Structural evolution and phase formation in cold-rolled aluminum–nickel multilayers

Abstract Multilayer samples of nickel and aluminum with the compositions of Al–20 at% Ni and Al–25 at% Ni were prepared by the repeated folding and cold rolling (F&R) of elemental foils. Characterization by X-ray diffraction, scanning electron microscopy and transmission electron microscopy/selected-area electron diffraction reveals that the rolling procedure results in a decrease in thickness of the elemental layers to below 0.1 μm and a reduction in grain size to below 50 nm, but does not induce formation of an intermediate phase. Differential scanning calorimetry (DSC) measurements on samples subjected to different numbers of F&R cycles show double exotherms related to an initial nucleation and lateral growth and a subsequent thickening of reactively formed Al3Ni. The DSC data agree qualitatively with predictions of an existing kinetic model for multilayer reactions, but a decisively improved quantitative fit is obtained when a distribution of layer spacings is considered, rather than a well-defined modulation wavelength. The modified kinetic model can be inverted to yield information on the evolution of the distribution of layer sizes during deformation from DSC data.