Ductility and toughness of cold-rolled metallic glasses

Cold rolling of Al87Ni7La6 amorphous ribbons was performed on ribbons embedded in pure Al foils and ribbons alone, in order to study their deformation under constraint. A change in behaviour was observed for the two series of samples due to a different load distribution, so that ribbons alone was deformed up to ɛ = 0.029 without formation of cracks while, for composite samples, small fragments were always formed. In ribbons rolled alone, along with a macroscopic strain, a plastic deformation was observed at a finer scale, in the cavities present on the ribbon surface. The locally induced strain was quantified by taking into account the size change of cavities in samples rolled to different extents. The formation of shear bands and fracture occurring during cold rolling was studied for composite samples: the shear offset, interband spacing and distribution of fracture angles were determined. A Zr55Al20Ni12Cu8Ti5 amorphous ribbon was rolled with Al foils and the toughness value was estimated from the shear band offsets finding good agreement with literature data. Therefore, the toughness was estimated also for the Al-based samples obtaining the value of Kc = 28 MPa m1/2.