Poisson's ratio and intrinsic plasticity of metallic glasses

Through a comparison of the activation barrier densities for plastic deformation and brittle fracture at the yield point, a condition for intrinsic plasticity versus brittleness of metallic glasses under shear loading is derived. The quantitative role of Poisson's ratio nu on fracture is revealed and additional effects due to local shear modulus (G) fluctuations are pointed out. The findings account for the onset of plasticity near reported nu values, as well as the brittleness of some high-nu alloys. Structural relaxation increases G and reduces fluctuations, incurring dual adverse effects on ductility. Implications for designing ductile metallic glasses are discussed. (c) 2008 American Institute of Physics.