Future development of erasable phase change recording requires a thorough understanding of the fundamental mechanisms involved in crystallization processes to be able to forecast the behavior of a new material or to guide its optimization when submitted to specific conditions. In this paper, we emphasize that a predictive simulation is valuable only if a good modeling and accurate values of the involved parameters are used. We will present the main characteristics of our phase change model (effect of the short-pulse laser excitation, chemical influence of the materials in contact with the PC layer, stabilization of the amorphous state for very thin film layers) and we will discuss experimental and simulated crystallization behaviors.

Recently, a homophase-fluctuation-mediated (HFM) mechanism of homogeneous nucleation, where concentration fluctuations in the liquid and structure fluctuations are considered as separate events, has been proposed and applied to binary liquids showing a tendency to phase separation. In the present contribution, the HFM mechanism is generalized to multicomponent liquid alloys. The thermodynamic and kinetic analysis leads to an expression of the frequency of nucleation where the pre-exponential factor appears to be lowered when the number of components is increased. This approach helps to quantify the so-called confusion principle often quoted in the literature to explain the enhanced glass-forming ability shown by some multicomponent liquid alloys.

Amorphous phases of NiZr, NiNb and PtSb have been synthesized by solid state reaction of composite metal mixtures produced by mechanical deformation of metal foil layers. Samples were made by winding two elemental foils of about 25 μm thickness in spiral form and then cold rolling them directly. The composites obtained were then sealed under vacuum in Pyrex tubes containing zirconium getters and annealed at appropriate temperatures. The resulting materials were investigated by means of scanning electron microscopy, X-ray diffraction and differential scanning calorimetry.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not.The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.Chauffage -ultra-rapide par dégagement contrôlé de la chaleur de mélange dans des composites de multicouches fines métal-métal F. Bordeaux, A.

Two similar high temperature furnaces (up to 2 000 °C) have been developed for large angle and small angle neutron scattering (SANS) experiments respectively. They are vacuum furnaces with a thin tungsten foil heating element supplied by two tantalum leads, and shielded by thin tungsten foils maintained in a tantalum box. In a neutron beam, the furnaces produce a very low scattering level (without any Bragg peaks) due to the openings in the heating element, the shields and the tantalum box for the incident, unscattered beam and the scattered beam at low angles. Thus the furnace absorption correction is also much easier. A platinum thermocouple controls temperature, very high temperatures are measured optically. A vacuum chamber has been especially designed for SANS experiments with two windows in polished sapphire. The furnaces have been successfully used for the study of liquid alloys on the D4, D11 and D17 spectrometers at the ILL.

Using the multilayer models for the interfaces of binary regular solutions, the liquid-vapor and liquid—liquid interfacial tensions of two liquids are calculated along the coexistence curve of the phase diagram. The results are discussed using two parameters, i.e., α which is the reduced molar exchange energy of a regular solution and β which is proportional to the difference between the liquid-vapor surface tensions of pure components A and B. We show that for systems with β/α < m (where m is the structural parameter typical of the liquid quasi-lattice) there exists a temperature TR (α, β/α) for which Antonow's rule is exactly valid. Above TR, contact angle θ is zero and no barrier exists for nucleation of liquid 2 from saturated liquid 1. Below this temperature, wetting is not perfect. For systems with β/α > m, wetting is more than perfect at every temperature. The predictions of multilayer-regular solution model are compared with those obtained from the phenomenological model of Cahn.

Les coefficients de viscosité de l'indium, du cadmium et de 11 alliages liquides Cd-In, répartis sur toute la gamme de concentration, ont été déterminés en fonction de la température par la méthode du creuset cylindrique oscillant. Les masses volumiques utilisées pour la détermination des coefficients de viscosité sont celles que nous avons déterminées antérieurement. Les isothermes de viscosité obtenues montrent un écart négatif important par rapport à une loi de variation linéaire. La valeur de cet écart est maximale (approximativement 40%) pour xIn = 0,4. Enfin la grande étendue de température étudiée nous a permis de déduire avec une bonne précision l'évolution de l'énergie d'activation du flux visqueux avec la concentration.

Les masses volumiques de l'indium, du cadmium et de huit alliages liquides Cd-In répartis sur toute la gamme de concentration ont été déterminées par la méthode absolue d'Archimède. Les relations suivantes traduisent les résultats obtenus pour les métaux purs: ρ(In) = 7,322 − 7,3 × 10−4T (g cm−3)ρ(Cd) = 8,584 − 9,24 × 10−4T (g cm−3) Les volumes d'excès des alliages très dilués en cadmium sont faiblement négatifs alors qu'ils sont positifs mais faibles pour les alliages concentrés.

In solid-liquid metallic binary systems, the variation of ρ = σSLσGB (ratio of solid-liquid interfacial tension to grain boundary tension of the solid solution) with temperature and composition of bulk phases, can be determined through the ‘dihedral angle’ method. We show that this information offers an experimental basis for evaluating interfacial adsorption: to do this, we present an analysis of ρ(T) curves which allows the signs of dσSLdT and dσGBdT be directly determined; and we establish a relation between the sign of dσSLdT and that of the absolute adsorption at solid-liquid interfaces. Moreover, a method is proposed to evaluate the solid-liquid interfacial tension of pure metals by extrapolation of the ρ(T) data of the binary alloys.

A l'aide d'un modèle de fluctuations adiabatiques, nous montrons pour la nucléation liquide-solide, que la notion d'une température de surfusion maximale, caractéristique d'un métal, peut être introduite d'une manière thermodynamique. Les valeurs de surfusions maximales et de tension interfaciales solide-liquide de métaux sont calculées par ce modèle et comparées aux résultats expérimentaux. Thermodynamical calculation of the liquid to solid homogeneous nucleation temperature of pure metals.

A statistical treatment which emphasizes the size effect is developed in order to describe correctly the experimental values of the surface tension for metallic systems such as AlPb, AlSn, ZnPb, ZnBi and CuPb. The experimental surface compositions deduced from Gibbs' adsorption equation and monolayer hypothesis are compared to those given by the model for the systems ZnPb and AlPb.

Experimental measurements of surface tensions of Al-Pb, Al-Bi, Al-Sn, Zn-Pb and Zn-Bi alloys have been performed using two different methods (maximum bubble pressure and sessile drop).The experimental results are compared with those given in the literature. In addition, calculations of surface adsorption are made from Gibbs equation for Al-Pb and Zn-Bi alloys.

Pour les alliages liquides caractérisés par de faibles interactions hétéroioniques et un effet de taille important les auteurs définissent un « indice d’interstitiel ». L’évolution de cet indice avec la température est discuté en s’appuyant sur l’exemple des systèmes BiZn et BiCu.

Experimental measurements of surface tensions of Al-Pb, Al-Bi, Al-Sn, Zn-Pb and Zn-Bi alloys have been performed using two different methods (maximum bubble pressure and sessile drop).The experimental results are compared with those given in the literature. In addition, calculations of surface adsorption are made from Gibbs equation for Al-Pb and Zn-Bi alloys.

Abstract Previous models of surface segregation have generally been interpreted by means of a decrease in surface free energy. Nevertheless the reduction in lattice strain-energy which accompanies the transfer of misfitting solute atoms from the lattice to the surface, constitutes also a driving force for that phenomenon. By the introduction of the concept of the partial elastic energy, it is possible to present a theory which combines the two different aspects into a single formalism, valid in a crude approximation, for all concentrations.

A statistical treatment which emphasizes the size effect is developed in order to describe correctly the experimental values of the surface tension for metallic systems such as AlPb, AlSn, ZnPb, ZnBi and CuPb. The experimental surface compositions deduced from Gibbs' adsorption equation and monolayer hypothesis are compared to those given by the model for the systems ZnPb and AlPb.

Les tensions superficielles d’alliages liquides Fe — Si à différentes compositions ont été déterminées en fonction de la température par la méthode de la goutte posée. Les valeurs obtenues sont comparées d’une part aux données de la littérature et d’autre part aux estimations déduites de l'application d’un modèle thermodynamique.

La viscosité de l'argent et des alliages Ag-Ge à différentes compositions ont été déterminées en fonction de la température par la méthode du creuset cylindrique oscillant. Les isothermes de viscosité sont tracées et interprétées en relation avec la structure des alliages liquides.