Biomedical Engineering Reference
In-Depth Information
Ning and Zhou [25, 26]. Neither HA and Ti is found in the 30Ti-
70HA composite, which has the lowest titanium content. In addition
to CaTiO
3
(ICDD: 22-0153) and CaO (ICDD: 4-777), some Ti
x
P
y
compounds were also detected. With the increase in titanium
content, Ti
2
O (ICDD: 11-218) and α-Ti appeared in addition to the
above phases. In the 70Ti-30HA composite, the main crystal phase
was only α-Ti. This result is in good agreement with our current
studies (see Fig. 7.4). The HA phase is unstable at high temperatures,
which is correlative with the features of its crystal structure [26].
Additionally, the decomposition of HA phase plays an important role
on the inal properties of the sintered Ti-HA nanocomposites [25].
7.2.2 MechanicalProperes
The change of processing parameters, like mechanical alloying
and annealing times, as well as the chemical compositions of Ti-
HA nanocomposites leads to a distribution of the properties.
For example, the Vickers hardness of bulk samples prepared by
application of mechanically alloyed for 10 h Ti-10 vol% HA powder
is low. On the other hand, the increase of milling time to 44 h
leads to a strong increase in hardness. For Ti-10 vol% HA and Ti-
20 vol% HA nanocomposites Vickers hardness are higher than of
pure microcrystalline Ti metal (250 HV) and reaches 1300 HV and
1050 HV, respectively. Additionally, the Vickers hardness of the
samples mechanically alloyed for 44 h and sintered at 1150°C
depends on annealing time. Hardness increases additionally with
increasing of the annealing time from 1300 HV to 1500 HV for 0.5 h
and 2 h of heat treatment time, respectively (for a sample containing
10 vol% HA) [23]. This effect is directly connected with structure
reinement and obtaining of nanostructure.
The research conducted by Popa
et al
. showed
that application
of higher pressure causes more swelling of samples [28]. Swelling
is due to the diffusion of calcium/phosphorus in the titanium
matrix. The phenomenon was proven by subsequent EDX analysis.
The higher loading of the grains in the metal matrix during the
compaction stage, the diffusion coeficient of elements from HA to
the Ti increases. This is caused by the more numerous lattice defects
induced by a more severe plastic deformation.
If the material is hot pressed, the plastic deformation and low
of Ti matrix and HA ceramic under the pressure can reduce the
