Phase equilibria and microstructures in the Fe–Si–Cr–Ti system

Having known that the (A2+D03) two-phase microstructure is obtained at below 873 K in the ternary Fe–Si–Cr alloy with 12–15 at.%Si at constant 10 at.%Cr, the effect of Ti additions to the ternary system on the possibility of having Huesler L21 phase in addition to D03 phase is examined. Microstructures of the quaternary Fe–10 and 12 at.%Si–10 at.%Cr–0.5 and 1 at.%Ti alloys are investigated by transmission electron microscopy through which identification and morphology of the phases precipitating within the A2 matrix are examined. It is found that the Ti addition to the ternary Fe–Si–Cr system provides (A2+L21) two-phase and/or (A2+D03+L21) three-phase regions. Morphology of the L21 phase is spherical or cuboidal, while that of D03 precipitates is rod-like, a difference which may be explained by the difference in magnitude of the misfit between the precipitate and the A2 matrix caused by the difference in partitioning of Ti to each phase.