京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第21889号 / エネ博第390号 / 新制||エネ||75(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー変換科学専攻 / (主査)教授 木村 晃彦, 教授 星出 敏彦, 教授 今谷 勝次 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

No description available.

A systematic study of iron-based binary and multi-component alloys was undertaken to study the structural evolution in these powders as a function of milling time during mechanical alloying. Blended elemental powders of Fe100-XBX (where x = 5, 10, 17, 20, 22, 25, 37.5 and 50 at. %) and a bulk metallic glass (BMG) composition (Fe60Co8Zr10Mo5W2B15) were subjected to mechanical alloying in a SPEX 8000 mixer mill. X-ray diffraction technique was employed to study the phase evolution, crystallite size, lattice strain and also to determine the crystal structure(s) of the phases. Depending on the milling time, formation of supersaturated solid solutions, intermetallics, and amorphous phases was noted in the binary Fe-B powder mixtures. A maximum of about 22 at. % B was found to dissolve in Fe in the solid state, and formation of FeB and Fe2B intermetallics was noted in some of the powder blends. However, an interesting observation that was made, for the first time, related to the formation of a crystalline phase on continued milling of the amorphous powder in the BMG composition. This phenomenon, termed mechanical crystallization, has been explored. Reasons for the mechanical crystallization of the amorphous powder using the X-ray diffraction and electron microscopy methods have been discussed. External heat treatments of the milled powder were also conducted to study the complete crystallization behavior of the amorphous phase. Preliminary attempts were made to consolidate the milled BMG powder to bulk shape by hot isostatic pressing (HIP) and magnetic compaction techniques. Full densification was not achieved. Nanoindentation and microhardness tests were performed to characterize the mechanical properties of the glassy alloy. Nanoindentation results gave an elastic modulus of 59 GPa, lower than the expected value of 184 GPa; due to the presence of porosity in the consolidated sample. Optimization of the consolidation parameters is required to achieve a fully dense material.

No description available.

Equiatomic composition of Ni and Ti was cryomilled with varying milling times to create Ni-Ti lamella structures with average spacings of 50 nm, 470 nm, and 583 nm in powder particles to vary the interfacial surface area per volume. These surfaces form interfaces for diffusion that are essential for solid state amorphization during low temperature annealing. To compare solid state amorphization in a relatively defect free multilayer system, elemental Ni and Ti were deposited by electron beam physical vapor deposition on titanium plates with comparable spacing as above. Both milled and deposited multilayers were annealed between 225 and 350°C for up to 50 hours. X-ray diffraction characterization and in situ annealing was conducted on cryomilled and deposited multilayers of Ni-Ti. Based on this characterization, an amorphization model based on the Johnson-Mehl-Avrami nucleation and growth equation has been established to predict the amorphization of both cryomilled and deposited multilayers. Cryomilled powders experienced much larger amorphization rates during annealing than that of deposited multilayer structures, for all layer spacings. This superior amorphization is seen despite the formation of amorphous phase during the milling process; the amount of which increases with increasing milling time. The difference in amorphization rates between cryomilled and deposited multilayers is attributed to excess driving force due to the extensive preexisting defects in the powders caused by cryomilling. Serial 3D reconstruction of cryomilled Ni-Ti powders was done by scanning electron microscopy and focused ion beam. Through 3D reconstruction it was observed that a random and non-linear lamella structure has been formed in cryomilled powders. Furthermore, lamellar spacing was seen to become smaller with increased milling time while at the same time becoming more homogeneous through the material's volume. 3D reconstruction of cryomilled Ni-Ti offers a unique insight into the microstructures and surface areas of cryomilled powder particles that has never been accomplished. / Ph. D.

Magnetic alloys that are amorphous exhibit soft magnetic properties; hence they play an essential role in electronic and electrical systems and devices. They are used in applications that include electrical power generation and transmission, electronic motors, solenoids, relays, magnetic shielding, and electromagnets. This work was an attempt to investigate the solid-state formation of Co-C amorphous alloys, their thermal stability and magnetic properties. Amorphous Co-C alloys with compositions of 2 to 40 at.% C were successfully synthesized from elemental Co and C (graphite) using mechanical alloying, a solid-state powder processing technique. All alloy compositions were milled for up 40 hours. After 20h of milling some of the alloys (≤ 20 at.% C) had partially amorphized, while the higher concentrations had completely amorphized. After 40h of milling, complete amorphization was observed in all alloys, except for the 2 and 5 at.% C alloys. The thermal analyses of the milled powders showed very interesting results. DSC results indicated that alloys with compositions through 20 at.% C crystalized in two steps; the lower temperature event precipitated metastable cobalt carbide from the amorphous phase, followed by the eventual transformation to fcc cobalt and graphite from both the remaining amorphous and the metastable carbide at the higher temperature. Two types of carbides were observed - Co3C in the 2 and 5 at.% C alloys, and Co2C in the higher carbon alloys through 20 at.% C. For compositions above 20 at.% C, only one step crystallization was observed, that of the decomposition of the amorphous phase to amorphous carbon and cobalt – primarily fcc phase. Activation energy calculations show that the low temperature carbide precipitation was controlled by carbon diffusion, while the high temperature decomposition reaction forming cobalt and amorphous carbon was controlled by cobalt diffusion. Room temperature magnetic measurements of the milled powders were made using vibrating sample magnetometer (VSM). High saturation magnetization (Ms) and very low coercivity (Hc) are desired for efficient performance of soft magnets. But in this study, Ms decreased with both carbon composition and milling time. It decreased from 195 Am2/kg for the un-milled pure Co to between 178 and 44 Am2/kg for the alloys, with the worst being the 40 at.% C sample milled for 40h. The Ms drop as function of composition made sense, as its related to the volume fraction of cobalt in the alloy. However, the Ms drop as a function of milling time is unclear. In the case of Hc, its value did drop from 12.7 kA/m for the un-milled pure Co to between 7.5 and 1.3 kA/m when the C content is less than 15 at.%. These gains are not significant enough to favor the use of these alloys as soft magnets. Amorphous metal alloys tend to have strengths that are much higher than their crystalline counterparts, and they have hardness values comparable to those of particulate ceramic materials used to reinforce metal matrices. The Co-C amorphous alloy with 40 at.% C that had been milled for 40h (the most stable of all the samples) was used to reinforce cobalt matrix by powder processing methods that included spark plasma sintering (SPS) at temperatures below those of crystallization. Volume fraction ranged from 1 to 20 % reinforcement. The densities of these composites were between 81 and 85 % of theoretical values, hence there were substantial porosities. Despite this the matrix strengthening of the cobalt matrix, as assessed by Vickers microhardness tests, was significant. Hardness increased from 210 HV for unreinforced matrix to 537 HV for the 20 vol.% amorphous. The primary contributor to the strengthening appears to be boundary strengthening by the particles whose average size of about 4 microns is comparable to the grain size of the matrices of the composites. The hardness data fits the Hall Petch-like relationship based on particle spacing. Having a reinforcement particle with a chemistry similar to that of the matrix as is the case in this study, has the potential to improve interfacial bonding and also minimize the difference between the components' coefficient of thermal expansions, which are major issues with the use of ceramics to reinforce metal matrices. The microstructures of the composites indicated good bonding at their interfaces. / Doctor of Philosophy / Magnetic alloys that are amorphous (have no long-range atomic order) exhibit soft magnetic material properties (easily magnetized and demagnetized); hence they play an essential role in electronic and electrical applications. This work investigated the solid-state formation of Cobalt-Carbon (Co-C) amorphous alloys, their thermal stability and magnetic properties. Amorphous Co-C alloys with compositions of 2 to 40 atomic weight % of C were successfully synthesized from elemental Co and C (as graphite) using a mechanical alloying technique (high-energy milling to alloy materials by impact). All alloy compositions were milled for up 40 hours. After 20h of milling some of the alloys (≤ 20 atomic weight % of C) had partially become amorphous, while the higher concentrations had completely become amorphous. After 40h of milling, complete amorphization was observed in all alloy compositions, except for the 2 and 5 atomic weight % of C alloys (2-5 atomic weight % of C). Thermal analyses (Differential Scanning Calorimetry, DSC) of the milled powders showed that alloys with compositions through 20 atomic weight % of C crystalized via a low temperature precipitation of a metastable cobalt carbide from the amorphous phase, followed by a high temperature transformation to a face centered cubic (fcc) cobalt and graphite phase from both the remaining amorphous and the metastable carbide. Activation energy calculations showed that the low temperature carbide precipitation was controlled by carbon diffusion, while the high temperature decomposition reaction forming cobalt and amorphous carbon was controlled by cobalt diffusion. High saturation magnetization (Ms) and very low coercivity (Hc) are desired for efficient performance of soft magnets. Thus, room temperature magnetic measurements of the milled powders were made using vibrating sample magnetometer (VSM). But in this study, Ms decreased with both carbon composition and milling time. The Ms drop as function of composition made sense, as its related to the volume fraction of cobalt in the alloy. However, the Ms drop as a function of milling time is unclear. In the case of Hc, its value did drop from 12.7 kA/m for the un-milled pure Co to between 7.5 and 1.3 kA/m when the C content is less than 15 atomic weight %. These gains are not significant enough to favor the use of these alloys as soft magnets. Amorphous metal alloys tend to have strengths that are much higher than their crystalline counterparts, and they have hardness values comparable to those of particulate ceramic materials used to reinforce metal matrices. The Co-C amorphous alloy with 40 atomic weight % of C that had been milled for 40h was used to reinforce cobalt matrix by powder processing methods (including spark plasma sintering (SPS) at temperatures below those of crystallization). The densities of these composites were between 81 and 85 % of theoretical values and hence there was substantial porosity. Despite this the matrix strengthening of the cobalt matrix, as assessed by Vickers microhardness tests, was significant. The primary contributor to the strengthening appeared to be boundary strengthening by the particles whose average size of about 4 microns was comparable to the grain size of the matrices of the composites. Having a reinforcement particle with a chemistry similar to that of the matrix has the potential to improve interfacial bonding and also minimize the difference between the components' coefficient of thermal expansions, which are major issues with the use of ceramics to reinforce metal matrices. The microstructures of the composites indicated good bonding at their interfaces.

Made available in DSpace on 2017-07-21T20:42:38Z (GMT). No. of bitstreams: 1 JOEVERTON IURP PEREIRA.pdf: 10346836 bytes, checksum: 7a9cb51468fd6451b35517266553a7b7 (MD5) Previous issue date: 2012-09-19 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The alloys of Ni-Cr-Al-C system were synthesized by mechanical alloying, as a proposal of an alternative processing route, in order to improve the microstructure control regarding to a more homogeneous distribution of both Ni3Al precipitates and dispersed chromium carbides, characteristics phases of NiCrAlC alloys. It were chosen 15 compositions, comprised within a range present in the literature, with carbon content variations between 0,5 to 1,5%wt, chromium between 7,5 to 11%wt, and aluminum in the same way as chromium. The milling products were compressed and sintered at 1200°C for a period of 2 hours, and the results of the analysis by Xray diffraction, optical microscopy, scaning electron microscopy (SEM), energy dispersion analysis (EDS) and hardness were compared with some foundry products presents in the literature. The NiCrAlC alloys studied at this work presented nanometric Ni3Al ( phase) precipitates, which provided a hardness that is comparable to that of alloys made by casting followed by heat treating, in spite of exhibit a significant porosity. At the same way, the chromium carbides showed finely dispersed in the matrix, and homogeneously distributed. / Ligas do sistema Ni-Cr-Al-C foram sintetizadas por moagem de alta energia, como proposta de uma rota alternativa de processamento, visando um melhor controle da microestrutura no que concerne a uma distribuição mais homogênea tanto dos precipitados de Ni3Al quanto dos carbetos de cromo dispersos, fases características das ligas NiCrAlC. Foram escolhidas 15 composições compreendidas dentro de uma faixa presente na literatura, com variações de carbono entre 0,5 e,1,5%, de cromo entre 7,5 e 11%, e alumínio da mesma forma que o cromo. Os produtos de moagem foram compactados e sinterizados à 1200°C por um período de 2h, e os resultados das análises de difração de raios x, microscopia ótica e eletrônica, análise por dispersão de raios x e dureza realizadas foram comparados com algumas ligas fundidas presentes na literatura. As ligas NiCrAlC estudadas apresentaram precipitados nanométricos de Ni3Al (fase ), que proporcionaram uma dureza comparável à das ligas produzidas por fusão seguidas de tratamento térmico, apesar de exibirem uma porosidade significativa. Do mesmo modo os carbetos de cromo mostraram-se finamente dispersos na matriz, e homogeneamente distribuídos.

Made available in DSpace on 2017-07-21T20:43:46Z (GMT). No. of bitstreams: 1 Alisson Kwiatkowski da Silva.pdf: 7462256 bytes, checksum: d2fc6ccafb0330bd52456a78fcf372e5 (MD5) Previous issue date: 2015-02-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Iron, chromium and niobium nitrides exhibit very interesting physical, chemical, electrical and/or magnetic properties both from the theoretical point of view and from the applications perspectives. Among the applications, these nitrides have found significant interest as materials for magnetic storage devices or in coating industry. The Fe-N, Cr-N and Nb-N systems consist of several interstitial solutions (α, γ, ε-FexN), chemical compounds (γ’-Fe4N, ζ-Fe2N, Cr2N, CrN, β-Nb2N, γ-Nb4N3, δ-NbN, ε-NbN) and metastable phases (α’ martensite, α”-Fe16N2, δ’-NbN). The present work investigates the viability of nitriding of iron, chromium and niobium powders by high energy cryogenic milling, i.e., the high energy milling of metal powders in liquid nitrogen, that accelerate the fracture process, as compared with the convention technic, and allows that the steady state of milling be reached quickly. In addition, some studies suggest the possibility of nitrogen introduction to the metallic powder during milling. In order to assess the nitriding possibility, iron, chromium and niobium powders were processed by high energy cryogenic milling during different milling times (0,5 h, 1,0 h, 2,0 h and 4,0 h). The milled powders were subsequently characterized by DTGA, DSC, TMA, FEG-SEM and DRX. The iron powder was compacted and sintered at 1200ºC during 1 h (N2 atmosphere), and the samples characterized by optical microscopy, SEM, WDS, Mossbauer spectroscopy, DRX, MFM and nanohardness. The chromium and niobium powders processed during 2 h by high energy cryogenic milling was compacted and sintered, respectively, at 1200ºC and 1300ºC during 1 h (N2 atmosphere), and the sample characterized by DRX. The results suggests that the iron powder can’t be nitrided by high energy cryogenic milling even after heat treatment in nitrogen atmosphere. By the other hand, chromium nitrides can be obtained after heat treatment in nitrogen atmosphere (high temperature nitration) and niobium nitrides can be obtained after heat treatment both in nitrogen and argon atmosphere. / Nitretos de ferro, cromo e nióbio apresentam propriedades físicas, químicas, elétricas e/ou magnéticas altamente interessantes tanto do ponto de vista teórico quanto das aplicações em perspectiva. Entre as suas aplicações, estes nitretos tem encontrado significativo interesse como materiais para dispositivos de armazenamento magnético ou na indústria de revestimentos. Os sistemas Fe-N, Cr-N e Nb-N consistem de várias soluções sólidas intersticiais (α, γ, ε-FexN), compostos químicos (γ’-Fe4N, ζ-Fe2N, Cr2N, CrN, β-Nb2N, γ-Nb4N3, δ-NbN, ε-NbN) e fases metaestáveis (martensita α’, α”-Fe16N2, δ’-NbN). O presente trabalho investiga a viabilidade de nitretação de pós de ferro, cromo e nióbio por moagem criogênica de alta energia, i.e., a moagem de alta energia de pós metálicos em nitrogênio líquido, a qual acelera o processo de fratura, em relação à técnica convencional, possibilitando que as condições estacionárias de moagem sejam atingidas mais rapidamente. Em adição, alguns estudos sugerem a possibilidade de introdução de nitrogênio ao pó metálico durante a moagem. Assim, de modo a se avaliar a possibilidade de nitretação, pós de ferro, cromo e nióbio foram processados por moagem criogênica de alta energia durante diferentes tempos de moagem (0,5 h, 1,0 h, 2,0 h e 4,0 h). Os pós moídos foram subsequentemente caracterizados por DTGA, DSC, TMA, FEG-SEM e DRX. O pó de ferro foi compactado e sinterizado à 1200ºC durante 1 h (atmosfera de N2), e as amostras caracterizadas por microscopia óptica e eletrônica, WDS, Espectroscopia Mössbauer, DRX, MFM e nanodureza. Os pós de cromo e nióbio processados durante 2 h por moagem criogênica de alta energia foram compactados e sinterizados, respectivamente, à 1200ºC e 1300ºC durante 1h (atmosfera de N2), e as amostras caracterizadas por DRX. Os resultados sugerem que o pó de ferro não pode ser nitretado pela técnica de moagem de alta energia criogênica (mesmo após tratamento térmico em atmosfera de nitrogênio) e que, por outro lado, nitretos de cromo podem ser obtidos após tratamento térmico em atmosfera de nitrogênio (nitrogenação em alta temperatura) e que nitretos de nióbio podem ser obtidos após tratamento térmico tanto em atmosfera de nitrogênio quanto em atmosfera de argônio.

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.

<p>This thesis reports on the results of investigating Fe-containing minerals in meteorites, with focus on Fe-Ni minerals and their magnetic properties, along with some synthetic Fe-Ni analogues. The New Halfa meteorite, which fell in Sudan 1994, has been studied using Mössbauer spectroscopy, X-ray diffraction, and electron microprobe analysis techniques, and classified as an ordinary L-type chondrite of petrologic type 4. Mössbauer spectra of taenite-enriched samples from the metal particles of the New Halfa (L4) and Al Kidirate (H6) meteorites identify the following γ (fcc) Fe-Ni phases: the ferromagnetic atomically ordered taenite (<i>tetrataenite</i>) with ~ 50 at % Ni, the ferromagnetic disordered taenite with ~ 50 at % Ni, the low-Ni (~ 25 at %) paramagnetic taenite (<i>antitaenite</i>). The presence of the superstructure of tetrataenite is confirmed by synchrotron X-ray diffraction.</p><p>Fe-rich γ (fcc) Fe-Ni alloys with compositions Fe₇₉Ni₂₁, Fe₇₆Ni₂₄, and Fe₇₃Ni₂₇, which serve as synthetic analogues of antitaenite, are prepared by mechanical alloying and subsequent annealing at 650 °C. The Mössbauer results indicate that these alloys are inhomogeneous and contain a high moment (HM) ferromagnetic Ni-rich phase (> 30 at % Ni) and a low moment (LM) paramagnetic Fe-rich phase, which orders antiferromagnetically at low temperature. The coexistence of these phases is attributed to phase segregation occurring on short range, probably nanometer scale, consistent with the Fe-Ni phase diagram below 400 °C where there is a miscibility gap associated with a spinodal decomposition in alloys with < 50 at % Ni.</p><p>The combined high field Mössbauer spectroscopy and SQUID magnetometry results on these alloys at room temperature indicate large induced local magnetic moments in the paramagnetic part of the sample, which increases with increasing the Ni content. The results, when compared with the high field Mössbauer results on antitaenite from the metal particle of Al Kidirate and New Halfa meteorites may be used to estimate the Ni content of antitaenite in meteorites.</p><p>High pressure ⁵⁷Fe Mössbauer spectroscopy measurements up to ~ 41 GPa have been carried out at room temperature using the diamond anvil cell (DAC) technique in order to investigate the magnetic properties of γ (fcc) ⁵⁷Fe₅₃Ni₄₇ alloy. The results indicate a pressure induced Invar effect at ~ 7 GPa and a non-magnetic or paramagnetic state above 20 GPa, demonstrating the volume dependence of the magnetic moment of γ (fcc) Fe-Ni alloys.</p>