V. I. Yukhvid

SHS Metallurgy of NiAl-Based Alloy

Highly caloric mixtures of metal oxides with reducing agents used in SHS metallurgy can burn at combustion temperatures well above the melting point of final products, which ensures formation of cast products. The data of basic research in the field allowed us to suggest methods for manufacturing new cast nickel aluminides based alloy.

Production of Al-Co-Ni Ternary Alloys by the SHS Method for Use in Nickel Based Superalloys Manufacturing

Abstract In this study, Al-Co-Ni ternary alloys were synthesized, in order to obtain low-cost starting material for Ni-based superalloy production, by a self-propagating high temperature synthesis (SHS) both under normal gravity conditions (a = 9.81 m/s2) and under high gravity conditions (up to 1000 g-force) by using a centrifugal machine. The mixture of Co3O4-NiO powder were reduced by Al powder for the production of SHS alloys with the estimated compositions of 5–10 mass% Al, 20–65 mass% Co, 25–75 mass% Ni. The effect of green mixture compositions and centrifugal overload on combustion temperature, alloy/slag separations, chemical composition and microstructure of final alloys were investigated. The chemical analysis results showed that production of SHS alloys were achieved by having up to 86.12% of Co and 92.32% of Ni recoveries. The highest metal recovery value was obtained in SHS alloy with the estimated composition of 10%Al-65%Co-25%Ni by the addition of 20% Al2O3 into the green mixture. The metal/slag separation efficiency increased by increasing the centrifugal overload.

Combustion of thermite systems in thin layers with an open surface

SHS combustion of thermite compositions in the form of thin layers without formation of a continuous layer of cast products is studied. It is shown that combustion of thin layers of high-temperature compositions can be accompanied by almost complete dispersion of liquid-phase combustion products. The height of filling material and the caloric content of the mixture are effective parameters to control the size of the dispersed particles of cast synthesis products. It is established that the macrostructure of synthesis products is formed in the vicinity of the combustion wave through coalescence and capillary drift of metal droplets.

Propagation of a burn front through a long channel

We studied experimentally the phenomenology, rules, and mechanism of the propagation of a burn front through iron—aluminum thermite in a long channel. We describe the dynamics of the change of orientation of the burn front as a function of the caloric content of the mixture, and we propose a mechanism for these dynamics. We show that there exist burn limits in the vertical and lengthwise directions dependent on the channel width and the caloric content of the mixture.

Self-propagating high-temperature synthesis of niobium silicide-based composite materials

We have studied general relationships in the fabrication of niobium silicide-based composite materials by self-propagating high-temperature synthesis in combination with spin casting, using thermite mixtures. Cast Nb–Si–Hf–Ti–Al and Nb–Si–Hf–Ti–Al–Cr materials with a composite structure have been obtained. Models have been proposed for chemical transformations in a combustion wave and the formation of a cast material in several steps.

SHS Metallurgy of Composite Materials Based on the Nb–Si System

Composite materials (CMs) based on niobium with functional and alloying additives (Si, Hf, Ti, Al, etc.) have prospects for industrial approval in aviation propulsion engineering. The authors previously showed that such CMs can be synthesized in an autowave mode (combustion mode) using highly exothermic mixtures of Nb2O5 with Al, Si, Hf, and Ti. It was found that hafnium actively participates in the reduction of Nb2O5, which complicates its introduction into the CM. This study is directed at investigating the possibility to synthesize Nb-based composite materials with a high Hf content using methods of centrifugal SHS metallurgy. It is shown in experimental investigations using a centrifugal installation under the effect of acceleration of 40 g that the replacement of active Hf by its less active compounds Hf–Al or Hf–Ti–Si–Al in the composition of the Nb2O5/Al mixtures makes it possible to transfer the combustion of the mixture from the explosion-like mode into the steady-state combustion mode. The content of Hf in the CM increases with an increase in the size of Hf–Al granules from 0–40 to 160–300 μm from 1.3 to 3.8 wt %. The introduction of Hf–Ti–Si–Al granules with a particle size from 1 to 3 mm into the initial charge makes it possible to form cast CMs based on niobium silicides with a Hf content up to 8.1 wt %. The integral composition and distribution of base and impurity elements in structure components of cast CMs, as well as their phase composition, were determined using electron microscopy and X-ray phase analysis. CMs with the maximal Hf content (8.1 wt %) contain three structural components: (1) the base, which includes Nb, Si, and Ti; (2) intergrain boundaries containing Nb, Ti, and Al; and (3) inclusions based on hafnium oxide. Three phases are revealed in the X-ray diffraction pattern of the CM, notably, solid solutions based on Nb and Nb5Si3, as well as a minor amount of Nb3Si.

Gravity-Assisted Metallothermic SHS of Titanium Aluminide with Al–Ca Mixture as a Reducing Agent

The gravity-assisted combustion synthesis of γ-TiAl from oxide raw materials by using Al–Ca mixture as a reductant was explored. The use of Al–Ca reductant markedly increased the yield of TiAl and decreased the amount of residual contaminants (such as oxygen, nitrogen, carbon) in target product.

Chemical and Phase Transformations in the Combustion of a CrO3/AlN Mixture

The possibility of combustion of a mixture of chromium peroxide with aluminum nitride is shown experimentally. The effect of initial pressure of nitrogen and ratio of reagents on an average linear burning rate, as well as on a relative mass loss in the combustion of a CrO3/AlN mixture is studied. The concentration limits of the burning rate of the test mixture are determined. The microstructure and phase and chemical compositions of the combustion products of the chromium–nitride-aluminum mixture are described.

Energy stimulation of autowave synthesis of hafnium aluminides

The production of hafnium aluminides from mixtures of hafnium or its oxide with aluminum in the combustion mode is impossible because of a near-zero thermal effect. The present study is aimed at stimulating autowave chemical transformation with the help of energetic formulations and producing cast hafnium aluminides by means of combustion methods. The characteristics of the autowave synthesis and the conditions for producing cast hafnium aluminides are determined, and their composition and structure are investigated.

Ti-Al-Nb Material for High-Temperature Applications: Combustion Synthesis from Oxide Raw Materials

This work is focused on preparation of Nb-doped Ti–Al material (Ti–29.3Al–17.6Nb wt %) by centrifugal SHS. Results of studying of combustion and synthesis regularities of intermetallic material on γ-TiAl base from oxide materials under high gravity are presented in the article. For the first time is used a reduction mixture on Al/Ca base which markedly increases the yield of Ti–Al–Nb and decreases the amount of non-metallic impurities (oxygen, nitrogen, carbon) in target product.