How the toughness in metallic glasses depends on topological and chemical heterogeneity
To gain insight into the large toughness variability observed between metallic glasses (MGs), we examine the origin of fracture toughness through bending experiments and molecular dynamics (MD) simulations for two binary MGs: Pd_(82)Si_(18) and Cu_(46)Zr_(54). The bending experiments show that Pd_(82)Si_(18) is considerably tougher than Cu_(46)Zr_(54), and the higher toughness of Pd_(82)Si_(18) is attributed to an ability to deform plastically in the absence of crack nucleation through cavitation. The MD simulations study the initial stages of cavitation in both materials and extract the critical factors controlling cavitation. We find that for the tougher Pd_(82)Si_(18), cavitation is governed by chemical inhomogeneity in addition to topological structures. In contrast, no such chemical correlations are observed in the more brittle Cu_(46)Zr_(54), where topological low coordination number polyhedra are still observed around the critical cavity. As such, chemical inhomogeneity leads to more difficult cavitation initiation in Pd_(82)Si_(18) than in Cu_(46)Zr_(54), leading to a higher toughness. The absence of chemical separation during cavitation initiation in Cu_(46)Zr_(54) decreases the energy barrier for a cavitation event, leading to lower toughness.
© 2016 National Academy of Sciences. Contributed by William A. Goddard III, May 13, 2016 (sent for review March 8, 2016; reviewed by Takeshi Egami and Evan Ma). Published ahead of print June 15, 2016. This work was supported by Defense Advanced Research Projects Agency Grant W31P4Q-13-1-0010 (to program manager, John Paschkewitz), the Army Research Laboratory under Cooperative Agreement W911NF-12-2-0022 [Materials in Extreme Dynamic Environments (MEDE)], and National Science Foundation Grant Division of Materials Research (DMR)-1436985 (to program manager John Schlueter). Author contributions: Q.A., W.L.J., and W.A.G. designed research; Q.A., K.S., M.D.D., M.C.F., D.O.D., and W.A.G. performed research; Q.A. and W.L.J. analyzed data; and Q.A., K.S., M.D.D., M.C.F., D.O.D., W.L.J., and W.A.G. wrote the paper. Reviewers: T.E., University of Tennessee; and E.M., Johns Hopkins University. The authors declare no conflict of interest. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1607506113/-/DCSupplemental.
Published - PNAS-2016-An-7053-8.pdf
Supplemental Material - pnas.201607506SI.pdf