Sophie d’Astorg

Coupled Electro-Thermo-Mechanical Finite Element Modeling of the Spark Plasma Sintering Technique

This paper deals with the development of a novel and predictive finite element method (FEM) model coupling electrical, thermal, and mechanical time-dependent contributions for simulating the behavior of a powdery material submitted to a spark plasma sintering (SPS) treatment by using COMSOL Multiphysics® software. The original approach of this work lies in the use of the modified Cam-Clay model to solve the mechanical phenomenon occurring during a SPS sintering treatment. As the powder properties and behaviors are different from the final sintered material and display a nonlinear dependence as a function of temperature and pressure, the model includes the description of the sample densification. In this way, numerical and experimental results obtained on conductive model material (aluminum) such as temperature, stress distributions, and shrinkage, were directly compared. This FEM model demonstrated the ability to predict the powder behavior during temperature-controlled experiments precisely, as they are typically performed in the SPS technique. This approach exhibits a remarkable level of interest because it takes into account the nature of the material and also the specific characteristics of the powder studied.

Tailoring of the Dielectric Properties of Some Low Sintering Temperature Ceramics

Bearing in mind the attractive dielectrics properties of Ba5Nb4O15, Zn3Nb2O8 and ZnTiO3, we have investigated the lowering of the sintering temperature of these dielectrics using ZnO-B2O3 glass frit addition. The control of the temperature coefficient of the permittivity has been also examined using two different methods. The first method consists in mixing the two oxides ZnTiO3 + TiO2 which exhibit a temperature coefficient with opposite sign. The second method is based on the stacking of two ceramic layers having opposite sign of temperature coefficients. This has been successfully tested in the Ba5Nb4O15 / Zn3Nb2O8 system.