Plastic deformation of Zr-based bulk metallic glasses under nanoindentation

The plastic deformation of two Zr-based bulk metallic glasses (BMGs), Zr55Cu30Ni5Al10 and Zr69.5Cu12Ni11Al7.5, was investigated by instrumented nanoindentation over a broad range of loading rates. It was found that the plastic flow of the two BMGs exhibited conspicuous serrations at low loading rates. The serrations, however, became less prominent as the rate of indentation increased. AFM showed a significant pile-up of materials around the indents, indicating that a highly localized plastic deformation occurred under nanoindentation. The mechanism governing the plastic deformation in BMGs was tentatively discussed in terms of the mode of strain-induced free volume.