Biomedical Engineering Reference
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Figure 10.22.
Microstructure of pure Al
2
O
3
sintered for 30 minutes at 1650 °C. [Anné, 2005a].
ZrO
2
100
Al
2
O
3
99
98
97
96
95
Al
2
O
3
/ZrO2 (50/50)
94
93
92
1550 °C
91
90
0
10
20
30
40
50
60
Time (min)
Figure 10.23.
Evolution of the density of Y-ZrO
2
, Al
2
O
3
and 50/50 (vol. %) composite at
1550 °C as a function of time. [Anné, 2005a].
Figure 10.24 gives an overview of the composition profi les of graded Al
2
O
3
/
ZrO
2
discs, leading to transverse cracks after sintering (Figure 10.25). These
cracks are not observed when the Al
2
O
3
content in the core of the graded plate is
≥
75 vol. %, indicating that a too large composition difference between surface
layer and the core gives internal defects. There is no quantitative dependence
found between the inter-crack distance and the composition profi le. Mostly, the
distance between two cracks is a few millimeters, but the number of cracks
increases with the ZrO
2
content in the core of the plates.
Microstructural investigation reveals that these cracks are perpendicular to
the surface (Figure 10.25) and are only present in the ZrO
2
rich core and not in
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