Tribological properties of a B2-type Al-Pd-Mn quasicrystal approximant

The tribological properties of a B2-type Al–Pd–Mn quasicrystal approximant were investigated and compared with those of an Al–Pd–Mn icosahedral quasicrystal. The approximant was of the _ phase, having a crystalline CsCl-type structure and nominal composition Al₄₈Pd₄₂Mn₁₀. Friction coefficients measured in ultrahigh vacuum between a pair of Al₄₈Pd₄₂Mn₁₀ samples having truly clean surfaces were found to be twice as high as those reported for the Al₇₀Pd₂₁Mn₉ quasicrystal. When the surfaces were oxidized by exposure to O₂ or H₂O, the friction coefficients decreased by roughly a factor of two for both materials but the friction coefficient for the approximant remained roughly twice that of the quasicrystal. The rate of oxidation of the approximant was found to be one order of magnitude higher than that of the quasicrystal. This corroborates findings that suggest that quasicrystals exhibit an inherent resistance to oxidation and corrosion. Vickers hardness measurements show that the quasicrystal is roughly three times as hard as the approximant.