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Internal Residual Stresses in Sintered and Commercial Low Expansion Li 2 O–Al 2 O 3 –SiO 2 Glass–Ceramics
Author(s) -
Serbena Francisco C.,
Soares Viviane Oliveira,
Peitl Oscar,
Pinto Haroldo,
Muccillo Reginaldo,
Zanotto Edgar D.
Publication year - 2011
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2010.04220.x
Subject(s) - materials science , thermal expansion , residual stress , composite material , ceramic , microstructure , dilatometer , sintering , nucleation , anisotropy , glass ceramic , mineralogy , optics , thermodynamics , chemistry , physics
We performed Synchrotron X‐ray diffraction (XRD) analyses of internal residual stresses in monolithic samples of a newly developed Li 2 O–Al 2 O 3 –SiO 2 (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.