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Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

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Figure 7.16 Microhardness as a function of CNT content for (a)<br />

SiC/MWNT <strong>and</strong> (b) SiC/SiC-coated MWNT nanocomposites.<br />

Reproduced with permission from [Chap. 5, Ref. 113]. Copyright Ó<br />

(2007) Elsevier.<br />

in fracture toughness of the nanocomposites by adding nanotubes with low aspect<br />

ratio (Type-B) as expected.<br />

7.5<br />

Nitride-Based Nanocomposites<br />

7.5 Nitride-Based Nanocompositesj205<br />

At present, only Si3N4/1% MWNT nanocomposite has been fabricated by conventional<br />

powder mixing <strong>and</strong> ball milling followed by either hipping or SPS treatment at<br />

elevated temperatures [Chap. 5, Ref. 43, Chap. 5, Ref. 119, Chap. 5, Ref. 120]. In<br />

general, ball milling of composite raw materials in ethanol does not yield adequate<br />

dispersion of nanotubes in silicon nitride matrix. In combination with high temperature<br />

consolidation, the beneficial effect of nanotube addition on mechanical<br />

properties of the Si3N4/1% MWNT diminishes. Table 7.5 lists the mechanical<br />

properties of monolithic Si3N4 <strong>and</strong> Si3N4/1 wt% MWNT nanocomposite prepared<br />

by SPS. The hardness values of nanocomposite sintered at 1500 <strong>and</strong> 1650 C are<br />

lower than those of monolithic silicon nitride sintered at these temperatures.<br />

The fracture toughness of nanocomposite spark plasma sintered at 1500 Cis<br />

comparable to that of monolithic Si3N4 fabricated at the same temperature. However,<br />

the toughness of nanocomposite sintered at 1650 C is inferior to that of Si3N4<br />

fabricated at the same temperature.

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