Kinetics and thermal stability of the Ni62Nb38–xTax（x=5, 10, 15,20 and 25） bulk metallic glasses

We studied thermal stability and its relationship to the glass-forming ability（GFA） of the Ni62Nb38–xTax（x=5, 10, 15, 20, 25） bulk metallic glasses（BMG） from a kinetic point of view. By fitting the heating-rate dependence of glass transition temperature（Tg onset）and crystallization temperatures(Txonset and Txpeak) of the Ni62Nb38–xTax BMG using the Vogel-Fulcher-Tammann（VFT） equation, we obtained the ideal glass transition and crystallization temperatures（Tg0 and Tx0） and the fragility parameter（m）, and also constructed continuous heating transition（CHT） diagrams for crystallization of the BMG. The CHT diagrams of the BMG indicate enhanced thermal stability by Ta addition; the Tg0 as well as the Tx0 also illustrates this improved stability limit. The compositional dependence of m, which agrees well with that of the reduced glass-transition temperature, indicates a strong correlation between liquid fragility and glass-forming ability in the present alloy system. These results provide new evidence for understanding thermal stability,liquid fragility, and GFA in BMG.