Intrinsic plasticity or brittleness of metallic glasses

Abstract The intrinsic plasticity or brittleness of crystalline metals correlates with the ratio of the elastic shear modulus μ to the bulk modulus B; when the ratio μ/B exceeds a critical value, the metal is brittle. Sufficient data on elastic moduli and toughness are now available to permit an assessment for metallic glasses. We find a similar correlation, with the critical value of μ/B for metallic glasses (0.41–0.43) more sharply defined than for crystalline metals. This critical value applies also for annealing-induced embrittlement of metallic glasses. The clear correlation between mechanical behaviour (plasticity or brittleness) and μ/B assists in understanding flow and fracture mechanisms, and in guiding alloy design to alleviate brittleness of metallic glasses. Acknowledgements We thank A. Kelly, A.H. Cottrell, W.L. Johnson, M.J. Stowell and the anonymous referees for useful comments. Experimental support for J.J.L. while on sabbatical leave at the University of Cambridge was provided by the Office of Naval Research, DARPA, and Reference Metals. The material presented is suitable for public release, distribution unlimited. Support from the National Science Foundation of China (for W.H.W.) and from the European Commission (for A.L.G.) is gratefully acknowledged.