Thermo-Mechanical behavior at Nano-Scale and Size Effects in Shape Memory Alloys

摘要

Shape Memory Alloys (SMA) undergo reversible martensitic transformation in response to changes in temperature or applied stress, exhibiting specific properties of superelasticity and shape memory. At present there is a high scientific and technological interest to develop these properties at small scale, to apply SMA as sensors and actuators in MEMS technologies. In order to study the thermo-mechanical properties of SMA at micro and nano scale, instrumented nano indentation is being widely used for nano compression tests. By using this technique, superelasticity and shape memory at the nano-scale has been demonstrated in micro and nano pillars of Cu-Al-Ni SMA. However the martensitic transformation seems to exhibit a different behavior at small scale than in bulk materials and a size effect on superelasticity has been recently reported. In the present work we will overview the thermo-mechanical properties of Cu-Al-Ni SMA at the nano-scale, with special emphasis on size effects. Finally, the above commented size effects will be discussed on the light of the microscopic mechanisms controlling the martensitic transformation at nano scale.