Amorphous materials are used as soft magnetic materials and also as surface coatings to improve the surface properties. Furthermore, the nanocrystalline materials derived from their amorphous precursors show superior soft magnetic properties than amorphous counter parts for transformer core applications. In the present work, laser based processing of amorphous materials will be presented. Conventionally, the nanocrystalline materials are synthesized by furnace heat treatment of amorphous precursors. Fe-based amorphous/nanocrystalline materials due to their low cost and superior magnetic properties are the most widely used soft magnetic materials. However, achieving nanocrystalline microstructure in Fe-Si-B ternary system becomes very difficult owing its rapid growth rate at higher temperatures and sluggish diffusion at low temperature annealing. Hence, nanocrystallization in this system is achieved by using alloying additions (Cu and Nb) in the ternary Fe-Si-B system. Thus, increasing the cost and also resulting in reduction of saturation magnetization. laser processing technique is used to achieve extremely fine nanocrystalline microstructure in Fe-Si-B amorphous precursor. Microstructure-magnetic Property-laser processing co-relationship has been established for Fe-Si-B ternary system using analytical techniques. Laser processing improved the magnetic properties with significant increase in saturation magnetization and near zero coercivity values. Amorphous materials exhibit excellent corrosion resistance by virtue of their atomic structure. Fe-based amorphous materials are economical and due to their ease of processing are of potential interest to synthesize as coatings materials for wear and corrosion resistance applications. Fe-Cr-Mo-Y-C-B amorphous system was used to develop thick coatings on 4130 Steel substrate and the corrosion resistance of the amorphous coatings was improved. It is also shown that the mode of corrosion depends on the laser processing conditions. The microstructure evolution and the corrosion mechanisms operating are evaluated using post processing and post corrosion analysis.

No description available.

This thesis is a study of tailoring amorphous Fe-B-Si based alloy to produce bulk glassy rods by adding Nb. We have prepared rapid quenched thin ribbons (thickness ~12 µm) by melt spinning, and glassy rods of diameter ~1mm by Cu-mold casting based on compositions (Fe0.78B0.13Si0.9)100-xNbx (x=0, 4, 8, 12), and studied their different physical properties. The melt-spun ribbons are found to be X-ray amorphous, whereas some nano-crystallinity is observed in the case of rods. All the ribbons show high saturation magnetization and low coercivity, which are the desirable characteristics of a soft ferromagnet. These ribbons are thus suitable for designing high frequency transformers, and sensors from an applications point of view. With increasing Nb content their saturation magnetization, ferromagnetic Curie temperature, and resistivity are found to decrease as expected. The temperature dependence of electrical resistivity shows small positive temperature co-efficient that is expected for a metallic disordered material. We have also studied the modification of the properties on thermal annealing the (Fe0.78B0.13Si0.9)96 Nb4 ribbon at different temperatures in a neutral atmosphere.

No description available.

Amorphous ribbons of alloy composition Fe75B10Si15 are cast by melt spinning and annealed to partially nanocrystalline states. The magnetic properties are investigated by VSM and MTGA. Structure is examined using XRD and SEM. Results obtained show nanostructured material with excellent soft magnetism in samples annealed at temperatures below the crystallization temperature as well as enhancement of magnetic hardness for annealing at high temperatures. This validates Herzer’s Random Anisotropy model of magnetism in nanostructured materials and provides basis for further inquiry into tweaking alloy compositions and/or manipulating annealing parameters. Also, increase of Curie temperature is noted with respect to increasing annealing temperatures arising from stress relaxation, validating a study on the relationship between the two.

No description available.

No description available.

Additive manufacturing (AM) procedures involving the fusion of metal powders or wires tend to produce textured columnar grains, which can have positive effects on the magnetic performance of Fe-Si electrical steels in soft magnetic applications. This work focuses on understanding the impact of energy density (fluence) evolution of grain morphology and texture in Fe-3.8wt%Si and Fe-6wt%Si alloys produced by fusion-based AM. The results show that the development of texture in these alloys is promising for transformers and motor core applications. The desired texture observed in these alloys is obtained in one step unlike conventional manufacturing techniques. The alloys with higher energy fluence exhibited columnar grains with preferential growth orientation along <001> along the build axis, while those with lower energy fluences showed growth orientation in <111> direction. Further, the presence of ordered B2, D03 phases observed in AM processed Fe-6wt%Si improved the overall magnetic performance of these alloys. Additionally, due to relatively high saturation magnetization and sustainability at high operating temperatures, Fe-Co-2V (Hiperco) is an attractive alternative for soft magnetic applications. In this study, Fe-Co-2V alloy is successfully manufactured using fusion based AM techniques and was found to exhibit equiaxed grains in the AM processed conditions. The microstructure was found to have a significant influence on the magnetic properties, leading to intriguing microstructure-property connections. This study will cover these links between microstructure and properties as well as how energy density (fluence) affects the microstructure of the two potential Fe-Si and Fe-Co-2V soft magnetic systems.

O presente trabalho objetiva o estudo, obtenção e caracterização da liga magnética macia Fe-Si-P produzida por metalurgia do pó convencional visando à futura aplicação em núcleos de máquinas elétricas, atualmente fabricados por estampagem de chapas. Escolheu-se com base em testes prévios a liga Fe-3%Si-0,75%P. Para a obtenção da liga, foi utilizada a rota de mecâno-síntese com diferentes tempos de moagem: 1 h, 3 h e 9 h, além do material sem moagem para comparação. Na sequência compactaram-se uniaxialmente a frio os corpos de prova a 600 MPa seguido de sinterização a 1150 ºC em atmosfera de gás argônio. A análise da influência do tempo de moagem nas propriedades físicas, mecânicas, magnéticas e elétricas no material sinterizado foi a meta central deste trabalho. A caracterização das propriedades físicas mostrou uma redução da densidade aparente do pó moído, um aumento da distribuição do tamanho de partícula e redução do mesmo com o aumento do tempo de moagem. No que se refere às propriedades magnéticas, evidenciou-se que o material moído durante 3h apresentou os melhores resultados de indução de saturação (1,15 T), apesar do aumento na coercitividade já previsto devido ao processo de mecâno-síntese. Além disso, a difração de raios-X detectou a formação da liga através da solução sólida dos elementos P e Si na matriz ferrita. A análise metalográfica revelou a diminuição do tamanho de grãos com o aumento do tempo de moagem. Por fim, realizou-se a simulação do protótipo para análise do desempenho do material visando à aplicação futura. Esta, realizada pelo método de elementos finitos em um núcleo de um gerador síncrono com ímãs permanentes de NdFeB resultou em uma densidade de fluxo (1,95T) para o material com 3h de moagem e um torque de apenas 13% inferior se comparado ao gerador convencional produzido com núcleos de chapas de aço elétrico. / The present work aims to study, obtaining and characterization of Fe-Si-P soft magnetic alloy produced by conventional powder metallurgy intended for the future application in electrical machines cores, currently manufactured by sheet metal forming. The alloy Fe-3%Si-0,75%P was chosen based on previous tests. To obtain the alloy was used mechanical alloying route with different milling times: 1 h, 3 h and 9 h, and the material without milling for comparison. In the sequence, the specimens were uniaxially cold compacted at 600 MPa followed by sintering at 1150 ° C in an atmosphere of argon. The analysis of the influence of milling time on the physical, mechanical, magnetic and electric properties of the sintered material was the central goal of this work. The physical properties characterization showed a reduction in the bulk apparent density of the milled powder, an increase in particle size distribution and reduction thereof with increasing milling time. As regards magnetic properties, it was observed that the milled material for 3 hours showed the best results of saturation induction (1.15 T), despite the increase in the coercivity as expected due to the inherent mechanical alloying process. Furthermore, the X-ray diffraction detected the alloy formation through the solid solution of P and Si elements in the ferrite matrix. The metallographic analysis showed the decrease in grain size with increasing milling time. Finally, were performed a simulation prototype for analysis of material performance in order to future implement. This, held by finite element method on a synchronous generator core with NdFeB permanent magnets, resulting in a flux density (1.95 T) for the material with 3h of milling and a torque of only 13% lower compared to conventional generator produced with cores of electric steel sheet.

A pulse hysteresisgraph system was constructed capable outputting current source and voltages source waveforms. MATLAB scripts were created to analyze the collected data. Three toroidal samples of soft magnetic materials were prepared. Theoretical modeling was done to predict the variation of effective applied magnetic fields inside the toroids from ideal assumptions due to three effects: wire spacing, cylindrical spreading, and eddy current generated fields. Data was collected under sinusoidal voltage source and sinusoidal current source excitation at 1 kHz. Large differences in core loss were noted especially at higher field excitations. Core loss under sinusoidal current source excitation was found to always be greater than or equal to core loss under sinusoidal voltage source. Normal magnetization curves under sinusoidal current and voltage source excitation were also compared. Significant differences were apparent in the magnetization curves of one sample toroid, and slight differences noted in the curves of the other two samples. Eddy currents were offered as a primary mechanism for the difference in core loss between sinusoidal current source and sinusoidal voltage source. A formula to predict the relative eddy current losses to be expected from an arbitrary, periodic voltage waveform shape is given. / text