György Kaptay

Electrochemical synthesis of refractory borides from molten salts

Abstract The electrochemical synthesis of refractory borides from molten salts has been reviewed. Non-current and electrolytic boriding of different metals has been considered first. Then, the electrochemical synthesis of refractory borides has been discussed, when the two components of the boride phase are jointly deposited on the cathode. Equilibrium Electrochemical Synthesis (EES) diagrams are presented to predict equilibrium phases to be formed during electrochemical synthesis. The possibility to produce borides of transition metals as first cathodic product has been reviewed using a thermodynamic principle. Kinetics of electrochemical synthesis and morphology of the phases obtained have also been considered. A summary table with basic information on all experiments of electrochemical synthesis of refractory borides is included with about 100 references.

Comparison of Different Theoretical Models to Experimental Data on Viscosity of Binary Liquid Alloys

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.

Modelling equilibrium grain boundary segregation, grain boundary energy and grain boundary segregation transition by the extended Butler equation

The Butler equation is extended to model equilibrium grain boundary (GB) energy and the equilibrium GB composition of a polycrystal, as a function of the following state parameters: bulk composition, temperature, pressure and the five degrees of freedom of the GB. In the simplest case of an ideal solution and equal atomic sizes of the components, the Butler equation reduces back to the well-known McLean equation of GB segregation. When the components repulse each other in the solid solution, grain boundary segregation transition (GBST) appears below the critical temperature of the bulk solid miscibility gap. The GBST line is a new equilibrium line in equilibrium phase diagrams. This new model is demonstrated for copper (Cu) segregation to the GBs in nickel (Ni) and for the phosphorous (P) segregation to the GBs in bcc iron (Fe). The GBST line appears in the Ni-rich (Fe-rich) corner of the Ni–Cu (Fe–P) phase diagram in coordinates of bulk Cu (P) mole fraction vs temperature at fixed pressure. The mole fraction of the solute (Cu or P), corresponding to the GBST line steadily increases with temperature. At a lower solute content (Cu or P), or at a higher temperature compared to the GBST line, the GB is composed mostly of the solvent atoms (Ni or Fe). Contrariwise, at a higher solute content (Cu or P), or at a lower temperature compared to the GBST line, the GB is composed mostly of the solute atoms (Cu or P). These low-segregation and high-segregation states of the GB are transformed into each other via a reversible first-order GBST. This latter process takes place when the GBST line is crossed by changing the bulk composition or the temperature. The results, theoretically estimated, are in agreement with earlier experimental results.

Modeling the Infiltration of Liquid Metals Into Porous Ceramics

A new “Closely Packed Equal Sphere” (CPES) infiltration model has been developed by us. It differs from the classical capillary infiltration model mainly in the value of the critical contact angle of spontaneous infiltration (50,7o, instead of 90o), and as a consequence, it also differs in the functional relationship between the threshold pressure and the contact angle. Our new equation becomes identical with the Carman equation for perfectly wettability. Our experimental results are in good agreement with these theoretical results.

Analysis of literature models on viscosity of binary liquid metallic alloys on the example of the Cu-Ag system

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.

On the temperature gradient induced interfacial gradient force, acting on precipitated liquid droplets in monotectic liquid alloys

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.

An Absolute Scale for the Cohesion Energy of Pure Metals

Cohesion energy is a basic energetic property of metals, determ ining the majority of their other physical properties. The reasons why the sublimation energy of metals cannot be a proper estimation for their absolute cohesion energy values are discussed. It i shown that cohesion energy is proportional to the melting point of metals. The absolute slope of t his correlation is found from the experimental surface tension value for liquid gold, and our recent t h ory between the surface tension and the cohesion energy of liquid metals. Based on that, a ta ble for the absolute values of the cohesion energy of metals has been prepared.

Interfacial Criteria for Producing Metal Matrix Composites and Ceramic Particle Stabilized Metallic Foams

Interfacial criteria to produce ceramic particle reinforced metal matrix composites and ceramic particle stabilized metallic foams are summarized in this paper. The interfacial forces and criteria are given for the following processes: introduction of ceramic particles into liquid metals, including the determination of the critical particle velocity in a gas flow, engulfment of ceramic particles by an advancing crystallization front, including the effect of the interfacial active solute element, infiltration of liquid metals into porous ceramic preforms, stabilization of gaseous bubbles by ceramic particles during production of metallic foams. The criteria given in the present paper can serve as guidelines in development of new classes of metal matrix composites and metallic foams.

On the possible mechanisms of porosity formation during laser melt injection (LMI) technology

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.

Stability of SiC in Al-Rich Corner of Liquid Al-Si-Mg System

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.