Growth and Characterization of Shape Memory Cu-Zn-Al Single Crystals

Abstract
To provide a better insight of shape memory alloys (SMA) behavior, Cu- Zn-Al single crystals were grown by the Bridgman technique. Melting was performed under pure argon in a graphite crucible allowing to obtain samples (total length 40 mm) with the final shape directly suitable for mechanical tests (cylinders with taper heads : 25 mm useful length, 4 mm in diameter). The chemical composition was checked by Differential Scanning Calorimetry and resistivity. It was found that a small zinc concentration gradient exists along the samples : it induces a difference less than 5 K for transformation temperatures in the useful length. The morphology, the shape deformation, crystal structure, sub-structure and orientation have been investigated by optical, transmission and scanning electron microscopy and by X-Ray diffraction. Pseudoelastic isothermal tensile tests and training under constant applied stress and variable temperatures were carried out. The training efficiency for these elaborated alloys is very large (about 80-90%).