Size effects in shape memory alloys

Conventional mechanical testing, nano- and micro-indentation, and in situ neutron diffraction at stress and temperature were used to investigate superelasticity and the shape-memory effect across geometrical and microstructural length scales. Aspects addressed in the context of superelasticity in NiTi include: homogeneous vs. heterogeneous deformation and the role of dislocation and interfaces vis-a-vis misfit strain accommodation, elastic strain energy, and frictional resistance contributions to the thermodynamics of the stress-induced phase transformation. In the case of shape-memory behavior, comparisons are made between results from micron-scaled wires and bulk cm-scaled specimens. Results from monotonic loading and constrained recovery (heating under load) experiments in a NiTiPd shape memory alloy are presented with emphasis placed on specimen fabrication and electropolishing methodologies.