Invited Paper AS+BI-TuA7
Surface Properties and Complexity of Al-based Intermetallics

Tuesday, October 29, 2013, 4:00 pm, Room 204

Quasicrystals represent the ultimate state of lattice complexity in a crystal. Shechtman, who discovered quasicrystals,¹ was awarded a Nobel Prize in Chemistry in 2011 for having led to a revolution in the way ordered solids are now understood in materials science. The talk will focus on a specific series of compounds, namely Al-based complex metallic alloys (CMAs) which comprise a significant number of crystalline compounds of changing lattice complexity, according to composition, and yield few icosahedral compounds that are thermodynamically stable and may be prepared into various sample shapes that allow for the measurement of surface physical properties.

Surface energy (γ_S) is one of the few fundamental properties of condensed matter: it defines the equilibrium shape of a crystal, it determines the interfacial behavior of any piece of liquid or solid against another body, etc. The talk will summarize a number of attempts to estimate the surface energy of a large variety of CMAs, including the stable, icosahedral Al-Cu-Fe and Al-Pd-Mn quasicrystals.

Pin-on-disk experiments, after appropriate calibration, lead to reliable data that fall in the range 0.5 < γ_S < 0.8 Jm^-2 for these compounds.² The average value of γ_S is about one half that of pure aluminum (γ_S = 1.15-1.2 Jm^-2), and less than a quarter that of iron (γ_S = 2.2-2.4 Jm^-2). It is consistent with the low wetting behavior and reduced adhesion force against hard steel observed in high vacuum for these quasicrystals. Correlation to specific features of the electronic density of states will be emphasized, in line with the varying complexity of the studied CMA compounds. Potential applications in high vacuum technology will be addressed.

References:

1- D. Shechtman, I. Blech, D. Gratias and J.W. Cahn, Phys. Rev. Lett., 1984, 53-20, 1951.

2- E. Belin-Ferré and J.M. Dubois, Int. J. Mat. Res., 97 (2006) 7.