Carbon Nanotube Reinforced Composites: Metal and Ceramic ...
Carbon Nanotube Reinforced Composites: Metal and Ceramic ...
Carbon Nanotube Reinforced Composites: Metal and Ceramic ...
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has also been reported by other researchers for the micro-nano ceramic composites<br />
[25–28]. The switch from intergranular to transgranular failure is a good<br />
indicator for the strength <strong>and</strong> toughness improvements in ceramic nanocomposites.<br />
Second-phase nanoparticles enhance grain boundary properties of ceramics by<br />
inducing residual stress as a result of thermal expansion mismatch between the<br />
matrix <strong>and</strong> particles. This internal stress causes an advancing crack to propagate in a<br />
tortuous manner rather than a catastrophic straight path. Moreover, second-phase<br />
nanoparticle additions also lead to the grain refinement of the ceramic matrix [37].<br />
Reducing grain size promotes the mechanical strength of crystalline materials<br />
according to the Hall–Petch relation. In some cases, second-phase nanoparticles<br />
also yield elongation of matrix grains. The elongated matrix grains with high aspect<br />
ratio increase the fracture toughness by dissipating the fracture energy through crack<br />
deflection <strong>and</strong> bridging mechanisms [30, 31]. Table 5.1 lists the properties of typical<br />
micro-nano <strong>and</strong> nano-nano ceramic composites.<br />
<strong>Carbon</strong> nanotubes (CNTs) with high aspect ratio, extraordinary mechanical<br />
strength <strong>and</strong> stiffness, excellent thermal <strong>and</strong> electrical conductivity are attractive<br />
nanofillers which produce high-performance ceramic composites with multifunctional<br />
properties. The reinforcing effect of CNTs with high aspect ratio is considered<br />
to be analogous to that of continuous or short-fiber-reinforcement. The superior<br />
flexibility of CNTs is very effective in improving the fracture toughness of brittle<br />
ceramics. This is accomplished by means of crack deflection at the CNT–matrix<br />
interface, crack-bridging <strong>and</strong> CNT pull-out mechanisms. Recently, Huang et al.<br />
reported that SWNTs exhibit superplastic deformation with an apparent elongation of<br />
280% at high temperatures [38]. This finding shows the potential application of CNTs<br />
Table 5.1 Mechanical properties of typical micro-nano <strong>and</strong> nano-nano ceramic composites.<br />
Investigators Materials<br />
5.2 Importance of <strong>Ceramic</strong>-Matrix Nanocompositesj135<br />
Bending<br />
strength<br />
(MPa)<br />
Fracture<br />
toughness<br />
(MPa m 1/2 )<br />
Anya Ref [25]<br />
Micro-nano type:<br />
Monolithic Al2O3 (3.5 mm) 430 3.2<br />
Al2O3(4.0 mm)/5 vol% SiC (200 nm) 646 4.6<br />
Al2O3(2.9 mm)/10 vol% SiC (200 nm) 560 5.2<br />
Al2O3(2.6 mm)/15 vol% SiC (200 nm) 549 5.5<br />
Gao et al. Ref [26] Monolithic Al2O3 350 3.5<br />
Al2O3(1.8 mm)/5 vol% SiC (70 nm) 1000 4.0<br />
Zhu et al. Ref [30] Monolithic Al2O3 380 3.9<br />
Al2O3/15vol%Si3N4 (200 nm,<br />
inter; 80 nm, intra)<br />
820 6.0<br />
Isobe et al. Ref [33] Monolithic Al2O3 (1.95 mm) 450 3.7<br />
Al2O3 (0.91 mm)/2.8 vol% Ni<br />
(150 nm, inter; 300 nm, intra)<br />
Nano-nano type:<br />
766 4.6<br />
Bhaduri Ref [34] Al2O3 (44 nm)/10 vol% ZrO2(12.7 nm) — 8.38