Biomedical Engineering Reference
In-Depth Information
Ti−50.3 at.% Ni thin film
973 K 3.6 ks − 773 K 3.6 ks W.Q.
(d) 316 K
600
(c) 299 K
400
(b) 283 K
(a) 262 K
200
0
2 4
Strain (%)
FIGURE 9.20
Stress-strain curves showing SME and SE in a Ti-50.3 at.% Ni thin film. (From Miyazaki, S., Ishida, A.,
Mater.
Sci. Eng.
, 273-275, 106-133, 1999, with permission from Elsevier.)
Texture and Transformation Strain Anisotropy
Specific texture developed in materials causes anisotropic characteristics to appear in
mechanical, electrical, and magnetic behavior. Shape memory and mechanical properties
of the TiNi films depends significantly on the orientation of the crystal grains. Deposition
conditions, film composition, and post-deposition thermomechanical treatment could
have important consequences on formation and evolution of the film texture. A strong
film texture may lead to anisotropic SME because the recoverable strain and deformation
behavior is highly dependent on the film crystallographic orientation (Shu et al., 1998; Liu
et al., 2005; Gall et al., 1999).
Figure 9.21a and b shows pole figures obtained using diffraction from {110}, {200}, and
{211} planes in Ti-52.2 at.% Ni and Ti-51.6 at.% Ni thin films, respectively. The Ti-52.2 at.%
Ni thin film shows a considerably uniform orientation distribution of grains with a weak
(302) fiber texture, the maximum axis density being only 3.9. On the other hand, the Ti-51.6
at.% Ni thin film shows a strong (110) fiber texture with a maximum axis density of 110.
Because the poles of the fiber textures are both normal to film planes, the in-plane crystal
orientation distribution is uniform so that transformation strain anisotropy is weak in both
(a)
(b)
Ti−52.2 at.% Ni
973 K−3.6 ks W.Q.
Ti−51.6 at.% Ni
673 K−3.6 ks W.Q.
I
max
= 3.9
I
max
= 110.1
{110}
{200}
{110}
{200}
RD
RD
RD
RD
TD
TD
TD
TD
FIGURE 9.21
(a) {110} and {200} pole figures in a Ti-52.2 at.% Ni thin film which was crystallized at 973 K for 3.6 ks; (b) {110}
and {200} pole figures in a Ti-51.6 at.% Ni thin films which were heat-treated at 673 K for 3.6 ks. Film was sput-
tered on substrate at 623 K. (From Miyazaki, S., Ishida, A.,
Mater. Sci. Eng.
, 273-275, 106-133, 1999, with permis-
sion from Elsevier.)
