Effect of crystallinity and microstructure on mechanical properties of CaO-Al2O3-SiO2 glass toughened by precipitation of hexagonal CaAl2Si2O8 crystals

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.