A series of alloy systems exhibit a peculiar property called shape memory effect which involves the repeated recovery of macroscopic shape of material at different temperatures. The origin of this phenomenon lies in the fact that the material changes its internal crystalline structure with changing temperature. On cooling from high temperature, these alloys undergo a displacive transition following two ordering transitions. This transition is called martensitic transition and responsible for the shape memory effect. In case these alloys are deformed in a temperature range in martensitic condition they change in shape and recover the original austenitic shape on heating over the reverse transition temperature after removing the strain. These materials regain the deformed shape on cooling to the martensitic state and cycle between deformed and undeformed shapes on cooling and heating. Shape memory alloys have attracted considerable interest as actuators and smart materials in engineering applications, to control the shape change and other properties. The choice of material as well as actuator and sensor to combine it with the host structure is very essential . Martensitic transformation and the associated mechanical shape reversibility in copper-based shape memory alloys is strongly influenced by cycling and ageing effects, due to the metastable character. These materials can be plastically deformed by variant transformations, in case of stress in the martensitic condition. The effects have been investigated on two shape memory CuZnAl and CuAlMn alloys. Ageing effects in CuZnAl alloys have been investigated by X-ray diffraction and optical microscopy. The alloys in the coil form were cycled between the closed and open coil shapes (deformed and undeformed conditions), and elongation parameters were measured following cycles under different loading conditions. Key Words: Shape memory effect, thermal actuators, and thermal cycles.

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1. X-Ray and electron diffraction studies on layered martensite structures of Copper based shape memory alloys
2. The Role of Ordering in Martensite Microstructures in Copper Based Shape Memory Alloys