Improving strength by controlling segregation in liquid phase sintered aluminium nitride ceramics

Klimera, Andreas; Raether, F.; Ruska, J.

doi:10.1016/j.jeurceramsoc.2006.04.098

Cited by 16 publications

(13 citation statements)

References 11 publications

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“…This was already shown for simple cubic and face centered cubic structures using triangular meshes. [20,18] Using triangular meshes, curvature of the interface energy curve becomes slightly positive at dihedral angles smaller than 90°. In contrast, curvature is negative for all dihedral angles using the voxel model (compare Figure 8).…”

Section: Resultsmentioning

confidence: 99%

“…On the other hand, specific interface [18,19] energy g may also change with sintering state and temperature: g ¼ g (r, T). [20] If the curve E M r ð Þ has a concave shape -as indicated in Figure 2-the interface energy in an intermediate state of sintering can be decreased by a separation of denser and more porous regions. We consider a sintered body with an average specific volume v m and assume that the mass in a volume V of this body is redistributed.…”

Section: Thermodynamic Criteriamentioning

confidence: 99%

“…This representation has been selected in our previous publications. [18,20] On the first view, this looks more convenient since specific volumes are rarely used in sintering science. But E V (r) does not represent a closed system with constant mass.…”

Section: Thermodynamic Criteriamentioning

confidence: 99%

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Parameters for Inherently Homogeneous Sintering Processes

Raether¹

2015

Adv Eng Mater

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Thermodynamic criteria are introduced to calculate the driving force for the formation of heterogeneous metastable states during sintering. As already shown for one special case of liquid phase sintering, these metastable states significantly affect the reliability of sintered ceramics. Inherently safe sintering processes are proposed, providing a homogeneous evolution of microstructure. A desintering parameter is defined which can be used for a quantitative evaluation of different sintering processes in terms of their tendency for formation of heterogeneity. The desintering parameter has been calculated using sintering simulations in 3D representative volume elements. For that, a deterministic model has been developed. It considers interface energy minimization and grain growth for random arrangements of particles. Computational effort could be significantly reduced by periodic continuation of the microstructure at the sides of the RVE. Basic parameters controlling inherently homogeneous sintering are presented. Surface diffusion is positive at large dihedral angles. Unexpectedly, grain growth can be advantageous as well, provided that it acts continuously during the entire sintering cycle.

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Section: Resultsmentioning

confidence: 99%

Section: Thermodynamic Criteriamentioning

confidence: 99%

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Parameters for Inherently Homogeneous Sintering Processes

Raether¹

2015

Adv Eng Mater

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“…Therefore, the main advantage of the kinetic field method is seen in its robustness relying on a large range of experimental data, the simple and model‐free prediction of shrinkage which can be used in FE simulations and the flexibility to include different thermally activated mechanisms. Additional criteria for process optimization come from the reduction of coarsening 14 and segregation 11 . Use of the macroscopic in situ measuring data for this optimization requires additional inverse simulations to obtain a microstructural interpretation of the measurands 11,39 .…”

Section: Discussionmentioning

confidence: 99%

“…The partial pressure of evolved species can be increased using closed crucibles but this excludes many well‐established in situ measuring methods. It was demonstrated that graphite furnaces and gas fired kilns have atmospheres that strongly interact with the ceramics during sintering 1,11 . Although it requires some effort, these atmospheres have to be reproduced in the lab furnace to ensure transferability of results.…”

Section: Introductionmentioning

confidence: 99%

Current State of In Situ Measuring Methods for the Control of Firing Processes

Raether

2009

Journal of the American Ceramic Society

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A combination of in situ measuring methods and computer simulation is suggested for the optimization of debinding and sintering processes in lab furnaces. From the optical measurement of sintering shrinkage and the mass loss measurement during debinding the respective reaction rates are derived. A high resolution of 1 lm and a reproducibility better than 0.3% were obtained for the optical measurement of sintering shrinkage. The atmospheres in the in situ measuring furnaces have to be closely matched to the production furnaces, to allow a transfer of the optimized heating cycles. A kinetic field method is used to obtain a model-free prediction of the debinding and sintering kinetics. Various other macroscopic in situ measuring methods are discussed, regarding their role during process optimization of ceramics. For example, heat transfer properties, required to calculate temperature and stress distributions during the heat treatment, were obtained by a modified laser-flash technique.

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Modeling Inherently Homogeneous Sintering Processes

Raether¹,

Seifert²

2018

Advcd Theory and Sims

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A novel Monte Carlo model for the simulation of sintering processes is introduced. Different from previous models, local interface curvature is considered in the acceptance of diffusion steps. This enables the investigation of the effects of interface energies on the sintering process. Sintering paths are calculated for various microstructures and interface energies. Results are interpreted in the framework of thermodynamic criteria for homogeneous sintering processes which were presented recently.Using Eq. (3), the grain boundary to surface energy ratio can be determined from the dihedral angle alone. [15] The surface energy

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Improving strength by controlling segregation in liquid phase sintered aluminium nitride ceramics

Cited by 16 publications

References 11 publications

Parameters for Inherently Homogeneous Sintering Processes

Parameters for Inherently Homogeneous Sintering Processes

Current State of In Situ Measuring Methods for the Control of Firing Processes

Modeling Inherently Homogeneous Sintering Processes

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