Fatigue and the beta-18R martensitic transition in Cu-Zn-Al single crystals: mechanical behavior, defects and diffusive phenomena

M. SADE, F.C. LOVEY, J. MALARRIA, C. DAMIANI, A. YAWNY

Metz

Conferencia; NATO Advanced Research Workshop on New Trends in Phase Transformations and their Applications to Smart Structures; 2002

The mechanical behavior during pseudoelastic cycling is one of the important properties of shape memory alloys. This presentation will focus its attention on Cu-Zn-Al single crystals. Several changes occur in this material during cycling by applying stresses at a constant temperature above Ms. Bulk defects consisting on dislocation bands with retained martensite and intrusion-extrusion surface defects are formed. The formation of the defects, density and other characteristics depend on the working temperature and alloy composition. In addition to this, the shape of the stress-strain curves are strongly affected by diffusive phenomena which take place in both phases involved, particularly above room temperature. Interaction of the atomic diffusion with the bulk defects has also been observed. The characteristics of all these processes must be known before a reliable simulation of the material behavior is performed. Controlled experiments where the kinetics of the diffusive phenomena could be analyzed together with their evolution during and after fatigue cycling is necessary. The interaction among mechanical behavior, defects and diffusion will be discussed. The effect of the bulk defects on the amount of martensite stabilization after fatigue will be presented.