Medical Applications of Sputter-Deposited Shape Memory Alloy Thin Films - Biological and Biomedical Coatings - page 396

(a) T < M f (b) M f < T < M s (c) M s < T < A s

σ M

Heating

(d) A s < T < T f (f ) T s < T

(e) A f < T < T s

σ M

Strain

FIGURE 9.12
Schematic stress-strain curves at various temperatures in a TiNi alloy. (From Miyazaki, S., in Miyazaki et al.,
eds., Thin Film Shape Memory Alloys: Fundamentals and Device Applications , 2009, reproduced with permission
from Cambridge University Press.)

increases with increasing temperature satisfying the Clausius-Clapeyron relationship.
The stress-induced martensite phase remains after unloading, because the temperature is
below A s . The shape of the stress-strain curve of Figure 9.12c is similar to those of Figure
9.12a and b. In the temperature range A s < T < A f , the deformation induced by the stress-
induced martensitic transformation recovers partially upon unloading as shown in Figure

Superelasticity

Shape memory effect

M f M s A s A f

Temperature

FIGURE 9.13
Schematic illustration of region of SME and SE: (a) critical stress for a high critical stress; (b) critical stress for a
low critical stress. (From Miyazaki, S., in Miyazaki et al., eds., Thin Film Shape Memory Alloys: Fundamentals and
Device Applications , 2009, reproduced with permission from Cambridge University Press.)