A FIELD-ION MICROSCOPY STUDY OF NANOCRYSTALLINE NI AND NI3AL

Electrodeposition with Ni has been shown to be a feasible technique to fabricate atom probe field-ion microscope (APFIM) specimens from ball-milled nanocrystalline Ni3Al powder particles. Field-ion images of the electro-deposited nanocrystalline Ni matrix revealed atomically sharp grain boundaries in the majority of the cases and occasionally some dark regions at the boundaries. Atom-probe analysis of the dark regions did not reveal any compositional differences. In some instances, an unidentified dark region was observed at the boundaries. Three distinct phases were identified from the field-ion images obtained from the ball-milled Ni3Al specimens. Brightly-imaging, well-defined atomic terraces were characteristic of the L1(2)-ordered phase, poorly-defined atomic terraces that were separated by darkly-imaging regions indicated the intermediate disordered phase and randomly-imaging spots gave some indication of the amorphous phase of Ni3Al.