A. Quivy

About the AlCuFe icosahedral phase formation

Abstract In the present work, results obtained by differential thermal analysis (DTA) and X-ray diffraction (XRD) confirm [5, 8] that the icosahedral phase (i-phase) is formed by a peritectic reaction. A single i-phase can be obtained after annealing around the compositions Al64Cu24Fe12Al61.75Cu25.5Fe12.75. For the composition Al62Cu25.5Fe12.5, the XRD lines of the i-phase are narrow whatever the annealing temperature (800 °C or 600 °C). Thus, this result establishes that there exists a single phase domain where the i-phase is perfect (without phasons) and remains stable at 600 °C. A provisional vertical section along the line Al70Cu20Fe10Al64Cu24Fe12Al58CuPin28Fe14 is proposed and shows the phases that exist equilibrium at various temperatures in this range of compositions.

The phase diagram and structures of the ternary AlCuFe system in the vicinity of the icosahedral region

Abstract The phase diagram of the ternary system (Al, Cu, Fe) has been systematically studied around the icosahedral region. At 680°C, the i-region extends approximately over a triangle with vertices of Al, Cu and Fe composition of respectively 62.4-24.4-13.2, 65-23-12 and 61-28.4-10.6. This region splits schematically into 3 fields: (i) the perfect icosahedral phase which is stable down to the lowest possible annealing temperature where atomic diffusion is active in a tiny region of composition close to Al62.3Cu24.9Fe12.8; (ii) a well defined periodic phase with rhombohedral lattice which transforms reversibly into ico near 710°C in the lower part of the triangle; (iii) a complex region characterized by additional diffraction effects (peak broadening, lineshapes, etc.) which may correspond to various approximant structures closely related to the i-phase.

Antiphase domains in icosahedral Al-Cu-Fe alloy

Abstract Electron microscopy observations of the newly discovered icosahedral phase in the Al‐Cu‐Fe ternary system show a domain structure as expected from a group‐subgroup formal decomposition from a primitive six-dimensional (6D) hypercubic unit cell to a face‐centred one with twice the lattice parameter, as suggested by Ebalard and Spaepen. The structure of Al65Cu20Fe15 can be seen as an ordered F superstructure of the usual primitive quasilattice with, at least, two motifs in the 6D representation. The smoothness of the observed antiphase boundaries and the relative weak intensities of the superstructure reflections suggest that the ordered motifs should share many geometrical features. A possibility could be that at least one of the orbits of a given atomic species arranges in space according to a 6D primitive skeleton and chemical ordering occurs on the remaining orbits.

A cubic approximant of the icosahedral phase in the (Al - Si) - Cu - Fe system

We present a stable simple cubic structure in the quaternary system (Al - Si) - Cu - Fe with the composition which corresponds to the p/q = 1/1 cubic approximant of the icosahedral Al - Cu - Fe phase. This cubic structure, with lattice parameter a = 12.330 A and density , contains roughly 135 atoms per unit cell. Preliminary studies of NMR and ME spectra as well as electric conductivity properties strongly suggest that this alloy shares most of the basic structural and physical properties of the parent icosahedral phase I-(Al - Cu - Fe).

A neutron diffraction determination of short-range order in a Ni63.7Zr36.3 glass

The total structure factors for amorphous Ni63.7Zr36.3 have been obtained by neutron diffraction for three different isotropic compositions of nickel. The use of a zero alloy leads to a direct determination of the Bhatia-Thornton structure factor SCC. The high value of the determinant of the system produces accurate partial structure factors. From which partial pair correlation functions have been calculated. The behaviour of the partial functions and the deduced partial coordination numbers show the existence of strong chemical short-range order, the nature of which is discussed.

On the stability and structure of Cu—Zr based glasses

Abstract Glassy Cu—Zr alloys with compositions ranging from Cu33Zr67 to Cu66Zr34 have been prepared. Their thermal behaviour, structure factor and density have been measured. These results are discussed in terms of an ideal substitutional solid solution and briefly compared to the predictions of the nearly free electron-like model for the stability of metallic glasses.

The effect of structural relaxation on the local structure of Cu40Zr60 amorphous alloys

Abstract Structural relaxation phenomena associated with heat treatments near the glass transition temperature range were investigated in liquid-quenched amorphous Cu40Zr60 alloys by means of differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS) and EXAFS. A kinetic study was performed by DSC in order to determine the evolution of the configurational enthalpy ( ‡ H σ ) against temperature (upon continuous heating or during isothermal annealing treatments) and to define the heat treatment suitable to obtain highly relaxed samples. SAXS results show that the structure of the relaxed samples remains homogeneous at the intermediate range of order up to at least 100 A, whatever be the previous heat treatment. EXAFS detects a slight change in the local structure only for the most highly relaxed samples; this change could be interpreted by a variation of 0.5 atom in the coordination numbers (probably of the ZrZr pairs) or by a change of the disorder parameter of about 0.01 A. No phase separation is detected in the relaxed amorphous Cu40Zr60 specimens.

Preparation of CUxZr1−x metallic glasses by sputtering and their thermal stability, electrical and optical properties☆

Amorphous CuxZr1−x (0.30 < x < 0.60) films were sputtered from an alloy target onto silica substrates held at room temperature. Their structure was checked by electron or X-ray diffraction depending on the thickness of the films. The crystallization process was followed by differential thermal analysis. The thermal stability of the samples was compared with that of samples obtained by rapid quenching from the melt. Measurements of the reflectance R and transmittance T were performed at normal incidence in air between 0.03 and 6.2 eV. The dielectric function was determined for thin films from R and T and for opaque samples from R using the Kramers-Kronig analysis. The effect of oxidation is discussed. Optical absorption spectra for the amorphous samples exhibit interband transitions at low energies as in pure zirconium and a broad peak around 3.5 eV, which could be due to transitions starting from the copper d band shifted to high energy with respect to its position in pure copper. These results agree with those from previous UV photoelectron spectroscopy measurements and could be an effect of compositional rather than of structural disorder.

The nature of the topological disorder in the rapidly quenched Al73Mn21Si6 icosahedral phase

Abstract A rapidly solidified Al73Mn21Si6 icosahedral alloy has been studied by X-ray powder diffraction and scanning and transmission electron microscopy. AH reflections were found to fit the icosahedral theoretical indexing to better than 10−3 A−1 The peak widths at half-maximum simultaneously depend on both the parallel and the perpendicular components of the six-dimensional momentum transfer, contrary to what is expected from an icosahdral glass. This momentum transfer dependence does not change with subsequent annealing of the samples.

Calorimetric evidence of structural changes in thermal aged CuZr and FeCoBSi amorphous alloys

Abstract Evidence of structural relaxation phenomena has been obtained by DSC in Cu-Zr and Fe-Co-B-Si amorphous alloys. Two major effects are described: an exothermic (irreversible) phenomenon which occurs during the first scan of the as-quenched sample, and an endothermic (reversible) one which is observed on the pre-annealed samples. Quantitative measurements of the endothermic phenomenon as a function of the annealing conditions are reported for several Cu-Zr alloys.