by Ng Kwok Leung = 納米鈀硅合金之機械特性 / 吳國良. / Thesis submitted in 2000. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Ng Kwok Leung = Na mi ba gui he jin zhi ji xie te xing / Wu Guoliang. / Acknowledgements --- p.ii / Abstract --- p.iii / 摘要 --- p.iv / Chapter Chapter 0 --- Prelude- A brief history of materials --- p.1 / Chapter Chapter 1 --- Introduction --- p.4 / Chapter 1.1 --- Introduction --- p.4 / Chapter 1.2 --- How are nanostructured materials produced? --- p.5 / Chapter 1.3 --- General properties of nanostructured materials --- p.7 / Chapter 1.4 --- Mechanical behaviour of nanostructured materials --- p.8 / Chapter 1.5 --- The solution --- p.12 / References --- p.20 / Figures --- p.22 / Chapter Chapter 2 --- Experimental --- p.30 / Chapter 2.1 --- Specimen preparation --- p.30 / Chapter 2.2 --- Means of analysis --- p.32 / Figures --- p.36 / Chapter Chapter 3 --- Synthesis of large nanostructured Pd82Si18 alloy --- p.39 / Abstract --- p.39 / References --- p.44 / Table and Figures --- p.45 / Chapter Chapter 4 --- Tensile behaviour of nanocrystalline Pd82Si18 alloy --- p.54 / Introduction --- p.54 / Experimental --- p.55 / Results --- p.57 / Discussions --- p.58 / References --- p.59 / Table and Figures --- p.60

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No description available.

B4C is an important engineering ceramic used in a number of different applications. One of the promising applications of B4C is in the nuclear industry. B4C has a high neutron absorption cross-section (600 barns) and that is why it can absorb neutrons without forming long lived radio nuclides. As a result, B4C is extensively used as control rods, shielding material and as neutron detectors in nuclear reactors. During the reactor’s operation, the B4C undergoes severe neutron radiation and defects, such as vacancies and helium bubbles, are generated in the structure. These defects are responsible for the degradation of mechanical performance of B4C and can make this material unsuitable for further exploitation. Therefore, both crystal structure and mechanical properties of B4C were studied before and after radiation, as well as for the case when irradiated by neutrons B4C samples has been annealed in order to heal the defects introduced by the radiation. Fully dense B4C ceramics were produced by hot pressing at 2100ºC, 30MPa, and 45 minutes dwell time. 120 small bars of 2×2.5×25mm were machined according to the MOR bar standard. 40 bars after machining were tested as they were, 80 bars were irradiated with neutrons in neutron source for 3.5 months. 40 out of the 80 irradiated bars were annealed at 400ºC for 1 hour with an attempt to heal the defects possibly introduced by the irradiation. iv 4-point bending strength, SEVNB fracture toughness, and Vickers hardness have been measured on as received B4C, B4C after radiation, and B4C after radiation and annealing. The Weibull parameters were determined for each set of the conditions. The fracture surfaces of the B4C samples before and after radiation as well as after radiation and annealing have also been analyzed using SEM. X-ray diffractometer was used to collect diffraction pattern of the B4C, and Raman spectrometer was used to evaluate the vibrational response of B4C. Thus the effect of neutron radiation and annealing on the mechanical performance and structure of B4C has been analyzed.

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No description available.

No description available.

Luk Wai-kwong. / Title also in Chinese. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1980. / Bibliography: leaves 101-102.

by Chan Chik-cheung. / Thesis (M. Phil.)--Chinese University of Hong Kong, 1980. / Bibliography: l. 126-128.

Friction stir processing (FSP), a solid-state post-processing technique that can provide localized modification and control of microstructures in near-surface layers of metallic components is developed based on the principles of friction stir welding (FSW). In this study, FSP was carried out in two phases. In Phase I, FSP was applied to one inch thick, sand casting A206 aluminum and 0.25 inch A367 bending fatigue sample. Optical microscope, SEM and EDS measurements have been performed to reveal a homogenous microstructure in the stirred zone, in which the porosities were quantitatively reduced, the second phase particles have been broken up and distributed in the Al matrix and there were some new components generated. Thermocouples have been applied to acquire the temperature gradient and thermo history during FSP. A range of material properties, including hardness and tensile measurement in A206, and bending fatigue test in A367 were examined. FSP resulted in an increase in hardness of the nugget compared to the hardness profile of the T4 condition. A significant improvement of the ductility of A206 was found after FSP compared to the ductility of T4 A206, but the FSP process slightly reduced the strength of A206. In Phase II, FSP was used for composite fabrication in the top layer of A206 substrate. The discontinuously reinforced aluminum (DRA) which contained 15% weight percent SiC was introduced into one inch thick sand cast A206 substrate. The surface composite layer is well bonded to the aluminum alloy substrate. Defects were not visible validating that FSP is an effective way for composite fabrication in Al cast alloys.