Tribological properties of quasicrystalline coatings
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J. von Stebut Laboratoire de Science et Genie des Surfaces (CNRS URA 1402), Ecole des Mines, Pare de Saurupt, F-54042 Nancy, France (Received 30 September 1992; accepted 8 June 1993)
Coatings of three different compositions (Al65Cu2oFe15, Al 64 Cu 18 Fe 8 Cr 8 , and Al67Cu9Fe1o.5Crio.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 HV0.03 ( 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.
I. INTRODUCTION Quasicrystals were discovered by Shechtman et al.1 in 1984 to the delight of crystallographers who are still facing great difficulties in understanding their structures2'3 and the reason why these materials escape the sacred rules of translational crystallography. Meanwhile, several laboratories looked for applications of quasicrystals since attractive physical properties are associated with both the lack of translational symmetry (i.e., the Brillouin zone breaks into many different zones in three-dimensional space) and the electronic structure carried by the multicomponent alloy. On the one hand, beneficial properties were discovered, e.g., the enhancement upon annealing of the very large electrical resistivity of A l - C u - F e icosahedral single crystals4 or the low temperature magnetic behavior of manganese or rare-earth-containing quasicrystals.5 As a matter of fact, detrimental properties have been pointed out as well. For instance, the A l - L i - C u icosahedral phase 6 happened to be extremely brittle and of no practical usefulness7 except possibly for its good resistance against oxidation. In certain stainless steel alloys,8 quasicrystalline precipitates seem to cause the initiation of cracks and may therefore jeopardize the safety of vessels or assemblages made of these alloys. Finally, let us summarize the mechanical behavior of some thermodynamically stable quasicrystalline phases of the Al-based alloys. At high temperature they are plastically deformable starting from temperatures of roughly half the melting J. Mater. Res., Vol. 8, No. 10, Oct 1993 http://journals.cambridge.org
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point.9"11 Conversely, at low temperature, most of the quasicrystals [e.g., A l - C u - ( M = Fe, Co, or Li)] show high hardness7'11 and low friction coefficients.12'13 Thes
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