Shape memory and superelasticity in polycrystalline Cu-Al-Ni microwires

We report a strategy to significantly improve the ductility and achieve large superelastic and shape memory strains in polycrystalline Cu-Al-Ni shape memory alloys that are normally brittle. We use a liquid-phase (Taylor) wire forming process to obtain microwires of 10-150 mu m diameter with a bamboo grain structure. The reduction of grain boundary area, removal of triple junctions, and introduction of a high specific surface area in the wire decrease constraints on the martensitic transformation, and permit both superelasticity and stress-assisted two-way shape memory with recoverable strains as high as 6.8%. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3257372]