Volgograd State Technical University, Volgograd, Russia:
V. G. Shmorgun, Dr. Eng., Prof., Dept. of Materials Science and Composite Materials, e-mail: mv@vstu.ru
V. P. Kulevich, Cand. Eng., Lecturer, Dept. of Materials Science and Composite Materials
A. I. Bogdanov, Cand. Eng., Associate Prof., Dept. of Materials Science and Composite Materials

The formation features of the aluminide coating structure on Cr15Al5 and Cr23Al5 alloys after aluminizing by immersing in aluminum and silumin melt are studied. The influence of Si on the transformation of the structure and phase composition of the aluminide coating under high-temperature heating conditions are studied. It is shown that aluminizing of the Fe–Cr–Al system alloys by immersion in an aluminum melt ensures the formation of a defect-free continuous coating on their surface, which is a crystallized eutectic mixture of Al + FeAl3 and a layered diffusion zone at the boundary with the substrate. Replacing the aluminum melt with silumin with 12 % Si leads to the appearance of the Al₇Fe₂Si ternary intermetallic compound in the coating composition, which almost completely replaces FeAl₃. In the process of hightemperature transformation of the coating structure, the presence of Cr and Si at the initial stage leads to the appearance in the coating composition intermetallic compounds (Cr,Fe)₅Al₈, Cr₃Si, Al₇Fe₂Si, Fe₃(Si,Al)₅ and Cr₅Si₃ along with Fe–Al binary, and at the final stage – does not affect the phase composition, forming solid solutions based on iron aluminides. It is shown that the oxidation of aluminide coating on the Fe–Cr–Al system alloys at its early stages is accompanied by the formation of a stable modification of α-Al₂O₃ aluminum oxide and (Fe,Cr)₂O₃ ternary oxide, and with long-term oxidation leads to the appearance of δ-Al₂O₃ metastable modification and FeAl₂O₄. It has been established that the Si-alloyed aluminide coating on the Cr15Al5 alloy has a lower corrosion penetration depth at 1100 °C. At the same time, the retention time of heatresistant properties for the aluminide coating on the Cr23Al5 alloy is ~20000 h, and on the Cr15Al5 alloy it is ~5000 h for the aluminide and 6000 h for aluminosilicide coatings.
The study was supported by the Russian Science Foundation grant No. 21-79-10246, https://rscf.ru/project/21-79-10246/.

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