Surface tension and mass density of liquid Cu–Ge alloys

We report a study on the mass density and surface tension of liquid Cu–Ge alloys in the temperature range between the liquidus line and 1373 K. The experiments have been carried out by means of the sessile-drop method. The temperature dependences of both properties are given in terms of linear relations for all alloys under investigation. Both, density and surface tension show remarkable deviations from linear mixing: The density is increased, and the surface tension reduced due to Ge acting as surfactant. The composition dependence of the surface tension is discussed in terms of a simple compound formation model which is well able to relate the results to previous findings on the short-range order of the alloys under investigation.     

Oxidation of single-phase Pb-In alloys

The oxidation of several single-phase Pb-In alloys has been studied in air at room temperature using AES (Auger electron spectroscopy) combined with sputter-depth profiling. Alloy samples with indium composition between 3 and 64 at.% In, which were prepared using a microtome, were oxidized in air. The oxidation of alloys with low In contents was found to be the same as that of Pb-2.9 at.% Sn.¹ Increasing the bulk composition of In increased the ratio of oxidized In to oxidized Pb in the oxide mixture, although Pb oxide was observed even on the surface of the oxide for samples up to 64 at.% In. The oxidation behavior of Pb-In alloys can be explained in terms of preferential oxidation of In due to its much greater affinity for oxygen than Pb.     

Recrystallisation in the semi-solid state in 7075 aluminium alloy

There is a strong drive to near net shape process 7000 series aluminium alloys, which are currently machined from the wrought state with much waste. Semi-solid processing is one potential near net shaping route. It relies on the thixotropic behaviour of alloys with non-dendritic, spheroidal microstructures in the semi-solid state. If such alloys are sheared they thin and flow to fill the die. One route to spheroidal semi-solid microstructure is by reheating worked material into the semi-solid state. During the reheating, recrystallisation occurs and as liquid forms it penetrates the recrystallised boundaries to form spheroids. Here we examine the formation of spheroids in as-supplied 7075 aluminium alloy. It is generally known that 7075 is very resistant to recrystallisation in the solid state due to the presence of dispersoid particles pinning grain boundaries. In this work, we have reheated 7075 in the extruded and T6 condition into the semi-solid state. As the temperature rises into the semi-solid regime there is a sudden increase in the appearance of spheroidal grains. The occurrence of recrystallised grains is closely associated with the location of the first liquid to form above the solidus. Fully spheroidal microstructures are obtained on reheating as-supplied material to temperatures in the region of 580 °C, although the fractions of liquid at that temperature are still low at around 5%. Conventionally there is extra cost involved in obtaining spheroidal microstructure feedstock for semi-solid processing because additional steps are introduced into the process route. The advantage here is that as-supplied material can be directly thixoformed once appropriate liquid fractions are attained.     

Validation of an effective oxidation pressure model for liquid binary alloys

Dynamic surface-tension measurements using the sessile drop method and acquisition times of a few seconds make it possible to study the evolution of the surface of molten metals and alloys and so reliably validate the predictive models of the interactions between pure liquid metals and an oxidizing atmosphere, in both an inert gas carrier and in a vacuum. The presence of active oxidation contributes to maintaining surface cleanness and then strongly affects the shape of the boundary separating oxidation and de-oxidation regimes. Recently the general physical–mathematical analysis we developed for pure liquid metals has been extended to liquid binary alloys and their oxides. In this work we present the experimental results of tests on some binary alloys chosen as test systems to try to obtain a preliminary validation of the extended model. The theoretical results obtained, indicating that the behaviour of the alloy towards oxidation tends to be similar to that of the less oxidizable component, have thus been confirmed experimentally.     

The dynamic viscosity of liquid Cu–Si alloys

The dynamic viscosity of liquid Cu–Si alloys is measured in the Cu-rich composition range (up to 40 at.% Si). The Arrhenius-law describing the temperature dependence of the viscosity holds for all alloys investigated. The viscosity isotherms, both experimental and from thermodynamic model calculations, show a broad maximum covering the homogenity ranges of the intermetallic phases. An interconnection of such findings with the atomic structure of the liquid alloys is briefly discussed.     

Deposition of CoPtP films from citric electrolyte

Magnetically hard CoPtP (up to 40 μm thickness) films for MEMS application were deposited from citrate electrolyte and considered in terms of their composition, structure, magnetic characteristics and deposition conditions. Films containing 83-92 at.% (a/o) Co were deposited in the presence of NaH₂PO₂ in the electrolyte, with current efficiency of about 20% (deposition rate 10-12 μm/h). Coercivity 2.7-2.8 kOe and remanence 3.0 kG were achieved magnetizing in the direction normal to the film plane. According to XRD analysis, films seem to consist of hexagonal phase of CoPt solid solutions. Current efficiency, composition and morphology of the films, as well as their magnetic characteristics, were influenced by the electrolyte prehistory and total charge passed through the electrolyte in previous operation.     

Calculation of solute-vacancy binding energy in dilute fcc and bcc alloys by diffusion

Due to excess charge of the solute with respect to solvent, the free energy of vacancy formation and migration in the neighbourhood of the solute will change. This results in a change in the solvent diffusivity. A relation for the solute vacancy binding energy for fcc and bcc lattices using enhancement factor has been derived considering the solute vacancy interactions to be limited to first neighbour and neglecting the changes in the solvent correlation factor.     

Configurational Entropies of Mixing in Solid Alloys

Entropy becomes an increasingly important contributor to the Gibbs energy at high temperatures with both non-configurational and configurational contributions to be considered. Some examples of where configurational entropies alone are important in determining the domain of phase stability of a solution phase are given. In phenomenological calculations, the modeling of configurational entropy should allow for short range order and be readily applicable to multicomponent systems. The use of Fowler-Yang-Li transforms is important in this regard by providing the opportunity for changing the functional variables in cluster calculations of the Gibbs energy from cluster probabilities or correlation functions to the considerably fewer point probabilities, just as in the Bragg-Williams approximation. This article was presented at the Multi-Component Alloy Thermodynamics Symposium sponsored by The Alloy Phase Committee of the joint EMPMD/SMD of The Minerals, Metals, and Materials Society (TMS), held in San Antonio, Texas, March 12-16, 2006, to honor the 2006 William Hume-Rothery Award recipient, Professor W. Alan Oates of the University of Salford, UK. The symposium was organized by Y. Austin Chang of the University of Wisconsin, Madison, WI. Patrice Turchi of the Lawrence Livermore National Laboratory, Livermore, CA, and Rainer Schmid-Fetzer of the Technische Universitat Clausthal, Clauthal-Zellerfeld, Germany.