Intermetallic phase formation during annealing of Al/Ni multilayers

The phase evolution during annealing of Al/Ni multilayer samples prepared by ion-beam sputtering with composition modulation wavelengths Λ between 10 and 400 nm was determined using x-ray diffraction and differential scanning calorimeter measurements. Samples with average compositions of Al0.40Ni0.60 and Al0.75Ni0.25 were investigated. For the Al0.40Ni0.60 samples the following results were obtained. A measure of the degree of periodicity and the sharpness of the interfaces in a sample with Λ=80 nm was the large number (over 20) of peaks observed in small-angle x-ray scattering measurements. A sample with Λ=10 nm was transformed by heat treatment directly to the AlNi phase. In the Λ=80 nm sample, the first phase formed after annealing was the metastable η phase. The η phase was identified as Al9Ni2. In the 400 nm wavelength sample, both the metastable η phase and the stable Al3Ni formed after the first exothermic reaction. For the Al0.75Ni0.25 samples two results were obtained. A Λ=11.4 nm sample transformed directly on annealing into Al3Ni. The η phase was the first phase formed on annealing a Λ=100 nm sample. The difference in the component diffusivities and the concentration gradient play an important role in controlling phase formation and evolution.