Relaxation behaviors of Vickers indentations in soda-lime glass

Permanent deformation of glass under a sharp diamond indenter can be divided into two modes; plastic (or shear) flow and densification. The former is a volume-conservative deformation process, and the latter includes volume contraction. It is very important to recognize how much these two processes contribute to the formation of indentation impression in order to understand permanent deformation of glass. In this study, using an atomic force microscope (AFM), annealing recovery of indentation impression in soda-lime glass was studied under several annealing conditions. After annealing, large shrinkage of Vickers indentation was observed and it was attributed to relaxation of densified volume under the indenter. The recovery ratio of indentation volume by annealing increased up to 71% with increasing the annealing temperature to the glass transition temperature (539°C). Relaxation of densified volume was observed even at a low annealing temperature (214°C). It is suggested that the recovered region by annealing at a given temperature is determined from the microscopic glass density which is affected by the pressure distribution under the Vickers indenter.