Abstract
The atom movements during the martensitic transformation are described by a combination of two shears: a long-wave primary and a secondary shuffle type shear which occur simultaneously. The primary and part of the secondary shear are equivalent to the Bain distortion, and the rest of the secondary shear corresponds to the lattice invariant shear of the phenomenological theories. This description permits us to obtain information on the multiplicity of the transformation-retransformation paths. It is shown that the shape-memory alloys have a single possible path when the matrix phase possesses long-range order. The selection of the activated shear systems can be correlated with their resistance against small displacements, given by the corresponding elastic constants. This permits us to classify and interpret the crystallography of a large body of martensitic transformations.
