Intermetallic compound formation in Pd/Al multilayer thin films

Nanolayered palladium/aluminium thin films, with an equiatomic average chemical composition and modulation periods of 5, 14 and 30 nm, were deposited by magnetron sputtering onto stainless steel substrates. The as-deposited Pd/Al multilayer films are composed of Pd- and Al-rich nanolayers, along with the formation of the metastable nanocrystalline compound AlPd at the interfaces, which is particularly evident for short periods. The structural evolution of the multilayer thin films towards the high temperature AlPd phase (HT-AlPd) was studied in-situ using hot X-ray diffraction. Heat treatment leads to a disruption of the nanolayered structure by interdiffusion followed by chemical reaction, leading to the formation of intermetallic compounds. Whatever the period, the films always evolve to the HT-AlPd equilibrium intermetallic compound with a similar phase sequence. In fact, for the Pd–Al system the formation of intermediate intermetallic compounds such as Al3Pd2 could not be avoided, not even by reducing the modulation period. The occurrence of reaction during deposition and the formation of intermediate phases limits the use of Pd/Al, one of the most promising energetic aluminium based multilayer systems, for joining purposes.