Mapping the deformation zone in oxide glasses during contact loading by in-situ X-ray nano diffraction

Oxide glasses are disordered materials with no macroscopic ductility, and they are also prone to defects that may
originate at different length scales. These defects act as stress concentrating zones during loading, which may cause
premature failure upon an applied tensile stress. However, at the nano and micro scales, oxide glasses can undergo
plastic deformation at conditions of high local temperature and stress states. For example, the latter can occur locally
during an indentation loading in the so-called “process zone”, that is in the vicinity of the impact site in glass by the
indentation tip. The process zone consists of various deformation mechanisms including elastic strain, densification,
shear flow, and, ultimately, cracking. These are known to be affected by defect concentration, compositional variation, and glass processing. Probing glasses’ deformation behaviour at such local scale over the entire process zone could aid in the development of new and more damage-resistant glasses. Despite the importance of structural changes in the process zone for the formation of cracks, a significant lack of experimental techniques exists. This is due to problems of simultaneously measuring glass structure under load. To overcome this lack of structural understanding, in this work, we utilized synchrotron-based X-ray nano diffraction to probe the structure particularly in the medium order range in-situ during nanoindentation. With this, we were able to map in two dimensions qualitatively and quantitatively, the densification from other structural changes and cracking in the process zone at a high spatial resolution of 100 nm. In detail, we report and compare the shape, size of the overall deformation zone, the extent of densification, shear flow and the eventual cracking pattern among different glasses over multi step loading using two different wedge indenter tips. This helps to clarify the indentation deformation behaviour from the structural response of oxide glasses with different Poisson’s ratio and having different network structures. In future we plan to extend the studies on structurally different systems such as glasses having floppy networks, phase separated glasses having local compositional variation, pre-densified glasses, and more complex glass-ceramics. Further research will also focus on comparing the obtained results to that of the Finite Element or Peridynamics simulation and extend the knowledge for a deeper understanding of the glass mechanics.