Patent ID: 6596102
Filing Date: 2003-07-22
Classification: C22F

Abstract:
A method of treating a shape memory alloy 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 in which the shape memory alloy is expected to move when used in an actuator after the completion of the treatment, wherein step (a) comprises the step of: (c) heating said raw shape memory alloy in a substantially amorphous state to or above the temperature at which recrystallization begins 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; and (e) heating said raw shape memory alloy to a temperature between Af 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.