Ductile behavior of glass–ceramics with precipitated CaF₂, xonotlite, and cristobalite

Glasswith a chemical composition of 69.7SiO 2 -7.9CaO-5.5Na 2 O-3.5K 2 O-1.4Al 2 O 3 -12CaF 2 (mol%) was crystallized via a simple heat treatment.CaF 2 and xonotlite precipitated above the glass transition temperature, followed by the precipitation of α-cristobalite above 900°C.Thermal expansion curve of the glass-ceramics containing α-cristobalite exhibited a steep increase around 270°C due to α-β phase transition of cristobalite.Ball indentation test on the glass-ceramics resulted in a clear circular dent in the glass-ceramics with precipitated cristobalite but only ring cracks in the glass-ceramics without cristobalite.X-ray computed tomography using synchrotron radiation revealed the formation of microcracks around cristobalite, with a greater number of microcracks observed after ball indentation.Therefore, it was concluded that the stress caused by a large volume change during the α-β phase transition of cristobalite induced the generation of microcracks in the glass-ceramics during cooling, eventually leading to ductile behavior.The glass-ceramics also exhibited ductile behavior in the bending test that was used to measure fracture toughness.The obtained findings offer valuable insights into the fabrication of a new type of glass-ceramics with ductile behavior, which is expected to expand the application scope of glass-ceramics.