Surface and bulk residual stresses in Li2O · 2SiO2 glass–ceramics

In the present work surface and bulk residual stresses generated in partially crystallized Li2O · 2SiO2 glass–ceramics are analyzed after different heat treatments. The phase specific residual stresses in the crystalline Li2Si2O5-phase are evaluated for the first time in the near-surface zone and the bulk of the samples using both medium and high energy synchrotron radiation. The results reveal that in the crystals within the bulk of the samples micro residual stresses generated by the thermal anisotropy of the isolated individual crystallites depend on the crystallographic direction. In contrast, the residual stress state in the near-surface zone is isotropic due to the superposition of thermal residual stresses in and around the crystals of the near-surface area. Residual stress calculations using a modified Selsing’s model yield a good estimate of the anisotropic residual stresses in the bulk crystallites, whereas the isotropic residual stress state in the crystallized surface layer can be described by an elastic stress model for thin films.