Microstructure and mechanical properties of nucleant-free glass-ceramics of the Li2O-CaO-SiO2 system

Reference	Presenter	Authors (Institution)	Abstract
10-039	Gisele Guimarães Santos	Santos, G.G.(Federal University of São Carlos); Serbena, F.C.(State University of Ponta Grossa); Fokin, V.M.(Vavilov State Optical Institute); Zanotto, E.D.(Federal University of São Carlos (UFSCar));	Glass-ceramics of the ${\mathrm{Li}}_2\mathrm{O}-\mathrm{CaO}-{\mathrm{SiO}}_2$ system may exhibit interesting properties, such as the possibility to obtain wollastonite (${\mathrm{CaSiO}}_3$) without the use of nucleating agents, since ${\mathrm{CaSiO}}_3$ can crystallize around the internally nucleated lithium metasilicate crystals, resulting in crystals with elongated morphologies, which potentially lead to tough materials. In this study, we investigated glass-ceramic compositions within the range of 30-50 mol% ${\mathrm{CaSiO}}_3$ (the rest being ${\mathrm{Li}}_2{\mathrm{SiO}}_3$) regarding microstructure, phase distribution and mechanical properties. DSC analyses were made to adjust double-stage heat treatments. The crystallized samples were characterized by XRD and SEM to examine size, morphology, phase distribution and crystallized volume fraction of the final microstructure. Hardness (Vickers), fracture toughness (double torsion), elastic modulus (nanoindentation) and biaxial strength (ball-on-three-balls) tests were conducted and correlated with crystal properties of the samples, such as size, morphology, etc. The best mechanical properties were exhibited by a composition containing 44mol% ${\mathrm{CaSiO}}_3$ heat-treated at 498$°$C for 24h (nucleation) and at 700$°$C for 2h (crystal growth) and are as follows: average ${\mathrm{Li}}_2{\mathrm{SiO}}_3$ crystal size of 8.5 $\mathrm{\mu }$m, fracture toughness of 2.3 $\pm$ 0.5 MPa.${\mathrm{m}}^{1/2}$, $\mathrm{\sigma }$m = 270 $\pm$ 20 MPa, Hv = 8.4 $\pm$ 0.7 GPa and E = 146 $\pm$ 8 GPa. These are exciting mechanical properties for glass-ceramics intended for load bearing applications.
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