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This article attempts to understand better the origin of low friction and zero solid–solid adhesion observed on quasicrystals placed in vacuum. We present an ensemble of experimental data that allows us on the one hand to estimate the true surface energy of unoxidized quasicrystals and approximants and on the other hand to point out a correlation with electronic densities of states. [ABSTRACT FROM AUTHOR]

We report the formation of several complex intermetallics as surface alloys upon the adsorption of Fe on Al 9 Co 2 (001) for different dosing conditions. Up to 4 monolayers equivalent (MLE) of Fe deposited on the substrate held at 593 K, the low energy electron diffraction pattern consists of a ( 2 × 2 )R45° phase with two additional domain types rotated by ± 8 ∘ from it. The scanning tunneling microscopy (STM) measurements show that these three types of domains have the same crystallographic structure. The lattice parameters and structural motifs point towards the formation of the high-temperature Al 8 Fe 5 phase (γ -brass of Zn 8 Cu 5 -type structure). For Fe deposition between 593 K and 873 K, we have identified the formation of two phases, tentatively assigned to a ternary disordered Al 9 (Co,Fe) 2 overlayer and to the monoclinic Al 13 Fe 4 (100). The stoichiometric evolution of the grown structures have been characterized by angle-resolved x-ray photoelectron spectroscopy measurements. Density functional theory based calculations have been performed to model the Al 8 Fe 5 (100)/Al 9 Co 2 (001) interface, its structural stability and to simulate the corresponding STM images. [Display omitted] • Epitaxial growth of simple binary to complex metallic alloy phases. • Growth of the high-temperature Al 8 Fe 5 phase as thin film on Al 9 Co 2 (001). • Identification of the Al 8 Fe 5 (100) surface termination by DFT calculations. • Substrate symmetry operations driving the alternating orientations of domains. • Formation of surface and interface structures of tuneable complexity. [ABSTRACT FROM AUTHOR]

[Display omitted] The (110) and (320) surfaces of the single-phase FeCrMnNiCo solid solution have been studied on two adjacent millimeter size grains using surface science and transmission electron microscopy (TEM) techniques. The structural and chemical evolutions of the high entropy alloy (HEA) surfaces have been determined for various sputtering conditions, annealing temperatures and durations. Up to 873 K, angle-resolved X-ray photoelectron spectroscopy measurements indicate a clear Mn and Ni surface co-segregation. We propose that the surface segregation of Mn is driven by its low surface energy. The attractive interaction between Mn and Ni promotes Ni segregation which accompanied the Mn diffusion to the surface. Regarding the structures investigated by low energy electron diffraction and scanning tunneling microscopy, the (320) surface presents a terraced morphology with an ordered structure consistent with a (1 × 1) termination. On the contrary, the (110) surface reveals an important degree of structural disorder and local reconstructions. Its highly anisotropic morphology resembles rows propagating along the [001] direction. Above 873 K, Mn desorption occurs while the Ni content keeps increasing linearly with the temperature. TEM analysis show no evidence for HEA decomposition into metallic or intermetallic phases even after repeated annealing and sputtering cycles. The above results set the upper temperature limit above which the surface stoichiometry departs from the quinary HEA concept. It also defines the temperature range for the use of FeCrMnNiCo based coating under high vacuum conditions and for aerospace applications. [ABSTRACT FROM AUTHOR]