• Lechelle, Jacques
• Martin, Sylvain
• Saikouk, Kacem, Ks
• Robert, Boyer

Abstract

International audience ; A sub-granular model development for solid state sintering of ceramics is ongoing to describe grain and pore sizeevolution during a free (or under gas pressure) sintering.Local changes in principal curvature radii at grain free surfaces and grain boundaries induce an extra stress upon theouter boundaries of the grains. The latter are regarded as single crystals, of elastic constitutive law. Navier-Lamé equationsresolution in the bulk of each grain gives the 3D-displacement field and hence the density of the elastic mechanical energy.Resulting Gibbs free energy variations along the grain interfaces (free surfaces and grain boundaries) induce surface andgrain boundary mass transport (Fick’s first law). Since matter is almost incompressible, locally accumulated matter ongrain surfaces makes the surface move (second Fick’s law). This results in an irreversible shape evolution.A 3D-software has been designed. At each time step the Navier-Lamé equations are solved using a finite element methodand Fick’s second law is treated by a finite volume-like method enabling boundary nodes to move in an irreversible way.Continuous media mechanics is taken as the origin of grains evolution although the granular nature of matter remains thecore of the model. The software has been developed for the simplified case of a chemically homogeneous material. Resultsreferring to the evolution of two initial spherical grains of the same size are checked against Coble’s works extended byCoblenz in the case of grain boundary and surface diffusion. A second simulation is compared to Coble’s model for grainboundary and volume diffusion. Discrepancies appear to be mainly attributed to the fineness of the mesh which accountsfor the real curvature in the vicinity of the grain boundary.

Topics

• density
• impedance spectroscopy
• pore
• surface
• single crystal
• grain
• grain boundary
• simulation
• elasticity
• ceramic
• sintering