The phase transformation of Fe90-XNb10BX (X = 10 and 30) amorphous alloys by annealing was studied by differential scanning calorimetry (DSC) and X-ray diffraction. The Fe60Nb10B30 alloy exhibits a large supercooled liquid region (i.e. the difference between the glass transition temperature (Tg) and the onset of crystallization temperature (Tx)), ΔTx (=Tx - Tg) of 67 K, whereas the Fe80Nb10B10 amorphous alloy transforms directly into crystalline phases. New metastable crystalline phases were found during the crystallization process of these alloys. In the crystallization process of the Fe80Nb10B10 alloy, the structure of the primary precipitation phase is α-Mn type, which transforms into α-Fe phase at a higher temperature. In case of Fe60Nb10B30 alloy, another metastable phase, Fe23B6-type structure, is formed corresponding to the first exothermic peak in the DSC curve. Although the metastable phases in the two alloys are completely different, the dissociated phases of α-Fe, Fe3B and Fe2B are formed in both alloys after the final stage of crystallization. The local atomic ordering structure in the α-Mn type is similar to that in an amorphous state of the Fe80Nb10B10 alloy. On the other hand, the formation of the Fe23B6-type structure requires a significant change in the geometrical rearrangements with relatively long-range ordering of the Fe60Nb10B30 alloy, which may be attributed to the high stability of the supercooled liquid.
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