D. E. Andreev

Centrifugal SHS metallurgy of nickel aluminide-based eutectic alloys

Cast nickel aluminide-based eutectic alloys of the equimolar composition NiAl-Mo (Cr, V, Nb) alloyed with boron and hafnium are fabricated by centrifugal SHS metallurgy. It is established experimentally that the acceleration range of 150–200 g is the most manufacturable. It is shown that the convective motion of the melt behind the combustion front under the effect of gravitation leads to an increase in the combustion rate, completeness of the chemical interaction in the combustion wave, and composition homogenization of combustion products over the melt bulk. It is established that alloys have the homogeneous composite structure of the NiAl grain with an insignificant amount of boride inclusions (MoB, V(Cr)B, Mo(Nb)B2), which are uniformly distributed in the matrix consisting of the β/γ eutectics. The density for all four compositions under study did not exceed 6.7 g/cm2.

SHS metallurgy of high-entropy transition metal alloys

The first positive experience in synthesis of cast high-entropy alloys in the combustion mode, referred to as SHS metallurgy (SHS is self-propagating high-temperature synthesis) has been reported. Analysis of the data obtained enables the conclusion that the one-stage SHS method is promising for the production of cast metal materials using a new principle of formation of high-entropy polymetallic alloys.

Fabrication of cast electrodes from nanomodified nickel aluminide-based high-boron alloy to fabricate spherical powders using the plasma rotating electrode process

A complex manufacturing method of billets from material based on high-boron nickel aluminide is proposed. The method includes manufacturing the semifinished alloy products using a combined method of self-propagating high-temperature synthesis and centrifugal casting from oxide feedstock and subsequent vacuum induction remelting with the introduction of Al-based foundry alloys containing nanosized ZrO2 and modifying the structure. The evolution of the microstructure and phase composition is investigated at all production stages. A cast ZrO2-modified cylindrical billet, which possess high purity in regards to gas impurities (O 0.005 wt % and N 0.0001 wt %) and is suitable for the further production of powders by the plasma rotating electrode process, is fabricated according to the proposed technology.

Cast NiAl/Ni20Al3B6 composites by centrifugal SHS

Cast NiAl/Ni20Al3B6 composites containing 2.3–3.5 wt % B have been prepared by centrifugal SHS for the first time. The composite materials comprised of a solid-solution matrix based on NiAl with inclusions of Ni20Al3B6 and complex boride (Mo, Cr)B. Best results were achieved at centrifugal accelerations 150–200 g in open air. Cast materials based on NiAl and τ-borides seem promising for use in turbine power units.

SHS-produced intermetallides as catalysts for deep oxidation of carbon monoxide and hydrocarbons

Investigated was the catalytic activity of multicomponent metal catalysts prepared by alkaline leaching of SHS-produced (NiAl3)x(CoAl3)y and (NiAl3)x(CoAl3)y(MnAl3)z intermetallides in deep oxidation of carbon monoxide and hydrocarbons. The morphology and composition of starting and leached intermetallides were characterized by SEM, while the specific surface of the catalysts was determined by BET method. The above preparation technique can be expected to open up a new route to synthesis of high-efficiency polymetallic catalysts for deep oxidation of CO and hydrocarbons.

Cast alloy production on the basis of titanium aluminide with centrifugal SHS method

The technique for cast alloy production on the basis of titanium aluminide with the SHS method is developed. It is shown that a combination of compounds with a minor thermal effect and “power” addition serves to realize the mode of burning wave self-propagation without extra heat sources and to obtain materials in cast form. Overloading provides the maximum yield of metal in the ingot and an even distribution of components in the alloy volume. Results of research can serve a basis for the development of technology aimed at producing a number of prospective alloys on the basis of titanium intermetallides.

Production of intermetallic catalysts of deep CO and hydrocarbon oxidation

The possibility of producing (Ni, Co, Mn) Alx intermetallides using the technique of self-propagating high-temperature synthesis and their subsequent processing with the purpose of using them as catalysis in the process of complete oxidation of CO and hydrocarbons is considered. Phase composition, microstructure, and morphology of alloys and catalysts based on them are studied. Dependences of activity and stability on composition are determined. These catalysts are shown to possess high activity and their development is considered to be a promising direction in the catalysis of deep oxidation processes.

Polymetallic catalysts for the Fischer–Tropsch synthesis and hydrodesulfurization prepared using self-propagating high-temperature synthesis

The synthesis, physicochemical characteristics, and operation of the previously proposed new multifunctional polymetallic catalysts in reduction processes are considered. The complex intermetallides of 3d metals and rare-earth elements, which are obtained by self-propagating high-temperature synthesis (SHS), are catalyst precursors. The catalyst structure includes a framework of lower intermetallic compounds covered with a strongly disordered highly amorphous metal oxide active phase. This phase forms two-level nanostructures (~10–100 nm) with a characteristic shape of flat hexahedrons on the surface. The catalysts possess high activity in the reactions of deep oxidation and reduction (the Fischer–Tropsch synthesis and the hydrodesulfurization of petroleum fractions); moreover, they do not require preliminary activation in the reduction processes.

Iron-based polymetallic catalysts with a nanostructured surface for deep oxidation processes

A new class of highly active polymetallic catalysts for deep oxidation based on iron with admixtures of other d-metals and rare earths has been developed. The precursors of the catalysts are multicomponent intermetallides obtained by selfpropagating high-temperature synthesis (SHS). The XPA spectra, specific surface, and the morphology of the surface according to the SEM results are studied. The catalytic properties are studied using the example of deep oxidation processes of carbon monoxide and propane. It has been shown that two-level metal–oxide nanostructures are common features of the surface for the catalysts studied. The lowest level represents granules 10–30 nm in diameter, of which flat hexahedrons are built with a diameter of about 1 μm and a thickness of ≤100 nm.

Chemical transformations of multicomponent thermite-type mixtures in combustion waves

Hightemperature multicomponent alloys are generally synthesized at high temperature by sintering andhot pressing. This synthesis can be efficiently performed using materialforming combustion processes(selfpropagating hightemperature synthesis, SHS),in which the high temperature required for the synthesis is created by converting the internal chemicalenergy of the initial systems [1, 2].Combustion can occur in various systems: mixturesof elemental substances (a metal with a nonmetal),thermitetype mixtures (mixtures of oxides withreducing metals and nonmetals), and others. Thecombustion temperature of thermitetype mixturescan exceed the melting point of the final products ofcombustion (oxide and nonoxide ceramics, compositematerials, and alloys), which allows to produce themas cast [3, 4]. The chemical transformation of the initial thermite mixture to the final product occurs in acombustion wave front, which forms after ignition ofthe surface layer, propagates in the mixture at a velocity of 0.1 to 10 cm/s, and ends in postprocesses.Behind the combustion wave front, a liquid–liquidtwophase medium emerges, in which the oxide product (reducingmetal oxide) forms a continuousmedium with distributed metal product particles.Under gravity, the metal and oxide phases having different densities are separated, and a twolayer productforms, which readily breaks up into layers after crystallization. The completeness of the gravity separation isdetermined by the ratio between the rates of melt cooling and gravity separation. The gravity separation rateincreases with relative centrifugal force; therefore, thesynthesis was performed in centrifugal units. The centrifugal force field helps increase the ingot yield of themetal phase [5, 6].The synthesis of multicomponent alloys by combustion methods is accompanied by the competitionof stages of the chemical transformation in the combustion wave, which complicates the introduction ofactive elements, such as Hf, Ti, and Nb, to the metalphase of the combustion products. In the chemicaltransformation zone of the combustion wave, theystrongly compete with the reducer (aluminum) andare largely consumed to reduce the initial oxides. Weshowed that the replacement of the active elements bytheir compounds allows one to significantly reduce oreliminate the participation of the former in reductionprocesses in combustion waves and to use combustionmethods for producing cast multicomponent alloyswith high contents of active elements. This enablesone to create new materials with controlled physicomechanical properties and develop efficient technologies for their production.The experiments were carried out in a centrifugalunit (Fig. 1) within the range