A. B. Shubin

Master alloys Al-Sc-Zr, Al-Sc-Ti, and Al-Ti-Zr: Their manufacture, composition, and structure

Ternary master alloys Al-Sc-Zr, Al-Sc-Ti, and Al-Ti-Zr are prepared. The complex aluminides Al3(ScxZr1−x), Al3(ScxTi1−x), and Al3(TixZr1−x) in them have the L12 cubic lattice, which ensures high structural and size matching with the crystal lattice of the matrix of the aluminum alloys modified by these master alloys. The action of low-frequency vibrations on the melts of the ternary master alloys favors the fragmentation of the aluminides down to sizes smaller than 10–30 μm and their uniform distribution in an alloy matrix.

Al-Ti-Zr master alloys: Structure formation

The effects of the composition of ternary Al-Ti-Zr master alloys, the overheating of their melts with respect to liquidus, and exposure to low-frequency vibrations on the structure formation in them are studied. It is shown that complex aluminide Al3(ZrxTi1 − x) with a metastable L12-type cubic lattice coinciding with the structure type of α Al primarily precipitates during the crystallization of Al-Ti-Zr melts under certain conditions. This fact makes such master alloys promising for modifying aluminum alloys.

Thermal Properties of CuGa2 Phase in Inert Atmosphere

Thermal decomposition of copper digallide was studied using experimental (thermal analysis) and theoretical (thermodynamic modeling) methods. The temperatures of CuGa2 incongruent melting are in satisfactory agreement between experimental and calculated values. Small differences with the phase diagram can be explained by minor non-stoichiometry of the alloy samples. The experimental studies of thermal diffusivity and thermal expansion of CuGa2 were performed in the temperature range 298-500 K. The heat conductivity coefficient was further calculated using literary data concerning the density and heat capacity of the copper digallide.

Enthalpies of mixing of rare-earth metal-aluminum alloys: Model calculations

Integral enthalpies of mixing ΔmixH for binary rare-earth metal (REM)-aluminum systems are calculated using the following three semiempirical approaches: an ideal solution model for interaction products, the Miedema model, and a specific calculation algorithm developed by us. Possible qualitative and, for a number of alloys, quantitative agreement of the calculation results with each other and the experimental data is demonstrated. The model parameters that allow the enthalpies of mixing to be calculated using simple relations are reported. The values of ΔmixH are calculated for Al-REM alloys over the entire composition range.

Problem of the thermodynamic properties of liquid aluminum alloys with scandium

The standard enthalpies of formation of intermetallic compounds in the Al-Sc system are calculated using a well-known semiempirical model. The determined values agree satisfactorily with the most reliable experimental data. The thermodynamic simulation made it possible to calculate the equilibrium characteristics for Al-Sc liquid alloys in the temperature range from 1873 to 2073 K.

Structural Features of Al–Hf–Sc Master Alloys

Microstructural features of new master alloys of the Al–Hf–Sc system with metastable aluminides with a cubic lattice identical to the lattice of a matrix of aluminum alloys are investigated using optical microscopy, scanning electron microscopy, and electron probe microanalysis. Binary and ternary alloys are smelted in a coal resistance furnace in graphite crucibles in argon. Alloys Al–0.96 at % Hf (5.98 wt % Hf) and Al–0.59 at % Hf (3.77 wt % Hf) are prepared with overheating above the liquidus temperature of about 200 and 400 K, respectively. Alloys are poured into a bronze mold, the crystallization rate in which is ~103 K/s. Metastable Al3Hf aluminides with a cubic lattice are formed only in the alloy overheated above the liquidus temperature by 400 K. Overheating of ternary alloys, in which metastable aluminides Aln(Hf1–xScx) formed, is 240, 270, and 370 K. Depending on the Hf-to-Sc ratio in the alloy, the fraction of hafnium in aluminides Aln(Hf1–xScx) varies from 0.46 to 0.71. Master alloys (at %) Al–0.26Hf–0.29Sc and Al–0.11Hf–0.25Sc (wt %: Al–1.70Hf–0.47Sc and Al–0.75Hf–0.42Sc) have a fine grain structure and metastable aluminides of compositions Aln(Hf0.58Sc0.42) and Aln(Hf0.46Sc0.54), respectively. Sizes of aluminides do not exceed 12 and 7 μm. Their lattice mismatch with a matrix of aluminum alloys is smaller than that for Al3Sc. This makes it possible to assume that experimental Al–Hf–Sc master alloys manifest a high modifying effect with their further use. In addition, the substitution of high-cost scandium with hafnium in master alloys can considerably reduce the consumption of the latter.

Al-Sc-Zr Master Alloy and Estimation of Its Modifying Capacity

An Al-1.1 Sc-1.1 Zr (wt %) master alloy with a uniform distribution of micron and submicron particles of aluminide phase Al3(Sc1 − xZrx) has been obtained by exposing of equal amounts of commercial Al-Sc and Al-Zr master alloys to short-time actions of low-frequency vibrations transferred to the alloy via an irradiating plunger. Zirconium substitutes up to 50% Sc in aluminides and retains its L12 lattice. The modifying capacity of the experimental master alloy is tested on cast alloy (wt %) Al-8Zn-2.4Cu-3Mg. Intense grain refinement of this alloy is achieved by its modification with a certain amount of the master alloy. At a certain Sc + Zr content, a grain dendrite structure completely disappears in the alloy.

Thermodynamic properties of liquid Sc-Al alloys: model calculations and experimental data

Thermodynamic information available for binary scandium-aluminium system has been obtained earlier by e.m.f. and calorimetry methods and also by semi-empirical approaches described in literature. In this work these data were reconsidered for all intermetallides in Sc-Al system. To calculate the excess thermodynamic functions of liquid Sc-Al alloys special computer program package have been used. The enthalpies of mixing of liquid scandium and aluminium were found in all the composition range of the phase diagram at the temperatures 1873, 1973 and 2073 K.

Thermodynamic Modeling of Phase Equilibria in the WO3-Zn System

There are no alloys in the W-Zn binary system. The combustion process in the WO3-Zn powder mixture gives mainly metallic tungsten and zinc oxide. The ZnO in the product can be easily leached (e.g., with HCl), so that from stoichiometric quantities of reagents, one can obtain W powder of good purity. Here we investigated the phase equilibria for the WO3-Zn system in the temperature range of 900-1500 K. The inert component (Ar) was introduced into the system to change the pressure within the range of 0.1-0.5 MPa. When the pressure is constant, the quantity of tungsten dioxide in the equilibrium mixture of components increases with rise in temperature, while the fraction of the zinc oxide decreases. The fraction of metallic tungsten in the mixture also decreases with temperature increase and becomes near zero at 1500 K and 0.1 MPa. Up to 1100 K, the output of tungsten is close to the limiting (stoichiometric) value in the whole considered pressure range (0.1-0.5 MPa).

Interaction of niobium and tungsten monocarbides in molten copper

The chemical interaction of uncompacted monocarbide NbC and WC powders, which were taken at mass carbide ratios NbC: WC = 10: 1, 3: 1, 1: 1, and 1: 3 and a total carbide content of 20 wt %, in molten copper is studied at 1300°C. The primary and secondary phase transformations that result in the appearance and decomposition of an (Nb,W)C solid solution are analyzed. The activating role of low-frequency vibration is shown.