Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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Figure 4.4 SEM micrographs showing tensile fracture surfaces of (a) 2024 Al/1 wt% MWNT and (b) 2024 Al/2 wt% MWNT nanocomposites. Reproduced with permission from [Chap. 2, Ref. 35]. Copyright Ó (2007) Elsevier. elongation of nanocomposites remains nearly unchanged by adding nanotubes up to 1 wt%; this is due to the superior flexibility of CNTs. As a result, CNTs can bridge advancing crack during tensile deformation, thereby improving the tensile ductility of nanocomposites having nanotube content 1 wt% (Figure 4.4(a)). On the other hand, pull-out of nanotubes can be readily seen in the fracture surface of 2024 Al/2 wt % MWNT nanocomposite, indicating poor interfacial nanotube–matrix bonding strength (Figure 4.4(b)). Nanocrystalline metals generally exhibit limited tensile plasticity due to a lack of work hardening capability. Therefore, cracks are readily initiated in nanocrystalline metals during the earlier stage of tensile deformation. Figure 4.5 shows typical tensile true stress–strain curve of nanocrystalline Al prepared by extruding ball-milled powders [18]. Apparently, nanocrystalline Al exhibits a high mechanical strength of Figure 4.5 Tensile true stress–strain curves of nanocrystalline (nc) Al and its composite reinforced with 0.7 vol% SWNT. These materials were prepared by hot extrusion of ball-milled powders. Reproduced with permission from [18]. Copyright Ó (2007) Elsevier. 4.2 Tensile Deformation Behaviorj109
110j 4 Mechanical Characteristics of Carbon Nanotube–Metal Nanocomposites Figure 4.6 High-resolution TEM image of ncAl/0.7 vol% SWNT composite showing tightly bonded nanotubes–matrix interface. Reproduced with permission from [18]. Copyright Ó (2007) Elsevier. 460 MPa but extremely low tensile elongation (less than 1%). The tensile elongation of nanocrystalline Al can reach up to 8% by adding 0.7 vol% SWNT. The excellent flexibility of SWNTs resists the growth of necks in the nanocomposite during tensile deformation. The large aspect ratio and tightly bonded interface of nanotube with the matrix facilitate load transfer capacity in the composite (Figure 4.6). 4.2.2 Magnesium-Based Nanocomposites Gupta and coworkers fabricated the Mg/MWNT nanocomposites containing nanotubes up to 0.30 wt% using conventional PM blending, sintering and hot extrusion [Chap. 2, Ref. 62]. The yield strength of magnesium increases from 127 to 133 MPa but the ultimate tensile strength slightly decreases from 205 to 203 MPa by adding 0.06 wt% MWNT. At 0.16 wt% MWNT, the yield strength increases to 138 MPa but the tensile strength remains almost unchanged (206 MPa). Further, agglomeration of MWNTs is observed in the fracture surface of Mg/0.3 wt% MWNT nanocomposite. As a result, little reinforcing effect is found by adding 0.3 wt% MWNT due to the nanotube clustering. In order to disperse CNTs more uniformly into Mg-based composites during PM processing, it is necessary to shorten the length of CVD-grown nanotubes. Shimizu et al. used a high-speed blade cutting machine to reduce the length of CVD prepared MWNTs to an average length of 5 mm [Chap. 2, Ref. 63]. Damaged nanotubes were then introduced into the AZ91D matrix. The AZ91D/CNT nanocomposites were prepared by mechanical milling, hot pressing and hot extrusion. Table 4.2 lists the tensile properties of AZ91D and its nanocomposites. The elastic modulus, yield strength and tensile strength increase with increasing nanotube content up to 1 wt%. At 3–5 wt% MWNT the mechanical properties deteriorate due to the clustering of nanotubes. Honma et al. also studied the tensile behavior of the AZ91D/CNF nanocomposites prepared by compocasting, squeeze casting and extrusion [Chap. 2, Ref. 58]. They reported that the yield stress and tensile strength of the nanocomposites
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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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Page 80 and 81: Figure 2.18 SEM micrographs of the
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Page 84 and 85: Figure 2.22 SEM micrographs of (a)
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Page 90 and 91: Figure 2.27 TEM image of electrodep
Page 92 and 93: Figure 2.29 SEM micrographs of (a)
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Page 98 and 99: Materials Science Forum, 534-536 (P
Page 100 and 101: composite. Materials Science and En
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160j 5 Carbon Nanotube-Ceramic Nano
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170j 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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