,6Cr23,3Fe9,1 com o intuito de estudar as propriedades magnéticas. As amostras das ligas quasicristalinas foram obtidas por moagem de alta energia com razão massa bolas de 20: 1, com rotação de 200 rpm, nos intervalos de tempo que variou de 1 hora até 40 horas em um moinho de bola planetário Frittsch Pulverisette 5. Avaliação das cararterizções físicas foram feitas por microscopia eletrônica de varredura apresentaram uma microestruturas com simetrias não uniforme e nódulos grandes. Adifração de raios-X fornece informações sobre identificações das fases decorrentes das ligas Al65Mn22Cu13 and Al67,6Cr23,3Fe9,1 as formações das fases Icosaedral, decagonal e intermetálicas e a presença de picos padrões de difração típicos da sua rede cristálografica. As medidas magnéticas realizadas foram em função da temperatura M (T), e também em função do campo aplicado M (H). Pode-se concluir que é possível a formação das fases quasicristalinas conforme o tempo de moagem e da velocidade para ligas Al65Mn22Cu13 and Al67,6Cr23,3Fe9,1 obtido pelo processo mecanossíntese.

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Made available in DSpace on 2014-10-09T12:27:20Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:14Z (GMT). No. of bitstreams: 0 / A obtenção do Cermet de níquel-zircônia via moagem de alta energia (Mechanical Alloying MA) foi estudado visando a preparação de anodos de células a combustível de óxido sólido (SOFC). O níquel metálico foi adicionado em três concentrações: 30, 40 e 50% em volume. As operações de moagem foram conduzidas em moinho vibratório de alta energia do tipo SPEX. Estudou-se a influência do tempo de moagem, a eficiência de aditivos para controle do processo, tipo e geometria dos potes de moagem. A influência destas variáveis foram avaliadas através de análises de tamanho de partículas, determinação de área superficial e morfologia do material resultante. O uso de pote de teflon resultou em contaminação por carbono. Por outro lado, o uso de pote de aço aumenta a contaminação por impurezas metálicas. As diversas geometrias projetadas para os potes mostraram que potes com maiores raios de concordância (R.15) apresentaram melhor rendimento. Após a conformação e sinterização a 1300°C em atmosfera de argônio, as amostras apresentaram valores de densidade entre 60 a 80% da densidade teórica. As microestruturas observadas por microscopia eletrônica de varredura revelaram uma boa homogeneidade na distribuição de fases do Cermet. A técnica de moagem de alta energia apresentou-se como boa opção na fabricação de Cermet Ni-ZrO2. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP