Formation of α-approximant and quasicrystalline Al–Cu–Fe thin films

Multilayered Al/Cu/Fe thin films have been deposited by magnetron sputtering onto Si and Al2O3 substrates with a nominal global composition corresponding to the quasicrystalline phase, 5:2:1. Subsequent annealing was performed on the samples up to 710 °C. It is found that when using Si as a substrate a film-substrate reaction occurs already below 390 °C, where Si diffuses into the film. This changes the composition, promoting the formation of the α-approximant Al55Si7Cu25.5Fe12.5 in the temperature range 400 to 650 °C over the quasicrystalline ψ-phase. When annealing the same Al–Cu–Fe thin film grown on Al2O3 substrates the Al62.5Cu25Fe12.5 icosahedral quasicrystalline phase is formed.

► The α-approximant forms during annealing of Al/Cu/Fe thin film on a Si substrate. ► Diffusion of Si into the film occurs at temperatures below 390 °C. ► The Si diffusion prevents the formation of the icosahedral ψ-phase. ► If an Al2O3 substrate is used with the same film the icosahedral ψ-phase is formed.