Multilayer samples of nickel and aluminum with the compositions of Al-20 at percent Ni and Al-25 at percent Ni were prepared by the repeated folding and cold rolling (FR) 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 #mu#m and 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 FR cycles show double exotherms related to an initial nucleation and lateral growth and a subsequent thickening of reactively formed Al_3Ni. 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.
展开▼
