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Autori: Leandru-Gheorghe Bujoreanu, Marcus L. Young, Susanne Gollerthan, Christoph Somsen, Gunther Eggeler
Editorial: International Journal of Materials Research, 101(5), p.623-630, 2010.
The influence of microstructure on the stress–strain behavior
of an Ni-rich NiTi shape memory alloy is examined.
Specimens cut from a large diameter-bar of Ni50.7Ti49.3
shape memory alloy were analyzed in two states: (i) annealed
and (ii) annealed and aged. The annealed state shows
a fully austenitic structure with no precipitates and no distortions
caused by residual stresses. The annealed and aged
state has coherent Ni4Ti3 particles precipitated in the proximity
of the austenite grain boundaries. The size of the precipitates
increases moving away from the grain boundaries
toward the grain interiors. The evolution of the two states
in the stress–strain–temperature space has been analyzed
using tensile specimens with special geometry. Due to the
complex effects of the coherent precipitates, the specimens
in the aged state exhibited lower stress plateaus in the tensile
loading–unloading curves, which enabled the occurrence
of transformation pseudoelasticity from room temperature
to 333 K.
Cuvinte cheie: Shape memory alloy; Martensitic transformation