Biomedical Engineering Reference
In-Depth Information
(b)
(a)
90.2
5
Ti−51.9 at.% Ni thin film
973 K 3.6 ks W.Q. − 773 K 36 ks W.Q.
Ti−51.9 at.% Ni thin film
973 K 3.6 ks W.Q. − 773 K 36 ks W.Q.
90.0
4
ε
A
(measured)
89.8
3
89.6
2
89.4
1
ε
R
(measured)
Rs
89.2
200
0
220
240
260
280
300
320
340
0
100
200
300
400
500
600
700
Temperature (K)
Applied stress (MPa)
FIGURE 9.18
Rhombohedral angle
α
of R-phase as a function of temperatures. (a, b) Transformation strains measured in
Ti-51.9 at.% Ni, which was crystallized at 973 K for 3.6 ks followed by aging at 773 K for 3.6 ks. (From Miyazaki,
S., Ishida, A.,
Mater. Sci. Eng.
, 273-275, 106-133, 1999, with permission from Elsevier.)
further increasing applied stress. The major reason for the increase in
ε
R
before the maxi-
mum point is that the most preferential variant grows with increasing the applied stress,
whereas the major reason for the decrease in
ε
R
after reaching the maximum point is that
the temperature range where the R-phase can exist becomes narrower with increasing
the applied stress, so that the lattice distortion of the R-phase becomes less as shown in
Figure 9.18b.
Table 9.2 shows the transformation strains
ε
A
, which were calculated on the basis of the
lattice distortion from the B2 phase to the M phase, along some specific crystal orienta-
tions and the average strain of
ε
A
. The average strain is 8.42%, which is about three times
that of the observed strain. The reason why the observed strain is so small is not attribut-
able to the texture because the x-ray diffraction pattern of the B2 phase does not reveal a
strong texture, although the (011) peak intensity is a little larger than that of a TiNi film
with randomly oriented grains. The possible reason is the strong internal structure con-
sisting of fine Ti
3
Ni
4
precipitates and fine grains of submicron size because such internal
structure will suppress the growth of the most preferentially oriented M variant. On the
other hand, Figure 9.19a shows the recovery strain
ε
A
in a Ti-50.5 at.% Ni thin film that was
solution-treated at 973 K for 3.6 ks. Because the solution-treated thin film does not contain
TABLE 9.2
Calculated Martensite Transformation Strains along Specific Orientations
CalculatedMartensitic
TransformationStrain(%)
CrystalOrientation
[0 0 1]
2.63
[0 1 1]
8.20
[1 1 1]
9.42
Average strain
8.42
Source:
Miyazaki, S., Ishida, A.,
Mater. Sci. Eng. A
, 273-275, 106-133, 1999, with per-
-275, 106-133, 1999, with per-
275, 106-133, 1999, with per-
-133, 1999, with per-
133, 1999, with per-
mission from Elsevier.
