On two-step strain–temperature behavior in Cu–Zn–Al shape memory alloy wireactuators

Abstract

Nowadays, some compositions of Cu–Zn–Al alloys are commercially available with thepotential to present shape memory properties after a suitable thermomechanical treatment.Applied as sensor and/or actuator, the smallest product of Cu-based shape memory alloys(SMA) are wires 0.5 mm in diameter. This paper focuses on Cu–25.3Zn–4.0Al (wt%) wires,0.5 mm in diameter, that were supplied by Societé Tréfimetaux (France) in a cold drawncondition, without any martensitic transformation. After betatization heat treatment of theSMA wires, physical characterization was carried out through an optical micrograph, DSCand x-ray diffraction while the thermomechanical behavior of the samples was verified bythermal cycling under a constant load. The results obtained have demonstrated theappearance of a two-step transformation which causes an important change in thestrain–temperature behavior. This phenomenon is rarely observed in these Cu–Zn–Al SMA.