Atom Probe Studies of Nanocrystalline Microstructural Evolution in Some Amorphous Alloys

This paper reviews our recent atom probe studies of nanocrystalline alloys fabricated by primary crystallization of amorphous alloys. Partitioning and segregation of alloying elements in the course of primary crystallization in Fe–Si–B–Nb–Cu, Fe–Ta–C, Fe–Zr–B and Al–Ni–Ce(–Cu) alloys were examined by atom probe field ion microscopy. Concentration fluctuations in alloying elements are commonly observed in the early stage of annealing, which is believed to induce a large number density of nucleation sites. During the growth stage of the crystalline phases, one or two following mechanisms work to control the crystal grain growth: (1) stabilization of the remaining amorphous phase by partitioning of amorphous forming elements, (2) segregation of slow diffusing solute element at the amorphous/crystal interface, (3) precipitation of thermally stable compound such as TaC.