Equilibrium viscosity of Zr-Cu-Ni-Al-Nb bulk metallic glasses

摘要

The equilibrium viscosities of the Zr_(57)Cu_(15.4)Ni_(12.6)Al_(10)Nb_5 and Zr_(58.5)Cu_(15.6)Ni_(12.8)Al_(10.3)Nb_(2.8) bulk metallic glasses are determined in three-point beam-bending experiments. The experimental data are described by the Vogel- Fulcher-Tammann equation. The fragility parameters are found to be 35.2 and 21.0, respectively. Viscosity measurements close to the glass transition show an initial relaxation into the supercooled liquid region, followed by partial crystallization of the amorphous matrix. This is evidenced by a dramatic increase in the viscosity into a new, metastable composition for longer annealing times.