Effects of Mn and Co addition on morphology of unidirectionally solidified FeSi2 eutectic alloys

Solidification structure was examined, which was obtained by the unidirectional solidification of various (FeSi2)100x(M)x, (M = Mn or Co, x = 1–3at.%) alloys. The transition of the solidification structure from irregular eutectic to well-aligned rod-like eutectic alloys occurred at a critical growth rate depending on alloys. Its value was 25 μm s−1 for the binary Fe-Si alloy and decreased by the small addition of Mn or Co. The effect of these elements on the transition was explained by the constitutional undercooling criterion in the ternary eutectic alloys. The rod spacing (λ) of the eutectic structure varied with the growth rate (R) and the value of λ2R was constant for a given alloy depending on the third element. The values of λ2R for the ternary alloys were larger than those for the binary alloy. The minimum undercooling assumption proposed by Jackson and Hunt can be applied in this case.