Atom Probe Studies of Supercooled Liquids

Phase transformations in the supercooled liquid region (between T, and T,,,), prior to the onset of crystallization, in amorphous Pd-Ni-P alloys remain controversial. It has been previously proposed that the amorphous alloy decomposes into two amorphous phases prior to the crystallization reaction when annealed in the supercooled liquid region. Investigations by DSC, Mossbauer spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) small-angle X-ray scattering (SAXS) and atom probe field ion microscopy (APFIM) have since corroborated or refuted phase separation prior to crystallization in the supercooled liquid region of PdNi-P alloys. The microstructural development during annealing in the supercooled liquid region of amorphous Pd46Ni36P18, which is supposedly of phase-separating composition, is compared and contrasted with those of Pd48Ni32P20 and Pd40NiloCu30P2~. TEM showed that the as-quenched alloys were fully amorphous and APFIM analysis showed random solute distributions, typical of amorphous materials. Annealing in their respective supercooled iiquid regions did not result in the formation of compositionally modulated microstructures prior to the onset of crystallization.