An experimental study on the influence of shear on the flow behavior, spontaneous crystallization, microstructure and mechanical properties of a fluorophlogopite glass-ceramic

The influence of a shear field acting in the molten state during the crystallization of a sodium fluorophlogopite glass-ceramic on the rheological behavior of the melt, the resulting microstructure, and the compressive strength of the solidified glass-ceramic, was investigated. Flow curves of the molten glass-ceramic show slightly non-newtonian behavior except in the vicinity of the crystallization temperature, where the crystallization starts. The temperature-dependent viscosity of the melt shows an untypical z-shaped behavior. The temperature of the turning point corresponds to the temperature of newtonian flow behavior of the melt. The microstructure of the solidified glass-ceramic samples treated under various thermomechanical conditions was analyzed with regard to the crystal sizes, shapes and corresponding distribution functions. The compressive strength of the solid is affected by the total deformation realized in the melt state during shearing and depends on the temperature at which the melt was sheared. Different correlations between the compressive strength and the crystal fraction, dependent on the shear conditions of the melt, were found.