Biomedical Engineering Reference
In-Depth Information
material between the pulser and the receiving transducer and does not
attempt to locate individual flaws. It follows that AU may be particularly
appropriate for non-destructive testing of ceramic nanocomposites as the
defects are usually small, numerous and dispersed: it can be used for
detecting flaws in ceramic nanocomposites, as has been shown for the
sensitivity of degree of crystallization of a glass-ceramic (De et al. 1987) and
for the evaluation of percentage porosity in sintered glass and carbon-
bonded carbon fibre based composites (Aduda and Rawlings 1990).
1.9
Conclusions
The design principles for the fabrication of different types of high-
performance thermal shock resistant ceramic nanocomposites with
improved mechanical properties have been highlighted in this chapter.
Pertinent factors such as interface characteristics, densification methods and
the role of nano-size particulate dispersion in the development of thermal
shock resistant and flame retardant nanoceramic materials have also been
reviewed. Various test methods for the characterization and evaluation of
ceramic nanocomposites have been briefly covered.
To obtain dense bulk ceramic nanocomposites, it is essential to decrease
either the sintering temperature or retention time at the highest point, or to
employ hot-pressing, hot isostatic pressing, gas pressure sintering or a fast
consolidation technique such as microwave sintering or spark plasma
sintering. The overall conclusion from the studies on ceramic nanocompo-
sites reported in this chapter can be summarized as follows.
1. A composite formation with nanostructured coatings based on ceramic
powders is very attractive for cutting tools and wear-resistant
applications. Pulsed electric current sintering can be used for the
fabrication of such nanocomposites.
2. Solid-state sintering processes are specifically applied for the processing
of oxide based nanocomposite materials and liquid-phase sintering
processes are applied for the processing of non-oxide based nanocom-
posite materials (Niihara 1991).
3. Monolithic Al
2
O
3
and MgO exhibit significant degradation of strength
at high temperatures, whereas Al
2
O
3
/Si
3
N
4
,Al
2
O
3
/SiC and MgO/SiC
nanocomposites show notable improvementes in high-temperature
strength up to 1000
8
C.
4.
Si
3
N
4
/SiC nanocomposites do not exhibit significant degradation of
strength up to 1400
8
C. The fracture strength at 1400
8
C was over
1000MPa and about 900MPa even at 1500
C for a 32 vol% SiC
nanocomposite in which nano-sized SiC particles were dispersed not
only within the Si
3
N
4
matrix but also at the grain boundaries.
8
