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’s modulus, shear modulus and Poisson’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’s modulus, shear modulus and Poisson’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.

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.

Thanks to a dedicated modelling of intensities, the depth sensitivity of X-ray photoemission is used to probe the segregation profile of aluminium at the (110), (100) and (111) low index surfaces of the body-centred Fe 0.85 Al 0.15 random alloy. Sputtered surface composition is close to the nominal bulk one, thus excluding preferential sputtering. Surface enrichment in aluminium upon annealing starts at around 700 K before reaching a stationary state above 1000 K. The average surface composition is close to Fe 0.5 Al 0.5 , corresponding to the B 2 CsCl structure on the phase diagram. The impacted depth, that is in the range of 2.5-3.5 nm, is quite significant. Although not evidenced previously in surface science conditions at FeAl single crystal surfaces, it is qualitatively in agreement with the segregation at grain boundaries and shear planes of Al-alloyed steels. This segregation tendency is rationalized through ab initio calculations.

By combining Scanning Tunnelling Microscopy, Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy, it was found that the surface of A 2 random alloy Fe 0.85 Al 0.15 (110) is significantly influenced by the segregation of aluminium but also of carbon bulk impurities. Below ∼ 900 K, carbon segregates in the form of self-organized protruding stripes separated by ∼ 5 nm that run along the [001] B bulk direction and cover up to 34 % of the surface. Their C 1s spectroscopic signature that is dominated by graphitic carbon peaks around 900 K. Above this temperature, the surface carbon concentration decays by redissolution in the bulk, whereas an intense aluminium segregation is observed giving rise to a hexagonal superstructure. The present findings is interpreted by a competitive segregation between the two elements.

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 Tunneling Microscopy, Low-Energy Electron Diffraction and Grazing-Incidence X-Ray Diffraction are combined to explore surface structures and topographies. 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 incommensurate 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.