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This work was undertaken to investigate the transpassive behaviour of the anodic film on two Fe-Cr alloys, namely Fe18Cr and Fe18Cr2Mo in acidic aqueous media in the pH range 0.5 to 3.8. Two electrochemical techniques were used, namely cyclic voltammetry and chronoamperometry. The two primary experimental variables in the cyclic voltammetric experiments were pH and sweep rate (2 - 800 mV/s). The main variables in the chronoamperometric experiments were the size of the potential step, the number of potential steps and the starting and ending potentials. Secondary experimental variables were temperature (25, 90°C), rotation rate (0, 150 rad/s), and the artificial addition of cations (Fe2+, Fe3+ and Cr3+) to some of the solutions. A voltammetric anodic peak, referred to as peak A, occurs in the transpassive region of the above Fe-Cr alloys, followed by a region of secondary passivity and then oxygen evolution. It was this peak that was investigated by cyclic voltammetric methods. The peak A current response was independent of rotation rate at pH 3.8 but was dependent on rotation rate at pH 0.5 with solutions of intermediate pH showing a gradual change in rotation rate dependence. This indicated a predominantly solid state process in less acidic solutions (pH 2.4 & 3.8) whereas in strongly acidic solutions (pH 0.5) the action of ions in solution must contribute significantly towards peak A processes. A method was developed to correct the peak A current response for the current due to oxygen evolution. The results of this method indirectly confirmed the hypothesis that more than one oxidation process contributes to the peak A current response. A diagnostic plot for diffusion control was applied to the peak height of peak A. The diagnostic involves plotting the peak height over the square root of the sweep rate versus the square root of the sweep rate. A process under diffusion control would give a horizontal line for this diagnostic plot. At pH 0.5 and at slow sweep rates (less than or equal to 60 mV/s) the diagnostic plot gave a positive deviation from the horizontal and this deviation was enhanced as the temperature was increased. As the pH was increased (towards pH 3.8), the deviation from the horizontal at slow sweep rates gradually became negative and this deviation was again enhanced when the temperature was increased. This phenomenon is explained in terms of the role of the hydronium ion. From the addition of Fe2+, Fe3+, and Cr3+ to pH 0.5 and pH 3.8 solutions it was noted that ferrous ions increased the peak A current response more than chromic ions of the same concentration. Ferric ions slightly decreased the peak A current response. Based on these results, reports in the literature, and the apparent role of the hydronium ion, a partial scheme was proposed in order to explain the role of Fe and Cr, from the alloy substrate, in the anodic film in the transpassive region. In chronoamperometric experiments, stepping to the transpassive region confirmed the phenomenon of the rising transient. A quantitative nucleation model - which was based on previous models from the literature - was generated. The model was successfully fitted to two rising transients, one from the pH 3.8, and the other from the pH 0.5 solution. The model also allows for the presence of a pre-existent laver at the starting potential of a chronoamperometric experiment after the electrochemical cleaning procedure. The model incorporates both diffusion controlled and charge transfer controlled steps. A key concept in the model is that of nucleation and "slow death" of corrosion pits growing into the electrode. "Death" of a pit occurs when it is covered by a nucleating and or growing passivating film. The rising transients were only obtained on Fe-Cr alloys (with one exception) when stepping to the transpassive region and also only in solutions where peak A was obtained in a cyclic voltammetric experiment. The exception to this was that in the pH 0.5 solution and at 90°C, rising transients were obtained when stepping to the passive region. This did not occur at 25°C. Rising transients were also obtained on pure iron when stepping to the passive region. In addition to the rising transient, a reverse rising transient was discovered. This reverse rising transient (which generated a cathodic current) was obtained when stepping the potential cathodically from the transpassive region. It was shown that the occurrence of the reverse rising transient was dependent on the presence of a stable, transpassive anodic film before the potential step. One indirect result from the discovery of the reverse rising transient was that it indicates that secondary passivity exists at least 200 mV into the oxygen evolution region. / Thesis (M.Sc.)-University of Natal, 1993.

The behavior of Fe-Cr alloys under irradiation is in part controlled by the characteristics of point defects generated by high energy collision. Radiation enhanced diffusion and radiation induced precipitation are among the mechanisms that lead to changes in the microstructure under irradiation, and are thus controlling effects such as swelling and a' precipitation. Point defects in Fe-Cr alloys are diverse in nature due to their interaction with a variety of local solute configurations. Ab initio results indicate that the magnetic structure of the alloy is critical in determining its energetics. The ability to model these properties with classic potentials is still to be proven. In this work a detailed comparison between ab initio and classic values of a variety of point defects configurations is performed, testing in this way the extent to which classic potentials can be reliably used for radiation damage studies, and evaluating the dependence of point defect formation energies on Cr concentration.

Ferritic chromium steels are important structural materials for future nuclear fission and fusion reactors due to their advantages over traditional austenitic steels, including low swelling rates, better thermal fatigue resistance, and lower thermal expansion coefficients. Radiation-induced segregation or depletion (RIS/RID) of solute atoms at grain boundaries is considered to be a potentially significant phenomenon for structural materials because of its potentially detrimental role in affecting microstructure and furthermore mechanical properties. However, the behaviour of Cr at grain boundaries in ferritic steels is not well understood. Both segregation and depletion of Cr at grain boundary under irradiation have been previously observed and no clear dependency on irradiation condition or alloy type has been presented. Furthermore, ferritic alloys are known to undergo hardening and embrittlement after thermal aging in the temperature range of 300-550DC and this phenomenon is related with a and a' phase separation occurring in the solid solution. However the low temperature a-a' miscibility gap in the currently used phase diagram is extrapolated from high temperature results and conflicts with many experimental observations. To understand the Cr behaviour at gram boundaries in ferritic steels under irradiation, a systematic approach combining SEM/EBSD, FIB specimen preparation and APT analysis has been developed and successfully applied to a Fe- 15.2at%Cr to investigate the effect of pre-irradiation chemistry, grain boundary misorientation, impurities, irradiation damage, irradiation depth, and other possible factors to get a better understanding of RIS/RID phenomena. Both low sigma boundaries and randomly selected high angle boundaries have been investigated in detail. Systematic differences between the behaviour of different classes of boundaries had been observed, and the operating mechanisms are also discussed in this thesis. The maximum separation method has been applied on APT data to study the C- enriched clusters and Cr-enriched clusters, which were not directly visible on the atom maps. The composition of the Cr-enriched clusters was consistent with a' phase and the irradiation was found to accelerate the nucleation rather than the growth of these clusters. Such results provided important information in re- determining the a-a' phase boundary.

Ku, Sin Yee = 添加鎳對網絡結構Fe₈₀C₂₀合金機械性能的影響 / 古倩儀. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Abstracts in English and Chinese. / Ku, Sin Yee = Tian jia nie dui wang luo jie gou Fe₈₀C₂₀ he jin ji xie xing neng de ying xiang / Gu Qianyi. / Abstract --- p.i / Acknowledgements --- p.v / List of Tables --- p.viii / List of Figures --- p.ix / Chapter Chapter 1: --- Introduction --- p.1 / Chapter 1.1 --- Composite Materials --- p.1 / Chapter 1.1.1 --- Parti culate-reinforced Composites --- p.2 / Chapter 1.1.2 --- Fibre-reinforced Composites --- p.2 / Chapter 1.1.3 --- Structural Composites --- p.3 / Chapter 1.1.4 --- Metal Matrix Composites --- p.3 / Chapter 1.2 --- Phase Transformations --- p.4 / Chapter 1.2.1 --- Introduction --- p.4 / Chapter 1.2.2 --- Stability and Equilibrium --- p.4 / Chapter 1.2.3 --- Undercooling --- p.6 / Chapter 1.2.4 --- Solidification of Undercooled Melts --- p.7 / Chapter 1.2.4.1 --- Nucleation --- p.8 / Chapter 1.2.4.1.1 --- Homogeneous Nucleation --- p.8 / Chapter 1.2.4.1.2 --- Heterogeneous Nucleation --- p.9 / Chapter 1.2.4.2 --- Growth --- p.11 / Chapter 1.2.5 --- Binary Systems with a Solid Miscibility Gap --- p.12 / Chapter 1.2.6 --- Phase Separation Mechanisms in a Solid Miscibility Gap --- p.14 / Chapter 1.2.6.1 --- Nucleation and Growth --- p.14 / Chapter 1.2.6.2 --- Spinodal Decomposition --- p.15 / Chapter 1.2.6.2.1 --- Uphill Diffusion --- p.16 / Chapter 1.2.6.2.2 --- Diffusion Equation of Spinodal Decomposition --- p.17 / Chapter 1.2.6.2.3 --- Solution to the Diffusion Equation --- p.19 / Chapter 1.2.7 --- Metastable Liquid Miscibility Gap --- p.21 / Chapter 1.3 --- Mechanical Properties --- p.22 / Chapter 1.3.1 --- Hardness --- p.22 / Chapter 1.3.2 --- Strength --- p.23 / Chapter 1.3.3 --- Ductility --- p.23 / Chapter 1.3.4 --- Strengthening Mechanisms --- p.25 / Chapter 1.3.4.1 --- Grain Boundary Strengthening --- p.25 / Chapter 1.3.4.2 --- Solid Solution Strengthening --- p.26 / Chapter 1.4 --- Objectives of This Project --- p.27 / Figures --- p.29 / References --- p.42 / Chapter Chapter 2: --- Experimental --- p.43 / Chapter 2.1 --- Formation of Bulk Network Nanostructured Alloys --- p.43 / Chapter 2.1.1 --- Preparation of Fused Silica Tubes --- p.43 / Chapter 2.1.2 --- Weighing and Alloying --- p.44 / Chapter 2.1.3 --- Fluxing and Quenching --- p.45 / Chapter 2.2 --- Sample Preparation --- p.46 / Chapter 2.2.1 --- "Cutting, Grinding and Polishing" --- p.46 / Chapter 2.2.2 --- Etching --- p.47 / Chapter 2.2.3 --- Sample Preparation for Transmission Electron Microscopy Analysis --- p.48 / Chapter 2.3 --- Mechanical Tests --- p.49 / Chapter 2.3.1 --- Microhardness Test --- p.49 / Chapter 2.3.2 --- Compression Test --- p.50 / Chapter 2.4 --- Microstructural Analysis --- p.51 / Chapter 2.4.1 --- Scanning Electron Microscopy Analysis --- p.51 / Chapter 2.4.2 --- Transmission Electron Microscopy Analysis --- p.52 / Chapter 2.4.2.1 --- Indexing Diffraction Patterns --- p.52 / Chapter 2.4.2.2 --- Energy Dispersive X-Ray Analysis --- p.53 / Chapter 2.4.2.3 --- Electron Energy Loss Spectroscopy --- p.53 / Figures --- p.55 / References --- p.62 / Chapter Chapter 3: --- Dependence of the Mechanical Properties of FesoC2o Network Alloys on the Addition of Ni --- p.63 / Chapter 3.1 --- Abstract --- p.63 / Chapter 3.2 --- Introduction --- p.64 / Chapter 3.3 --- Experimental --- p.64 / Chapter 3.4 --- Results --- p.66 / Chapter 3.5 --- Discussions --- p.74 / Chapter 3.6 --- Conclusions --- p.79 / Tables --- p.80 / Figures --- p.82 / References --- p.100 / Bibliography --- p.101

Chung, Kam Chuen = 鐵基/鐵三鋁基/鋁基金屬基複合材料的合成和表徵 / 鍾錦銓. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Chung, Kam Chuen = Tie ji/tie san lü ji/lü ji jin shu ji fu he cai liao de he cheng he biao zheng / Zhong Jinquan. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgement --- p.v / Table of contents --- p.vi / List of tables --- p.x / List of figures --- p.xi / Chapter Chapter 1 --- Introduction --- p.1-1 / Chapter 1.1. --- Metal matrix composites (MMCs) --- p.1-1 / Chapter 1.1.1. --- Introduction --- p.1-1 / Chapter 1.1.2. --- Matrix materials --- p.1-1 / Chapter 1.1.3. --- Reinforcements --- p.1-2 / Chapter 1.1.4. --- Fabrication techniques --- p.1-3 / Chapter 1.1.5. --- Applications --- p.1-7 / Chapter 1.2. --- MMCs in this work --- p.1-9 / Chapter 1.2.1. --- Metal matrices --- p.1-9 / Chapter 1.2.2. --- Reinforcements --- p.1-11 / Chapter 1.3. --- Previous works --- p.1-13 / Chapter 1.4. --- Objectives and current works --- p.1-15 / Chapter 1.5. --- Thesis layout --- p.1-16 / References --- p.1-18 / Chapter Chapter 2 --- Methodology and Instrumentation --- p.2-1 / Chapter 2.1. --- Powder metallurgy (PM) --- p.2-1 / Chapter 2.1.1. --- Mixing --- p.2-1 / Chapter 2.1.2. --- Compacting --- p.2-1 / Chapter 2.1.3. --- Sintering --- p.2-2 / Chapter 2.2. --- Sample preparation --- p.2-3 / Chapter 2.2.1. --- Mixing and compacting --- p.2-3 / Chapter 2.2.2. --- Tube furnace sintering --- p.2-3 / Chapter 2.2.3. --- Arc melting --- p.2-4 / Chapter 2.3. --- Sample characterization --- p.2-4 / Chapter 2.3.1. --- DTA and DSC --- p.2-5 / Chapter 2.3.2. --- XRD --- p.2-6 / Chapter 2.3.3. --- SEM --- p.2-6 / Chapter 2.3.4. --- TEM --- p.2-6 / Chapter 2.3.5. --- Microhardness test --- p.2-7 / Chapter 2.3.6. --- VSM --- p.2-7 / References --- p.2-9 / Chapter Chapter 3 --- Synthesis of magnetic hercynite in Fe-based MMC --- p.3-1 / Chapter 3.1. --- Introduction --- p.3-1 / Chapter 3.2. --- Experiments --- p.3-2 / Chapter 3.3. --- Results and discussion --- p.3-2 / Chapter 3.3.1. --- DTA and XRD results --- p.3-2 / Chapter 3.2.2. --- SEM and EDS results --- p.3-3 / Chapter 3.3.3. --- Reaction mechanisms --- p.3-5 / Chapter 3.3.4. --- Thermodynamic model for the reactions --- p.3-8 / Chapter 3.3.5. --- Saturation magnetization --- p.3-9 / Chapter 3.3.6. --- Microhardness --- p.3-11 / Chapter 3.4. --- Conclusions --- p.3-11 / References --- p.3-13 / Chapter Chapter 4 --- Synthesis of reinforced Fe3Al-based MMC --- p.4-1 / Chapter 4.1. --- Introduction --- p.4-1 / Chapter 4.2. --- Experiments --- p.4-2 / Chapter 4.3. --- Results and discussion --- p.4-4 / Chapter 4.3.1. --- AI2O3-reinforced samples --- p.4-4 / Chapter 4.3.2. --- MgO-reinforced samples --- p.4-8 / Chapter 4.3.3. --- MgAl204-reinforced samples --- p.4-11 / Chapter 4.3.4. --- Microhardness and densities --- p.4-14 / Chapter 4.4. --- Conclusions --- p.4-16 / References --- p.4-18 / Chapter Chapter 5 --- Formation of Al-Fe intermetallics in Al-based MMC…… --- p.5-1 / Chapter 5.1. --- Introduction --- p.5-1 / Chapter 5.2. --- Experiments --- p.5-2 / Chapter 5.3. --- Results and discussion --- p.5-3 / Chapter 5.3.1. --- DTA and XRD results --- p.5-3 / Chapter 5.2.2. --- "SEM, TEM and EDS results" --- p.5-4 / Chapter 5.3.3. --- Reaction mechanisms --- p.5-9 / Chapter 5.3.4. --- Phase transformation in solidification --- p.5-11 / Chapter 5.3.5. --- Microhardness --- p.5-13 / Chapter 5.4. --- Conclusions --- p.5-14 / References --- p.5-15 / Chapter Chapter 6 --- Conclusions and future work --- p.6-1 / Chapter 6.1. --- Conclusions --- p.6-1 / Chapter 6.2. --- Future work --- p.6-3

M.S. / Materials Science and Engineering / The goal of this thesis is to determine the corrosion behavior of a new class of advanced materials, namely: titanium carbide reinforced iron composites containing chromium (Fe-Cr-TiC) and chromium and manganese (Fe-Cr-Mn-TiC). TiC has excellent physical properties, such as high melting point, low density, high Vickers hardness value, high electrical resistivity and low thermal expansion. Due to their great wear resistance characteristics and toughness, these materials show potential applications in pulp and paper industries, mining and mineral processing industries, metallurgical industries, cement industries, and electric industries. Some components made of these materials may work under a combined action of corrosion and wear. This study is aimed at determining the corrosion behavior using electrochemical methods such as potentiodynamic and potentiostatic. Two different electrolytes were used in this research: 1N (0.5 M) sulfuric acid (H2SO4) and 1N (0.5 M) sodium sulfate (Na2SO4). The experiments were performed on the following materials; Fe-TiC, Fe-Cr-TiC, Fe-Cr-Mn- TiC and their matrix materials.