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In the automotive industry, Al-Si alloy is widely used for manufacturing of various engine parts. Machinability of die-cast Al-12Si alloy is challenging due to severe abrasion and adhesion wear of the tools. Form tapping is a common method for generating internal threads in engine blocks. It is usually a finishing process on a production line. An unexpected tap failure may lead to significant scrap and high rework costs. The objective of this research was to investigate the wear mechanisms of high-speed steel form taps when machining Al-12Si alloy. This research involved replicating the same process conditions as the industry partner to determine a feasible solution without changing the tap geometry or process parameters. A critical region of wear on the crest was identified where the aluminum adhesion was acute. Intense abrasion wear occurred on the crest and flanks due to hard silicon precipitates. In this study, two methods were proposed for measuring linear and volumetric wear on the chamfered threads. The second and third chamfered threads experienced the most significant wear on the tap. To improve wear-resistance of the form tap, PVD surface coatings were deposited on it. The preliminary tests of 12 surface coatings showed coating-delamination mostly on the critical region. A progressive wear study of the TiAlN coating showed an improvement in tap performance over the ZrN coating currently used. By the 4320th hole, the volumetric wear of the TiAlN coated tap was reduced by nearly 200% and 50% when compared against the uncoated and ZrN coated taps, respectively. / Thesis / Master of Applied Science (MASc)

A series of compositions across the niobium-rhodium- silicon ternary diagram from Nb₃Rh to 75 atomic percent niobium-25 percent silicon, were prepared by arc-melting compacts of high-purity powders. Both x-ray diffractometer and camera techniques were used to analyze the resulting structures. No measurable amount of silicon was found to substitute for rhodium in the Nb₃Rh structure. The 75 percent niobium-25 atomic percent silicon composition contains niobium plus an unidentified phase assumed to be Nb₅Si₃. The Nb-Rh sigma phase extends into the ternary system to at least 10 atomic percent silicon. All ternary alloys investigated contained three phases. These phases were one or more unidentified phases combined with either A₃B or sigma or both. / M.S.

Additive manufacturing (AM) procedures involving the fusion of metal powders or wires tend to produce textured columnar grains, which can have positive effects on the magnetic performance of Fe-Si electrical steels in soft magnetic applications. This work focuses on understanding the impact of energy density (fluence) evolution of grain morphology and texture in Fe-3.8wt%Si and Fe-6wt%Si alloys produced by fusion-based AM. The results show that the development of texture in these alloys is promising for transformers and motor core applications. The desired texture observed in these alloys is obtained in one step unlike conventional manufacturing techniques. The alloys with higher energy fluence exhibited columnar grains with preferential growth orientation along <001> along the build axis, while those with lower energy fluences showed growth orientation in <111> direction. Further, the presence of ordered B2, D03 phases observed in AM processed Fe-6wt%Si improved the overall magnetic performance of these alloys. Additionally, due to relatively high saturation magnetization and sustainability at high operating temperatures, Fe-Co-2V (Hiperco) is an attractive alternative for soft magnetic applications. In this study, Fe-Co-2V alloy is successfully manufactured using fusion based AM techniques and was found to exhibit equiaxed grains in the AM processed conditions. The microstructure was found to have a significant influence on the magnetic properties, leading to intriguing microstructure-property connections. This study will cover these links between microstructure and properties as well as how energy density (fluence) affects the microstructure of the two potential Fe-Si and Fe-Co-2V soft magnetic systems.

This thesis evaluates the suitability of silicon-germanium technology for electronic systems intended for extreme environments, such as ambient temperatures outside of military specification (-55 degC to 125 degC) range and intense exposures to ionizing radiation. Silicon-germanium devices and circuits were characterized at cryogenic and high-temperatures (up to 300 degC) and exposed to ionizing radiation, providing empirical evidence that silicon-germanium is an excellent platform for terrestrial and space-based electronic applications.

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Hong Sin Yi, Grace. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 50-51). / Acknowledgments / Abstract / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Metallic Glass and its application --- p.1 / Chapter 1.2 --- Glass Forming Ability (GFA) --- p.2 / Chapter 1.3 --- Equilibrium Phase --- p.3 / Chapter 1.4 --- Nucleation and Growth --- p.6 / Chapter 1.5 --- Spinodal Decomposition --- p.8 / Chapter 1.6 --- Morphology Comparison between Nucleation and Growth and Spinodal --- p.13 / Figures --- p.14 / References --- p.24 / Chapter Chapter 2 --- Experimental Method / Experimental Method --- p.25 / Figure --- p.29 / References --- p.30 / Chapter Chapter 3 --- Metastable liquid miscibility gap in Pd-Si and its glass forming ability / Introduction --- p.32 / Experimental --- p.33 / Results --- p.34 / Discussion --- p.36 / Figures --- p.40 / References --- p.49 / Bibliography --- p.50

The objective of the research presented in this dissertation is to explore the achievable dynamic range limits in high-performance RF front-ends designed using SiGe HBTs, with a focus on complementary (npn + pnp) SiGe technologies. The performance requirements of RF front-ends are high gain, high linearity, low dc power consumption, very low noise figure, and compactness. The research presented in this dissertation shows that all of these requirements can easily be met by using complementary SiGe HBTs. Thus, a strong case is made in favor of using SiGe technologies for designing high dynamic range RF front-ends. The contributions from this research are summarized as follows: 1. The first-ever comparison study and comprehensive analysis of small-signal linearity (IIP3) for npn and pnp SiGe HBTs on SOI. 2. A novel comparison of large-signal robustness of npn and pnp SiGe HBTs for use in high-performance RF front-ends. 3. A systematic and rigorous comparison of SiGe HBT compact models for high-fidelity distortion modeling. 4. The first-ever feasibility study of using weakly-saturated SiGe HBTs for use in severely power constrained RF front-ends. 5. A novel X-band Low Noise Amplifier (LNA) using weakly-saturated SiGe HBTs. 6. Design and comprehensive analysis of RF switches with enhanced large-signal linearity. 7. Development of novel methods to reduce crosstalk noise in mixed-signal circuits and the first-ever analysis of crosstalk noise across temperature. 8. Design of a very high-linearity cellular band quadrature modulator for use in base-station applications using first-generation complementary SiGe HBTs.

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Mémoire (M.Eng.)-- Université du Québec à Chicoutimi, 1994. / Document électronique également accessible en format PDF. CaQCU