M. Somerday et al., A SYSTEMATIC ANALYSIS OF TRANSFORMATION STRESS ANISOTROPY IN SHAPE-MEMORY ALLOYS, Philosophical magazine. A. Physics of condensed matter. Structure, defects and mechanical properties, 75(5), 1997, pp. 1193-1207
Prior experimental observations reveal that the transformation stress
and strain of single-crystal shape memory alloys (SMAs) are strongly a
nisotropic and moderately asymmetric. Models capable of evaluating the
anisotropy of transformation stress are now available for unconstrain
ed and constrained transformation of single crystals. In the present i
nvestigation, anisotropy and asymmetry indices are systematically eval
uated for a set of seven SMAs, for both the unconstrained and the cons
trained transformation. Within the group Cu-Al-Ni, Cu-Zn-Al, Cu-Zn-Ga,
Cu-Zn and NIAl, the anisotropy decreases with increasing misorientati
on of the habit plane and shear direction from the ideal {011}{0(1) ov
er bar1$} shear system orientation. On the basis of this observation,
it is hypothesized that low anisotropy is an essential feature of tech
nologically useful SMAs. The anisotropy indices for several synthetic
SMAs are examined to evaluate the changes needed to decrease the aniso
tropy of SMAs such as Cu-Zn and NiAl.