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M-plane non-polar GaN grown on different substrates are analyzed and compared in this thesis. The crystal quality, morphology and spectra of the m-plane non-polar GaN are measured by field-emission electron microscopy (FESEM), high resolution X-ray diffraction (HRXRD), electron back-scatter diffraction (EBSD), and Cathodoluminescence (CL). The temperature dependent and acceleration voltage dependent CL spectra are compared with transmission electron microscopy (TEM) image to understand the concern of CL spectra and dislocation.

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Creep is a time-dependent deformation of materials under stress at elevated temperatures. The phenomenon of creep allows materials to plastically deform gradually over time, even at stress levels below its yield point or below its transformation temperature. The issues involving creep are especially significant for magnesium alloys, since they are susceptible to creep deformation from temperatures as low as 100 ºC, which inhibits their potential application in areas such as automotive engines. The University of Canterbury has developed a significant level of experience and infrastructure in the field of Electron Backscatter Diffraction (EBSD). EBSD allows microstructures to be characterized by imaging the crystal structure and its crystallographic orientation at a given point on a specimen surface, whereby the process can be automated to construct a crystallographic “orientation map” of a specimen surface. In light of this, the creep of magnesium and its alloys was studied using a novel technique, in which a conventional tensile creep test was interrupted at periodic intervals, and the EBSD was used to acquire the crystallographic orientation maps repeatedly on a same surface location at each interruption stages. This technique allows simultaneous measurement of the rate of creep deformation and the evolution of the specimen microstructure at various stages of creep, bringing further insight into the deformation mechanisms involved. This thesis summarizes the study of the microstructural and crystallographic texture evolution during creep of pure magnesium and a creep resistant magnesium alloy Mg- 8.5Al-1Ca-0.3Sr. Pure magnesium exhibit a conventional “power-law” type creep, and although its creep properties are well established in the past literatures, there has been little in terms of reconciliation between the observed creep rates and the underlying deformation mechanisms. The alloy Mg-8.5Al-1Ca-0.3Sr, on the other hand, is a modern die casting alloy used in the automotive industry for engine and gearbox applications, and despite its superior creep resistance, little is known about the microstructural contributions to its creep properties. This research was conducted to provide a link between the creep properties, observed microstructures, and theories of creep deformation by the use of advanced microscopy techniques. For the first time, the detailed, sequential microstructural development of magnesium and its alloys during creep has been revealed.

The effect of billet homogenization on final grain size and texture along with mechanical properties after indirect extrusion of a ZE20 magnesium (Mg) alloy were studied. As-cast and homogenized ZE20 billets were indirectly extruded at 454 degrees C. and an extrusion ratio of 25. Electron backscatter diffraction was used to characterize texture and grain size changes. Quasi-static mechanical testing at room temperature was conducted to determine effects on mechanical properties. The investigation of a thermal treatment on as-cast ZE20 prior to being extruded revealed an increase in ductility as well as a decrease in texture intensity of the homogenized billets.

Cast iron and steel alloys are commonly used for tooling and structural components in Al production, Al die-casting and the aluminizing industry due to their favourable properties including high strength, good formability and low cost. However, the iquid Al corrosion of these materials is one of the crucial concerns in maintaining the efficient production. Al is produced by the electrolytic smelting of alumina. Cast iron and/or cast steel pipes - commonly known as „tapping pipes‟ - are used to extract the liquid Al produced by smelting. Tapping pipes mainly degrade by material loss because liquid Al reacts with nearly all metals. Failure of tapping pipes is a significant contributor to the maintenance expenses; therefore, the primary aim of this research is to develop a material to enhance the life time of tapping pipes. Various test methods were developed in order to examine the effect of molten Al environment on cast iron and steel alloys. The corrosion resistance of these alloys was determined under different conditions of Al flow and temperature. The intermetallic compounds formed by exposing the ferrous to liquid Al were characterized using the Energy Dispersive X-ray Spectroscopy (EDS) and Electron Back Scatter Diffraction (EBSD) techniques. The formation, growth and nature of reaction products were revealed to establish a link to the liquid Al corrosion resistance. A relationship between the chemical composition and liquid Al corrosion resistance of cast irons could not established in the past. In the present work, the corrosion rate was found to depend upon the graphite morphology and fraction of each Fe-C phase of cast iron matrix, which can be controlled by selecting the chemical composition. Moreover, present research suggested the guidelines for producing a cast iron with enhanced liquid Al corrosion resistance. The presence of C-rich phases, graphite flakes and cementite was found to be effective in enhancing the liquid Al corrosion resistance of gray cast irons. Conversely, a higher Si content was found to enhance the susceptibility of cast irons to liquid Al corrosion. The corrosion mechanisms for ferrous alloys in liquid Al are not fully understood. Thus the subsequent analysis of the dissolution data was supported by investigating the reaction products formed between Al and substrate materials. In addition to commonly existent ε-Fe2Al5 and ζ-FeAl3 phases, the formation of Al4C3 and κ-Fe3AlC compounds was confirmed for the first time in the intermetallic layers of ferrous alloys. The Fe3Si phase in the intermetallic layers of high Si cast irons was found, which was believed to facilitate the high corrosion rates of high Si cast irons. Moreover, the mechanism by which C in Fe-substrates affects the liquid Al corrosion resistance can be better understood given the present work. Furthermore, the analysis presented here gives an understanding of the nature, growth and dissolution of intermetallic compounds in several cast iron alloys. Higher Si additions to cast irons played an important role in molten metal corrosion by accelerating the material loss and changing the nature of intermetallic layers. The results of this study clearly indicated that the dissolution and the growth of intermetallic compounds are interrelated and the dissolution and/or spallation of the intermetallic layers may be the primary mode of liquid Al corrosion of ferrous alloys.

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WhisperGenTM heater head components are currently machined from the austenitic stainless steel Sandvik 253MA. The inner surface of the heater heads is subjected to the working gas of the engine, which is a high-pressure, high-temperature nitrogen-based environment with carbonaceous impurities. As a result of this exposure, a scale forms during operation and eventually spalls. This spalled scale causes abrasive damage to piston seals and guides, which leads to pressure loss and eventual failure of the engine. The aim of the present work was to compare the performance of the austenitic alloy 253MA with two alternative alloys, Incoloy 800H and AISI 310, thereby enabling a material recommendation. A literature review provided information about many general aspects of high temperature corrosion in similar alloys. However, little was found about the application of these alloys in environments similar to those experienced by a WhisperGenTM heater head. Therefore, laboratory experiments were conducted to indicate the relative performance characteristics of the three potential alloys (253MA, Incoloy 800H and AISI 310). To overcome the difficulties with testing at high temperatures and pressures, Thermo-Calc™ was used to calculate gas mixtures at 1 bar that approximated the chemical potentials of carbon and nitrogen in the working gas at 24 bar. Comparisons of the different materials were made via weight loss/gain measurements and metallographic analysis, which included optical microscopy, scanning electron microscopy, X-ray mapping and electron back scatter diffraction (EBSD). The laboratory test sample results were also compared with results from heater heads of the same materials that were run in an actual WhisperGenTM engine. The experimental results taken in total indicate that 253MA is the least suitable alloy for the heater head application because it exhibited poor spalling performance, internal oxidation and formation of a large amount of Cr23C6. AISI 310 was shown in all cases to develop the detrimental sigma phase, although this alloy was the least susceptible to internal oxidation. Incoloy 800H was the most resistant alloy to all forms of degradation and is thus recommended for the heater head application.

This diploma thesis deals with the oldest recognized deformation microstructure of felsic granulites of Blanský les (southern Bohemian Massif) in order to understand their lower crustal deformation history later altered during exhumation. Moreover, the study is focused on decomposition of ternary feldspars in the proto-phase of evolution of granulite microstructure. Based on the structural and microstructural analyses of the less developed cleavage I. and the more developed cleavage II., it was possible to distinguish between two deformation structures. The S1 is defined by compositional banding of alternating quartz bands with bands rich in plagioclase, garnets and with porphyroclasts of alkaline feldspars. The S1 cleavage is transposed into the S2 cleavage. During intense reworking of S1 into S2, the quartz bands were decomposed and recrystallized into the ribbons. The feldspar thermometry of the cleavage I. and II. allowed to distinguish the three stages of decomposition of feldspars. A continuous temperature decrease was observed as reflected by the individual microstructures. The quantitative microstructural analysis indicate the shape preferred orientation of the grain boundaries of two-feldspar matrix. The shape preferred orientation of cleavage I. is controlled by the albite rim, however after its...

The giant Detour Lake deposit is a Neoarchean orogenic Au ore body located in the northwestern Abitibi district within the Superior Province. The deposit is situated along the high strain Sunday Lake Deformation Zone (SLDZ) parallel to the broadly E-W trending Abitibi greenstone belt. The lower amphibolite facies assemblage (Act-Bt-Pl-Ep-Alm ±Cal ±Qz ±Ilm) suggests maximum temperatures reaching 550°C, exceeding conditions for pyrite plasticity, an important and ubiquitous Au-bearing phase that may ultimately represent the source for Au at orogenic style Au deposits. The metamorphic assemblage also obscures the relationship between Au and biotite, a visual indicator mineral within Au-rich ore zones. This work combines microstructural, geochemical and geochronological analyses to assess the influence of regional scale deformation and alteration on Au mineralization. EBSD and LA-ICP-MS analyses on pyrite reveal Au enrichment at microstructures supporting a syn- to post-peak metamorphic and deformation-assisted Au upgrading model. EMPA and 40Ar/39Ar analyses on biotite reveal one chemically homogeneous population, which yield variably reset ages that post-date regional metamorphism and Au mineralization.