Solidification Behavior and Cooling Curves for Hypereutectic Fe-21 At. Pct B Alloy

The cooling curves for Fe-21 at. pct B hypereutectic alloy were measured, which are correlated with the solidification behaviors. At small undercoolings, the cooling curve has two recalescences, corresponding to L → Fe2B and L → Fe2B + Fe, respectively. At moderate undercoolings, also two recalescences can be observed from the cooling curve, corresponding to L → Fe3B and L + Fe3B → Fe2B + Fe. At large undercoolings, the cooling curve has only one recalescence, corresponding to L → Fe3B + Fe. From TEM analysis, the matrix phase is α-Fe in cases of solidification at small and moderate undercoolings, but is Fe3B in case of large undercooling. HRTEM analysis shows that α-Fe stores deformation energy by irregular atom region, but intermetallic phase (Fe2B or Fe3B) stores deformation energy by increasing grain boundaries and stacking faults, which can explain why α-Fe has good deformation ability and small hardness, but the Fe2B or Fe3B phase on the contrary.