Biomedical Engineering Reference
In-Depth Information
(a)
(c)
(010)
(b)
10 nm
5 nm
FIGURE 9.27
(a) High-resolution electron micrograph of a T-48.2 at.% Ni thin film heated at 745 K for 3.6 ks and (b) cor-
responding diffraction pattern. (c) Enlarged micrograph of a part of (a), showing details of plate precipitates.
(From Miyazaki, S., Ishida, A.,
Mater. Sci. Eng.
, 273-275, 106-133, 1999, with permission from Elsevier.)
Ni which was heated at 773 K for 0.3 ks (5 min) as shown in Figure 9.28a. The correspond-
ing diffraction pattern in Figure 9.28b shows a (100) zone pattern of the B2 parent phase.
This observation indicates that the nonequilibrium Ti-rich platelets can be formed at the
initial stage of heating even at considerably high temperatures. Figure 9.29a and b shows a
bright-field image and the corresponding diffraction pattern of the same alloy film which
was heated at 773 K for 3.6 ks. Figure 9.29a reveals spherical precipitates which appear as
Moiré patterns in addition to the Ti-rich platelets. These spherical precipitates can be dis-
tinguished from the Ti-rich platelets by taking a picture in random orientation, as shown
in Figure 9.29c. The formation of the spherical precipitates produces extra spots in the dif-
fraction pattern in addition to the streaks due to the platelets (Figure 9.29b). These extra
spots could be indexed as a Ti
2
Ti2Ni phase.
Figures 9.30a and b show bright-field images of a Ti-48.2 at.% Ni thin film annealed at
773 K for 36 ks. The corresponding electron beams are parallel to the (100) and (111) of B2,
respectively. In both figures, the spherical precipitates are distinguished by Moiré pat-
terns. Moiré fringes are parallel to the {110} planes of B2. The Ti
2
Ti2Ni is an equilibrium phase.
However, such uniform distribution of Ti
2
Ti2Ni precipitates in grains is not of an equilibrium
state. In case of Ti-rich TiNi bulk materials, the Ti
2
TiNi precipitates preferentially distribute
along grain boundaries. Such equilibrium distribution of Ti
2
Ti2Ni can be formed in the film
when it is heated for a longer time or at higher temperatures. More detailed information
can be found in the study of Zhang et al. (2006).
(a)
(b)
010
001
50 nm
FIGURE 9.28
(a) Bright-field image and (b) the corresponding diffraction pattern of a Ti-48.2 at.% Ni thin film heated at
773 K for 0.3 ks. (From Miyazaki, S., Ishida, A.,
Mater. Sci. Eng.
, 273-275, 106-133, 1999, with permission from
Elsevier.)
