Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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Ductile phase toughening involves the incorporation of a ductile metal phase into brittle ceramics to facilitate yielding of the metal particle and blunting of the propagating cracks. In this regard, energy is dissipated through the deformation of the ductile phase and crack blunting at the ductile particle. In most cases, bridging ligaments along the crack profiles are also produced [5–7]. In general, large amounts of metallic particles (30–70%) are needed to improve the fracture toughness of ceramics [8]. Addition of a large amount of metal microparticles deteriorates the sinterability of ceramics significantly. Further, failure of such MMCs originates from cavities in large metal inclusions [9]. Fracture toughness of ceramics can also be improved by the addition of ceramic reinforcements in the forms of particulates, whiskers, and fibers to form ceramicmatrix composites (CMCs) [10–14]. The reinforcing effect of fibers is much higher that that of particulates and whiskers. Continuous silicon carbide and carbon fibers have been widely used to reinforce ceramics [15–17]. The toughening mechanisms of fiber-reinforced CMCs are mainly attributed to the crack deflection at the fiber–matrix interface, crack bridging and fiber pull-out. It has been demonstrated that weak fiber–matrix interfacial bonding facilitates the fiber pull-out toughening mechanism to operate. This is because strong interfacial bonding allows the crack to propagate straight through the fibers, resulting in low fracture toughness [15]. Continuous fiber-reinforced CMCs are generally fabricated by chemical vapor infiltration or polymer infiltration and pyrolysis (PIP). However, these processing techniques are costly and time consuming. 5.2 Importance of Ceramic-Matrix Nanocomposites In the past few years, considerable attention has been paid to the development of nanocrystalline ceramics with improved mechanical strength and stiffness, and enhanced wear resistance [18–20]. Decreasing the grain size of ceramics to the submicrometer/nanometer scale leads to a marked increase in hardness and fracture strength. However, nanocrystalline ceramics generally display worse fracture toughness than their microcrystalline counterparts [18]. The toughness of nanoceramics can be enhanced by adding second phase reinforcements. Grain size refinement in ceramics and their composites can yield superplasticity at high strain rates [21, 22]. Superplasticity is a flow process in which crystalline materials exhibit very high tensile ductility or elongation prior to final failure at high 3 Figure 5.1 Schematic illustrations of three toughening mechanisms in ceramics: (a) phase transformation toughening showing transformed monoclinic zirconia (1) from metastable tetragonal zirconia (2); (b) ductile phase toughening through (1) ductile phase 5.2 Importance of Ceramic-Matrix Nanocompositesj133 deformation or crack blunting and (2) crack bridging; (c) fiber toughening showing (1) crack deflection, (2) crack bridging and (3) fiber pullout. Reproduced with permission from [1]. Copyright Ó (2005) Elsevier.
134j 5 Carbon Nanotube–Ceramic Nanocomposites temperatures. Superplastic deformation is of technological interest because it allows lower processing temperature and time, and enables near net shape forming of ceramic products. The ability to prevent premature failure of ceramics at high strain rates can have a large impact on the production processes. From the concept of new materials design, Niihara classified the nanocomposites into four types based on their microstructural aspects that is, intra, inter, intra/inter and nano-nano [23]. The first three types describe the dispersion of second-phase nanoparticles within matrix micrograins, at the grain boundaries or both. These composites are commonly known as ceramic nanocomposites but are more precisely referred to as micro-nano composites. For the nano-nano type, second-phase nanoparticles are embedded within nanograined matrix. Most of the nanocomposites reported in the literature belong to the micro-nano type [24–33]. Less information is available for the nano-nano ceramic composites [34–36]. Mukherjee later proposed a new classification of ceramic composites: nano-nano, nano-micro, nanofiber and nano-nanolayer [35]. In this classification, the matrix phase is continuous nanocrystalline grains of less than 100 nm while the second phase could be in the form of nanoparticles, microparticles, fibers (or whiskers) or a grain boundary nanolayer (Figure 5.2). Niihara et al. reported that the incorporation of 5% SiC nanoparticles into microcrystalline alumina increased the flexural strength from 350 MPa to 1.1 GPa, and further annealing increased the strength to more than 1.5 GPa. The fracture toughness improved from 3.5 MPa m 1/2 to 4.8 MPa m 1/2 . Addition of SiC nanoparticles to alumina matrix also produced a change in the fracture mode of the matrix from predominantly intergranular to transgranular mode [23]. Transgranular failure Figure 5.2 Mukherjee s classification of nanocomposite types, based on nanosized matrix grains and second-phase particle of different morphologies and sizes. Reproduced with permission from [35]. Copyright Ó (2001) Elsevier.
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Sie Chin Tjong Carbon Nanotube Rein
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Sie Chin Tjong Carbon Nanotube Rein
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Contents Preface IX List of Abbrevi
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5 Carbon Nanotube-Ceramic Nanocompo
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Preface Carbon nanotubes are nanost
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XII List of Abbreviations HIP hot i
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1 Introduction 1.1 Background Compo
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Figure 1.2 Transmission electron mi
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1.3 Synthesis of Carbon Nanotubes 1
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MWNTs can be as high as 70% of the
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Figure 1.7 In situ TEM images recor
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1.3 Synthesis of Carbon Nanotubesj1
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show TEM images of MWNTs synthesize
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Since then, large efforts have been
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1.3.4 Patent Processes Carbon nanot
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1.4 Purification of Carbon Nanotube
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Table 1.3 Patent processes for the
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Figure 1.13 Schematic illustration
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1.5 Mechanical Properties of Carbon
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Figure 1.14 Carbon nanotubes in hig
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Figure 1.15 In situ tensile deforma
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Table 1.7 Theoretical and experimen
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Nomenclature ~a 1 , ~a 2 Unit vecto
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carbon nanotubes. Physical Review L
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70 Jang, I., Uh, H.S., Cho, H.J., L
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108 Shelimov, K.B., Esenaliev, R.O.
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Bonnamy, S., Beguin, F., Burnham, N
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2 Carbon Nanotube-Metal Nanocomposi
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isostatic pressing. In certain case
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This implies the absence of effecti
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coating material, the plasma gun an
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Table 2.4 Changes in the size and v
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Figure 2.6 (a) Low and (b) high mag
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Figure 2.8 SEM micrographs showing
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Figure 2.11 Bright field TEM microg
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Figure 2.13 TEM image of bulk Al/5
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2.5 Magnesium-Based Nanocomposites
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limited improvement in ultimate ten
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Figure 2.18 SEM micrographs of the
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Figure 2.19 (a) Low and (b) high ma
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Figure 2.22 SEM micrographs of (a)
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Figure 2.25 (a) TEM micrograph show
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2.8 Transition Metal-Based Nanocomp
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Figure 2.27 TEM image of electrodep
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Figure 2.29 SEM micrographs of (a)
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Figure 2.31 Schematic representatio
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einforcement content SiCp/Al compos
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184j 6 Physical Properties of Carbo
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186j 7 Mechanical Properties of Car
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Table 8.1 Patent processes for maki
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218j 8 Conclusions development of c
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220j 8 Conclusions Figure 8.2 TEM m
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222j 8 Conclusions increase in Vick
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224j 8 Conclusions References 1 Cha
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226j 8 Conclusions nano-matrix. Scr
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228j Index l laser ablation 7 load
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