Papers by Author: György Kaptay

Abstract: Bulk, surface and interface thermodynamics of immiscible liquid alloys are considered within a unified theoretical framework. For bulk thermodynamic functions the exponential and the combined linear-exponential equations are discussed, obeying the 4th law of thermodynamics. Surface phase transition is discussed in details. For surface and interface thermodynamics the monolayer Butler equation is compared to the multilayer model. During further assessment of bulk thermodynamic data of immiscible liquid alloys their experimentally measured surface tension and interfacial energy should be also taken into account, coupled with the models presented here.

Abstract: The paper deals with the stability of centerline inhomogenity of continuously cast slabs and hot rolled products. The centerline segregation is a disadvantageous failure of slabs which can affect the quality properties of the final products. During hot rolling of the slabs the centerline segregation pattern will become thin and stretched and it can also be detected in the middle part of heavy plates and coils. It is a common experience that the centerline segregation of heavy plates can not be easily decreased by post heat treatment. The pattern of the centerline segregation was modeled physically by preparing a sandwich structure of steel plates with different levels of carbon and alloying elements. Homogenization experiments were performed and the samples were examined metallographically. Diffusional calculations proved the governing role of carbon activity which is influenced by the distribution of alloying elements.

Abstract: The wettability of graphite and glassy carbon surfaces by molten alkali chlorides was measured by the sessile drop method. Pure NaCl, KCl and CsCl, binary NaCl-CsCl and NaCl-KCl and ternary NaCl-KCl-CsCl compositions were measured. CsCl was found to be an interfacially active component (at the solid/liquid interface) in both binary NaCl-CsCl and ternary NaCl-KCl- CsCl systems. From the composition dependence of the interfacial energy in the NaCl-CsCl system the hypothesis is made on the possibility of the existence of 3[ 4 ] Cs NaCl complex.

Abstract: In the present study the analysis of 5 different mechanisms of porosity formation during laser melt injection (LMI) technology were performed. Experiments were supported by thermodynamic and fluid-flow analysis. Special attention should be paid to i. clean the surface of the substrate, ii. use inert shielding gas, iii. use proper particle size and gas velocity, iv. use proper laser power and laser beam velocity to control bath temperature and v. deoxidize the surface of the added particles.

Abstract: In the present paper the wettability of a liquid metal by another liquid metal is studied theoretically, based on a recent model on interfacial energies in metallic systems. It appears that in all practical cases the liquid metal with a lower surface tension will perfectly wet (with a zero contact angle) the liquid metal with a higher surface tension practically at any temperature, and therefore will encapsulate it. As a result, the first order surface phase transition will start in monotectic metallic systems at 0 K. The phenomenon of the surface phase transition is considered in some details, based on a recent paper.

Abstract: Six different theoretical equations are compared in the present paper with experimental data, measured for 28 binary liquid metallic systems. General conclusions are drawn on the ability of the different theoretical models to describe the concentration and temperature dependence of the viscosity of liquid alloys. A new equation is derived, being able to predict the viscosity in multicomponents alloy even if the viscosities of the pure components are not known.

Abstract: The final morphology of liquid metallic emulsions, produced in a temperature gradient, depends on the interfacial gradient force acting on small metallic droplets. This force is proportional to the temperature coefficient of the interfacial energy between the two immiscible liquid phases. In the present paper first a widely used equation of Young, Goldstein and Block for the steady-state velocity of liquid droplets under the influence of the temperature gradient is discussed. Then a new equation is proposed for the temperature dependence of the interfacial energy.

Abstract: Penetration of model solid particles (polymer, teflon, nylon, alumina) into transparent model liquids (distilled water and aqueous solutions of KI) were recorded by a high speed (500 frames per second) camera, while the particles were dropped from different heights vertically on the still surface of the liquids. In all cases a cavity has been found to form behind the solid particle, penetrating into the liquid. For each particle/liquid combination the critical dropping height has been measured, above which the particle was able to penetrate into the bulk liquid. Based on this, the critical impact particle velocity, and also the critical Weber number of penetration have been established. The critical Weber number of penetration was modelled as a function of the contact angle, particle size and the ratio of the density of solid particles to the density of the liquid.

Abstract: The thermodynamic analysis of the SiC/Al-Si-Mg system has been performed in order to find the conditions to produce SiC/Al-Si-Mg composite materials with the stable SiC/alloy interface (for both a-SiC and b-SiC) and with the solidification of primary a-Al solid solution. The conditions to avoid the formation of Al4C3 are expressed as function of temperature, and the silicon and magnesium content of the liquid aluminium alloy. It has been shown that to ensure stabilization of (the more stable) b-SiC, lower Si-content is needed and higher working temperature is allowed, compared to the requirements to stabilize (the less stable) a-SiC.

Abstract: The aim of this paper is to review all the existing literature models on the concentration dependence of the viscosity of binary liquid alloys and to check them against the measured viscosity values in the binary liquid Cu-Ag system at 1373K.