E. A. Pastukhov

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.

Synergetic effect in modifying with master alloys having an aluminide cubic structure

Experimental data on the preparation of test master alloys Al–Sc–(Zr, Ti, Y), Al–Zr–(Ti, Y), and Al–Ti–Y, which contain two transition metals and are characterized by the formation of aluminides with the L12 cubic lattice (which is identical to the crystal lattice of an aluminum-alloy matrix), are presented. The growth forms of aluminides in alloys of various compositions are demonstrated. Using Al–4% Cu model alloys (experiments were carried out with 15 and 200 g samples cooled at different cooling rates), the modifying ability of the test ternary master alloys and industrial binary master alloys (used for comparison) has been estimated. Synergetic effects of two transition metals, which consist in grain refining in Al–4% Cu alloys, and a substantial difference in the modifying effects of the binary and ternary master alloys have been shown.

Interaction between vanadium carbide and aluminum and copper melts

The effect of low-frequency vibrations on the interaction between molten metals (Al,Cu) and vanadium carbide is studied. These vibrations are shown to initiate wetting of the V8C7 carbide by a copper melt and a chemical interaction in the Al-V8C7 system, resulting in the formation of vanadium aluminides and aluminum carbide.

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.

Synthesis of niobium carbides in copper melts

The production of cast composite Cu-NbC alloys by synthesizing of niobium carbides in a copper melt is studied. The processes of carbide formation are intensified by the mechanical activation of niobium and graphite powders, which are mixed with a copper melt, in a high-speed ball mill and by the action of low-frequency vibrations on copper melts.

Interaction of tungsten with tungsten carbide in a copper melt

The chemical interaction between tungsten and tungsten carbide in a copper melt with the formation of W2C at 1300°C is studied. It is shown that the mechanical activation of a composition consisting of copper melt + W and WC powders by low-temperature vibrations initiates not only the chemical interaction of its solid components but also their refinement.

Pseudocavitation during low-frequency treatment of melts

Low-frequency and ultrasonic treatments of a melt are compared theoretically. The phenomenon caused by low-frequency treatment of a melt and called pseudocavitation is considered. The conditions of the appearance of this phenomenon are revealed, and an experiment on mixing of a “light” aluminum powder with “heavy” Wood’s alloy is performed under pseudocavitation conditions.

Carbide formation in aluminum melts processed by low-frequency elastic vibrations

The temperature and time conditions of carbide formation in binary aluminum melts subjected to elastic low-frequency vibrations transferred through a graphite vibrating piston are studied to develop an in situ technology for the production of composite materials. Our experiments demonstrate that the carbide-forming abilities of components dissolved in aluminum cannot be estimated from the changes in the standard free energies ΔGT of formation of their carbides from pure elements. Although energies ΔGT of formation of titanium and zirconium carbides from pure elements are close, only titanium dissolved in aluminum has a high carbideforming ability. This specific feature is used to synthesize titanium carbides in an aluminum melt and to produce aluminum-based composite materials hardened by titanium carbides.

Kinetics of redox processes in manganese oxides

The redox processes in ceramic and powder samples of α-Mn2O3 (kurnakite) and β-Mn3O4 (hausmannite) have been studied in the temperature range 20–1000°C. The results demonstrate that the conversion of α-Mn2O3 to β-Mn3O4 in the binary system Mn-O is essentially irreversible, even if there are nucleation centers in the form of the higher oxide α-Mn2O3 during the oxidation of hausmannite. It is shown that the high reactivity of hausmannite ground in a WC mill is not due to a mechanochemical effect. Grinding-induced contamination has a significant effect on the oxidation behavior of the system: the impurities incorporated into the sample during grinding in a mill favor complete (WC contamination) or partial (Fe contamination) conversion of hausmannite to kurnakite. Hausmannite contaminated with tungsten carbide oxidizes by a catalytic mechanism. In the case of Fe impurities, oxidation follows a solid-state mechanism, through the formation of restricted FexMn2−xO3 solid solutions.

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.