Biomedical Engineering Reference
In-Depth Information
X-ray diffraction was employed to study the effect of mechanical
alloying on Ti-SiO
2
composites. Fig. 7.8 a, b shows the XRD patters
of the starting titanium and amorphous silica powders. During MA
process, the intensity of diffraction line of titanium decreases with
milling time and after 20 h of milling has transformed completely
to an amorphous phase, without the formation of any other phases
(Fig. 7.8c).
TEM results shows that the powder milled for 20 h was mostly
amorphous (Fig. 7.9a). SEAD pattern contains broad rings at position
expected for Ti with hexagonal structure. Fig. 7.9b shows the high-
resolution image of grain containing nanoparticles of titanium with
visible lattice planes. The interplanar distance was 0.234 and 0.224
nm, which corresponds to the crystallographic planes of titanium.
Apart from grains with nano Ti particles, the milled powders
contained small amount of crystals of Ti. The same structure was
observed for Ti-3 vol% SiO
2
composite. Lack of any sharp relections
in the XRD pattern suggests that the amount of the crystalline
phase is very low and/or it forms during TEM observation. During
TEM studies, it has been found that the amorphous powders was
unstable upon exposure to electron beam and underwent some
crystallization.
Figure 7.9
TEM micrographs of the milled Ti-10 vol% SiO
2
sample for
20 h: (a) typical amorphous parts with corresponding SAED
pattern, (b) grain with nanoparticles of titanium [24].
