Microstructural characterization of reactions in Al–Zr thin film couples

Abstract

The mechanisms of reaction in sputter-deposited Al–Zr thin film couples have been investigated using extensive transmission electron microscopy (TEM) observations of cross-sectional specimens prepared by the novel use of an ultramicrotome. The TEM observations greatly facilitated understanding of composition-depth profiles obtained by Rutherford backscattering spectroscopy (RBS). The reaction between Al and Zr in thin films, and the influence of Cu on this reaction, was shown by the TEM to be much more complex than previously reported in studies that largely used RBS. Reaction of Al and Zr in sputter-deposited films occurs in two stages. Initially reaction occurs by growth of an amorphous layer at the Zr interface and is promoted by intermixing of Al and Zr during deposition. Growth of an amorphous layer in an Al-transition metal thin film couple has not been reported previously. Subsequently, the amorphous layer is consumed by growth of microcrystalline Al3Zr from the Zr/reaction layer interface. The transition from growth of amorphous to microcrystalline Al3Zr results in thickening of the reaction layer with an overall growth rate exponent of 1/3. The Al3Zr grows with the metastable L12cubic structure, except in the presence of Cu, when it grows with the tetragonal DO23structure. The fine initial Al and Zr grain sizes limit the influence of Cu on the morphology of the reaction; in all cases, a continuous and uniform reaction layer thickness is observed by TEM.