No data available.

Please log in to see this content.

You have no subscription access to this content.

No metrics data to plot.

The attempt to load metrics for this article has failed.

The attempt to plot a graph for these metrics has failed.

The full text of this article is not currently available.

Microscopic dynamics perspective on the relationship between Poisson's ratio and ductility of metallic glasses

### Abstract

In metallic glasses a clear correlation had been established between plasticity or ductility with the Poisson's ratio ν Poisson and alternatively the ratio of the elastic bulk modulus to the shear modulus, K/G. Such a correlation between these two macroscopic mechanical properties is intriguing and is challenging to explain from the dynamics on a microscopic level. A recent experimental study has found a connection of ductility to the secondary β-relaxation in metallic glasses. The strain rate and temperature dependencies of the ductile-brittle transition are similar to the reciprocal of the secondary β-relaxation time, τ β . Moreover, metallic glass is more ductile if the relaxation strength of the β-relaxation is larger and τ β is shorter. The findings indicate the β-relaxation is related to and instrumental for ductility. On the other hand, K/G or ν Poisson is related to the effective Debye-Waller factor (i.e., the non-ergodicity parameter), f 0, characterizing the dynamics of a structural unit inside a cage formed by other units, and manifested as the nearly constant loss shown in the frequency dependent susceptibility. We make the connection of f 0 to the non-exponentiality parameter n in the Kohlrausch stretched exponential correlation function of the structural α-relaxation function, . This connection follows from the fact that both f 0 and n are determined by the inter-particle potential, and 1/f 0 or (1 − f 0) and n both increase with anharmonicity of the potential. A well tested result from the Coupling Model is used to show that τ β is completely determined by τ α and n. From the string of relations, (i) K/G or ν Poisson with 1/f 0 or (1 − f 0), (ii) 1/f 0 or (1 − f 0) with n, and (iii) τ α and n with τ β , we arrive at the desired relation between K/G or ν Poisson and τ β . On combining this relation with that between ductility and τ β , we have finally an explanation of the empirical correlation between ductility and the Poisson's ratio ν Poisson or K/G based on microscopic dynamical properties.

© 2014 AIP Publishing LLC

Received 04 November 2013
Accepted 07 January 2014
Published online 30 January 2014

Acknowledgments:
The work performed by Li-Min Wang and Riping Liu at the State Key Lab of Metastable Materials Science and Technology, Yanshan University, was supported by the NSF of China (Grant Nos. 51131002, 51271160, and 51071138), and by W. H. Wang at the Institute of Physics, Chinese Academy of Sciences, Beijing, by the NSF of China (Grant Nos. 51271195 and 11274353). We thank Professor V. N. Novikov for stimulating discussion on the relation between the effective Debye-Waller factor and elastic constants.

Article outline:

I. INTRODUCTION
II. RELATING *K/G* (OR ν_{ Poisson }) TO THE EFFECTIVE DEBYE-WALLER FACTOR *f* _{0}
III. 1/*f* _{0} OR (1 − *f* _{0}) CORRELATES WITH *n*
IV. CORRELATION OF *τ* _{ α }/*τ* _{ β } WITH *n* FOR FIXED *τ* _{ α }
V. CORRELATION OF DUCTILITY OR *K*/*G* (OR ν_{ Poisson }) WITH *n*, AND WITH *τ* _{ α }/*τ* _{ β } FOR A FIXED VALUE OF *τ* _{ α }
VI. CORRELATION OF DUCTILITY WITH RELAXATION STRENGTH Δ_{ β } OF THE *β*-RELAXATION ON ANNEALING
VII. CORRELATION OF POISSON’S RATIO WITH PACKING DENSITY
VIII. DERIVATION OF THE CORRELATION BETWEEN DUCTILITY AND *K*/*G* (OR ν_{ Poisson })
IX. DISCUSSIONS AND CONCLUSIONS

/content/aip/journal/jcp/140/4/10.1063/1.4862822

http://aip.metastore.ingenta.com/content/aip/journal/jcp/140/4/10.1063/1.4862822

Article metrics loading...

Commenting has been disabled for this content