Fe-B熔體可鑄造成網絡狀合金的微觀結構。研究顯示，熔融狀態的Fe₈₄B₁₆在275 K 過冷時將發生形態轉變。實驗結果指出熔融狀態的Fe-B合金存在一亞穏液態互溶區。該互溶區範圍為Fe₈₄B₁₄.到Fe₈₂B₁₈.。Fe-B網絡狀合金的微觀結構，由一個易碎的Fe₃B子網絡和一個具延展性的αFe子網絡組成。因此Fe-B網絡狀合金擁有具吸引性的物理性能。 / 由於Fe₈₄B₁₆網絡狀合金並不存在任何微孔，因此我們可推斷合金在結晶的過程中，兩個子網絡的固體/液體界面將一起生長。而且，在固體/液體界面前並不具有硼原子的濃度梯度。因此我們提出了一個生長模型來分析Fe-B網絡狀合金來自掃瞄電子顯微鏡和透射電子顯微鏡的檢測結果。Fe-B網絡狀合金的結晶動力學和微觀結構均得到解釋。研究顯示，合金中的兩個子網絡均擁有特定的生長方向，並且以樹枝晶的方式來生長。 / Molten Fe₁₀₀-{U+2093}B{U+2093} melts, where x = 14 to 18, can be cast into ingots of network morphology. It was found that there is a morphological transition in molten Fe₈₄B₁₆.with undercooling of 275 K. The experimental results indicate that there is a metastable liquid miscibility gap in undercooled Fe-B melts. The network morphology consists of two interconnected subnetworks, which are αFe subnetwork and Fe₃B subnetwork respectively. The Fe-B network alloys have attractive mechanical properties. / As micropore does not exist in the Fe₈₄B₁₆ network ingot, it is proposed that the solid/liquid interfaces of the two subnetworks advance together during solidification. In addition, there is no composition gradient of boron atoms at the growth front. A growth model is proposed to explain the results by scanning electron microscopy and transmission electron microscopy. It was found that there is special crystallinity in Fe₈₄B₁₆ network ingots. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wong, Tak Cheung = 鐵硼網狀合金的形成和結晶動力學 / 黃德彰. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstracts also in Chinese. / Wong, Tak Cheung = Tie peng wang zhuang he jin de xing cheng he jie jing dong li xue / Huang Dezhang. / Abstract --- p.ii / Acknowledge --- p.iv / List of Table --- p.vii / List of Figures --- p.viii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Phase diagram --- p.1 / Chapter 1.1.1 --- Undercooling --- p.1 / Chapter 1.2 --- Nucleation and Growth --- p.2 / Chapter 1.2.1 --- Homogeneous Nucleation --- p.3 / Chapter 1.2.2 --- Heterogeneous Nucleation --- p.3 / Chapter 1.2.3 --- Growth --- p.6 / Chapter 1.2.3.1 --- Growth of Pure Metal --- p.6 / Chapter 1.2.3.2 --- Solid/Liquid interface stability --- p.7 / Chapter 1.2.3.3 --- Solidification of Single Phase Binary Alloys --- p.8 / Chapter 1.2.3.3.1 --- Equilibrium Solidification --- p.8 / Chapter 1.2.3.3.2 --- Non-Equilibrium Solidification --- p.8 / Chapter 1.2.3.3.3 --- Morphology Change --- p.9 / Chapter 1.2.3.4 --- Solidification of the Binary Eutectic Alloy --- p.10 / Chapter 1.2.3.4.1 --- Growth of Lamellar Eutectics --- p.10 / Chapter 1.2.3.4.2 --- Off-Eutectic Alloys --- p.11 / Chapter 1.3 --- Binary Systems with a Solid Miscibility Gap --- p.11 / Chapter 1.4 --- Phase Separation Mechanisms in a Solid Miscibility Gap --- p.12 / Chapter 1.4.1 --- Nucleation and Growth --- p.12 / Chapter 1.4.2 --- Spinodal Decomposition --- p.13 / Chapter 1.4.4.1 --- The initiation of Spinodal Decomposition --- p.13 / Chapter 1.4.4.2 --- Diffusion Equation of Spinodal Decomposition --- p.14 / Chapter 1.4.4.3 --- Solution to the Modified Diffusion Equation --- p.17 / Figures --- p.18 / References / Chapter Chapter 2 --- Experimental --- p.29 / Chapter 2.1 --- Preparation of fused silica tube --- p.29 / Chapter 2.2 --- Alloying and fluxing --- p.29 / Chapter 2.3 --- Undercooling --- p.30 / Chapter 2.4 --- Sample Preparation --- p.31 / Chapter 2.4.1 --- Cutting, Grinding and Polishing --- p.31 / Chapter 2.4.2 --- Sample preparation for Scanning Electron Microscopy (SEM) --- p.32 / Chapter 2.4.3 --- Sample preparation for Transmission Electron Microscopy (TEM) --- p.32 / Chapter 2.5 --- Microhardness Test --- p.33 / Chapter 2.6 --- Compression Test --- p.33 / Chapter 2.7 --- Microstructure Analysis --- p.34 / Chapter 2.7.1 --- Scanning Electron Microscopy Analysis --- p.34 / Chapter 2.7.2 --- Transmission Electron Microscopy Analysis --- p.34 / Chapter 2.7.3 --- Indexing Diffraction Patterns --- p.34 / Figures --- p.36 / Chapter Chapter 3 --- Formation of Fe-B network alloys --- p.38 / Chapter 3.1 --- Abstract --- p.38 / Chapter 3.2 --- Introduction --- p.39 / Chapter 3.3 --- Experimental --- p.40 / Chapter 3.4 --- Results --- p.42 / Chapter 3.5 --- Discussion --- p.47 / Chapter 3.6 --- Conclusions --- p.48 / Figures --- p.50 / References --- p.69 / Chapter Chapter 4 --- SEM and TEM studies of Fe84B16 70 alloys of network morphology --- p.70 / Chapter 4.1 --- Abstract --- p.70 / Chapter 4.2 --- Introduction --- p.71 / Chapter 4.3 --- Background --- p.71 / Chapter 4.4 --- Experimental --- p.73 / Chapter 4.5 --- Results --- p.74 / Chapter 4.6 --- Discussions --- p.81 / Chapter 4.7 --- Conclusions --- p.85 / Figures --- p.87 / References --- p.106

The microstructural chemistry of the commercial aluminium alloy 7150, containing Al, Zn, Mg, Cu and some trace impurities, was investigated in detail. This alloy is a precipitation hardening alloy, deriving most of its strength from the fine distribution of solute rich precipitates formed during thermal processing. At peak strength this alloy suffers from the common problem of stress corrosion cracking, leading to unpredictable premature failure in the presence of a corrosive environment. Failure is mainly intergranular, thus the structure and chemistry of the grain boundary regions is of interest. A large number of previous investigations have failed to correlate any individual parameter with the stress corrosion cracking behaviour. As the analytical techniques have improved over the last three decades, more complex investigations of the microstructure and the microchemistry have been attempted, in order to more fully characterise the development of this alloy during thermal processing. This thesis presents the results of two of the highest resolution techniques available for microchemical analysis. Scanning transmission electron microscopy X-ray analysis, using a VG-HB501 dedicated scanning transmission electron microscope, enables chemical analysis with a 2nm electron probe, while atom probe analysis, using a VG-FIM100 atom probe with an additional position sensitive detector, enables single atom chemical identification with sub-nanometre spatial resolution. However, both of these techniques have their own experimental limitations which restrict the accuracy of the results obtainable. A detailed description of the many factors limiting both techniques is presented. Combining these techniques has enabled chemical analysis of all the microstructural features present in this alloy on the nanometre scale. A description of the chemical changes occurring during age hardening of this alloy is given in summary.

研究證實，助焊劑能將溶融合冷卻至其溶點之下，仍保持溶液態，亦即達到過冷態。這些溶液因而能夠進液態調幅分。它們凝固之後，會有種互相接的相。在這篇文，這種結構的合簡稱為網絡合。近期研究顯示，白鑄鐵Fe₈₀C₂₀ 亦可憑上述方法，冶成網絡合。其網絡合由種相構成。它們分別是αFe 子網絡及Fe₃C 子網絡，前者柔韌後者堅硬，因此這種網絡合有很優越的機械性能。 / 久之前，有報告研究Fe₇₉.₅B₆.₅C₁₄ 及Fe₈₄B₁₆ 網絡合的結晶過程。這篇文中，研究會集中在過冷Fe₈₀C₂₀ 的結晶過程。其微觀結構分為三區：區由無序網絡構成，十分細小。區之外遍佈高碳的Fe₃(C,B)，由於成份上與Fe₇₉.₅B₆.₅C₁₄的C區相，因此Fe₈₀C₂₀A區外的區稱作C₁ 區及C₂ 區，以相對照。C₁ 區的種子網絡成棒。C₂ 區與Fe₇₉.₅B₆.₅C₁₄ 的C 區一樣，網絡有明顯方向性，且長成樹幹圖案，其Fe₃(C,B) 子網絡屬多晶結構。 / 我們認為合的碳含是引致Fe₈₄B₁₆，Fe₇₉.₅B₆.₅C₁₄，Fe₈₀C₂₀ 三種網絡合，於微觀結構上有差別的原因。高碳的Fe₃(C,B)比低碳的Fe₃(C,B)難生長。以此，我們解釋上述三個合的結晶過程。在Fe₈₀C₂₀ 系統，大碳原子堆積於生長中的固體/液體界面前，這引致細小的A區､C₁ 區的高碳Fe₃(C,B)枝晶出現。 / By employing a fluxing technique, molten alloys can be undercooledsubstantially below its liquidus. The melts carry out phase separation by liquid state spinodal decomposition. After crystallization, solids with interconnected phases are obtained. They are called network alloy in this work. Recently, it is reported that a Fe₈₀C₂₀ eutectic ingot can be cast into a network alloy. The network alloy has two constituent phases. One of which is a ductile αFe subnetwork and the other one is a strong Fe₃C subnetwork. Therefore the network alloy has attractive mechanical properties. / The kinetics of crystallization in undercooled Fe₇₉.₅B₆.₅C₁₄ and Fe₈₄B₁₆ are latelyreported. In this thesis, the kinetics of crystallization in undercooled Fe₈₀C₂₀ alloy was studied. The microstructure can be classified into three zones. Zone A is a small random network. Outside zone A, the microstructure contains high-carbon Fe₃(C,B). In terms of the composition of Fe₃(C,B), they are analogous to the zone C inFe₇₉.₅B₆.₅C₁₄ system. Therefore the two zones outside zone A are named zone C₁ and C₂. Zone C₁ contains dendrites of the two subnetworks. Zone C₂ is the same as thezone C in Fe₇₉.₅B₆.₅C₁₄ systems, which is an aligned network structure showing patterns. The structure of Fe₃(C,B) subnetwork is polycrystalline. / The difference in microstructures between Fe₈₄B₁₆, Fe₇₉.₅B₆.₅C₁₄ and Fe₈₀C₂₀ isattributed to the carbon concentration. The formation of high carbon Fe₃(C,B) is less favoured than low carbon Fe₃(C,B). By this, the kinetics of crystallization in the 3 systems is explained. In Fe₈₀C₂₀, a high concentration of carbon atoms is established in front of the growing solid/liquid interface. This results in the presence of a small zone A and high carbon Fe₃(C,B) dendrites (zone C₁). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Yip, Kai Hou = 因過冷引致相分離的網絡結構Fe₈₀C₂₀合金的結晶動力學 / 葉繼豪. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstracts also in Chinese. / Yip, Kai Hou = Yin guo leng yin zhi xiang fen li de wang luo jie gou Fe₈₀C₂₀ he jin de jie jing dong li xue / Ye Jihao. / Abstract --- p.i / Acknowledgements --- p.v / List of Figures --- p.ix / Chapter Chapter 1: --- Introduction --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Composites --- p.1 / Chapter 1.2.1 --- Different Types of Composites --- p.1 / Chapter 1.2.2 --- Fabrication of Composites --- p.3 / Chapter 1.3 --- Phase Transformation --- p.3 / Chapter 1.4 --- Nucleation --- p.5 / Chapter 1.4.1 --- Homogeneous Nucleation --- p.5 / Chapter 1.4.2 --- Heterogeneous Nucleation --- p.6 / Chapter 1.5 --- Growth --- p.7 / Chapter 1.5.1 --- Solidification in Pure Metals --- p.8 / Chapter 1.5.2 --- Solidification in Alloys --- p.9 / Chapter 1.5.2.1 --- Growth of Single-Phase Alloys --- p.9 / Chapter 1.5.2.2 --- Solidification in Eutectic Binary Alloys --- p.11 / Chapter 1.6 --- Phase Separation by Spinodal Decomposition --- p.12 / Chapter 1.6.1 --- Spontaneous Phase Separation --- p.12 / Chapter 1.6.2 --- Uphill Diffusion --- p.13 / Chapter 1.6.3 --- Modified Diffusion Equation --- p.14 / Chapter 1.6.4 --- Solution to the Equation --- p.16 / Chapter 1.6.5 --- Morphology Resulted from Spinodal Decomposition --- p.17 / Chapter 1.7 --- Aim of This Project --- p.18 / Figures --- p.20 / References --- p.28 / Chapter Chapter 2: --- Experiment --- p.30 / Chapter 2.1 --- Introduction --- p.30 / Chapter 2.2 --- Preparation of Fused Silica Tube --- p.30 / Chapter 2.3 --- Sample Preparation --- p.31 / Chapter 2.3.1 --- Preparation of Eutectic Fe₈₀C₂₀ ingots --- p.31 / Chapter 2.3.2 --- Fluxing with Dehydrated B₂O₃ --- p.32 / Chapter 2.4 --- Optical Microscopy Analysis --- p.33 / Chapter 2.5 --- Scanning Electron Microscopy (SEM) Analysis --- p.34 / Chapter 2.6 --- Transmission Electron Microscopy (TEM) Analysis --- p.34 / Chapter 2.6.1 --- TEM Specimen Preparation --- p.34 / Chapter 2.6.1.1 --- Polishing --- p.35 / Chapter 2.6.1.2 --- Ion Milling --- p.35 / Chapter 2.6.2 --- TEM Characterization: Indexing Diffraction Patterns --- p.36 / Chapter 2.6.3 --- TEM Characterization: Electron Energy Loss Spectrum (EELS) --- p.37 / Figures --- p.39 / References --- p.43 / Chapter Chapter 3: --- Kinetics of crystallization in undercooled phase-separated molten Fe₈₀C₂₀ alloys --- p.44 / Chapter 3.1 --- Introduction --- p.45 / Chapter 3.2 --- Experimental --- p.45 / Chapter 3.3 --- Results --- p.46 / Chapter 3.3.1 --- SEM studies --- p.47 / Chapter 3.3.2 --- TEM studies --- p.49 / Chapter 3.4 --- Discussion --- p.55 / Chapter 3.5 --- Conclusion --- p.61 / Figures --- p.62 / References --- p.92 / Bibliography --- p.93

No description available.

Neste trabalho, avaliou-se o efeito da substituição parcial do Ni pelos elementos Co, Cu e Sn, e do La e Mg pelo Pr em ligas do tipo AB5 para as ligas nominais La0,7Mg0,3Al0,3Mn0,4Cu0,5Ni3,8, La0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8 e La0,7Mg0,3Al0,3Mn0,4Sn0,5Ni3,8, La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8, Pr0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8 sem e com tratamento térmico de 750° e 850°C por 9 e 16 horas. Estas ligas absorvedoras de hidrogênio foram utilizadas como material ativo em eletrodos negativos de baterias de Ni-HM. Avaliou-se a influência destas substituições e do tratamento térmico na microestrutura e nas propriedades eletroquímicas nas ligas. A substituição parcial do Ni pelo Co com o tratamento térmico de 750°C por 16 horas apresentou duas novas fases Al6Mn e PrCo13. Na substituição parcial do Ni pelo Sn formou a fase LaNi2Sn2 na liga. Utilizou-se caracterização de raios-X com refinamento de Rietveld para quantificar as fases em cada composição. Mediu-se a absorção de hidrogênio utilizando um Aparato Sieverts para obtenção das curvas PCT. Observou-se que as ligas La0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8 e La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8 apresentaram as melhores capacidades de absorção de hidrogênio. Verificou-se o comportamento destas ligas na capacidade de descarga, estabilidade cíclica das baterias de Ni-HM. Comparando as ligas, a maior capacidade de descarga medida foi para a substituição parcial do Ni pelo Co, alcançando 406,1 mAh após o tratamento térmico de 850° C por 16 horas. A melhor capacidade de absorção obtida na analise de PCT, foi para a liga La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8 com valor de H/M de 0,980. Também, foi avaliada uma correlação das propriedades eletroquímicas com a capacidade de absorção obtida na analise da curva PCT. / In this work, it was evaluated the effect of the partial substitution of Ni by the elements Co, Cu and Sn and of the La and Mg by the Pr in type AB5 alloys to the nominal alloys La0,7Mg0,3Al0,3Mn0,4Cu0,5Ni3,8, La0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8, La0,7Mg0,3Al0,3Mn0,4Sn0,5Ni3,8, La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8 and Pr0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8, as castting and with annealing treatment of 750 °C and 850 °C for 9 and 16 hours. These hydrogen-absorbing alloys were used as active material on negative electrodes of Ni-HM batteries. The influence of these substitutions and the annealing treatment on the microstructure and on the electrochemical properties in the alloys was evaluated. The partial substitution of Ni by Co with the annealing treatment of 750 °C for 16 hours presented two new phases Al6Mn and PrCo13. In the partial substitution of Ni by Sn formed the LaNi2Sn2 phase in the alloy. It was characterized by X-ray diffraction using Rietveld\'s refinement to quantify the phases in each composition. Hydrogen absorption was measured using the Sieverts apparatus to obtain the PCT curves. It was observed that the alloys La0,7Mg0,3Al0,3Mn0,4Co0,5Ni3,8 and La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8, presented the best capacities of hydrogen absorption. The behavior of these alloys in the discharge capacity, the cyclic stability of the Ni-HM batteries, was verified. Comparing the alloys, the biggest discharge capacity measured was for the partial substitution of Ni by Co alloy, reaching 406.1 mAh after the annealing treatment of 850 °C for 16 hours. The finest absorption capacity obtained in the PCT analysis was for the La0,7Pr0,3Al0,3Mn0,4Co0,5Ni3,8 alloy with an H/M value of 0.980. Also, a correlation of the electrochemical properties with the absorption capacity obtained in the analysis of the PCT curve was evaluated.