Study of phase equilibria, diagrams and transformations in the Fe-Co-Si ternary system

A 1000 °C isothermal phase diagram in the total composition range of the Fe-Co-Si ternary system is constructed featuring the interconnected ε-(Fe,Co)Si, large bcc-structure (αFe), and fcc-structure (γFe,αCo) phases. In addition, a vertical magnetic plus ordering transition phase diagram of Fe80-xCoxSi20 alloys is also constructed. It is shown that the magnetic transition (D03ferro./para.) temperature increases with the Co concentration and reaches a maximum value (845 °C) at 50 at. % Co in the investigated Fe80-xCoxSi20 alloys. Meanwhile, the B2/D03 ordering transition temperature versus Co content dependence exhibits an initial slight rise followed by a gradual decrease to ∼67 at. % Co. Furthermore, a fcc/bcc martensitic transformation was revealed in several Co-rich ternary alloys under study. The resulting lath martensitic microstructures of the studied alloys include numerous twins and dislocations defects, revealing a similarity with the FeNi-based alloy system. [Display omitted] •A 1000 °C isothermal section of the Fe-Co-Si ternary system is established.•The magnetic transition (D03ferro./para.) and ordering transition (D03/B2) temperatures of Fe80-xCoxSi20 alloys is constructed.•The fcc/bcc martensitic transformation is revealed in several Co-rich ternary alloys.