Energy dissipation in fracture of bulk metallic glasses via inherent competition between local softening and quasi-cleavage

Abstract

Compression, tension and high-velocity plate impact experiments were performed on a typical tough Zr_41.2Ti_13.8Cu₁₀Ni_12.5Be_22.5 (Vit 1) bulk metallic glass (BMG) over a wide range of strain rates from ∼10⁻⁴ to 10⁶ s⁻¹. Surprisingly, fine dimples and periodic corrugations on a nanoscale were also observed on dynamic mode I fracture surfaces of this tough Vit 1. Taking a broad overview of the fracture patterning of specimens, we proposed a criterion to assess whether the fracture of BMGs is essentially brittle or plastic. If the curvature radius of the crack tip is greater than the critical wavelength of meniscus instability [F. Spaepen, Acta Metall. 23 615 (1975); A.S. Argon and M. Salama, Mater. Sci. Eng. 23 219 (1976)], microscale vein patterns and nanoscale dimples appear on crack surfaces. However, in the opposite case, the local quasi-cleavage/separation through local atomic clusters with local softening in the background ahead of the crack tip dominates, producing nanoscale periodic corrugations. At the atomic cluster level, energy dissipation in fracture of BMGs is, therefore, determined by two competing elementary processes, viz. conventional shear transformation zones (STZs) and envisioned tension transformation zones (TTZs) ahead of the crack tip. Finally, the mechanism for the formation of nanoscale periodic corrugation is quantitatively discussed by applying the present energy dissipation mechanism.

Acknowledgements

The authors are grateful to Professor B. C. Wei and Dr J. S. Gu for their assistance in material preparation. Financial support from the Natural Science Foundation of China (Grants Nos. 10725211, 10721202) and the Key Project of Chinese Academy of Sciences (Nos.KJCX-SW-L08 and KJCX2-YW-M04) is acknowledged.