High temperature decomposition of the β 1 phase in a Cu–Al–Ni shape memory alloy

Abstract

The copper-based shape memory alloys (SMA) are susceptible to be decomposed by precipitation beyond 220 °C. In this paper, the effects of isothermal and continuous heating on eutectoid Cu-based SMA up to 400 °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 α s and an intermetallic compound γ 2, i.e., β 1 → α s + γ 2. The second process results from α s evolving into a nanometric globular precipitates of γ 2 and an unsaturated α, i.e., α s → γ 2 + α.