Improvement of the technology of melting ingots of nickel based alloys by vacuum arc remelting (VAR)
DOI:
https://doi.org/10.30838/J.PMHTM.2413.250619.45.321Keywords:
smelting charge, alloying element, nickel alloy, metal melting, ingot, structure, propertiesAbstract
Abstract. Purpose. Improvement of the technological modes for the melting of nickel-based cathodes of composition Ni−Cr−Al−Y in order to improve their quality, namely, reducing the total number of defects in the form of discontinuities, pores, non-melts and increasing the homogeneity of the structure and chemical composition. Methods. To prepare the smelting charge for melting, the raw materials were chopped to the required size and mixed, which made it possible to ensure uniform distribution of the alloying elements in the entire volume of the smelting charge. To obtain experimental ingots, a vacuum-arc furnace was used. The mass of smelting-charge loading per melting was 4 000…6 000 g. Testing of melting modes was carried out by experimental implementation of the process. The range of modes is as follows: I = 450...1 800A, U = 30...45 V, t = 25...35 min, preliminary creation of a vacuum of 1∙10-4 mbar. The operating fluid is Ag/He gas mixture (70/30), pressure 0.5 bar, temperature of chill mold heating − 250…800 °С, melt temperature before pouring − 1 400…1 700 °С. For a comprehensive assessment of the chemical composition, a study was conducted in two zones of ingot fragment, in the central part of the sample and on its surface. The chemical composition studies were performed using a multipurpose scanning electron microscope REM 106І equipped with a microanalysis system. Metallographic studies of the obtained structure of the ingot were carried out using optical and electronic microscopes. Results. It has been established that the use of vacuum-arc remelting process to produce nickel-based alloys using preparation methods of smelting-charge with various size and refining the melting process parameters allows to produce ingots with a minimum number of proper defects, with the formation of a uniform structure and uniform distribution of alloying elements in the entire alloy. Scientific novelty. The regularities of the influence of the technological parameters of the charge preparation and the melting process on the structure and properties of nickel-based superalloys are established. Practical significance. Practical use of the obtained results will significantly improve the homogeneity of ingots in the production of cathodes for coating, which in turn will have a positive effect on the quality of applied coatings and the total resource of parts.
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