Impacts of Post‐Annealing Parameters on Structure and Mechanical Properties of Chemically Strengthened LAS Glasses

ABSTRACT The structure and mechanical response of peraluminous chemically strengthened lithium aluminosilicate glass under different post‐annealing conditions below the glass transition temperature were investigated. Changes in surface structure and mechanical properties were evaluated based on measurements of the compressive stress, depth of layer, electron probe microanalysis, Raman spectroscopy, hardness, and coaxial double‐ring flexural strength after sub‐T g post‐annealing at various temperatures and times. The results demonstrate that sub‐T g post‐annealing in two‐step chemically strengthened peraluminous LAS glass is associated with a coupled evolution of residual stress relaxation and alkali‐ion redistribution, rather than reconstruction of the aluminosilicate network. Raman spectroscopy shows that post‐annealing below T g does not induce significant changes in the average bonding configuration of the aluminosilicate network or in the stretching‐dominated network connectivity, indicating that the silicate backbone remains essentially stable. Under this structural constraint, post‐annealing promotes a coupled evolution of residual stress relaxation and alkali‐ion redistribution. As the post‐annealing temperature and time increase, K + ions migrate inward from the near‐surface region, whereas Na + ions undergo bidirectional redistribution toward both the surface and the glass interior. This process involves reorganization of alkali charge‐compensation environments around tetrahedral AlO 4 − units, together with a progressive redistribution of alkali ions within the near‐surface compressive stress layer, and is associated with the opposite evolution of CS and DOL. Therefore, the compressive stress decreases while depth of layer increases, accompanied by a reduction in effective packing efficiency in the near‐surface region. The reduced packing efficiency leads to gradual degradation of mechanical properties, manifested by decreases in flexural strength and Vickers hardness. These findings provide quantitative insight into the thermal stability of the compressive stress layer in chemically strengthened LAS glass and offer practical guidance for strength reliability after coating‐related sub‐T g thermal cycles, such as those encountered during post‐annealing of conductive ITO thin films.