Lifetime of superelastic Cu-Al-Be single crystal wires under bending fatigue

Many applications of shape memory alloys require cyclic deformation, making fatigue behavior of material an important consideration in component design. Cu-Al-Be alloys are thermically very stable and show a high superelasticity especially in single crystalline form. In order to study fatigue lifetime of these alloys, tests were performed on Cu-Al-Be single crystal wires using a bending apparatus with imposed strain. For large deformation (10%), Cu-Al-Be single crystals have shown good fatigue properties, comparable to Ni-Ti at a deformation of 3%. As cycling proceeded, superficial striations patterns appeared, which were linked with the imposed strain. In surface striations, microcracks were observed which are assumed to cause the failure.