Effect of microstructural evolution on the mechanical properties of lepidolite based glass-ceramics

In this paper, effect of microstructural evolution on mechanical property of lepidolite based glass-ceramics of MgO–Al2O3–SiO2–Li2O–R2O–F(R=Na, K) system during the crystallization process has been studied. The results show that two distinct regions of strength dependence on grain size are found. The critical values of the flake diameter and aspect ratio of lepidolite are 1.8 and 4.6μm, respectively. The crystallization temperature (TC) of critical point locates at 1060 °C. When TC⩽1060 °C, the bending strength increases with heat-treatment temperature ascribing to the randomly oriented and interlocked lepidolite crystallites, which cause crack divert or blunt to limit the further development of the flaw size and increase the surface energy of fracture. While TC> 1060 °C, the increased boundary shear stress arising from the mismatch of thermal coefficient between the lepidolite crystallite and the residual glass phase results in the decrease of strength.