Dynamics of the strong metallic glass Zn₃₈Mg₁₂Ca₃₂Yb₁₈

Zn₃₈Mg₁₂Ca₃₂Yb₁₈ bulk metallic glass (BMG) presents higher corrosion resistance, lower glass transition temperature and lower density than most BMGs. Dynamic properties of Zn₃₈Mg₁₂Ca₃₂Yb₁₈ BMG were investigated by mechanical spectroscopy. The structural (α) process in the isothermal spectra is well described by a Kohlrausch-Williams-Watts (KWW) function with β_KWW = 0.505. At high frequency, an extra contribution to the α process (i.e. an excess wing) is observed with a much smaller frequency dependence of the loss shear modulus G″(f) ∼ f^{- 0.37}, indicating the presence of a submerged secondary peak. The temperature behaviour of the α relaxation time, τ_α, is characterized by a very small steepness index (i.e. strong behaviour). We find that results for this BMG show a deviation of the correlation between fragility and β_KWW generally found in glass formers_. Results in the literature for other BMGs suggest that this deviation may not be an exception for BMGs, since very similar values of β_KWW (∼ 0.5) have been found for BMGs independently of their steepness index.