Isothermal internal friction behaviour of a Zr based bulk metallic glass with large supercooled liquid region

In this paper, the internal friction behaviour of Zr-Ti-Cu-Ni-Be bulk metallic glass (BMG) containing 2 at% Fe at elevated temperatures has been studied in isothermal dynamic mechanical analysis experiments. The experiments lead to the determination of metastable equilibrium internal friction , as a function of temperature, which can be well described by the Maxwell model with viscosity, η(T), following a Vogel-Fulcher-Tammann (VFT) relation or Arrehnius law. Comparison with the Zr-Ti-Cu-Ni-Be glass-forming liquid shows that a small addition of Fe results in a stronger liquid behaviour of the alloy, exhibiting a higher strength parameter as well as lower VFT temperature and therefore correlates better glass forming ability and thermal stability. From the isothermal internal friction data, the activation energies for viscous flow and primary crystallization of the Zr based supercooled metallic liquid are also derived. It is found that the former is comparable to the activation energy controlling the diffusion process of atoms, e.g. the Ni element of medium size and higher mobility among the components of this alloy, while the latter to that of atoms, e.g. the Ti element of larger size and lower mobility. Thus, it is proposed that both isothermal viscous flow and primary crystallization of the alloy in the supercooleld liquid region are atom diffusion-controlled processes. However, the dominating atomic species are different from each other in the multicomponent Zr based BMG. © 2006 IOP Publishing Ltd.