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Internal Residual Stresses in Sintered and Commercial Low Expansion Li2O–Al2O3–SiO2 Glass–Ceramics

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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.
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Document Type: Research Article

Affiliations: 1: Department of Physics, State University of Ponta Grossa (UEPG), CEP 84030-900, Ponta Grossa, PR, Brazil 2: Vitreous Materials Laboratory (LaMaV), Department of Materials Engineering (DEMa), Federal University of São Carlos (UFSCar), CEP 13565-905, São Carlos, SP, Brazil 3: Department of Materials, Aeronautic and Automotive Engineering, Engineering School of São Carlos (EESC), University of São Paulo (USP), CEP 13566-590, São Carlos, SP, Brazil 4: Center of Science and Technology of Materials, Energy and Nuclear Research Institute (IPEN), CEP 05508-900,São Paulo, SP, Brazil

Publication date: 01 April 2011

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