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 deg. C. In this paper, the effects of isothermal and continuous heating on eutectoid Cu-based SMA up to 400 deg. 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 αs and an intermetallic compound γ2, i.e., β1 → αs + γ2. The second process results from αs evolving into a nanometric globular precipitates of γ2 and an unsaturated α, i.e., αs → γ2 + α.