The effect of barium content on the crystallization and microhardness of barium fluormica glass-ceramics

Mica glass-ceramics are easily machined due to their "House-of-Cards" microstructure. Barium fluormica glass ceramics were developed and indicated good mechanical properties. This work studies the effect of varying barium content on the crystallization and microhardness of mica glass-ceramics. Four glasses were produced with different baria contents, then converted to mica glass-ceramics using a two-step heat treatment. They were characterized using Differential Scanning Calorimetry [DSC], X-ray Diffraction [XRD], Scanning electron microscopy [SEM] and Vickers microhardness. DSC showed some formulations indicated bulk crystallisation as the dominant mechanism. XRD showed the crystallization of Barium fluorphlogopite in all the compositions with minor secondary phases. SEM showed the formation of "House-of-Cards" microstructures and with an increase in BaO content, a decrease in contrast was observed in back scattered mode. Exceptionally low hardness values (< 2 GPa) were obtained for longer heat treatments/holding times and are related to the well-developed house-of-cards microstructures formed.