Environmental Engineering Reference
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Fig. 10.24 Schematic representation of
the shape-memory and superelastic effects in the
stress
-
temperature phase diagram (up),
together with typical shape-memory (down-left) and
superelastic (down-right) behaviours
transformation is performed quickly enough by means of a high stress or strain rate
(adiabatically or close to it), the material heats up when loaded (transformed from
austenite to martensite) and cools down when unloaded (transformed from mar-
tensite to austenite).
Even though the
rst shape-memory effect was observed already in the 1930s in
Au
Zn alloys, the breakthrough occurred in 1963, when what is still the
most widely used Ni
-
Cd and Cu
-
Ti shape-memory alloy was discovered. In subsequent years,
a number of shape-memory and superelastic alloys were developed and charac-
terized, which can, in general, be divided into three groups [
91
]:
-
Ni
Ti-based alloys doped with Cu, Co, Nb, Pd, etc.
-
Cu-based alloys doped with Al, Ni, Zn, Mn, etc.
Fe-based alloys doped with Mn, Si, Ni, Pd, etc.
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