Tribological properties of quasicrystalline coatings

Coatings of three different compositions (Al₆₅Cu₂₀Fe₁₅, Al₆₄Cu₁₈Fe₈Cr₈, and Al₆₇Cu₉Fe_10.5Cr_10.5Si₃) were realized by various thermal deposition techniques. They were studied in the as-deposited state and after annealing. In view of potential applications, these quasicrystalline coatings were examined from the point of view of tribology: friction and wear. Some basic components of friction such as roughness, plowing, and adhesion have been studied in scratch testing. The friction resistance of the coating is strongly dependent on its inherent porosity, hardness, and thickness. The damage of the coatings is essentially brittle though some ductile behavior is observed. Static indentation hardness is in the range 500–600 HV_0.03 (5–6 GPa), whereas the scratch hardness varies from 1.4 to 2.4 GPa depending on the percentage of porosity. Friction coefficients (measured at constant load of 20 N) were found to be typically 0.07 and 0.20 for diamond (tip radius R = 0.79 mm) and AISI 52100 (radius R = 0.79 mm) indenters, respectively.