Дисертації з теми "Magnesium metal matrix nanocomposites"

Le magnésium est le plus léger des métaux, ce qui lui confère un fort potentiel pour être utilisé dans des applications où l’allégement des structures est requis. Pour autant, sa résistance mécanique est très faible, et doit donc être augmentée afin de rivaliser avec d’autres métaux légers tels que l’aluminium ou le titane. Une solution consiste à renforcer le magnésium et ses alliages en introduisant des nanoparticules d’oxydes. De par sa structure cristalline hexagonale compacte, le magnésium présente des propriétés plastiques complexes telles qu’une très forte anisotropie plastique et une prédisposition au maclage. La compréhension de ces mécanismes de déformation est essentielle pour le développement de nanocomposites plus performants en vue d’une utilisation industrielle plus répandue. Dans ce travail, nous nous sommes intéressés à l'élaboration et à la caractérisation de nanocomposites de magnésium pur renforcés par des particules d’oxydes. Différentes techniques ont été testées pour l’élaboration des nanocomposites : la solidification assistée aux ultrasons et le procédé de friction malaxage. L’homogénéité de la dispersion des particules a été vérifiée en 2D par observations en microscopie électronique et également en 3D par tomographie aux rayons X. On montre ainsi que le procédé de friction malaxage permet d'obtenir une distribution homogène des particules, tout en réduisant leur taille. Des essais de traction ont permis de mettre en évidence une augmentation de la limité d’élasticité pour une fraction volumique aussi faible que 0.3 %. Afin d’isoler le rôle des particules de celui des joints de grains sur le comportement plastique du nanocomposite, nous avons réalisé des essais de micro-compression sur des micro-piliers monocristallins usinés par canon à ions focalisés (FIB) dans des échantillons ayant préalablement subis un traitement thermique favorisant la croissance anormale des grains. Différentes orientations cristallines et tailles de micro-piliers ont été testées en vue d'étudier l’influence des particules d’une part sur la plasticité dans le plan basal par mouvement de dislocations et d’autre part sur la déformation par maclage. Contre toute attente, les essais sur monocristaux favorablement orientés pour un glissement basal ne montrent pas l’effet durcissant observé macroscopiquement. Nous attribuons cet effet à la densité initiale de dislocations mobiles, plus importante dans les nanocomposites que dans le magnésium pur, du fait des concentrations de contraintes autour des particules. Ces densités initiales de dislocations mobiles tendent également à supprimer l'effet de taille classiquement observé dans le magnésium pur. Les particules modifient également le mécanisme de déformation par maclage en favorisant l’apparition simultanée de plusieurs macles dans le micro-pilier qui interagissent entre elles au cours de la déformation alors que les micro-piliers de magnésium pur présentent généralement une macle unique (dans certains cas deux) qui envahi tout le monocristal. Ces résultats constituent une contribution originale à la compréhension du rôle des nanoparticules dans la déformation plastique des monocristaux de nanocomposites à base de magnésium<br>Magnesium is the lightest of all structural metals, which gives it a huge potential to be used in applications that require lightweighting. However, its strength needs to be increased in order to compete with other light metals such as aluminum and titanium. A solution is the reinforcement of magnesium and its alloys with the addition of oxide nanoparticles. The hexagonal close packed crystalline structure is responsible for the complex plasticity of magnesium, which is characterized by a very strong plastic anisotropy as well as a complex twinning activity. Understanding these deformation mechanisms is crucial for the development of more performant nanocomposites, allowing widespread industrial application. The present work focuses on the processing and characterization of magnesium based nanocomposites reinforced with oxide particles. Two different processing techniques have been compared: friction stir processing and ultrasound assisted casting. The homogeneity of the dispersion of the reinforcement particles has been verified in 2 and 3 dimensions using electron microscopy and X-ray tomography, respectively. Friction stir processing produces nanocomposites with a more homogeneous dispersion of particles, while reducing their size. Tensile tests have shown strengthening of magnesium with the addition of a volume fraction of only 0.3 % of reinforcement. An annealing heat treatment has then been performed in order to promote abnormal grain growth and single crystalline microcolumns for microcompression testing have been machined by focused ion beam (FIB). The purpose is to isolate the role of particles. The orientation dependent mechanism of deformation and the size effects have been studied in order to understand the influence of the reinforcement particles on the plasticity for orientations favorable for basal slip or tensile twinning. Differently from the strengthening observed macroscopically, no clear strengthening effect is observed on microcolumns when dislocation glide operates. The reason is the higher density of potentially mobile dislocations that is generated due to stress concentrations around the reinforcement particles. In addition, the size effects usually observed on pure magnesium have also been suppressed with the addition of particles. The reinforcement particles seem to affect the twin nucleation stress and twin morphology: particles induce the nucleation of multiple twins inside a microcolumn, whereas in pure magnesium, only one or two twins have been observed. These results provide relevant insights on the role of nanoparticles on the onset of plastic deformation, as well as size effect, in single crystalline magnesium nanocomposites

Magnesium (Mg) Metal matrix composites (MMCs) reinforced by ceramic reinforcements are being developed for a variety of applications in automotive and aerospace because of their strength-to-weight ratio. Reinforcement being considered includes SiC, Al2O3, Carbon fiber and B4C in order to improve the mechanical properties of MMCs. Microstructural and interfacial characteristics of MMCs can play a critical role in controlling the MMCs' mechanical properties. This study was carried out to understand the microstructural and interfacial development between Mg-9wt.Al-1wt.Zn (AZ91) alloy matrix and several reinforcements including SiC, Al2O3, Carbon fibers and B4C. X-ray diffraction, scanning electron microscopy and transmission electron microscopy was employed to investigate the microstructure and interfaces. Al increase in hardness due to the presence of reinforcements was also documented via Vicker's hardness measurements. Thermodynamic consideration based on Gibbs free energy was employed along with experimental results to describe the interfacial characteristics of MMCs. Reaction products from AZ91-SiC and AZ91-Al2O3 interfaces were identified as MgO, since the surface of SiC particles is typically covered with SiO2 and the MgO is the most thermodynamically stable phase in these systems. The AZ91-Carbon fiber interface consist of Al4C3 and this carbide phase is considered detrimental to the mechanical toughness of MMCs. The AZ91-B4C interface was observed to contain MgB2 and MgB2C2. In general, Vicker's hardness increased by 3X due to the presence of these reinforcements.<br>ID: 031001275; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: Yongho Sohn.; Title from PDF title page (viewed February 22, 2013).; Thesis (M.S.M.S.E.)--University of Central Florida, 2012.; Includes bibliographical references (p. 49-51).<br>M.S.M.S.E.<br>Masters<br>Materials Science Engineering<br>Engineering and Computer Science<br>Materials Science and Engineering

Metal matrix nanocomposites (MMNCs) can significantly improve mechanical properties of light alloys such as aluminium alloys beyond the properties of conventional metal matrix composites (where the reinforcement particles are micronsized). Therefore, MMNCs are potentially strong candidates for use in the automotive industry, where the mechanical performance and energy conservation are highly demanded. However, the challenge is to incorporate ceramic nanoparticles into liquid metals due to their large surface – to – volume ratio and poor wettability. In the present study, several nanoparticle feeding mechanisms (the most critical factor in the fabrication of nanocomposites by the ultrasonic method) were explored. SiC and TiB2 nanoparticles with an average diameter between 20nm and 30nm were dispersed through liquid A356 alloy with a green compact nanoparticle incorporation method under ultrasonic cavitation and streaming. The green compact method which has been developed during this project was found to be a promising mechanism achieving the engulfment and relatively effective distribution of the nanoparticles into the melt. Advanced FEGSEM and TEM techniques were used for the microstructural characterisation of the nanocomposites. The microstructural studies reveal that the nanoparticles were embedded into A356 alloy without any observed intermediate phase between the particles and matrix. It has been shown that with only 0.8 wt.% addition of the nanoparticles, the hardness was considerably improved. The nanocomposite billets were reheated into the semi-solid state to be thixoformed at a solid fraction between 0.65 and 0.70 for near net shape components with reduced porosity. The feasibility of thixoforming for aluminium nanocomposites was demonstrated. The microstructures, hardness and tensile mechanical properties of the thixoformed nanocomposites were investigated and compared with those of the asreceived A356 and thixoformed A356 alloys. The tensile properties of the thixoformed nanocomposites were enhanced compared to thixoformed A356 alloy without reinforcement, indicating the strengthening effects of the nanoparticles.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, May, 2020<br>Cataloged from the official PDF of thesis.<br>Includes bibliographical references (pages 203-224).<br>Carbon nanotube (CNT) assemblies are seeing increasing use in engineering applications due to their advantaged, mass-specific physical properties. The high strength-to-weight ratio, electrical and thermal conductivity, and elastic properties make CNTs ideal for many aerospace, automotive, and electrical applications. In structural materials, CNTs are an outstanding candidate to provide nano-reinforcement, both in hybrid composites and nanocomposites, and they have been found to improve the hardness, yield strength, and conductivity of their matrix material. Additional enhancement of these matrices can be realized by using aligned CNTs (A-CNTs) of increased volume fraction, as explored in this work.<br>In this thesis, ceramic matrix nanocomposites (CMNCs), specifically A-CNT/carbon matrix nanocomposites (A/C-NCs), are synthesized by first infusing a carbon precursor resin into A-CNT arrays with CNT volume fractions (v[subscript f]) ranging from 1-30 vol%, and then pyrolyzing the resin to create a carbon matrix around the A-CNTs. Previous work with A/C-NC hardness suggests that such a lightweight, superhard material may rival the density-normalized hardness of diamond at high v[subscript f]. Various processes were refined and tested in this work, yielding microscale void-free A/CNCs up to 30% v[subscript f], with an ~7% improvement in hardness over baseline pyrolytic carbon (PyC) for 1% v[subscript f] A/C-NCs and <10% improvement in hardness for 5% v[subscript f] A-CNTs. A reinfusion (i.e. an initial infusion/pyrolysis cycle with three additional reinfusion/pyrolysis cycles) procedure was developed and implemented, and testing is recommended as immediate future work.<br>Although hardness determination of these reinfused samples is left for future work, the X-ray CT images of the final A/C-NCs after the fourth infusion show excellent infusion and few voids, suggesting that high hardness will be achieved. This thesis also explores and develops synthesis techniques for metal matrix nanocomposites (MMNCs), focusing on an aluminum matrix. As the surface energy of ACNTs is not conducive to wetting by Al (and many other metals), this surface energy must first be altered to allow Al matrix infusion for consistent composite fabrication. TiO₂ is conformally decorated onto ~100 [mu]m-tall A-CNT arrays via atomic layer deposition (ALD). A reduction process for the TiO₂ coating was developed, and a reduction to TiH₂ was determined to be promising, as the TiH₂ will not oxidize prior to Al infusion but can easily be reduced in a vacuum oven apparatus designed specifically to meet the needs of Al infusion.<br>Towards MMNCs, both solder and aluminum matrices are infused into the TiO₂-decorated A-CNTs. The solder experiments yielded mixed success, as the results suggest that both the reduction and the vacuum infusion steps are important factors determining successful wetting. Although Al infusion into an A-CNT array was unsuccessful without a dedicated Al infusion apparatus, molten Al was found to wet Ti well, which suggests that the Ti coating may allow for successful A-CNT wetting. Additional recommendations are provided to further refine the A/Al-NC fabrication process to improve Al infusion.<br>by Amy Ruth Vanderhout.<br>S.M.<br>S.M. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics

High shear mixing offers a promising solution for particle dispersion in a liquid with intensive turbulence and high shear rate, and has been widely used in the chemical, food and pharmaceutical industries. However, a practical high shear mixing process has not yet been adapted to solve the particle agglomeration in metallurgy due to the high service temperature and reactive environment of liquid metal. In this study, the effect of high shear mixing using the newly designed rotor-stator high shear device have been investigated with both Al and Mg matrix composites reinforced with SiC particles through casting. The microstructural observation of high shear treated Al and Mg composites show improved particle distribution uniformity in the as-cast state. Increased mechanical properties and reduced volume fraction of porosity are also obtained in the composite samples processed with high shear. With the melt conditioning procedure developed for twin roll casting process, two distinct solutions has been provided for thin gauge Mg strip casting with advanced microstructure and defect control. The melt conditioning treatment activates the MgO as heterogeneous nuclei of α-Mg through dispersion from continuous films to discrete particles. Thus enhanced heterogeneous nucleation in the twin roll casting process not only refines the α-Mg grain size but also eliminates the centre line segregation through equiaxed grain growth and localized solute distribution. The grain refinement of the α-Mg through SiC addition has also been studied through EBSD and crystallographic approaches. Two reproducible and distinct crystallographic orientation relationships between α-SiC (6H) and α-Mg have been determined: [1010]SiC//[2113]Mg, (0006)SiC//(1011)Mg, (1216)SiC//(2202)Mg and [0110]SiC//[1100]Mg, (0006)SiC// (0002)Mg, (2110)SiC//(1120)Mg.

Foundry aluminum alloys play a fundamental role in several industrial fields, as they are employed in the production of several components in a wide range of applications. Moreover, these alloys can be employed as matrix for the development of Metal Matrix Composites (MMC), whose reinforcing phases may have different composition, shape and dimension. Ceramic particle reinforced MMCs are particular interesting due to their isotropic properties and their high temperature resistance. For this kind of composites, usually, decreasing the size of the reinforcing phase leads to the increase of mechanical properties. For this reason, in the last 30 years, the research has developed micro-reinforced composites at first, characterized by low ductility, and more recently nano-reinforced ones (the so called metal matrix nanocomposite, MMNCs). The nanocomposites can be obtained through several production routes: they can be divided in in-situ techniques, where the reinforcing phase is generated during the composite production through appropriate chemical reactions, and ex situ techniques, where ceramic dispersoids are added to the matrix once already formed. The enhancement in mechanical properties of MMNCs is proved by several studies; nevertheless, it is necessary to address some issues related to each processing route, as the control of process parameters and the effort to obtain an effective dispersion of the nanoparticles in the matrix, which sometimes actually restrict the use of these materials at industrial level. In this work of thesis, a feasibility study and implementation of production processes for Aluminum and AlSi7Mg based-MMNCs was conducted. The attention was focused on the in-situ process of gas bubbling, with the aim to obtain an aluminum oxide reinforcing phase, generated by the chemical reaction between the molten matrix and industrial dry air injected in the melt. Moreover, for what concerns the ex-situ techniques, stir casting process was studied and applied to introduce alumina nanoparticles in the same matrix alloys. The obtained samples were characterized through optical and electronic microscopy, then by micro-hardness tests, in order to evaluate possible improvements in mechanical properties of the materials.

Philosophiae Doctor - PhD<br>The main objective of this study was to advance kinetic performances of formation and decomposition of magnesium hydride by design strategies which include high energy ball milling in hydrogen (HRBM), in combination with the introduction of catalytic/dopant additives. In this regard, the transformation of Mg → MgH2 by high energy reactive ball milling in hydrogen atmosphere (HRBM) of Mg with various additives to yield nanostructured composite hydrogen storage materials was studied using in situ pressure-temperature monitoring that allowed to get time-resolved results about hydrogenation behaviour during HRBM. The as-prepared and re-hydrogenated nanocomposites were characterized using XRD, high-resolution SEM and TEM, as well as measurements of the mean particle size. Dehydrogenation performances of the nanocomposites were studied by DSC / TGA and TDS; and the re-hydrogenation behaviour was investigated using Sieverts volumetric technique.

Cette thèse est consacrée à l'étude de composés riches en magnésium innovants destinés au stockage solide de l'hydrogène. Le but est de déstabiliser l'hydrure de Mg et d'accélérer sa cinétique de sorption par des effets d'alliage et de nano-structuration. La première famille de composés concerne les phases pseudo-binaires Mg6Pd1-xMTx (MT = Ni, Ag, Cu). Leurs propriétés structurales et les effets de substitution du Pd ont été étudiés par diffraction des rayons X, microscopie électronique à balayage et microsonde de Castaing. Les propriétés thermodynamiques et cinétiques d'hydrogénation de ces matériaux ont ensuite été déterminées par réaction solide-gaz. Différents mécanismes d'hydrogénation sont mis en jeu en fonction de l'élément de substitution. La nature des phases formées lors de la réaction d'hydrogénation modifie la stabilité des systèmes métal-hydrogène. Ainsi, la transformation de métal à hydrure est caractérisée par au moins deux plateaux de pression. Le premier plateau a lieu à une pression proche de celle de Mg/MgH2, alors que le second se produit à pression plus élevée. La détermination des valeurs d'enthalpie et d'entropie de réaction ont permis de quantifier la déstabilisation atteinte. Les meilleures cinétiques de désorption sont obtenues pour l'alliage au Ni, grâce à l'effet catalytique de la phase Mg2NiH4 formée lors de l'hydrogénation. La seconde approche vise à combiner les effets d'alliage et de nano-structuration. Des nanoparticules de Mg6Pd atteignant des tailles aussi petites que 3 nm sont confinées dans des matrices carbonées nano-poreuses. En comparant leurs propriétés d'hydrogénation à celles de l'alliage massif équivalent, on démontre non seulement que la cinétique de (dés)hydrogénation des nanoparticules est bien plus rapide, mais aussi que leur état hydrogéné est déstabilisé. Enfin, des nano-composites MgH2-TiH2 ont été synthétisés par broyage mécanique sous atmosphère réactive. L'ajout d'un catalyseur (TiH2) et la nano-structuration du Mg permettent de considérablement accélérer les cinétiques d'absorption et désorption d'hydrogène dans le Mg. Afin de comprendre le rôle de la phase TiH2 sur les propriétés cinétiques remarquables de ces nano-composites, leurs propriétés structurales ont été déterminées par diffraction des rayons X et des neutrons. L'existence d'une interface cohérente entre les phases Mg et TiH2 est d'importance majeure pour faciliter la mobilité de H au sein du nano-composite. De plus, il est démontré que les inclusions de TiH2 freinent la croissance de grain de Mg/MgH2, permettant ainsi de maintenir la nano-structuration des composés lors de leur cyclage<br>This thesis is dedicated to the study of novel magnesium-rich compounds for solid state hydrogen storage. The aim is to destabilize Mg hydride and accelerate its sorption kinetics by alloying and nanostructuration. The first family of compounds concerns the Mg6Pd1-xTMx (TM = Ni, Ag, Cu) pseudo-binary phases. Their structural properties and the effects of Pd substitution have been studied by X-ray diffraction, scanning electron microscopy and electron microprobe analyses. Their thermodynamics and kinetics of hydrogenation have been determined by solid-gas reaction. Different hydrogenation mechanisms take place depending on the substituting element. The stability of the metal-hydrogen system is altered by the nature of the phases formed during hydrogenation reaction. Thus, metal to hydride transformation is characterized by at least two absorption plateau pressures. The pressure of the first plateau is similar to that of Mg/MgH2 while the second one occurs at higher pressure. The enthalpy and entropy of reaction are determined to quantify the destabilizing effect of Pd by TM substitution. Best desorption kinetics are found for the Ni containing alloy thanks to the catalytic effect of the Mg2NiH4 phase formed on hydrogenation. The second approach aims to combine alloying with nanostructuration effects. Nanoparticles of Mg6Pd as small as 3 nm are confined into nanoporous carbon matrix. By comparing their hydrogenation properties with those of the bulk alloy, we demonstrate that not only the (de)hydrogenation kinetics are much faster for the nanoparticles, but also that their hydrided state is destabilized. Finally, MgH2-TiH2 nanocomposites were synthesized by mechanical milling under reactive atmosphere. The addition of a catalyst (TiH2) and Mg nanostructuration allow strongly accelerating the sorption kinetics of hydrogen in Mg. To understand the role of the TiH2 phase on the outstanding kinetics of these nanocomposites, their structural properties have been determined by X-ray and neutron diffraction. The existence of a coherent interface between Mg and TiH2 phases is of major importance to facilitate H-mobility within the nanocomposite. Furthermore, it is shown that the TiH2 inclusions inhibit the Mg/MgH2 grain growth, thus maintaining the composites nanostructure during their cycling

Metal matrix composites (MMCs) are emerging as advanced engineering materials for application in aerospace, defence, automotive and consumer industries (sports goods etc.). In MMCs, a metallic base material is reinforced with ceramic fiber, whisker or particulate in order to achieve a combination of properties not attainable by either constituent individually. Aluminium or its alloy is favoured as metallic matrix material because of its low density, easy fabricability and good engineering properties. In general, the benefits of aluminium metal matrix composites (AMCs) over unreinforced aluminium alloy are increased specific stiffness, improved wear resistance and decreased coefficient of thermal expansion. The conventional reinforcement materials for AMCs are SiC and AI2O3. In the present work, boron carbide (B4C) particles of average size 40μm were chosen as reinforcement because of its higher hardness (very close to diamond) than the conventional reinforcement like SiC, AI2O3 etc. and of its density (2.52 g cm"3) very close to Al alloy matrix. In addition, due to high neutron capture cross-section of 10B isotope, composites containing B4C particle reinforcement have the potential for use in nuclear reactors as neutron shielding and control rod material. Al-5%Mg alloy was chosen as matrix alloy to utilize the beneficial role of Mg in improving wettability between B4C particles and the alloy melt. (Al-5%Mg)-B4C composites containing 10 and 20 vol% B4C particles were fabricated. For the purpose of inter-comparison, unreinforced Al-5%Mg alloy was also prepared and characterized. The Stir Cast technique, commonly utilized for preparation of Al-SiC, was adapted in this investigation.The Composites thus prepared was subsequently hot extruded with the objective of homogenization and healing minor casting defects. Finally the unreinforced alloy and its composites were characterized in terms of their microstructure, mechanical and thermo-physical properties, sliding wear behaviour and neutron absorption characteristics. The microstructures of the composites were evaluated by both optical microscope and scanning electron microscope (SEM). The micrographs revealed a relatively uniform distribution of B4C particles and good interfacial integrity between matrix and B4C particles. The hot hardness in the range of 25°C to 500°C and indentation creep data in the range of 300°C to 400°C show that hot hardness and creep resistance of Al-Mg alloy is enhanced by the presence of B4C particles. Measurement of coefficient of thermal expansion (CTE) of composites and unreinforced alloy upto 450°C showed that CTE values decrease with increase in volume fraction of reinforcement. Compression tests at strain rates, 0.1, 10 and 100 s-1 in the temperature range 25 - 450 °C showed that the flow stress values of composites were, in general, greater than those of unreinforced alloy at all strain rates. These tests also depicted that the compressive strength increases with increase in volume fraction of reinforcements. True stress values of composites and unreinforced alloy has been found to be a strong function of temperature and strain rate. The kinetic analysis of elevated temperature plasticity of composites revealed higher stress exponent values compared to unreinforced alloy. Similarly, apparent activation energy values for hot deformation of composites were found to be higher than that of self-diffusion in Al-Mg alloy. Tensile test data revealed that the modulus and 0.2% proof stress of composites increase with increase in volume fraction of the reinforcements. Composites containing 10%BUC showed higher ultimate tensile strength values (UTS) compared to unreinforced alloy. However, composites with 20%B4C showed lower UTS compared to that of the unreinforced alloy. This could be attributed to increased level of stress concentration and high level of plastic constraint imposed by the reinforcing jparticles or due to the presence solidification-induced defects (pores and B4C agglomerates ). Sliding wear characteristics were evaluated at a speed of 1 m/s and at loads ranging from 0.5 to 3.5kg using a pin-on-disc set up. Results show that wear resistance of Al-5%Mg increases with the addition of B4C particles. Significant improvement in wear resistance of Al-5%Mg is achieved with the addition of 20% B4C particles. SEM examination of worn surfaces showed no pull-out of reinforcing particles even at the highest load of 3.5 kg, thus confirming good interfacial bonding between dispersed B4C particles and Al alloy matrix. The neutron radiography data proved that (Al-5%Mg)-B4C composites possess good neutron absorbing characteristics. From the experimental data evaluated in the "study, it may be concluded that (Al-5%Mg)-B4C composites could be a candidate material for neutron shielding and control rod application. The enhanced elevated temperature-strength and favourable neutron absorption characteristics of these composites are strong points in favour of this material.

Thesis (M.S.)--University of Wisconsin--Madison, 2007<br>Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 60-62).

碩士<br>國立交通大學<br>材料科學(工程)研究所<br>82<br>The effect of adding magnesium on the aging behavior of Al-Zn- Mg alloy reinforced with aluminum (Al2O3) was studied using differential scanning calorimeter(DSC) technique, hardness measurement. The magnesium contents were varied from 1.23wt% to 2.97wt%. The addition of magnesium was found to increase the amount of η'-phase formation in composites. The formation enthalpy of composites was 0.932cal/g and 1.375cal/g for lower magne- sium content(1.23wt%) and higher magnesium content(2.97 wt%) respectively. The time needed for the saturation of precipiat- ing in the composites changed from 12 hr to 48hr as the magne- sium content increased from 1.23wt% to 2.97wt%. The maximum hardness occurred in composites with 2.97wt% Mg that contained a maximum amounts of η'-phase precipitates. The hardness of the composites was always less than that of monoli- thic alloys because of alumina fibers caused suppression of η' formation in composites. Difference of wearability between composites and Al-Zn-Mg alloy was also performed in this study. The weight loss decreased with increasing the volume fraction of alumina and with increasing the magnesium content.

Choi Ching Yeung = 鎂和氧化銀粉反應制備鎂基復合材料 / 蔡靜洋.<br>Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.<br>Includes bibliographical references.<br>Text in English; abstracts in English and Chinese.<br>Choi Ching-Yeung = Mei he yang hua yin fen fan ying zhi bei mei ji fu he cai liao / Cai Jingyang.<br>Abstract --- p.i<br>摘要 --- p.iii<br>Acknowledgement --- p.iv<br>List of Figures --- p.xi<br>List of Tables --- p.xvi<br>Chapter Chapter 1 --- Introduction --- p.1.1<br>Chapter 1.1 --- Metal matrix composites (MMCs) --- p.1.1<br>Chapter 1.1.1 --- Introduction --- p.1.1<br>Chapter 1.1.2 --- Reinforcement in metal-matrix composites --- p.1.1<br>Chapter 1.1.2.1 --- Particle-reinforced composites --- p.1.2<br>Chapter 1.1.2.2 --- Laminated composites --- p.1.2<br>Chapter 1.1.2.3 --- Fibre-reinforced composites --- p.1.2<br>Chapter 1.1.3 --- Conventional fabrication of metal matrix composites --- p.1.6<br>Chapter 1.1.3.1 --- Liquid state processes --- p.1.6<br>Chapter 1.1.3.1.1 --- Liquid infiltration --- p.1.6<br>Chapter 1.1.3.1.2 --- Pressure infiltration --- p.1.8<br>Chapter 1.1.3.1.3 --- Spray forming --- p.1.10<br>Chapter 1.1.3.2 --- Solid-state process --- p.1.11<br>Chapter 1.1.3.2.1 --- Powder consolidation --- p.1.11<br>Chapter 1.1.3.2.2 --- Diffusion bonding --- p.1.11<br>Chapter 1.1.3.2.3 --- In-Situ processes --- p.1.13<br>Chapter 1.1.4 --- Properties of metal matrix composites --- p.1.13<br>Chapter 1.2 --- Magnesium based metal matrix composites --- p.1.14<br>Chapter 1.2.1 --- Properties of Mg-based metal matrix composites --- p.1.14<br>Chapter 1.2.2 --- Application of Mg-based metal matrix composites --- p.1.16<br>Chapter 1.3 --- Magnesium and silver (I) oxide --- p.1.16<br>Chapter 1.3.1 --- Magnesium --- p.1.16<br>Chapter 1.3.2 --- Silver (I) oxide --- p.1.17<br>Chapter 1.4 --- Pervious works --- p.1.17<br>Chapter 1.5 --- Aims of Current works --- p.1.18<br>Chapter 1.6 --- Thesis layout --- p.1.20<br>References --- p.1.21<br>Chapter Chapter 2 --- Methodology and fabrication --- p.2.1<br>Chapter 2.1 --- Introduction --- p.2.1<br>Chapter 2.1.1 --- Powder metallurgy --- p.2.1<br>Chapter 2.1.1.1 --- Powder production --- p.2.3<br>Chapter 2.1.1.2 --- Powder consolidation --- p.2.4<br>Chapter 2.1.1.3 --- Sintering process --- p.2.6<br>Chapter 2.1.1.4 --- Properties of sintered parts --- p.2.10<br>Chapter 2.2 --- Sample preparation --- p.2.12<br>Chapter 2.3 --- Characterization methods --- p.2.13<br>Chapter 2.3.1 --- Thermal analysis - Differential Thermal Analysis (DTA) --- p.2.13<br>Chapter 2.3.2 --- Phase determination - X-ray Powder Diffractometry (XRD) --- p.2.13<br>Chapter 2.3.3 --- Microstructure analysis --- p.2.14<br>Chapter 2.3.3.1 --- Scanning electron microscopy (SEM) --- p.2.14<br>Chapter 2.3.3.1 --- Transmission electron microscopy (TEM and HRTEM) --- p.2.14<br>Chapter 2.3.4 --- Physical property - Thermomechanic analyser (TMA) --- p.2.14<br>Chapter 2.3.5 --- Mechanical property - Vickers hardness measurement --- p.2.15<br>References --- p.2.16<br>Chapter Chapter 3 --- Thermal analysis of Mg-Ag20 --- p.3.1<br>Chapter 3.1 --- Introduction --- p.3.1<br>Chapter 3.2 --- Experiments --- p.3.2<br>Chapter 3.3 --- Results --- p.3.2<br>Chapter 3.3.1 --- DTA curve of the Mg-30wt%Ag20 --- p.3.5<br>Chapter 3.3.2 --- DTA curve of the pure Ag20 powder --- p.3.7<br>Chapter 3.4 --- Discussions --- p.3.7<br>Chapter 3.5 --- Conclusions --- p.3.10<br>References --- p.3.11<br>Chapter Chapter 4 --- Fabrication and characterization of Mg-£-AgMg3 MMCs --- p.4.1<br>Chapter 4.1 --- Introduction --- p.4.1<br>Chapter 4.2 --- Experiments --- p.4.2<br>Chapter 4.2.1 --- Sample preparation --- p.4.2<br>Chapter 4.2.1.1 --- Effect of temperature --- p.4.2<br>Chapter 4.2.1.2 --- Effect of time --- p.4.3<br>Chapter 4.2.1.3 --- Effect of composition --- p.4.3<br>Chapter 4.2.1.4 --- Effect of cooling rate --- p.4.3<br>Chapter 4.3 --- Results --- p.4.4<br>Chapter 4.3.1 --- Samples sintered at different temperatures --- p.4.4<br>Chapter 4.3.1.1 --- XRD spectra --- p.4.4<br>Chapter 4.3.1.2 --- SEM micrographs and EDS analysis --- p.4.7<br>Chapter 4.3.1.3 --- Discussions --- p.4.11<br>Chapter 4.3.2 --- Sample with different dwelling times --- p.4.13<br>Chapter 4.3.2.1 --- SEM micrographs --- p.4.13<br>Chapter 4.3.2.2 --- Weight loss against dwelling time --- p.4.16<br>Chapter 4.3.2.3 --- Discussions --- p.4.18<br>Chapter 4.3.3 --- Samples with varied weight percentage of Ag2O --- p.4.19<br>Chapter 4.3.3.1 --- SEM micrographs --- p.4.19<br>Chapter 4.3.3.2 --- Discussions --- p.4.22<br>Chapter 4.3.4 --- Samples with different cooling rate --- p.4.23<br>Chapter 4.3.4.1 --- XRD patterns --- p.4.23<br>Chapter 4.3.4.2 --- Optical photographs --- p.4.25<br>Chapter 4.3.4.3 --- SEM micrographs --- p.4.28<br>Chapter 4.3.4.4 --- TEM micrographs and high-resolution TEM micrographs…… --- p.4.31<br>Chapter 4.3.4.5 --- Discussions --- p.4.35<br>Chapter 4.3.4.5.1 --- XRD spectra --- p.4.35<br>Chapter 4.3.4.5.2 --- Optical photographs --- p.4.35<br>Chapter 4.3.4.5.3 --- SEM micrographs --- p.4.35<br>Chapter 4.3.4.5.4 --- TEM micrographs --- p.4.36<br>Chapter 4.4 --- Conclusions --- p.4.37<br>References --- p.4.38<br>Chapter Chapter 5 --- Mechanical hardness and thermal expansion of Mg-Ag20 --- p.5.1<br>Chapter 5.1 --- Introduction --- p.5.1<br>Chapter 5.2 --- Mechanical properties --- p.5.1<br>Chapter 5.2.1 --- Experiments --- p.5.1<br>Chapter 5.2.2 --- Results --- p.5.2<br>Chapter 5.2.3 --- Discussions --- p.5.8<br>Chapter 5.3 --- Thermal properties --- p.5.9<br>Chapter 5.3.1 --- Experimental details --- p.5.9<br>Chapter 5.3.2 --- Results --- p.5.10<br>Chapter 5.3.3 --- Discussions --- p.5.12<br>Chapter 5.4 --- Conclusions --- p.5.13<br>References --- p.5.14<br>Chapter Chapter 6 --- Conclusions and future works --- p.6.1<br>Chapter 6.1 --- Conclusions --- p.6.1<br>Chapter 6.2 --- Further works --- p.6.2

碩士<br>國立中正大學<br>機械工程學系暨研究所<br>99<br>The mechanical characteristics of magnesium metal matrix composites (Mg MMCs) are superior to those of the pure metal alloy; Adding the reinforcement, such as particles, shot fibers, and continuous fibers, to the metal matrix can improve the composite’s mechanical properties. SiCP is dissolved into AZ61 by the stir-casting method, and then the Mg-based composite is fabricated. The Mg-based composites are extruded under the conditions of 300oC and 400oC and the material plastic flow inside the die is analyzed with the finite element simulations. After extrusion, solid solution treatment of the products are conducted to improve their mechanical properties. Eventually, the mechanical properties of the composite before and after the extrusion with aging treatment are discussed. From the experimental results, it is known that the yielding strength and hardness of AZ61-Billet are 58MPa and 55.94HV, respectively. The yielding strength and hardness were improved by 7.4% and 5.4%, respectively, for 5wt%SiCp Billet. The yielding strength and hardness of AZ61-tube are 129MPa and 63.9HV, respectively, under extrusion temperature of 400oC, and its yielding strength and hardness are improved by 9.3% and 3.1%, respectively, after adding 5wt%SiCp; whereas, 10.9% and 8.9% increases are obtained under extrusion temperature of 300oC. After T5 aging treatment, the yielding strength and hardness of AZ61-tube are further increased by 10.1% and 8.3% under extrusion temperature of 400oC; and 12.4% and 18.4% with 300oC. With extrusion temperature of 400oC and T5 aging treatment, the ultimate strength obtained is 315MPa, the yielding strength is 145MPa, the ductility is 15.6%, and the hardness is 75.63HV.

by Man-Ling Wong.<br>Thesis (M.Phil.)--Chinese University of Hong Kong, 2002.<br>Includes bibliographical references.<br>Text in English; abstracts in English and Chinese.<br>by Man-Ling Wong.<br>Acknowledgments --- p.i<br>Abstract --- p.ii<br>摘要 --- p.iv<br>Table of contents --- p.v<br>Chapter Chapter 1 --- Introduction --- p.1-1<br>Chapter 1.1 --- Overview of metal matrix composites --- p.1 -1<br>Chapter 1.1.1 --- Types of MMCs --- p.1-1<br>Chapter 1.1.2 --- The matrices --- p.1 -2<br>Chapter 1.1.2.1 --- Mg-based matrix --- p.1 -2<br>Chapter 1.1.2.2 --- Al-based matrix --- p.1-2<br>Chapter 1.1.2.3 --- Ti-based matrix --- p.1 -3<br>Chapter 1.2 --- Fabrication methods of MMCs --- p.1 -3<br>Chapter 1.2.1 --- Solid-liquid reaction --- p.1-4<br>Chapter 1.2.2 --- Vapor-liquid-solid (VLS) reaction --- p.1 -4<br>Chapter 1.2.3 --- Solid-Solid reaction --- p.1-5<br>Chapter 1.2.4 --- Liquid-liquid reaction --- p.1-5<br>Chapter 1.3 --- Applications of MMCs --- p.1 -6<br>Chapter 1.4 --- Previous works versus our work --- p.1 -7<br>Chapter 1.5 --- Layout of the thesis --- p.1 -8<br>Figures --- p.1-9<br>References --- p.1-10<br>Chapter Chapter 2 --- Methodology and Instrumentation --- p.2-1<br>Chapter 2.1 --- Introduction --- p.2-1<br>Chapter 2.2 --- Powder metallurgy --- p.2-1<br>Chapter 2.3 --- Sample preparation --- p.2-2<br>Chapter 2.3.1 --- Cold pressing --- p.2-2<br>Chapter 2.3.2 --- Sintering --- p.2-3<br>Chapter 2.4 --- Characterization methods --- p.2-4<br>Chapter 2.4.1 --- Differential Thermal Analyzer (DTA) for thermal analysis --- p.2-4<br>Chapter 2.4.2 --- X-Ray powder Diffractometry (XRD) for phase determination --- p.2-5<br>Chapter 2.4.3 --- Scanning Electron Microscopy (SEM) and Electron Dispersive X-ray analysis (EDX) for structural analysis --- p.2-6<br>Chapter 2.4.4 --- Mechanical properties --- p.2-7<br>Chapter 2.4.4.1 --- Relative density --- p.2-7<br>Chapter 2.4.4.2 --- Porosity --- p.2-9<br>Chapter 2.4.4.3 --- Tensile strength --- p.2-10<br>Chapter 2.4.4.4 --- Hardness test --- p.2-10<br>Figures --- p.2-12<br>References --- p.2-18<br>Chapter Chapter 3 --- Formation of the Mg-ZnO MMCs --- p.3-1<br>Chapter 3.1 --- Thermal analysis on the reactions between Mg and ZnO --- p.3-1<br>Chapter 3.1.1 --- Introduction --- p.3-1<br>Chapter 3.1.2 --- Experiments --- p.3-1<br>Chapter 3.1.3 --- Results and Discussions --- p.3-1<br>Chapter 3.2 --- Characterization of the Mg-ZnO MMCs --- p.3-2<br>Chapter 3.2.1 --- Introduction --- p.3-2<br>Chapter 3.2.2 --- Experiments --- p.3-3<br>Chapter 3.2.3 --- Results and Discussions --- p.3-3<br>Chapter 3.2.3.1 --- Scanning electron microscopy (SEM) and Electron dispersive X-ray analysis (EDX) --- p.3-3<br>Chapter 3.2.3.2 --- X-ray Diffraction (XRD) --- p.3-4<br>Chapter 3.2.3.3 --- Mg-Zn intermetallics Phases --- p.3-5<br>Chapter 3.2.4 --- Model of formation of Mg-ZnO MMCs --- p.3-5<br>Chapter 3.2.4.1 --- Chemical reactions --- p.3-5<br>Chapter 3.2.4.2. --- Order of priority of reactions --- p.3-6<br>Chapter 3.2.4.3 --- Diffusion during sintering --- p.3-7<br>Chapter 3.2.4.4 --- Reaction Model --- p.3-8<br>Chapter 3.2.5 --- Conclusions --- p.3-8<br>Figures --- p.3-10<br>References --- p.3-18<br>Chapter Chapter 4 --- Mechanical properties of the Mg-ZnO MMCs --- p.4-1<br>Chapter 4.1 --- Introduction --- p.4-1<br>Chapter 4.2 --- Experiments --- p.4-1<br>Chapter 4.3 --- Results and Discussions --- p.4-2<br>Chapter 4.3.1 --- Relative density --- p.4-2<br>Chapter 4.3.2 --- Porosity --- p.4-3<br>Chapter 4.3.3 --- Tensile strength --- p.4-4<br>Chapter 4.3.4 --- Hardness --- p.4-6<br>Chapter 4.4 --- Conclusions --- p.4-7<br>Figures --- p.4-9<br>References --- p.4-23<br>Chapter Chapter 5 --- Reinforcement in Mg-ZnO MMCs --- p.5-1<br>Chapter 5.1 --- Introduction --- p.5-1<br>Chapter 5.2 --- Experiments --- p.5-1<br>Chapter 5.3 --- Results and Discussions --- p.5-1<br>Chapter 5.3.1 --- Microstructure of the Mg-ZnO MMCs --- p.5-2<br>Chapter 5.3.2 --- Fracture of Mg-ZnO MMCs --- p.5-5<br>Chapter 5.3.2.1 --- Fracture surface --- p.5-5<br>Chapter 5.3.2.2 --- Fracture mode --- p.5-7<br>Chapter 5.4 --- Conclusions --- p.5-8<br>Figures --- p.5-9<br>References --- p.5-18<br>Chapter Chapter 6 --- Conclusions and Future Works --- p.6-1<br>Chapter 6.1 --- Conclusions --- p.6-1<br>Chapter 6.2 --- Future Works --- p.6-2<br>References --- p.6-4

博士<br>國立臺灣科技大學<br>機械工程系<br>107<br>In this work, heat treatment (homogenization and ageing heat treatment processes) and extrusion plus A route type equal channel angular pressing (ECAP) severe plastic deformation methods were used to improve the microstructural and mechanical properties of as-cast SiCp/AZ61 magnesium metal matrix composites (Mg MMCs) fabricated by stir casting method. Different weight percentages (0%, 2% and 5%) of SiC particles (SiCp) were considered to study the effects of contents of reinforcements at different treatment conditions. Microstructural changes due to heat treatment processes, the number of ECAP passes and SiCp weight percentages were assessed using optical microscope (OM), scanning electron microscope (SEM), microhardness test and X-ray diffraction (XRD) patterns analysis. Enhanced mechanical properties were analyzed based on the Charpy impact and the uniaxial tensile test data. Furthermore, the brittle-ductile properties were testified by using scanning electron microscopy (SEM) features of Charpy impact and tensile test fracture surfaces. The work-hardening behavior of AZ61 magnesium alloy and SiCp/AZ61 Mg MMCs deformed by ECAP plastic deformation were studied by considering strain hardening rate (θ). The details of plastic deformation mechanisms and plastic deformation stages were identified by using a Crussard-Jaoul method based on the Ludwik equation. The response surface methodology in the design of experiments (DOE) wizard and Gurson-Tvergaard-Needleman (GTN) model were employed to estimate the optimum GTN damage parameters and to validate their significant effects respectively on the ductile fracture behavior of ECAP deformed AZ61 magnesium alloy. Hollomon flow stress was applied to identify uniform deformation and non-uniform deformation regions to investigate the void nucleation and coalescence processes separately. From the results obtained, ageing heat treatment process was seen significant on the 12 h aged 2 wt% SiCp/AZ61 Mg MMC which induced lower microhardness values and results in the formations of particle free regions and discontinuous secondary phases. At a higher number of ECAP passes and higher SiCp weight percentage, higher elastic modulus was seen enhanced. The strength, ductility and work-hardening behaviors were varied for both ECAP plastic deformation and SiCp weight percentage variations. The results of ductile fracture behavior of ECAP deformed AZ61 magnesium alloy showed that varying both stress triaxiality and damage variables simultaneously can greatly affect the curve fitting process of experimental, simulation and GTN model curves. The main contribution of this research work is enhancing the mechanical properties of SiCp/AZ61 Mg MMCs by modifying the presence and amount of microstructural constituent phases and by improving their uniform distribution.

In this thesis, a novel in-situ method for incorporating nanoscale ceramic particles into metal has been developed. The ceramic phase is introduced as an organic-polymer precursor that pyrolyzes in-situ to produce a ceramic phase within the metal melt. The environment used to shield the melt from burning also protects the organic precursor from oxidation. The evolution of volatiles (predominantly hydrogen) as well as the mechanical stirring causes the polymer particles to fragment into nanoscale dispersions of a ceramic phase. These “Polymer-based In-situ Process-Metal Matrix Composites” (PIP-MMCs) are likely to have great generality, because many different kinds of organic precursors are commercially available, for producing oxides, carbides, nitrides, and borides. Also, the process would permit the addition of large volume fractions of a ceramic phase, enabling nanostructural design, and production of MMCs with a wide range of mechanical properties, meant especially for high temperature applications. An important and noteworthy feature of the present process, which distinguishes it from other methods, is that all the constituents of the ceramic phase are built into the organic molecules of the precursor (e.g., polysilazanes contain silicon, carbon, and nitrogen); therefore, a reaction between the polymer and the host metal is not required to produce the dispersion of the refractory phase. The polymer precursor powder, with a mean particle size of 31.5 µm, was added equivalent to 5 and 10 weight % of the melt (pure magnesium) by a liquid metal stir-casting technique. SEM and OM microstructural observations show that in the cast structure the pyrolysis products are present in the dendrite boundary region in the form of rod/platelets having a thickness of 100 to 200 nm. After extrusion the particles are broken down into fine particles, having a size that is comparable to the thickness of the platelets, in the 100 to 200 nm range, and are distributed more uniformly. In addition, limited TEM studies revealed the formation of even finer particles of 10-50 nm. X-ray diffraction analysis shows the presence of a small quantity of an intermetallic phase (Mg2Si) in the matrix, which is unintended in this process. There was a significant improvement in mechanical properties of the PIP-MMCs compared to the pure Mg. These composites showed higher macro-and micro-hardness. The composite exhibited better compressive strength at both room temperature and at elevated temperatures. The increase in the density of PIP-composites is less than 1% of Mg. Five weight percent of the precursor produced a two-fold increase in the room-temperature yield strength and reduced the steady state creep rate at 723 K by one to two orders of magnitude. PIP-MMCs showed higher damping capacity and modulus compared to pure Mg, with the damping capacity increasing by about 1.6 times and the dynamic modulus by 11%-16%. PIP-composites showed an increase in the sliding wear resistance by more than 25% compared to pure Mg.

D. Tech. Mechanical Engineering.<br>Discusses the main objective of this study was to extend the hybrid method developed by Paskaramoorthy, et al (1988). This objective was to study the effect of elastic wave on any particulate reinforced metal matrix composite (PRMMC). The specific objectives were: to compare the effect of plane wave and shear vertical wave on a particular particulate reinforced metal matrix composite (PRMMC)-Mg/TiC, using analytical method ; to use the extended hybrid method to determine the effect of particle size and single interface layer on Mg/TiC.

碩士<br>國立中山大學<br>材料與光電科學學系研究所<br>104<br>The friction stir process was employed to make a composite magnesium alloy AZ31B containing hydroxyapatite. Followed by hydrothermal method, hydroxyapatite (HA) film was deposited onto the sample surface. Hydrothermal reagents are composed of 0.25mol / M of Ca-EDTA and KH2PO4, and sodium hydroxide as a buffer to maintain the pH of the solution at 8.9 and the temperature controlled at 90 ° C. Magnesium in the surface would have replacement reaction with the solution in the system with the time of 3,6,12 hours. A Scanning Electron Microscope (SEM) was used to examine the specimen surface morphology and composition variations X-ray Energy Dispersive Spectrometer (EDS) and back-scattered electron imaging (BEI). Experimental results showed a bonding layer with thickness about 100 nm exists between the substrate and the coating. The bonding layer would become joining surface for substrate and Hap. The earlier forming of coating is probably calcium deficient hydroxyapatite (CDHA) , and the top of coating is probably hydroxyapatite (HA). The chemical solution also brings demineralization to form some vertical cracks. Keywords: hydroxyapatite , calcium deficient hydroxyapatite, friction stir process, coating technology , cracks, hydrothermal method , bonding layer.

Nan Gang Ma.<br>"October 2003."<br>Thesis (Ph.D.)--Chinese University of Hong Kong, 2003.<br>Includes bibliographical references.<br>Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.<br>Mode of access: World Wide Web.<br>Abstracts in English and Chinese.<br>Nan Gang Ma.