Residual stress effect on the fracture toughness of lithium disilicate glass‐ceramics

Abstract

In glass‐ceramics (GCs), on cooling from the crystallization temperature, internal residual stresses are generated due to the difference between the thermal expansion coefficient (TEC) of the crystal phase(s) and the residual glass. These stresses could degrade or promote their mechanical properties. In this work, we varied the magnitude of the residual stresses in lithium silicate GCs by designing their microstructures. The level of internal stresses was measured using (Synchrotron) X‐ray diffraction. The effects of anisotropy of thermal expansion, crystal shape, and intensity of the residual stresses were analyzed and compared using theoretical models. We extended the Hsueh‐Becher model to include the thermal expansion anisotropy of the orthorhombic lithium disilicate (LS2) crystals. We found that the average residual stresses within the LS2 crystals are compressive or null (−100 to ~0) and highly anisotropic. Most importantly, within the limits of this study, we found no evidence for the influence of (compressive or null) residual stresses on the fracture toughness of the studied GCs. Within the crystal size range from 1 to 5 μm, a highly crystallized volume fraction coupled to relatively large crystals (5 μm) of high elastic modulus improved the glass‐ceramic fracture toughness. This result can guide the microstructural design of novel tough GCs.

Lithium disilicate glass produced at high pressure: Characterization of structural, thermal and mechanical properties

“…H IT and E IT increased significantly for all glasses produced at HPHT compared to the reference glass, as shown in Figure 4. The results are compatible with values obtained for glass‐ceramics 3,4,6,7 , depending on the crystalline fraction. For example, Villas‐Boas et al 4 obtained H IT of 7.3 GPa and E IT of 107 GPa for LS 2 glass‐ceramic after heat treatment at 466ºC(15 min) +589ºC(15 min) +805ºC(2 h) at atmospheric pressure.…”

“…The results are compatible with values obtained for glass‐ceramics 3,4,6,7 , depending on the crystalline fraction. For example, Villas‐Boas et al 4 obtained H IT of 7.3 GPa and E IT of 107 GPa for LS 2 glass‐ceramic after heat treatment at 466ºC(15 min) +589ºC(15 min) +805ºC(2 h) at atmospheric pressure. Buchner et al 3 obtained H IT of 6.3 GPa and E IT of 80 GPa for LS 2 glass‐ceramic produced by heat treatment at 455ºC(2 h) + 610ºC (30 min) at atmospheric pressure.…”

“…Improvement of mechanical properties of glasses is relevant for several technological applications [2][3][4] . Distinct approaches have been successfully used to increase hardness (H IT ) and elastic modulus (E IT ), such as controlled modification of the glass composition 5 or formation of glass-ceramics [2][3][4][6][7][8] .…”

Thermal Evolutions to Glass-Ceramics Bearing Calcium Tungstate Crystals in Borate Glasses Doped with Photoluminescent Eu3+ Ions

“…Monolithic materials of glass-ceramics have recently attracted a lot of interest because of their potential applications as toughened ceramics for biomedical uses [ 1 , 2 , 3 ], ionic conductors for energy conversions [ 4 , 5 , 6 ], and luminescence phosphors for efficient illuminations and display devices [ 7 , 8 , 9 ]. To design the synthesis of glass-ceramics with a targeted crystal, a choice of starting glass composition is to be carefully considered.…”

Surface properties of a new lithium disilicate glass-ceramic after grinding

“…Approximately 50 formulations and hundreds of thermal treatments were tested. Some of these new LS2-based materials can be hot-pressed or processed by a CAD/CAM machining for application as dental prosthesis [ 9 , 10 ].…”