Size Independent Shape Memory Behavior of NickelTitanium

While shape memory alloys such as NiTi have strong potential as active materials in many small-scale applications, much is still unknown about their shape memory and deformation behavior as size scale is reduced. This paper reports on two sets of experiments which shed light onto an inconsistent body of research regarding the behavior of NiTi at the nanoto microscale. In situ SEM pillar bending experiments directly show that the shape memory behavior of NiTi is still present for pillar diameters as small as 200 nm. Uniaxial pillar compression experiments demonstrate that plasticity of the phase transformation in NiTi is size independent and, in contrast to bulk single crystal observations, is not influenced by heat treatment (i.e., precipitate structure).