Materials Transactions Online

Materials Transactions, Vol.48 No.11 (2007) pp.2923-2927
© 2007 The Japan Institute of Metals

Theory of Shear Banding in Metallic Glasses and Molecular Dynamics Calculations

Futoshi Shimizu1,2, Shigenobu Ogata3 and Ju Li2

1Center for Computational Science & e-Systems, Japan Atomic Energy Agency, Tokyo 110-0015, Japan
2Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210, USA
3Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, Osaka 560-8531, Japan

The aged-rejuvenation-glue-liquid (ARGL) shear band model has been proposed for metallic glasses (Acta Mater. 54 (2006) 4293), based on small-scale molecular dynamics simulations up to 20,000 atoms and thermomechanical analysis. The model predicts the existence of a critical lengthscale ∼10 nm, above which melting could occur in shear-alienated glass. Large-scale molecular dynamics simulations with up to 5 million atoms have directly verified this prediction. When the applied stress exceeds the glue traction (computed separately before in a shear cohesive zone, or an amorphous-amorphous ``generalized stacking fault energy'' calculation), we indeed observe maturation of the shear band embryo into bona fide shear crack, accompanied by melting. In contrast, when the applied stress is below the glue traction, the shear band embryo does not propagate, becomes diffuse, and eventually dies. Thus this all-important quantity, the glue traction which is a property of shear-alienated glass, controls the macroscopic yield point of well-aged glass. We further suggest that the disruption of chemical short-range order (``chemical softening'') governs the glue traction microscopically. Catastrophic thermal softening occurs only after chemical alienation and softening in our simulation, after the shear band embryo has already run a critical length.

(Received 2006/12/1; Accepted 2007/8/17; Published 2007/10/18)

Keywords: shear cohesive zone, chemical softening, incubation lengthscale, thermal softening

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