Role of densification in deformation behaviors of model metallic glasses under 3-D nanoindentation studied in molecular dynamics simulation

Under sharp contact loading, glass deforms elastically and then plastically via densification as well as shear flow. Stress build-up during loading, residual stress build-up after unloading, and possible ultimate cracking all depend sensitively on the competition and interplay between densification and shear flow. The crack resistance was shown in experimental studies to generally improve with the increasing contribution of densification in glasses where shear deformation plays a dominant role under indentation. In this work, the role of densification in deformation behaviors of model metallic glasses under sharp contact loading was studied by 3-D nanoindentation tests using indenters with different sharpness in classical molecular dynamics simulations. Starting from a model metallic glass that favors shear deformation, a Lennard-Jones potential was modified to describe model metallic glasses with different abilities of instantaneous densification under compression and permanent densification after decompression. Our studies show that model metallic glass with a higher densification ability under indentation has less stress build-up and less localized shear deformation during loading, as well as smaller residual stress build-up after unloading. However, our study indicates that both instantaneous and permanent densification need to be tuned for designing damage resistant glasses.