Characteristic free volumes of bulk metallic glasses : measurement and their correlation with glass-forming ability

Abstract

A convenient method is proposed for the measurement of the characteristic free volumes, viz., the amount of excess free volume annihilation in structural relaxation V[sub f-sr] and the amount of new free volume production in glass transition V[sub f-gt] of bulk metallic glasses (BMGs) by thermal dilation (DIL) test. Through the DIL tests, the characteristic free volumes are found to be sensitive to the change of glass forming ability (GFA). The Pd₄₀Cu ₃₀Ni₁₀P₂₀BMG has a quite small V[sub f-sr]. For a series of Fe–Cr–Mo–C–B–(Er) BMGs, Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Er₂with the largest GFA is identified to have the largest V[sub f-gt] and smallest V[sub f-sr]. The correlation between V[sub f-sr] and the squares of critical diameters of these iron-based BMGs can be fitted as a negative exponential function with high accuracy.