Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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Table 4.2 Density and mechanical properties of AZ91D/MWNT nanocomposites. Materials Density (g cm 3 ) Elastic modulus (GPa) Tensile strength (MPa) Yield stress (MPa) Ductility (%) AZ91D 1.80 0.007 40 2 315 5 232 6 14 3 AZ91D/0.5%CNT 1.82 0.008 43 3 383 7 281 6 6 2 AZ91D/1%CNT 1.83 0.006 49 3 388 11 295 5 5 2 AZ91D/3%CNT 1.84 0.005 51 3 361 9 284 6 3 2 AZ91D/5%CNT 1.86 0.003 51 4 307 10 277 4 1 0.5 Reproduced with permission from [Chap. 2, Ref. 63]. Copyright Ó (2008) Elsevier. 4.2 Tensile Deformation Behaviorj111 increase slowly with increasing CNF content from 1.5 to 7.5 wt%. The yield stress and tensile strength of the AZ91D/1.5% CNF nanocomposite are 342 and 400 MPa, respectively. The yield stress and tensile strength of the AZ91D/7.5% CNF nanocomposite further increase to 416 and 470 MPa, respectively. The strengthening effect of nanofibers is pronounced and can be attributed to better dispersion of nanofibers in the magnesium alloy matrix. This arises from the employment of multiple casting processes and extrusion as well as the improvement in the wettability of nanofibers through the use of silicon coating. The mechanisms responsible for the strengthening of AZ91D/CNF nanocomposites include load transfer effect (Equation 4.4) and grain refinement strengthening (Hall–Petch relationship). Furthermore, the contribution of load transfer to the yield stress enhancement is twice of that of grain refinement. In addition to squeeze casting, disintegrated melt deposition (DMD) seems to be an effective technique for depositing near net shape metal-matrix composites [Chap. 2, Ref. 61]. Gupta and workers used the DMD technique to fabricate the Mg/MWNT nanocomposites containing fillers from 0.3 up to 2 wt%. The resulting nanocomposites were then extruded [Chap. 2, Ref. 5, 19]. Figure 4.7 shows the stress–strain curves of pure Mg and Mg/MWNT nanocomposites. The density and mechanical properties of these specimens are listed in Table 4.3. Apparently, the density of nanocomposites remains almost unchanged by adding nanotubes up to 1.6 wt%. At 2 wt% MWNT, the density begins to decrease due to the formation of micropores. Tensile test data show that the yield and tensile strengths as well as tensile ductility of Mg-based nanocomposites increase with increasing nanotube content up to 1.3 wt%. At 1.6 and 2 wt% MWNT, the yield stress, tensile strength and ductility reduce considerably due to the agglomeration of nanotubes and micropore formation. The improvement in tensile ductility of nanocomposites with MWNTcontent 1.3 wt% is attributed to the high activity of the basal slip system and the initiation of prismatic hai slip [Chap. 2, Ref. 5, 19]. Magnesium generally exhibits low tensile ductility due to its hexagonal close-packed (HCP) structure having only three independent slip system. MWNTs assist the activation of prismatic and cross-slip in the matrix during extrusion. Texture analysis reveals that the basal planes of magnesium matrix tend to align with the extrusion direction (Figure 4.8). Such dislocation slip behavior has been confirmed by transmission electron microscopyTEM observations.
112j 4 Mechanical Characteristics of Carbon Nanotube–Metal Nanocomposites Figure 4.7 Tensile stress–strain curves of pure Mg and Mg/MWNT nanocomposites. Reproduced with permission from [19]. Copyright Ó (2008) Elsevier. 4.2.3 Copper-Based Nanocomposites Copper nanopowders do not mixed properly with CNTs even after ball milling. For instance, Hong and coworkers fabricated Cu/5 vol% MWNT and Cu/10 vol% MWNT nanocomposites by spark plasma sintering of ball-milled Cu and nanotube powder mixtures and cold rolling. The microstructure of cold-rolled nanocomposites consists of a nanotube-rich surface region and a nanotube-free inner region [Chap. 2, Ref. 81]. Figure 4.9(a) shows the tensile stress–strain curves of pure Cu and its nanocomposites. Carbon nanotube additions improve the yield and tensile strengths of copper at the expense of tensile ductility. The variation of elastic modulus, yield and tensile strengths with nanotube content is shown in Figure 4.9(b). Careful examination of Figure 4.9(a) reveals the presence of two yield points owing to the Table 4.3 Density and mechanical properties of Mg/MWNT nanocomposites. Materials Density (g cm 3 ) 0.2% Yield stress (MPa) UTS (MPa) Ductility (%) Mg 1.738 0.010 126 7 192 5 8.0 1.6 Mg/0.3 wt% MWNT 1.731 0.005 128 6 194 9 12.7 2.0 Mg/1.3 wt% MWNT 1.730 0.009 140 2 210 4 13.5 2.7 Mg/1.6 wt% MWNT 1.731 0.003 121 5 200 3 12.2 1.72 Mg/2 wt% MWNT 1.728 0.001 122 7 198 8 7.7 1.0 Reproduced with permission from [Chap. 2, Ref. 5]. Copyright Ó (2006) 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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Page 78 and 79: limited improvement in ultimate ten
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)
Page 86 and 87: Figure 2.25 (a) TEM micrograph show
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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)
Page 94 and 95: Figure 2.31 Schematic representatio
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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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162j 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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