Initial phase formation and dissociation in the thin-film Ni/Al system

We have investigated the interactions of Al/Ni, Al/NiAl/Ni, Al/Ni3Al, and NiAl3/Ni thin films between 300 and 425 °C. The films were prepared by sequential evaporation and coevaporation, then vacuum annealed and analyzed by Rutherford backscattering and x-ray diffraction. The reaction always started at the interface in contact with the most Al-rich film and resulted in formation and growth of NiAl3, unless that was the most Al-rich layer. Subsequently the reaction proceeded to Ni2Al3. We conclude that the kinetics rather than the thermodynamics is responsible for determining the growth of these phases.