Student Number : 0413336G - MSc(Eng)dissertation - School of Chemical and Metallurgical Engineering - Faculty of Engineering and the Built Environment / This dissertation reports systematic work aimed at determining the plastic deformation mechanisms that led to strains at fracture as high as 4.7% in WC-Co alloys at 1000°C when subjected to 3-point bending tests. The three grades investigated have a Co content of 15wt% and WC grain sizes of 1.3, 0.35 and 0.3 μ m respectively and were received after they were tested in bending. Fractography, macrostructural and microstructural investigations were carried out in attempts to identify the mechanisms leading to the large strains. Techniques used included light microscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and quantitative image analysis. Through comparisons of the results from the three grades at various temperatures, it was possible to establish that the large strain at 1000°C are mainly due to cracking and cobalt drift. During the fractographic investigations it was found that the grades which contained VC as a grain refiner exhibited steps on the WC grains and that fracture propagated preferentially along the stepped WC grain boundaries.

High-temperature processing of rice needs close attention due to the susceptibility of rice grains to fissures. The present study was carried out to redress the lack of information on the quality of rice dried at high-temperatures using a range of drying air temperatures from 160 - 200??C and grain moisture contents varying from 27 to 33%wb. A laboratory type high temperature dryer-oven was developed and constructed, and the performance was compared with commercial fluidized-bed and spouted-bed dryers. The new column type treatment plant, targeted at small-scale rice farmers was designed to reduce milling breakages was tested for high-temperature treatments. Short term drying (160 ??? 180 seconds) of high moisture rough rice at high-temperatures such as 160 - 200??C increased head rice yield by 5 - 8% in long grain rice and 7 - 11% in medium grain rice. The head rice yield increase achieved was very close to the highest potential head rice recovery possible for a given sample. The head rice yield increase was mainly due to a hardened surface layer of the rice kernel, formed by two effects, a surface fusion and surface gelatinization during high-temperature treatment. This stress protection layer is only effective for a short period (1 - 2 minutes) at high temperatures. Tempering of treated grains, either by storing in gunny bags or rapid cooling, can secure the grains to some extent from grain breakage. The highest head rice yield increase was obtained by ceasing the high-temperature effect at the grain moisture level of 24 - 25%wb. The colour and appearance of high-temperature treated grains were closer to those of untreated grains with the toughness closer to that of parboiled rice. The setback values of high-temperature treated rice measured by RVA, which is a preferred character by consumers, were closer to aged rice. High-temperature treatments did not affect the cooking qualities except a slight increase in water absorption. The alterations in the grain due to high-temperature treatment are limited to only for 8 - 9% of the total volume (mainly outer region) of the rice grain, preserving more than 90% of the grain with raw-rice quality. Structural changes such as complexing of amylose ??? lipid, amylose -protein and denaturation of protein play a dominant role on quality changes than gelatinization. A new method introduced to measure the degree of gelatinization of pre-gelatinized rice, using hot paste viscosity by rapid visco analyser (RVA), was successful. The peak viscosity parameter in the RVA was more suitable for measuring the chemical changes in high-temperature treated rice. Spouted-bed drying technology is not suitable for high-temperature treatment due to the unfavourable conditions for the formation of a hardened layer under intermittent heating and cooling. Fluidized-bed dryers could be used for high-temperature drying, but is not cost effective for the small-scale farmer level. The novel type treatment plant was successful in reducing the amount of broken grains to almost zero, increasing the head rice yield by 50 - 120kg per 1000kg of rough rice. It was also effective as a germination arrester, inhibiting the germination ability within a very short period such as 30 - 60 seconds. This equipment is more effective as a treatment Plant as it reduces moisture by only 1.5 - 2.0% at highest head rice yield recovery. An empirical model was successfully established (R2 = 0.99) for grain moisture content (db) and drying temperature during high-temperature processing. In model validation process, a good agreement was found between predicted and experimental data. The modelling between head rice yield and high-temperature drying was unsuccessful (R2 = 0.89) mainly due the interference from other factors such as initial moisture stress due to re-wetting and uncontrolled post treatment drying environment conditions. The study revealed some breakthrough for the rice industry in addition to its quantitative evaluation of increase in head rice yield. 1. Ability to produce grains with twice the toughness of milled untreated rice, without losing colour and appearance. 2. Fissured grains, previously weakened due to moisture-stress (considered as a loss), can be successfully recovered by treating this high-temperature technique. Currently there is no method available to increase the head rice yield of this type of fissured grains except parboiling, which is not widely accepted among consumers. 3. Drying at 200??C drying temperature completely destroyed the viability of seeds within 40 -60 seconds, hence providing a remedy for germination problems in wet harvests. 4. Since high-temperature drying needs wet rough rice, early harvesting can be done which will reduce shattering losses. This enable the farmers to use the field for an inter-seasonal crop which can utilise higher residual soil moisture in the paddy fields compared to other crops.

Graduation date: 1997

Graduation date: 1996

SUMMARY GTD-111 DS is a directionally solidified superalloy currently used in turbine engines. To accurately predict the life of engine components it is essential to examine and characterize the microstructural evolution of the material and its effects on material properties. The as-cast microstructure of GTD-111 is highly inhomogeneous as a result of coring. The current post-casting heat treatments do not effectively eliminate the inhomogeneity. This inhomogeneity affects properties including tensile strength, fracture toughness, fracture path, and corrosion behavior, primarily in terms of the number of grains per specimen. The goal of this work was to link microstructural features to these properties. Quantitative fractography was used to determine that the path of cracks during failure of tensile specimens is influenced by the presence of carbides, which are located in the interdendritic regions of the material as dictated by segregation. The solvus temperature of the precipitate phase, Ni3(Al, Ti), was determined to be 1200C using traditional metallography, differential thermal analysis, and dilatometry. A heat-treatment was designed to homogenize the microstructure for tensile testing that isolates the carbide by dissolving all of the eutectic Ni3(Al, Ti) precipitate phase, which is also found in the interdendritic areas. High temperature oxidation/sulfidation tests were conducted to investigate the corrosion processes involved when GTD-111 DS is utilized in steam and gas combustion turbine engines. The kinetics of corrosion in both oxidizing and sulfidizing atmospheres were determined using thermogravimetric analysis. Additionally, metallography of these samples after TGA revealed a correlation between the presence of grain boundaries and sulfur attack, which led to catastrophic failure of the material under stress-free conditions in a sulfur bearing environment. In summary, this work correlates the inhomogeneous microstructure of GTD-111 DS to tensile fracture, and the corrosion process in turbine engines.

Magnetic bearings have been researched by the National Aeronautics and Space Administration (NASA) for a very long time to be used in wide applications. This research was to assemble and test an axial thrust electromagnetic bearing, which can handle 1000 lb-f of axial thrust load, when rotating at high speed, in a high temperature environment of 1000 0F. This high temperature magnetic bearing system would be used in high performance, high speed and high temperature applications like space vehicles, jet engines and deep sea equipment. An experimental procedure was developed to measure actual load capacity of the designed bearing in the test rig. All the results obtained from the experiment were compiled and analyzed to determine the relation between bearing force, applied current and temperature. The thesis incorporates the assembly, testing of the electromagnetic bearing at various speeds and temperatures and compare predicted to measured force vs. speed, current, gap and temperature. The results showed that the high temperature thrust magnetic bearing is capable of handling 1000 lb-f at 10000F and 5500 rpm.

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published_or_final_version / abstract / toc / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

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