Structure and properties of aluminized alloys of the Fe–Cr–Al system

Abstract

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/.