3.4.2.4 Zirconium
Oxide Toughend Aluminium Oxide
In practice, this is usually simply known
as ZTA (zirconia toughened
alumina). Its properties depend strongly
on the mixing ratio of aluminium oxide to zirconium oxide,
and on the details of the processing.
Figure 16: Microstructure of a ZTA with a
low proportion of zirconium oxide
Low proportions of zirconium oxide, up to
approx. 10% by volume, allow improved values, in comparison
with aluminium oxide, for
- bending strength
- KIC factor,
- modulus of elasticity and
- larger coefficients of linear expansion to be achieved.
Versions of the material containing higher concentrations
of zirconium oxide, if appropriately processed, develop platelets
in the microstructure, which contributes to an improvement
in some material properties (ZPTA ceramics). These and other
measures taken to optimise properties permit the achievement
of outstanding figures for
- bending strength
- modulus of elasticity and
- thermal behaviour
that are superior to those of Y-ZTP (tetragonal zirconium
oxide stabilised with yttrium oxide).
Figure 17: ZTA with a high proportion of
zirconium oxide, shown as a breakage
microstructure in order to reveal the platelets
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