Properties of Interface Boundaries in Segregating Metallic Melts

Abstract

Interface tension and adhesion were determined in a number of binary and ternary metallic systems with immiscibility gaps. In ternary systems, compositions of equilibrium phases were preliminarily defined. Concentrations of components on phase boundaries were estimated.The interface boundary between two segregating metallic melts has not yet been investigated as fully as that between liquid metals and liquid salts or oxides. Nevertheless, interface characteristics such as interface tension ση, adhesion Wa, compositions of surface layers xf, are not only of scientific interest. They are necessary for the analysis of emulsification processes of melts, for the definition of phase adhesion in the production of composition materials and in other processes.In this report, these properties are considered in a number of binary and temaiy metallic systems. The investigations were carried out in the laboratory of the chair of "Theory of Metallurgical Processes" at the Urals State Technical University. METHODSOne of the most suitable methods of definition of interface tension ση at a phase boundary of immiscible metallic melts is calculation of its value by using magnitudes of the surface tensions σχ and σι of mutually saturated phases and the contact angle α (Fig. 1). For this purpose a drop of one liquid alloy is placed in a cup, and the other melt is placed in a surrounding circular groove /!/. Fig. 1: Substrate (3) for equilibrium contact angle (a) of two melts (1 and 2), definition and scheme of action of surface forces. Calculations were made according to the equation J/2(1)Since the magnitude of interface tension is very sensitive to impurities, metals with a total content of impurities of no more than 0.01% were used in our experiments. The experiments were usually performed at a vacuum of 10^ Pa, and for metals possessing a high affinity for oxygen, they were carried out in a protective atmosphere of purified hydrogen. A special vacuum furnace with a quenching bath was used for determination of the mutual solubility of liquid phases and for quenching of metallic emulsions. BINARY SYSTEMSSome tens of metallic pairs, demonstrating limited miscibility in the liquid state, are known. Unfortunately, 255Brought to you by | Purdue University Libraries the limits of immiscibility gaps have not been reliably established in the majority of the cases. This fact prevents studies of interface boundary properties. The experimental difficulties may be related to high chemical activity and saturated vapor pressure of one of the components in the experimental temperature interval.Here the interface boundary properties of Fe-Ag, Ni-Ag, Co-Ag 12,7)1, Fe-Sn /4/ ,Ga-Bi, Ga-Pb systems are discussed.In the first three systems, interface tension has been defined only at one value of temperature owing to the absence of data on the temperature dependencies of solubilities. In the rest polytherms of σ 12 were determined, too.The solubility of silver in iron is negligible and it does not exceed 0.1 mole % at 1823 K. In this limit no influenc...