In the paper K. L. Ngai et al. , [J. Chem. 140, 044511 (2014)], the empirical correlation of ductility with the Poisson's ratio, ν Poisson , found in metallic glasses was theoretically explained by microscopic dynamic processes which link on the one hand ductility, and on the other hand the Poisson's ratio. Specifically, the dynamic processes are the primitive relaxation in the Coupling Model which is the precursor of the Johari–Goldstein β-relaxation, and the caged atoms dynamics characterized by the effective Debye–Waller factor f 0 or equivalently the nearly constant loss (NCL) in susceptibility. All these processes and the parameters characterizing them are accessible experimentally except f 0 or the NCL of caged atoms; thus, so far, the experimental verification of the explanation of the correlation between ductility and Poisson's ratio is incomplete. In the experimental part of this paper, we report dynamic mechanical measurement of the NCL of the metallic glass La60 Ni 15 Al 25 as-cast, and the changes by annealing at temperature below T g. The observed monotonic decrease of the NCL with aging time, reflecting the corresponding increase of f 0, correlates with the decrease of ν Poisson . This is important observation because such measurements, not made before, provide the missing link in confirming by experiment the explanation of the correlation of ductility with ν Poisson . On aging the metallic glass, also observed in the isochronal loss spectra is the shift of the β-relaxation to higher temperatures and reduction of the relaxation strength. These concomitant changes of the β-relaxation and NCL are the root cause of embrittlement by aging the metallic glass. The NCL of caged atoms is terminated by the onset of the primitive relaxation in the Coupling Model, which is generally supported by experiments. From this relation, the monotonic decrease of the NCL with aging time is caused by the slowing down of the primitive relaxation and β-relaxation on annealing, and vice versa.
The financial supports of the NSF of China (Grant No. 51271195) and MOST 973 of China (No. 2015CB856800). Z.W. would like to acknowledge the support of the German Academic Exchange Service (DAAD) through the DLR-DAAD Research Fellowship.
I. INTRODUCTION II. EXPERIMENTAL METHODS III. EXPERIMENTAL RESULTS AND DISCUSSIONS IV. THEORETICAL CONSIDERATIONS A. Effects of annealing on the JG β-relaxation and embrittlement B. Effects of annealing on the NCL V. CONCLUSION