Effect of Thermal History on the Crystallization Behaviour and Hardness of a Glass-ceramic in the CaO(MgO)-Al2O_3-SiO_2 System Tang Liying; Cheng Jinshu; Yuan Jian ( Engineer, Institute of Material Science and Engineering, WUT, Wuhan 430070, China.) In this paper,the glass-ceramic in CaO(MgO)-Al2O3-SiO2 system was examined to determine the dependence of indentation hardness on heat-treatment temperature. The effect of thermal history on the crystallization behaviour was studied. X-ray diffraction (XRD) was used to determine the type of crystal phases present and to relate this to the hardness results. It was shown that hardness increased with heat-treatment temperature. CaO(MgO)-Al_2O_3-SiO2 system; glass-ceramic; thermal history; indentation hardness; crystallization