Indirect assessment of the surface energy of the Al–Cu–Fe quasicrystal

This work summarizes an attempt to estimate the surface energy of the stable, icosahedral Al–Cu–Fe quasicrystal (i-ACF hereafter). To this end, samples of i-ACF were prepared by sintering a powder produced by ball milling and heat treating a master ingot of composition Al₅₉Cu₂₅.₅Fe₁₂.₅B₃ (at.%), icosahedral lattice structure, and containing negligibly small amounts of contaminating crystalline phases. This powder was then sintered in the shape of a cylinder appropriate for pin-on-disk tests in ambient air. Variable amounts of either Sn or Bi were added to the powder prior to sintering. These elements do not dissolve in the quasicrystal and form small pockets of pure Sn or Bi that are either isolated or percolating, depending on the added volume of metal. Analysis of pin-on-disk data deduced from tests performed at room temperature allows us to conclude that the surface energy of the quasicrystal itself falls between the respective surface energies of the pure metals: γBᵢ ≤ γQC ≤ γSₙ or 0.5 ≤ γᵢ₋ACF ≤ 0.8 J/m².