  The nucleation of bcc austenite in a single crystal of a mechanically
stabilized 2H-martensite of Cu-Al-Ni shape-memory alloy is studied. The
nucleation process is induced by localized heating and observed by optical
microscopy. It is observed that nucleation occurs after a time delay and that
the nucleation points are always located at one of the corners of the sample (a
rectangular bar in the austenite), regardless of where the localized heating is
applied. Using a simplified nonlinear elasticity model, we propose an
explanation for the location of the nucleation points, by showing that the
martensite is a local minimizer of the energy with respect to localized
variations in the interior, on faces and edges of the sample, but not at some
corners, where a localized microstructure can lower the energy.
