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International audience; The oxidation resistance of receivers is a critical point in the development of plants using solar tower technology. Intermetallics in Mo-Si-Al system present oxidation maximum temperature and creep resistance superior to the ones of the currently used Ni-based alloys. We followed here the oxidation resistance of such intermetallic exposed to different treatments in air: long-term oxidation (up to 700 h) at 1373 K, and for several cycles of 20 minutes in solar furnace. The normal spectral emissivity is measured up to 1640 K in air, and our main positive conclusion is this property is not degraded by the oxidation.

International audience; 1-pyrrolidine dithiocarbamate (PDTC) effect on galvanic coupling resistance of AA 2024-T3 alloy in0.2 g L1 NaCl was evaluated by different electrochemical/gravimetric methods and surface analysis.The results obtained from polarization curves and electrochemical quartz crystal microbalance measurementsshowed that PDTC forms an adsorbed film on the Cu-rich particles, likely through a CuI–PDTC complex.At high concentrations, PDTC significantly decreases the alloy reactivity thereby providing a markedcorrosion protection. SEM–EDX analysis showed that PDTC adsorbs preferentially on the Al–Cu–Mgparticles. Electrochemical impedance spectroscopy measurements corroborate these results and showfurthermore that PDTC addition increases the galvanic coupling resistance.

International audience; We report on the existence in the Uâ€"Ruâ€"Al system of a novel compound, URu2Al10, crystallizing in the orthorhombic YbFe2Al10-type structure, where the uranium atoms are caged in Ruâ€"Al polyhedra, forming a clathrate-like structure. Results of the magnetic susceptibility, electrical resistivity in zero and in magnetic fields up to 8 T, thermopower and specific heat, performed in a wide temperature range, are presented. No magnetically ordered state down to the lowest temperature measured has been found. On the basis of (i) the susceptibility anomaly occurring at about 50 K and (ii) the positive magnetoresistivity, growing with applied magnetic field as αBn (n ≈ 3/2), (iii) a characteristic temperature variation of the thermopower, as well as (iv) a moderate value of the Sommerfeld coefficient, a mixed-valence state of uranium in this compound has been postulated. This points to similarities between the presently studied compound and the behaviour of other Ru-containing uranium ternaries, such as U2Ru2Sn and U2RuGa8, classified earlier as valence-fluctuating type materials.

cited By 52; International audience; Structural relaxation process in Cu46Zr45Al 7Y2 and Zr55Cu30Ni 5Al10 bulk metallic glasses during annealing below the glass transition temperature Tg was investigated by differential scanning calorimetry (DSC). The features of enthalpy relaxation are sensitive to both annealing temperature and annealing time. For a given annealing time ta, the results indicated that the relaxation time ta decreases with increasing the annealing temperature Ta, in good agreement with results relative to other bulk metallic glasses. Additionally, the enthalpy relaxation behaviour of the bulk metallic glasses appears independent on the cooling rate used before the physical aging experiments, i.e. on the initial as-cast state. The recovered enthalpy evolution of the bulk metallic glasses is well described by the Kohlrausch-Williams-Watts (KWW) exponential relaxation function as ΔH(Ta) = ΔH eq1 - exp[-(ta/τ)β]. Kohlrausch exponent β and enthalpy relaxation time τ are sensitive to the composition of the bulk metallic glasses. Finally, the influence of different heating treatment processes on the enthalpy relaxation in the bulk metallic glasses is presented and shows that this phenomenon is mainly reversible. The structural relaxation behaviour is interpreted by free volume model and quasi-point defects model. Kinetic fragility parameters m in Cu 46Zr45Al7Y2 and Zr 55Cu30Ni5Al10 bulk metallic glasses are 72 and 69, respectively, indicating therefore that these alloys are intermediate glasses. Crystallization process was also investigated by DSC experiments. According to the Kissinger model, corresponding activation energy is 3.18 eV in Cu46Zr45Al7Y2, and 3.19 eV in Zr55Cu30Ni5Al10, respectively. © 2010 Elsevier Ltd. All rights reserved.

cited By 14; International audience; Compared with conventional bulk metallic glasses, Ce-based and Zn-based bulk metallic glasses have received considerable attention because of their possible application as structural and functional materials. Kinetic fragility parameter m in amorphous material presents degree of deviations from the Arrhenius law above the glass transition temperature (Tg) of the material. Kinetic fragility parameter (m) and Kauzmann temperature (T K) in (Ce0.72Cu0.28)90-x Al 10Fex (x = 0, 5 or 10) and Zn38Mg 12Ca32Yb18 bulk metallic glasses have been determined by differential scanning calorimetry (DSC). Results show that Zn 38Mg12Ca32Yb18 presents a higher m than (Ce0.72Cu0.28)90-x Al10Fe x (x = 0, 5 or 10). The activation energies Eg for glass transition are 1.51 eV (x = 0), 1.59 eV (x = 5) and 1.83 eV (x = 10) in (Ce 0.72Cu0.28)90-x Al10Fex (x = 0, 5 or 10), and 3.59 eV in Zn38Mg12Ca 32Yb18, respectively. The values of Eg increase with increasing the Fe content in (Ce0.72Cu0.28) 90-x Al10Fex (x = 0, 5 or 10) bulk metallic glasses. Kinetic fragility parameter m of bulk metallic glasses increases with the glass transition temperature Tg of bulk metallic glasses, in agreement with previous investigations. © 2011 Elsevier Ltd. All rights reserved.

cited By 52; International audience; Structural relaxation process in Cu46Zr45Al 7Y2 and Zr55Cu30Ni 5Al10 bulk metallic glasses during annealing below the glass transition temperature Tg was investigated by differential scanning calorimetry (DSC). The features of enthalpy relaxation are sensitive to both annealing temperature and annealing time. For a given annealing time ta, the results indicated that the relaxation time ta decreases with increasing the annealing temperature Ta, in good agreement with results relative to other bulk metallic glasses. Additionally, the enthalpy relaxation behaviour of the bulk metallic glasses appears independent on the cooling rate used before the physical aging experiments, i.e. on the initial as-cast state. The recovered enthalpy evolution of the bulk metallic glasses is well described by the Kohlrausch-Williams-Watts (KWW) exponential relaxation function as ΔH(Ta) = ΔH eq1 - exp[-(ta/τ)β]. Kohlrausch exponent β and enthalpy relaxation time τ are sensitive to the composition of the bulk metallic glasses. Finally, the influence of different heating treatment processes on the enthalpy relaxation in the bulk metallic glasses is presented and shows that this phenomenon is mainly reversible. The structural relaxation behaviour is interpreted by free volume model and quasi-point defects model. Kinetic fragility parameters m in Cu 46Zr45Al7Y2 and Zr 55Cu30Ni5Al10 bulk metallic glasses are 72 and 69, respectively, indicating therefore that these alloys are intermediate glasses. Crystallization process was also investigated by DSC experiments. According to the Kissinger model, corresponding activation energy is 3.18 eV in Cu46Zr45Al7Y2, and 3.19 eV in Zr55Cu30Ni5Al10, respectively. © 2010 Elsevier Ltd. All rights reserved.

International audience; In the present work, the Nb-B binary system was thermodynamically optimized. The stable phases in this system are BCC (niobium), Nb3B2, NbB, Nb3B4, Nb5B6, NbB2, B (boron) and liquid L. The borides Nb3B2, NbB, Nb3B4 and Nb5B6 and the B (boron) were modeled as stoichiometric phases and the liquid L, BCC (niobium) and NbB2 as solutions, using the sublattices model, with their excess terms described by the Redlich-Kister polynomials. The Gibbs energy coefficients were optimized based on the experimental values of enthalpy of formation, low temperature specific heat, liquidus temperatures and temperatures of invariant transformations. The calculated Nb-B diagram reproduces well the experimental values from the literature.

International audience; The corrosion behaviour of 2024 aluminium alloy in sulphate solutions was studied; attention was focused on the influence of coarse intermetallic Al2CuMg particles on the corrosion resistance of the alloy. Model alloys representative of the aluminium matrix and of Al2CuMg coarse intermetallics were synthesized by magnetron sputtering. Open-circuit potential measurements, current–potential curve plotting and galvanic coupling tests were performed in sulphate solutions with or without chlorides. Further explanations were deduced from the study of the passive films grown on model alloys in sulphate solutions. The results showed that model alloys are a powerful tool to study the corrosion behaviour of aluminium alloys.

International audience; While the main features of the Fe-Ni-Ti system are well known at low Ti content, literature review of the Ti-rich corner revealed inconsistencies between experimental reports. This investigation presents new experimental results, defined to remove the uncertainties concerning melting behavior and solid-state phase equilibria of the (Ni,Fe)Ti2 phase with the adjacent (Fe,Ni)Ti (B2, CsCl-type structure) and Beta-Ti (A2, W-type) phases. Six samples have been prepared and examined by differential thermal analysis performed in yttria and alumina crucibles, and by scanning electron microscopy in the as-cast state as well as equilibrated at 900°C.