Free-volume changes in the bulk metallic glass Zr46.7Ti8.3Cu7.5Ni10Be27.5 and the undercooled liquid

Volume changes in Zr46.7Ti8.3Cu7.5Ni10Be27.5 bulk metallic glass have been observed by positron-annihilation and density measurements. Excess volume of the order of 1% is quenched in the bulk glass at cooling rates as low as 1-2 K/s. The isothermal relaxation kinetics obey a Kohlrausch law with beta exponents of similar to 0.3 between 180 and 230 degrees C. The effective activation energy is similar to 0.7 eV. Structural relaxation is not accompanied by severe embrittlement. The outer surface is shown to play a crucial role in annealing of excess volume. Relaxed excess volume is restored completely after heat treatment in the undercooled liquid state. The observed free-volume changes contrast with the behavior of perfectly strong glasses. [S0163-1829(98)09017-1].