In situ study of the β phase decomposition process in a Cu-Al-Ni shape memory alloy processed by powder metallurgy

The precipitation of the stable phases in Cu-Al-Ni shape memory alloys (SMA) limits the maximum using temperature since the decomposition of beta phase degrades very quickly the martensitic transformation. In this paper, the precipitation processes of the metastable beta phase during heating in a Cu-14.37 Al-4.2 Ni (wt. %) SMA processed by powder metallurgy have been studied by Differential Scanning Calorimetry (D.S.C.) and in situ neutron powder diffraction. The pro-eutectoid gamma(1) precipitation and the eutectoid decomposition has been observed during heating, followed by the posterior dissolution at higher temperature. The transformation temperatures have been determined by D.S.C. The Rietveld analysis performed on the neutron diffraction spectra allows to determine the volume fraction of the different precipitated phases and their evolution during heating. The activation energy of the primary gamma(1) precipitation has been determined.