CYCLING EFFECTS ON TRANSFORMATION BEHAVIOR IN SHAPE-MEMORY CUZNAL ALLOYS

Shape memory alloys transform martensitically to close packed structur es and have internally faulted structures in martensitic condition, an d they are very sensitive to cycling and ageing effects. In noble meta l copper based alloys, martensitic transformation occurs from a cubic structure with B2 (or DO3) order to a long period layered structure 9R (or 18R). In a single crystal of parent phase, 24 martensite variants grouped around six {110}(infinity) matrix planes can be formed at tem peratures below M(s). These alloys deform by variant transformations, in case they are stressed in the martensitic condition. Cycling effect s on transformation behaviour in two shape memory CuZnAl alloys receiv ed in the closed-coil form called shape memory actuator which have ori ginally open-coil form in austenitic condition have been investigated. Shape memory alloys remain in the deformed shape in martensitic condi tion and recover the original form in austenitic condition and the sha pe memory actuators cycle between the open and closed-coil configurati ons on heating above A(f) and cooling below M(f) temperatures. These e ffects are attributed to the reversible transition between the austeni te and martensite phases. These alloys are metastable in martensitic c ondition, and cycling effects also contribute to the martensite stabil ization.