Biomedical Engineering Reference
In-Depth Information
700
HA
600
500
400
300
200
100
0
10
20
30
40
50
60
2
/ degrees
Fig. 3. X-ray diffraction pattern of the HA ceramics.
2.3 HA/Ti Bonding and its adhisive properties
It is seen that the shrinkage started at approximately 90°C. This temperature is close to the
dehydration temperature of DCPD. Thus, it is thought that the shrinkage is initiated by the
dehydration of DCPD. The shrinkage rate became larger with the increasing temperature,
and then the shrinkage rate became smaller. The shrinkage continued during the HHP
treatment. The pressure was held at 40MPa constant for the whole period of HHP treatment.
As given in Fig.3, X-ray diffraction analysis showed that the DCPD and Ca(OH)
2
powder
materials were completely transformed into HA by the HHP treatment. As demonstrated in
Fig.4, the HA ceramics could be bonded to the Ti disks at the low temperature of 150°C
using the above-mentioned HHP treatment. The density of the HA ceramics prepared by the
HHP in this study was 1.9 g/cm
3
. In addition to the DCPD powder, three different types of
powders were used as a starting material: HA and -tri calcium phosphate (-TCP). No
bonding with a Ti disk was observed, when the above starting powders were used and
treated by the HHP under the conditions of 150°C and 40MPa. Thus, DCPD was the only
starting material that produced HA/Ti bonded bodies among the precursors for HA used in
this study.
Fig.5 shows a photograph of the fracture surface in the bonded HA/Ti body after 3-point
bending test. It can be noted that the crack initiated from the pre-crack tip and propagated
not along the HA/Ti interface, but into the HA. This observation suggests that the fracture
toughness of the HA/Ti interface is close to or higher than that of the HA ceramics only. The
critical stress intensity factor
K
c
was 0.30 MPam
1/2
for the HA ceramics, and 0.25 MPam
1/2
for the bonded HA/Ti. The toughness data are the average value obtained from at least five
specimens. The
K
c
value for the bonded HA/Ti body gives a slightly lower value than that
of the HA ceramics only. The difference in
K
c
data is potentially due to the residual stress
