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International audience; The formation of an ultra-thin aluminum oxide film at Fe0.85Al0.15(110) surface (A2 random alloy) has been studied by a variety of surface sensitive techniques (X-ray photoemission, low-energy electron diffraction, surface X-ray diffraction and scanning tunneling microscopy) supplemented by ab initio atomistic simulations. Since iron is not oxidized in the used conditions, the study focused on the coupling between aluminum oxidation and segregation processes. Compared to the bare surface, whose average composition (Fe0.6Al0.4) is closer to the B2-CsCl structure over a ∼ 3 nm depth, the oxidation hardly affects the subsurface segregation of aluminum. All the structural and chemical fingerprints point to an oxide film similar to that found on NiAl(110). It is a bilayer (∼ 7.5Å thick) with a composition close to Al10O13 and a large (18.8 × 10.7)Å 2 nearly rectangular unit cell; an almost perfect match between substrate periodicity and the (1 × 2) oxide supercell is found. Nevertheless, microscopy reveals the presence of anti-phase domain boundaries. Measured Al 2p and O 1s core level shifts match calculated ones; their origin and the relative contributions of initial/final state effects are discussed. The ubiquity of the present oxide on different supports asks for the origin of its stability.

International audience; Based on previous photoemission findings, the influence of newly observed aluminum surface segregation at the low (110), (100) and (111) index surfaces of the A 2 body-centered Fe 0.85 Al 0.15 random alloy is explored. Scanning Tun-neling Microscopy, Low-Energy Electron Diffraction and Grazing-Incidence X-Ray Diffraction are combined to explore surface structures and topogra-phies. The formation of a surface composition close to the B 2 Fe 0.5 Al 0.5 occurs with the appearance of (i) a long-range pseudo-hexagonal incommen-surate superstructure with a periodicity of ∼ 18Å on the (110) surface, (ii) a (1 × 1) termination on the (100) surface and (iii) a intense vicinal faceting of the (111) surface in the form of triangular pits.

Ni3Al-based superalloys have excellent mechanical properties which have been widely used in civilian and military fields. In this study, the mechanical properties of the face-centred cubic structure Ni3Al were investigated by a first principles study based on density functional theory (DFT), and the generalized gradient approximation (GGA) was used as the exchange-correlation function. The bulk modulus, Young&rsquo, s modulus, shear modulus and Poisson&rsquo, s ratio of Ni3Al polycrystal were calculated by Voigt-Reuss approximation method, which are in good agreement with the existing experimental values. Moreover, directional dependences of bulk modulus, Young&rsquo, s ratio of Ni3Al single crystal were explored. In addition, the thermodynamic properties (e.g., Debye temperature) of Ni3Al were investigated based on the calculated elastic constants, indicating an improved accuracy in this study, verified with a small deviation from the previous experimental value.

A2 Fe0.85Al0.15 single crystals with low-index orientations (110), (100) and (111) have been chosen as a model system to study the Al segregation and oxidation of industrial Al-alloyed steels by using combined techniques (LEED, XPS, STM, GIXD). All clean surfaces are prone to intense Al segregation when annealed at > 700 K. After 1000 K, a quasi-equilibrium is reached and the impacted layer of 2-3 nm has a composition close to the B2 structure. But all the surfaces behave differently in terms of reconstruction. The (110) surface develops a 2 nm pseudo-hexagonal superstructure with an incommensurate in-plane modulation. The (100) surface is always (1×1) terminated with a marbled-like appearance assigned to an electronic and chemical contrast. The (111) surface is locally rough with nanometric three-fold protrusions due to seg-regation-induced faceting involving (111) vicinal surfaces. The segregation trend is confirmed through ab initio calculations. The oxidation with O2 of all surfaces at high temperature results in selective oxidation of Al and alumina formation with a 1-2 nm self-limited thick-ness. Ordered oxides are found on (110) and (100) faces while a disordered 3D oxide grows on (111). Subsurfaces of oxidised (110) and (111) are de-pleted in Al and adopt the D03 structure, while (100) subsurface composi-tion is insensitive to oxidation. At (110) surface, a two-domain alumina grows with a (18.5 × 10.5) Å2 nearly rectangular rotated unit cell with a (2×1)ox matching. The oxide film at (100) surface presents two (2×1) do-mains in the form of nanometric orthogonal stripes; a likely explanation is the formation of a distorted θ-Al2O3 structure.; Des monocristaux A2 de Fe0.85Al0.15 de terminaison (110), (100) et (111) ont servi de modèle pour étudier la ségrégation d'Al et l'oxydation d'aciers industriels à l'Al en combinant LEED, XPS, STM et GIXD. Toutes les surfaces propres sont sujettes à une intense ségrégation d'Al lors de recuits > 700 K. Au-delà de 1000 K, un quasi-équilibre est atteint et la couche concernée de 2-3 nm adopte une composition proche de la structure B2. Cependant, toutes les surfaces se comportent différemment en termes de reconstruction. La surface (110) développe une superstructure pseudo-hexagonale de 2nm avec une modulation incommensurable dans le plan. La surface (100) est toujours terminée (1×1) avec une apparence marbrée attri-buée à un contraste électronique et chimique. La surface (111) est locale-ment rugueuse avec des protrusions triangulaires nanométriques en raison d'un facettage induit par la ségrégation. La tendance à la ségrégation est con-firmée par des calculs ab initio. L'oxydation à haute température par O2 de ces surfaces conduit à une oxy-dation sélective de l'Al et à la formation de films d'alumine d'épaisseur 1-2nm. Des oxydes ordonnés croissent sur les faces (110) et (100) alors que des îlots apparaissent sur la face (111). Les sous-surface de (110) et (111) oxydés sont déplétées en Al et adoptent la structure D03 alors que celle de (100) ne varie pas. A la surface (110), l'alumine croit sous forme de deux domaines ayant une maille quasi-rectangulaire de (18.5 × 10.5) Å2 et un ac-cord (2×1)ox. Le film d'oxyde à la surface (100) présente deux domaines (2×1) sous la forme de bandes orthogonales; une explication plausible est la formation d'une structure distordue θ-Al2O3.

A2 Fe0.85Al0.15 single crystals with low-index orientations (110), (100) and (111) have been chosen as a model system to study the Al segregation and oxidation of industrial Al-alloyed steels by using combined techniques (LEED, XPS, STM, GIXD). All clean surfaces are prone to intense Al segregation when annealed at > 700 K. After 1000 K, a quasi-equilibrium is reached and the impacted layer of 2-3 nm has a composition close to the B2 structure. But all the surfaces behave differently in terms of reconstruction. The (110) surface develops a 2 nm pseudo-hexagonal superstructure with an incommensurate in-plane modulation. The (100) surface is always (1×1) terminated with a marbled-like appearance assigned to an electronic and chemical contrast. The (111) surface is locally rough with nanometric three-fold protrusions due to seg-regation-induced faceting involving (111) vicinal surfaces. The segregation trend is confirmed through ab initio calculations. The oxidation with O2 of all surfaces at high temperature results in selective oxidation of Al and alumina formation with a 1-2 nm self-limited thick-ness. Ordered oxides are found on (110) and (100) faces while a disordered 3D oxide grows on (111). Subsurfaces of oxidised (110) and (111) are de-pleted in Al and adopt the D03 structure, while (100) subsurface composi-tion is insensitive to oxidation. At (110) surface, a two-domain alumina grows with a (18.5 × 10.5) Å2 nearly rectangular rotated unit cell with a (2×1)ox matching. The oxide film at (100) surface presents two (2×1) do-mains in the form of nanometric orthogonal stripes; a likely explanation is the formation of a distorted θ-Al2O3 structure.; Des monocristaux A2 de Fe0.85Al0.15 de terminaison (110), (100) et (111) ont servi de modèle pour étudier la ségrégation d'Al et l'oxydation d'aciers industriels à l'Al en combinant LEED, XPS, STM et GIXD. Toutes les surfaces propres sont sujettes à une intense ségrégation d'Al lors de recuits > 700 K. Au-delà de 1000 K, un quasi-équilibre est atteint et la couche concernée de 2-3 nm adopte une composition proche de la structure B2. Cependant, toutes les surfaces se comportent différemment en termes de reconstruction. La surface (110) développe une superstructure pseudo-hexagonale de 2nm avec une modulation incommensurable dans le plan. La surface (100) est toujours terminée (1×1) avec une apparence marbrée attri-buée à un contraste électronique et chimique. La surface (111) est locale-ment rugueuse avec des protrusions triangulaires nanométriques en raison d'un facettage induit par la ségrégation. La tendance à la ségrégation est con-firmée par des calculs ab initio. L'oxydation à haute température par O2 de ces surfaces conduit à une oxy-dation sélective de l'Al et à la formation de films d'alumine d'épaisseur 1-2nm. Des oxydes ordonnés croissent sur les faces (110) et (100) alors que des îlots apparaissent sur la face (111). Les sous-surface de (110) et (111) oxydés sont déplétées en Al et adoptent la structure D03 alors que celle de (100) ne varie pas. A la surface (110), l'alumine croit sous forme de deux domaines ayant une maille quasi-rectangulaire de (18.5 × 10.5) Å2 et un ac-cord (2×1)ox. Le film d'oxyde à la surface (100) présente deux domaines (2×1) sous la forme de bandes orthogonales; une explication plausible est la formation d'une structure distordue θ-Al2O3.