The initial stages of the  precipitation in a dilute Ni-Al binary alloy, Ni-11.6 at.%Al, were studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), electron diffraction and electron microscopy (FEG-SEM and TEM) techniques. Three samples were similarly solution treated and then cooled to room temperature under different cooling rates, 170، 25 and 0.03oCs-1. The results indicate a clearly homogenous  nucleation during rapid quenching which takes place via simultaneous ordering and phase separation. However, by decreasing the cooling rate to 25oCs-1 the nucleation mechanism changes to heterogeneous on the preferred nucleation sites. The capability of the mentioned empirical techniques for studying the initial stages of the γ′ is another subject which is studied in this article.

Keywords: Ni-Al alloys, γ′ precipitation, cooling rate, homogenous nucleation, heterogeneous nucleation, FEG-SEM, DSC.

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