Glass Transition Behavior of (Fe, Co, Ni)–Si–B Amorphous Alloys

Amorphous Ni–Fe–Si–B and Ni–Fe–Co–Si–B alloys have been found to exhibit a glass transition phenomenon before crystallization. The glass transition temperature (Tg) increases continuously with increasing Si, B, Fe and Co contents. The temperature span ΔTx(=Tx−Tg) between crystallization temperature (Tx) and Tg and the change in specific heat by the glass transition (ΔCp,s→1) have the largest values of about 30 K and 12.2 J/mol-K for (Ni0.6Fe0.4)75Si8B17 and (Ni0.53Fe0.33Co0.14)75Si8B17, respectively. Furthermore, the addition of a small amount of Nb increases the values of Tg, ΔTx and ΔCp,s→1, with a more distinct appearance of the glass transition. It should be noticed that the alloy compositions with the largest values of ΔTx and ΔCp,s→1 agree with those which have been reported to have the largest glass-forming capacity. This result is explained by the high stability of the supercooled liquids against the precipitation of crystalline phases. The high stability is presumably because the supercooled liquids at their compositions possess an atomic configuration with an optimum bonding state to suppress the nucleation and growth of crystalline phases.