Friction between single-grain Al70Pd21Mn9 quasicrystal surfaces

An UHV tribometer was used to make measurements of friction between the fiv e-fold surfaces of two single-grain Al70Pd21Mn9 quasicrystals. The surfaces of these quasicrystal samples were either truly clean or modified by contr olled adsorption of desired species. The results of many (similar to 200) s ingle-pass friction measurements using clean quasicrystal surfaces indicate that the average static friction coefficient is mu(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 b ut is higher than those measured on quasicrystal surfaces exposed to air. U nder shear the quasicrystal surfaces slide over one another without exhibit ing stick-slip behavior or adhesion. This behavior differs from clean metal surfaces that often exhibit adhesion after being brought into contact in u ltra-high vacuum. Studies were performed to determine the effects of surfac e oxidation, surface structure and surface composition on quasicrystal fric tion. During the early stages of oxidation the static friction coefficient decreased to a limit of mu(s) = 0.35 +/- 0.05. More subtle changes to the q uasicrystal surfaces such as adsorption of sulfur or formation of a thin Al -Pd-Mn alloy of CsCl structure produced no significant changes in the stati c friction coefficient. (C) 1999 Elsevier Science B.V. All rights reserved.