Influence of beryllium on thermal stability and glass-forming ability of Zr-Al-Ni-Cu bulk amorphous alloys

Thermal stability and glass-forming ability of Zr65-xAl10Ni10Cu15Bex (x = 0, 3, 6, 9, 12.5, 16) bulk metallic glasses were investigated by differential scanning calorimetry, differential thermal analysis, X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). The results show that the substitution of beryllium for zirconium strongly affects the supercooled liquid region (DeltaT(x) = T-x - T-g(onset)), the reduced supercooled liquid region (DeltaT(rg) = (T-g(onset))/(T-i - T-g(onset))) and the reduced glass transition temperature (T-rg = T-g/T-i). With increasing of x values, the three parameters that were used to indicate the glass forming ability and thermal stability increase first and then decrease. It is in agreement with the result that these glasses gradually change from an off-eutectic composition into a eutectic one (x = 12.5) that favours higher glass-forming ability, and then there is again a departure from the eutectic composition. Consequently, a moderate Be content will favor to increase the glass forming ability and thermal stability in Zr65-xAl10Ni10Cu15Bex bulk amorphous alloys. The effect of Be was explained in terms of Miedema's theory, electronegativity difference and atomic size parameter of the amorphous alloys. (C) 2004 Elsevier B.V. All rights reserved.