Unusual room temperature ductility of glassy copper–zirconium caused by nanoparticle dispersions that grow during shear

It has recently been reported that some Cu-based metallic glasses containing a dispersion of embedded nanocrystals can sustain more than 50% room temperature compressive plastic strains. By carefully observing shear bands containing 3–8 nm crystallite particle dispersions using in situ deformation in tension in a transmission electron microscope, we have found and report here direct evidence of systematic shear delocalisation in the form of shear band thickening and zigzagging as well as crack blunting and zigzagging. Since it is well established that both temperature and free volume rise in active shear bands, it is found that the matter in shear bands containing such small nanoparticle dispersions deforms like a semi-solid slurry. The glassy matrix behaves liquid-like and the nanoparticles constitute a growing solid fraction. Shear delocalisation and crack blunting occur through sharp viscosity increase occurring as the crystallite (solid) fraction grows in the shear band slurry leading to the shear being displaced to neighbouring regions with lower crystalline volume fraction.