Vol 2018, No 12 (2018)

The microstructure and the phase composition of an experimental Ni₃Al-based intermetallic alloy containing (wt %) 7.8 Al, 14.5 Ta, 0.9 Mo, 0.5 W, 0.5 Re, 0.15 C, and Ni for balance, which was prepared by slow (6 mm/h) high-gradient (15°C/mm) directional solidification and selective laser melting, are studied, and the lattice parameters of phases and solidus and liquidus temperatures are determined. The phase compositions of the intermetallic alloy samples prepared by these technologies are found to be identical and consist of a γ'-phase matrix and TaC carbide particles.

A thermal model is developed for the ingot solidification during vacuum arc remelting (VAR) and is applied to calculate pool profiles for a VT3-1 alloy. The pool profiles are calculated for two remelting schedules, and the calculation results are compared with radiography data. The model calculation results are shown to agree satisfactorily with experimental data. The model is used in practice to develop conditions for the final remelting of a VT3-1 alloy to exclude the formation of segregation defects, namely, β flakes and macrosegregation. The developed model can be used for technological calculations and can give important information on the dynamics of VAR ingot solidification.

The mechanisms of alumina formation from metallic aluminum in aqueous solutions and in molten salts are considered. The author technology of processing of dump slags from secondary metallurgy with the preparation of an aluminum deoxidizer alloy and the technology of the electrochemical oxidation of metallic aluminum with the formation of high-purity alumina (raw materials for manufacturing synthetic sapphires) are examined. The behavior of aluminum and alumina in the key technological process (electrolysis), in particular, in an oxyfluoride melt and in an aqueous salt solution, is considered when analyzing the technologies. The influence of the electrolyte composition on the electrolysis and side processes of dissolution of various metals (iron, copper, zinc, and others) is analyzed. The thermodynamic evaluation of possible reactions in the working medium (electrolyte) affecting the quality of the final product is performed. The possibilities of the retention of the proper quality of the final product are considered on the basis of thermodynamic calculations. Measures for decreasing the probability of unfavorable reactions are proposed. The technological preparation of an aluminum deoxidizer alloy and high-purity alumina using the electrochemical method is found to be possible only due to the high affinity of aluminum to oxygen. The main requirements imposed on the final products of the considered technologies are presented, and the priority areas of their application are designated.

The softening and the strength of the welded joints of high-temperature complex alloyed aluminum 1151 alloy sheets fabricated by friction stir welding and nonconsumable electrode welding are analyzed. The strain hardening of the 1151 alloy welds formed by friction stir welding provides a higher level of their strength than fusion welding does. The welded joints of the 1151 alloy exhibit a high stress corrosion and intergranular corrosion resistance.

The oscillations of the mass velocity of melting during cyclic electroslag remelting of ChS-82 steel ingots under laboratory and industrial conditions are studied. The data on the mass velocity, the remelting current, and the furnace voltage that form by an automatic control system during the process in the form of electronic tables are processed. An analysis of these data demonstrates that the oscillations of these parameters that accompany melting substantially affect the ingot quality.

The paper reports the results of studying the phase compositions of the metallic compounds that participate in the aluminum and chromium transfer from powders on the metal surface upon vacuum chromoaluminizing and the life characteristics of combined condensation-diffusion coatings containing Cr, Al, Ta, W, Hf, and Y. The presence of high-temperature metals in the sublayer of aluminide coatings is found to increase the life of the parts operating at temperatures up to 1100–1150°C substantially.

A technique for the local strengthening of cast materials by introducing wear-resistant inserts based on refractory carbides into a polystyrene foam model is proposed. Experiments are carried out and dispersion-reinforced castings are manufactured. The structure and properties of the castings are investigated. The proposed technique can be used to create locally strengthened regions in casting.

The methods of organization of technologically efficient electromagnetic mixing of a liquid metal (EMLM) in dc electric arc furnaces are considered. The relations between the melt velocity in a furnace bath, the design parameters, and the electric parameters are found for a series of electric arc furnaces with a capacity of 0.5–25 t using physical and mathematical simulation. The liquid metal velocities during EMLM in operating dc arc furnaces with a capacity of 5, 12, and 15 t are measured.

An energy-saving, ecologically safe, and resource-saving technology is proposed to fabricate a powder material from the wastes of cobalt–chromium alloys with a given size and shape distribution of particles, which can be used for additive technologies.

The prospects of development of the steelmaking in the world and Russia are estimated using information in the period 2009–2017. Recommendations on predicting crisis phenomena on the world and Russian steel markets are given in short-, medium-, and long-term time periods. The situation on the first processing world market of steelmaking is shown to be rather stable, and sharp changes in the business activity of steel market players on the regional level are possible.