Sommaire:

Indentation experiments on borosilicate glass used for the immobilization of long-lived radionuclides have demonstrated that their hardness is decreased after being subjected to irradiation. In this study we have performed multi-million atom nanoindentation simulations on three sodium borosilicate glasses, in order to better understand the origin of this decrease. Alongside the pristine structures, we have prepared and indented the corresponding disordered ones by simulating the effects of irradiation damage.

The correlation of the structural properties with the resulting hardness values of the glasses has shown that the hardness will most prominently depend on the SiO2 content of the glass, as well as its percentage of three-coordinated boron and non-bridging oxygen. The subsequent analysis of the microstructure has shown that boron and sodium atoms increase coordination during the nanoindentation, while silicon remains perfectly coordinated. We have also calculated the local density around each atom in order to map the form of the densified region around the imprint mark and have found that densification will be promoted by the SiO2 content and the amount of free volume. Finally, by following the evolution of the interatomic bonds we could indicate that almost no shear flow appears close to silicon and boron atoms, while its presence is more pronounced in sodium-rich regions of the glass.

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