High temperature decomposition of the β1 phase in a Cu-Al-Ni shape memory alloy

The copper-based shape memory alloys (SMA) are susceptible to be decomposed by precipitation beyond 220 degrees C. In this paper, the effects of isothermal and continuous heating on eutectoid Cu-based SMA up to 400 degrees C are evaluated by using differential scanning calorimetry (DSC), X-ray energy dispersion spectroscopy (EDX), X-ray diffraction (XRD) and scanning electron microscope/transmission electron microscope (SEM/TEM) techniques. The experiments show that a succession of two precipitation processes appears. The first process to appear is a cellular process composed of a supersaturated Al solid solution alpha(s) and an intermetallic compound gamma(2), i.e., beta(1) -> alpha(s) + gamma(2). The second process results from alpha(s) evolving into a nanometric globular precipitates of gamma(2) and an unsaturated alpha, i.e., alpha(s) -> gamma(2) + alpha. (C) 2008 Elsevier B.V. All rights reserved.