Constrained Sintering of a Glass Ceramic Composite: II. Symmetric Laminate

Abstract

The sintering behavior of symmetric laminates has been experimentally measured and modeled. Two cases are distinguished: (i) sintering of a viscous layer between viscous substrates and (ii) sintering of a viscous layer between elastic substrates. A simple model based on a persisting isotropic microstructure allowed computation of developing in‐plane stresses. These in conjunction with a viscous Poisson's coefficient were taken to predict out‐of‐plane stresses and finally densification rate. This approach, however, proved unsuccessful to predict the large observed differences in densification rate between laminates constrained by either green or dense alumina substrates. The discrepancy was found to be due to widely different microstructures developing with different degrees of elastic constraint. Pore area and pore and particle orientation were determined to quantify these microstructural changes.

Anisotropic kinetic of the kaolinite to mullite reaction sequence in multilayer ceramics

“…At 1400 • C, we propose that the behavior of the layered porcelain is similar to that of a laminate glass ceramic composite, 35 where viscous layers are in-between layers of elastic materials. The experimental strain rateε exp that is in plane of one layer is related to applied stress σ by: ε free is the free strain rate from sintering.…”

“…In a same way, E is the uniaxial viscosity or elastic modulus. Applying the force balance and boundary conditions between adjacent layers of viscoplastic and elastic materials, 35 we obtain:…”

Partial Constrained Sintering of Ceramic Layers on Metallic Substrates: A Comparison Between Modeling and Experiments

“…4, the thickness evolution of both layers can also be followed: the alumina layer is predicted to shrink from 50 to 45.4 mm (experimentally B44.770.5 mm) and from 150 to 136 mm. 22 No significant effect of film thickness can be highlighted, and the density gradient is very limited: from 78.62% at the interface to 80.55% at the top free surface for the 50-mm-thick layer (and from 79.07% to 80.25% for the thicker one, as the stress gradient is smaller in that case). The densification behavior of both alumina layers is very similar and ends up just below a relative density of 80% after 1 h of isothermal time (79.56% and 79.62% for the 50 and 150 mm thick layers, respectively).…”

“…22 This ratio was 5 when sintered on a porous alumina substrate. For example, for the same LTCC material at a given density, the average pore size was found to be 25 times larger than for free sintering when a dense alumina substrate was used.…”

Free‐Standing Patterned Ceramic Structures Obtained by Soft Micromolding

“…For LTCC layers densifying by viscous flow, [22] the use of a green substrate (with Young's modulus E % 10 GPa), more compliant than dense alumina (E % 300 GPa at the sintering temperature) greatly affected both densification and microstructure. Under the same heating conditions, higher density and finer microstructure were the results of a more compliant substrate.…”