In-Situ TEM Phase Formation in Cold Rolled Aluminum-Nickel Multilayers

ABSTRACTMultilayer samples of Nickel and Aluminum with an overall composition of Al-20Ni were prepared by cold rolling of elemental foils. The sample microstructures and phases were characterized by XRD, SEM and TEM/SAED, and the reactive phase formation was then examined by DSC measurements. XRD, SEM and TEM measurements show that the rolling procedure results in a decrease of the Al and Ni layer thicknesses (down to 100 nm in average) and a decrease of the grain size (down to less than 50 nm). No phase formation is observed during the cold rolling procedure. In isochronal DSC scans of the Al-Ni multilayers, the formation of the Al3Ni phase was found to be a two step reaction process due to 2-dimensional nucleation and lateral growth and a 3-dimensional phase thickening. While XRD measurements showed Al3Ni as the only phase that forms, more detailed TEM investigations of the samples after DSC treatment also showed a small amount of an amorphous Al-Ni phase, formed by a thermally activated solid state amorphization reaction (SSAR). In-situ TEM heating of the amorphous areas under the electron beam in the microscope yielded the crystallization of the amorphous phase to a B2 structure and a growth of the B2 grains up to 100 nm in size.