PhD Thesis_RuiMSMartins.pdf - RUN UNL

In-situ XRD studies during growth of Ni-Ti SMA films and their complementary ex-situ characterization
which the crystalline phase forms [123]. For films crystallized during deposition, a strong
fibre texture is commonly observed for the B2 cubic structure [96], suggesting that the
crystalline phase nucleates on the surface of the heated substrate assuming an orientation that
minimizes surface energies [65, 109]. Miyazaki and Ishida [23] have study the texture in films
deposited on unheated and heated substrates. Figure 1.40 show pole figures of Ni-Ti B2 phase
nominally measured in the Bragg peaks B2(110) and B2(200): (a) Ti-52.2at%Ni film which
was crystallized at 700°C for 1 h (deposited at RT); (b) Ti-51.6at%Ni film heat-treated at
400°C for 1 h (the film was sputtered at 350°C).
(a)
(b)
Fig. 1.40: Pole figures of Ni-Ti B2 phase nominally measured in the Bragg peaks B2(110)
and B2(200); (a) Ti-52.2at%Ni film which was crystallized at 700°C for 1 h, (b) Ti-
51.6 at%Ni film heat-treated at 400°C for 1 h (the film was sputtered at 350°C) [23].
The Ti-52.2at%Ni film exhibits a considerably uniform orientation distribution of
grains with a maximum axis density of only 3.9 [Fig. 1.40(a)]. In contrast, the Ti-51.6 at%Ni
film [Fig. 1.40(b)] shows a maximum axis density of 110. The second strongest peak density
is observed on a circle with 60° apart from the centre of the {110} pole figure. This unique
axis density distribution demonstrates a typical fibre texture with a fibre axis
Chapter 1 - Background and Literature Review 72