We performed Synchrotron X‐ray diffraction (XRD) analyses of internal residual stresses in monolithic samples of a newly developed Li2O–Al2O3–SiO2 (LAS) glass–ceramic produced by sintering and in a commercial LAS glass–ceramic, CERAN®, produced by the traditional crystal nucleation and growth treatments. The elastic constants were measured by instrumented indentation and a pulse‐echo technique. The thermal expansion coefficient of virgilite was determined by high temperature XRD and dilatometry. The c‐axis contracts with the increasing temperature whereas the a‐axis does not vary significantly. Microcracking of the microstructure affects the thermal expansion coefficients measured by dilatometry and thermal expansion hysteresis is observed for the sintered glass–ceramic as well as for CERAN®. The measured internal stress is quite low for both glass–ceramics and can be explained by theoretical modeling if the high volume fraction of the crystalline phase (virgilite) is considered. Using a modified Green model, the calculated critical (glass) island diameter for spontaneous cracking agreed with experimental observations. The experimental data collected also allowed the calculation of the critical crystal grain diameters for grain‐boundary microcracking due to the anisotropy of thermal expansion of virgilite and for microcracking in the residual glass phase surrounding the virgilite particles. All these parameters are important for the successful microstructural design of sintered glass–ceramics.

We have tested a modified form of the Clusters model of sintering for the complex case of non-isothermal sintering with concurrent crystallization of a multicomponent lithium aluminum silicate (LAS) glass having a broad size distribution of jagged particles. We compared experimental and simulated densification data using a constant heating rate. Only one adjustable parameter was used: the particle shape factor (K s ). We discuss the results in light of some complicating factors, such as temperature gradients within the powder compacts and compositional shifts of the residual glass matrix due to crystallization, which lead to changes of viscosity. The modified Clusters model accurately predicted the temperature dependence of densification and the final (saturation) density of the glass particle compacts.

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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.

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