Jean-Marie Dubois

Abstract:

The talk will focus at friction and wetting on Al-based quasicrystals and complex metallic alloys (CMAs), which comprise a significant number of crystalline compounds of changing lattice complexity, according to composition. Such compounds are thermodynamically stable and may be prepared into various sample shapes that allow measurement of surface physical properties. Surface energy (I³S) 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 AlCuFe and AlPdMn quasicrystals. Pin-on-disk experiments, after appropriate calibration, lead to reliable data that fall in the range 0.5 < I³S < 0.8 J/m2 for these quasicrystals. This average value of I³S is about one half that of pure aluminum (I³S = 1.15-1.2 J/m2), and less than a quarter that of iron (I³S = 2.2-2.4 J/m2). It is consistent with the low wetting behavior and reduced adhesion force against hard steel observed in high vacuum for these quasicrystals. The 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 low-wetting and high vacuum technologies will be addressed with a view to finding sustainable, alternative coating solutions to fluorinated surface layers.