The influence of lithia content on the properties of fluorphlogopite glass-ceramics. II. Microstructure hardness and machinability

The influence of heat treatment time and temperature on microstructure, hardness and theoretical machinability of glass-ceramics based on 8SiO2 3Al2O3 (3−S)MgO 3MgF2 (1−Z)BaOZK2OSLi2O where lithia was substituted for magnesia and baria for potassia were investigated. Lithia and potassia were found to promote the crystal coarsening of the fluorphlogopite phase and the development of a house of cards microstructure. Hardness was found to decrease slightly on formation of the fluorphlogopite phase, but to decrease markedly on development of the house of cards microstructure. The formation of the house of cards microstructure was promoted by heat treatments close to the observed melting endotherms and was associated with good machinability. Incorporation of lithia was found to suppress the formation of cordierite in the bulk.