IADR Abstract Archives
Mechanistic Fundamentals of Crystal Size/Fraction in Model Dental Li2Si2O5 Glass-Ceramics
Objectives: Glass-ceramics produced by controlled crystallization can be toughened and strenghened by fine-tuning of crystallinity parameters such as crystal-size and -fraction. Here we attend to the gap in the structure-property relationship map by synthesizing a stoichiometric lithium disilicate glass and inducing the crystallization of Li2Si2O5 spherulites in different sizes and fractions. We computed fracture mechanics parameters such as fracture toughness (KIc), strength (σ) and fatigue exponent (n) were obtained.
Methods: Stoichiometric Li2O-2SiO2 glass samples were produced by the melt/quench route, resulting in annealed beams (4x3x25 mm3) and square plates (1.5x11.5x11.5 mm3). Nucleation and crystallization experiments (time/temperature protocols) were devised to produce glass-ceramics with crystals sizes of 5µm, 10µm and 35µm in fractions of 5vol.%, 30vol.% and 80vol.% in a tubular furnace. The Chevron-Notched-Beam and the Surface-Crack-in-Biaxial-Flexure were employed for the measurement of KIc, and the inert strength in oil on mirror polished biaxial specimens was measured using the ball-on-three-balls method, analogous to cyclic fatigue tests in water. The fatigue exponent n was obtained from the Weibull distributions and velocity-K diagrams.
Results: Spherulite size induced toughening of the glass-ceramics in all sizes and fractions. Concerning size, a significant increase in KIc) occurred from 5µm to 10µm, but not with further crystal growth (i.e. 35µm). Although crystalline fraction revealed an overall linear relationship to KIc, a distinctive bump was detected at low fractions (5vol.%). Strength did not follow the same trend as KIc, and small crystal fractions tended to weaken the material by acting as critical flaws. Cyclic crack growth was delayed for glass-ceramics as compared to the glass, with a strong dependency on both crystal size and volume fraction.
Conclusions: Crystal size and fraction are microstructural parameters that can toughnen and strengthen the glass in static and cyclic loading, and their interplay can be tailored to maximize their effect.
Methods: Stoichiometric Li2O-2SiO2 glass samples were produced by the melt/quench route, resulting in annealed beams (4x3x25 mm3) and square plates (1.5x11.5x11.5 mm3). Nucleation and crystallization experiments (time/temperature protocols) were devised to produce glass-ceramics with crystals sizes of 5µm, 10µm and 35µm in fractions of 5vol.%, 30vol.% and 80vol.% in a tubular furnace. The Chevron-Notched-Beam and the Surface-Crack-in-Biaxial-Flexure were employed for the measurement of KIc, and the inert strength in oil on mirror polished biaxial specimens was measured using the ball-on-three-balls method, analogous to cyclic fatigue tests in water. The fatigue exponent n was obtained from the Weibull distributions and velocity-K diagrams.
Results: Spherulite size induced toughening of the glass-ceramics in all sizes and fractions. Concerning size, a significant increase in KIc) occurred from 5µm to 10µm, but not with further crystal growth (i.e. 35µm). Although crystalline fraction revealed an overall linear relationship to KIc, a distinctive bump was detected at low fractions (5vol.%). Strength did not follow the same trend as KIc, and small crystal fractions tended to weaken the material by acting as critical flaws. Cyclic crack growth was delayed for glass-ceramics as compared to the glass, with a strong dependency on both crystal size and volume fraction.
Conclusions: Crystal size and fraction are microstructural parameters that can toughnen and strengthen the glass in static and cyclic loading, and their interplay can be tailored to maximize their effect.