The magnetic properties, coercivity, Hc, and weight-specific magnetic saturation, CoM, are two important quality characteristics in cemented carbides and ceramic metals, cermets. These properties give information about grain size and binder phase content, and are influenced by the different stages in the sintering process. This master thesis aim to investigate how the magnetic properties in cemented carbides are influenced by the top temperature during sintering and how the sintering processes used for cermets can be optimized in order to gain better magnetic properties in the final products. During the first part of the project, the temperature range investigated was 1380°C–1520°C. The results indicate that Hc in cemented carbides has a strong temperature dependence, where increasing top temperature results in lower Hc. In order to have approval limits for the furnace control pieces that follow the process directives, the limits used today need to become narrower. Furthermore, the results show that CoM also has a temperature dependence, although not as strongly as Hc. During the second part of the project, already existing data of the magnetic properties in four different cermet grades were evaluated. The results indicate that the two sintering processes used in the DDK furnace are generating too high results in Hc and CoM. Optimization tests were conducted and changes implemented in order to gain better results, where the DJ1430 process now has an increased time during the solid state sintering and the DF1480 process now has an increased time during the liquid phase sintering.

No description available.

We study boundary value problems for linear elliptic differential operators of order one. The underlying manifold may be noncompact, but the boundary is assumed to be compact. We require a symmetry property of the principal symbol of the operator along the boundary. This is satisfied by Dirac type operators, for instance. We provide a selfcontained introduction to (nonlocal) elliptic boundary conditions, boundary regularity of solutions, and index theory. In particular, we simplify and generalize the traditional theory of elliptic boundary value problems for Dirac type operators. We also prove a related decomposition theorem, a general version of Gromov and Lawson's relative index theorem and a generalization of the cobordism theorem.

Metallic glasses produced with Selective Laser Melting (SLM) often contain internal mechanic stress. This internal stress can have an impact on the magnetic properties of the material due to its connection to the magnetic anisotropy of the material. Therefore the effect of different heat treatments aimed to reduce the effect of internal stress on the magnetic properties of an Fe-based Metallic Glass (MG) and how this relates to the crystallization of the material was examined in this project. The magnetic properties were measured with a Vibrating Sample Magnetometer (VSM) and the Longitudinal Magneto-Optic Kerr Effect (L-MOKE) and structural changes to the material from the heat treatments, such as crystallization, was examined with X-Ray powder Diffraction (XRD) before and after heat treatment. From the measurements we found that heat treatments close to and above the crystallization temperature Tx lead to crystallization and a decrease in magnetic saturation MS. Heat treatments below Tx around 430°C showed a smaller reduction in MS but did not show any crystallization. The measurements with L-MOKE showed no consistent change in coercivity so no conclusion could be drawn from these. / Metallglas som tillverkats med den additiva tillverkningstekniken Selective Laser Melting (SLM) innehåller ofta interna mekaniska spänningar. Dessa spänningar kan på grund av deras koppling till materialets magnetiska anisotropi ha en påverkan på materialets magnetiska egenskaper. I detta projekt har därför effekten av olika värmebehandlingar utförda för att minska de interna spänningarnas påverkan på de magnetiska egenskaperna av ett Fe-baserad metallglas och hur detta relaterar till kristalliseringen av materialet undersökts. De magnetiska egenskaperna av materialet mättes med en Vibrating Sample Magnetometer (VSM) och Longitudinal Magneto-Optic Kerr Effect (L-MOKE). Strukturella förändringar, så som kristallisering, hos materialet orsakade värmebehandlingarna undersöktes med X-Ray powder Diffraction (XRD). Samtliga mätningar genomfördes före och efter värmebehandling. Från mätningarna fann vi att värmebehandlingar nära kristalliseringstemperaturen Tx gav kristalltillväxt samt minskade mättnadsmagnetisering MS. Värmebehandlingar under Tx runt 430°C gav en lägre reducering av MS samt gav ej någon kristalltillväxt. L-MOKE-mätningarna gav ingen konsekvent förändring i materialets koercivitet och inga slutsatser kunde därmed dras från dessa.

Chapas de aço elétrico (0,7% Si e 0,3% Al) foram laminadas a diferentes graus de deformação e recozidas (760º C, 2h) de modo a obter diferentes tamanhos de grão por recristalização. Um outro conjunto de chapas do mesmo material foi recozido a tempos e temperaturas diferentes de modo a obter tamanho de grão variado por crescimento de grão. Os tamanhos de grão foram medidos pelo método dos interceptos e os parâmetros da distribuições de tamanho de grão determinados por um método semi-analítico que se baseia na medição das áreas individuais de cada grão na micrografia. A partir do ensaio quase-estático de histerese magnética no quadro de Epstein obtiveram-se os campos coercivos de cada amostra, a diferentes induções máximas (0,6 0,8 1,0 1,2 1,4 e 1,5T). Notou-se que o conjunto dos dados se enquadra com menos de 4% de desvio médio absoluto uma lei fenomenológica do tipo: Hc aBmax^c /TG bBmax^d Na qual Hc é o campo coercivo, TG é o tamanho de grão, Bmax é a indução máxima do ensaio de histerese e a, b, c e d são os parâmetros de ajuste. A partir da inserção do efeito do campo desmagnetizante no contorno de grão no modelo físico de Mager obteve-se uma boa estimativa para os valores dos parâmetros independentes da indução a e b, além de propor um significado físico para os mesmos. Com a integração dos modelos Mager e Preisach, determinou-se uma equação diferente para o ajuste dos dados, a qual oferece um valor aproximado de c. Para que o modelo físico explique completamente a relação fenomenológica resta ainda elucidar o parâmetro d. / Electrical steel sheets (0,7% Si and 0,3% Al) were cold-rolled and annealed (760º C, 2h) in order to obtain different grain sizes through recrystallization. Another set of sheets from the same material were annealed at different temperatures and time-frames, so as to produce different grain sizes through grain growth. Grain size was measured through the intercept method and grain size distribution parameters were determined via a semi-analytical method based on measurement of individual grain areas upon micrographs. From quasistatic hysteresis measurements in an Epstein frame, the coercive field of each sample was determined at various maximum induction values (0,6 0,8 1,0 1,2 1,4 e 1,5T). The data set fits with less than 4% average deviation a phenomenological law of the type: Hc aBmax^c /TG bBmax^d In which Hc is the coercive field, TG is the grain size, Bmax is the maximum induction value and a, b, c and d are the fitting parameters. By introducing the grain boundary demagnetizing field effect on Magers physical model, a good estimate of the values of a and b was obtained, as well as a reasonable explanation to their physical meaning. Integrating Mager and Preisach models, a different equation for the data was obtained, which offered an approximate value of c. In order for physical models do fully explain the phenomenological equation, there is still need to understand the parameter d.

Chapas de aço elétrico (0,7% Si e 0,3% Al) foram laminadas a diferentes graus de deformação e recozidas (760º C, 2h) de modo a obter diferentes tamanhos de grão por recristalização. Um outro conjunto de chapas do mesmo material foi recozido a tempos e temperaturas diferentes de modo a obter tamanho de grão variado por crescimento de grão. Os tamanhos de grão foram medidos pelo método dos interceptos e os parâmetros da distribuições de tamanho de grão determinados por um método semi-analítico que se baseia na medição das áreas individuais de cada grão na micrografia. A partir do ensaio quase-estático de histerese magnética no quadro de Epstein obtiveram-se os campos coercivos de cada amostra, a diferentes induções máximas (0,6 0,8 1,0 1,2 1,4 e 1,5T). Notou-se que o conjunto dos dados se enquadra com menos de 4% de desvio médio absoluto uma lei fenomenológica do tipo: Hc aBmax^c /TG bBmax^d Na qual Hc é o campo coercivo, TG é o tamanho de grão, Bmax é a indução máxima do ensaio de histerese e a, b, c e d são os parâmetros de ajuste. A partir da inserção do efeito do campo desmagnetizante no contorno de grão no modelo físico de Mager obteve-se uma boa estimativa para os valores dos parâmetros independentes da indução a e b, além de propor um significado físico para os mesmos. Com a integração dos modelos Mager e Preisach, determinou-se uma equação diferente para o ajuste dos dados, a qual oferece um valor aproximado de c. Para que o modelo físico explique completamente a relação fenomenológica resta ainda elucidar o parâmetro d. / Electrical steel sheets (0,7% Si and 0,3% Al) were cold-rolled and annealed (760º C, 2h) in order to obtain different grain sizes through recrystallization. Another set of sheets from the same material were annealed at different temperatures and time-frames, so as to produce different grain sizes through grain growth. Grain size was measured through the intercept method and grain size distribution parameters were determined via a semi-analytical method based on measurement of individual grain areas upon micrographs. From quasistatic hysteresis measurements in an Epstein frame, the coercive field of each sample was determined at various maximum induction values (0,6 0,8 1,0 1,2 1,4 e 1,5T). The data set fits with less than 4% average deviation a phenomenological law of the type: Hc aBmax^c /TG bBmax^d In which Hc is the coercive field, TG is the grain size, Bmax is the maximum induction value and a, b, c and d are the fitting parameters. By introducing the grain boundary demagnetizing field effect on Magers physical model, a good estimate of the values of a and b was obtained, as well as a reasonable explanation to their physical meaning. Integrating Mager and Preisach models, a different equation for the data was obtained, which offered an approximate value of c. In order for physical models do fully explain the phenomenological equation, there is still need to understand the parameter d.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Os aÃos Fe-Cr-Mo sÃo amplamente usados em tubulaÃÃes e componentes que estÃo constantemente sujeitos a processos de degradaÃÃo nas indÃstrias petroquÃmicas. A exposiÃÃo desses aÃos em ambientes agressivos por um perÃodo prolongado quando submetidos a elevadas temperaturas tem como consequÃncias alteraÃÃes microestruturais, precipitaÃÃes na forma de carbonetos que atuam nos aÃos afetando sua resistÃncia a fluÃncia e a corrosÃo. Os aÃos Fe-Cr-Mo possuem propriedades ferromagnÃticas que podem ser exploradas com o objetivo de fornecer informaÃÃes sobre essas alteraÃÃes microestruturais. Nesse trabalho foram analisadas as propriedades magnÃticas das ligas Fe-9Cr-XMo (X = 1%, 5%, 7% e 9%) e a relaÃÃo dessas propriedades com a formaÃÃo de precipitados. Para isso as amostras foram submetidas a tratamentos tÃrmicos de solubilizaÃÃo (com exceÃÃo da liga contendo 1% de Mo) e envelhecimento. As anÃlises das propriedades magnÃticas foram feitas usando ciclos de histerese obtidos pela tÃcnica de magnetometria de amostra vibrante. Os parÃmetros magnÃticos analisados foram o campo coercivo, a magnetizaÃÃo residual e a magnetizaÃÃo de saturaÃÃo. A anÃlise dos precipitados foi feita usando micrografias obtidas por microscopia eletrÃnica de varredura e espectros de EDS, alÃm de histogramas obtidos com auxÃlio do software ImageJ que mostram a distribuiÃÃo e o tamanho mÃdio de precipitados. Os resultados obtidos permitem concluir que existe uma relaÃÃo entre a distribuiÃÃo e tamanho mÃdio dos precipitados com o campo coercivo. Em geral, o aumento na densidade de precipitados contribui de forma significativa para o aumento na dureza magnÃtica do material, esse mecanismo està relacionado a um processo de ancoragem das paredes de domÃnio magnÃtico. A magnetizaÃÃo de saturaÃÃo à afetada tanto pela formaÃÃo de precipitados quanto pelo teor de molibdÃnio na liga. / Cr-Mo steels are widely used in pipes and components constantly subjected to degradation processes in the petrochemical industries. The exposure of these steels in harsh environments for extended periods when subjected to elevated temperatures lead to microstructural changes, such as carbide precipitation which affect its creep and corrosion resistance. Fe-Cr-Mo steels have ferromagnetic properties that can be investigated in order to provide information on these microstructural changes. In this work we analyzed the magnetic properties of Fe-9Cr-Xmo (X = 1%, 5%, 7% and 9%) alloys and the relation between these properties and related to the formation of precipitates. For this, the samples were first subjected to solution heat treatments (except alloy containing 1% Mo) and then aged. The analysis of the magnetic properties was carried out by hysteresis loops obtained by vibrating sample magnetometry. The magnetic parameters analyzed were the coercive field, the residual magnetization and the saturation magnetization. The precipitates were analyzed by scanning electron microscopy and EDS spectra, and their distribution and average size were calculated through histograms obtained by the ImageJ software. The results indicate that the distribution and average size of the precipitates are related to the coercive field. In general, the increase in the density of precipitates contributes signicantly to the increase in the magnetic hardness of the material. This mechanism is related to a process of pinning the magnetic domain walls. The saturation magnetization is affected both by the formation of precipitates and by the molybdenum content in the alloy.

The FeCo-V alloy, commercially referred to as Hiperco, is known for its great soft magnetic properties. However, the high cost of production has limited the usage of this alloy to small-scale applications, where the small volume and high magnetic performance are critical. Additive manufacturing (AM) has the potential to solve the production problems that exist in Hiperco manufacturing. The present research has focused on selective laser melting (SLM) based AM processing of Hiperco. The goal was to perform a detailed examination of SLM processed Hiperco and determine how the process parameters affect the microstructure, mechanical and magnetic properties. While a systematic set of SLM process parameters were employed, the results indicate that the energy density was quite similar for this set of process parameters, resulting in similar properties. Overall, the saturation magnetization (Ms) values were very good, but the coercivity (Hc) values were very high, in the case of all as SLM processed conditions. Additionally, a large variation in porosity was observed in the as SLM processed samples, as a function of process parameters. Interestingly, long-term heat-treatments of these samples in an Ar+H2 atmosphere resulted in substantial decreases in the Hc values. These results are presented and discussed.

No description available.

<p>Ni-Fe alloys have been used in industrial applications over the past century due to their unique mechanical and magnetic properties. Currently, researchers are interested in enhancing the performance of Ni-Fe alloys by modifying their microstructure. An example of this would be the use of ultra-fine nanocrystalline Ni-Fe alloys for magnetic shielding products that are uniquely shaped and cost effective. These nanocrystalline materials usually exhibit good soft magnetic properties, such as high saturation magnetization, low coercivity and good magnetic permeability. The following study has been devoted to the magnetic properties of electrodeposited nanocrystalline Ni-Fe alloys.</p> <p>The structure and texture of electrodeposited Ni-Fe alloys was studied by two-dimensional XRD. The Ni-Fe alloys with Fe content from 24.9at. % to 54.2at. % were comprised exclusively of the FCC phase. For 60.2at. % Fe sample, a mixed phase of BCC and FCC structure was found. The lattice parameter increased with increasing Fe content until 54.2at. %, and then decreased due to the presence of BCC structure. The increase in lattice parameter was attributed to the iron replacement of nickel in the Ni crystalline lattice. Texture analysis shows that all Ni-Fe alloys with different Fe content exhibit the fiber texture with a major component of theaxis aligned perpendicular to the sample plane. A second component iswith a significantly lower volume fraction. It also shows that the Ni-Fe alloy with 44.2at. % Fe exhibits the highest volume fraction of random orientation.</p> <p>Magnetic measurements showed that all Ni-Fe nanocrystalline alloys exhibit soft magnetic properties with narrow hysteresis loops. The saturation magnetization increased linearly with increasing Fe content. The magnetization at T = 2K were slightly higher than that at T = 298K. The lowest coercivity~6Oe was obtained at 44.2 at. % Fe content.</p> <p>Good agreement between Random Anisotropy Model (RAM) theory and experimental data for all the Ni-Fe alloys has been obtained. By fitting the high field magnetization curve with the Law of Approach to Saturation (LATS), the magnetocrystalline anisotropy constant (K_eff) were obtained. K_eff decreased with increasing temperature. Also, the ferromagnetic exchange lengths for each Ni-Fe alloy were calculated. They are 26nm, 21nm, 19nm, 18nm, 17nm for Ni-24.9at.%Fe, Ni-33.1at.%Fe, Ni-44.2at.%Fe, Ni-54.2at.%Fe, Ni-60.2at.%Fe at room temperature, respectively. The exchange lengths are larger than the average grain size (D) for all of the samples. The results confirmed the feasibility of Random Anisotropy Model for the prediction of the magnetic properties of the nanocrystalline Ni-Fe alloys fabricated by electrodeposition.</p> / Master of Applied Science (MASc)