The characterization of high-strength surface-crystallized glasses

Abstract

Controlled surface crystallization has become established as a method of significantly improving the mechanical strengths of glasses. Previous work has indicated that the surface state of the glass prior to crystallization can profoundly influence the microstructure of the surface-crystallized layer and thereby modify the mechanical strength of the material produced. The purpose of the present investigation was to study the effects of different surface-abrasion treatments, prior to crystallization, upon the microstructure of the surface-crystallized layer and the mechanical properties of two glasses. Indentation fracture was employed to characterize the glass surface and electron microscopy to investigate the microstructures that developed. For a calcium zinc aluminosilicate glass, although the microstructure of the surface-crystallized layer was dependent on the prior surface state of the glass, there was no clear cut relationship with the mechanical strength of the surface-crystallized glass. This was attributed to surface flow of the glass during heat-teatment. For a calcium aluminate composition, the microstructure of the crystallized layer was clearly dependent on the prior surface state of the glass and evidence was provided that flaws in the surface served to provide crystal nucleation sites. The mechanical strength of the surface-crystallized glass was markedly dependent on the microstructure and with a suitable surface treatment a mean modulus of rupture of 510 MN m−2 was achieved.