Patent ID: 6946040

Claim:
A shape memory alloy being polycrystallane and having a substantially uniformly fine-grained crystal structure, crystal orientations thereof being arranged substantially along a direction suitable for an expected operational direction wherein said shape memory alloy is selected from the group consisting of a wire having a solid round cross section, a plate, and a coil, and wherein said shape memory alloy is prepared by a process comprising the steps of: (a) providing a raw shape memory alloy having a substantially uniformly fine-grained crystal structure; and (b) arranging crystal orientations of said raw shape memory alloy substantially along a direction suitable for an expected operational direction wherein step (a) comprises the step of: (c) heating said raw shape memory alloy in an amorphous state or a state similar thereto to the temperature at which recrystallization begins or a little above for a short period of time, with a stress applied to said raw shape memory alloy in said expected operational direction at least in the stage where a recovery recrystallization begins, to produce a substantially uniform fine-grained crystal structure with an anisotropy in said expected operational direction, while relaxing the internal stress generated in said raw shape memory alloy in said expected operational direction; and step (b) comprises the steps of: (d) subjecting said raw shape memory alloy to a high level of deformation by means of a stress in said expected operational direction at a very low temperature at which the austenite phase does not remain in said raw shape memory alloy so that a slide deformation is introduced into the crystal grains of said raw shape memory alloy which have been transformed completely into the martensite phase within a reversible range along the direction of said stress; (e) heating said raw shape memory alloy to a temperature between A f and the recrystallization temperature with a stress applied to said raw shape memory alloy in said expected operational direction so that the directions of reversible slip motions of the respective crystal grains of said raw shape memory alloy are arranged in a direction suitable for said expected operational direction.