Patent ID: 6946040
Filing Date: 2005-09-20
Classification: C22F

Abstract:
1. 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