Friction between single-grain Al₇₀Pd₂₁Mn₉ quasicrystal surfaces

An UHV tribometer was used to make measurements of friction between the five-fold surfaces of two single-grain Al₇₀Pd₂₁Mn₉ quasicrystals. The surfaces of these quasicrystal samples were either truly clean or modified by controlled adsorption of desired species. The results of many (approximately 200) single-pass friction measurements using clean quasicrystal surfaces indicate that the average static friction coefficient is μ_s = 0.60±0.08. The friction coefficient of the perfectly clean quasicrystal surfaces is lower than those reported for the perfectly clean surfaces of many pure metals but is higher than those measured on quasicrystal surfaces exposed to air. Under shear the quasicrystal surfaces slide over one another without exhibiting stick-slip behavior or adhesion. This behavior differs from clean metal surfaces that often exhibit adhesion after being brought into contact in ultra-high vacuum. Studies were performed to determine the effects of surface oxidation, surface structure and surface composition on quasicrystal friction. During the early stages of oxidation the static friction coefficient decreased to a limit of μ_s = 0.35±0.05. More subtle changes to the quasicrystal surfaces such as adsorption of sulfur or formation of a thin Al-Pd-Mn alloy of CsCl structure produced no significant changes in the static friction coefficient.