Abstract
In order to identify the most effective level of crystallinity and microstructure to increase the toughness of CaO–Al2O3–SiO2 glass with precipitated hexagonal-CaAl2Si2O8 crystals, we measured the fracture toughness and investigated the microcracking behavior of samples containing different amounts of the crystalline phase. The glass-ceramics were prepared in the range of 10–48 wt% crystallinity by changing the parent glass composition. Five glass compositions, xCaO–yAl2O3–zSiO2 wt% (x= = 25.6–22.7, y= = 18.0–28.1, z= = 56.4–49.2), were examined by Single Edge V-Notched Beam (SEVNB) method for fracture toughness measurement, and Vickers indentation tests for hardness measurement. Although the fracture toughness increased for a crystal content of up to 21 wt%, it remained constant at 21–40 wt%, and then started to decrease at 48 wt%. The Vickers hardness showed a minimum in the range of 21–35 wt% crystallinity. Microcrack formation around indentations was clearly observed in the same range of crystallinity. Also, non-elastic behavior was found at the same levels of crystallinity during bending tests for measurement of fracture toughness, with more fractured surface area. The microstructure of these glass-ceramics was characterized as a “house-of-cards” structure, suggesting that this microstructure was most effective at decreasing the brittleness of the glass by microcrack toughening.
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