GROWTH AND CHARACTERIZATION OF SHAPE-MEMORY CU-ZN-AL SINGLE-CRYSTALS

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