Numerical Simulation of Ceramic Sintering

Sintering is a key process in the manufacture of ceramics. Since these materials have very high melting points, it is more advantageous to shape them by sintering at temperatures below their melting points. At these temperatures, thermally activated mechanisms, such as diffusion, become active and enable the transformation of a green body composed of powders into a dense solid. The driving forces behind the process are primarily capillary forces at the grain surfaces, the possible application of external pressure, or a chemical reaction (reactive sintering).

Various sintering methods exist. Natural sintering (without pressure) involves placing the green parts in a furnace to consolidate and densify the material through diffusion. Ceramics that are difficult to densify, such as ultra-refractories or those with low surface energies, can be processed by liquid-phase sintering (with the aid of sintering aids) or pressure sintering. These processes also make it possible to lower processing temperatures and preserve fine-grained microstructures, resulting in improved mechanical properties. Reactive sintering, on the other hand, is particularly well-suited for producing ceramics from precursors by controlling reactions and generating specific microstructures and phases. Other variants exist (low-temperature sintering, solvothermal sintering), but this article focuses on high-temperature sintering. Natural sintering remains the most widely used process in industry, as it allows for the simultaneous production of a large number of parts while preserving their initial geometries.

In this context, simulation plays a central role. It serves a predictive function, enabling the understanding and optimization of process parameters, as well as the prevention of defects that would be costly to identify through experimentation alone. Indeed, defining optimal sintering conditions can be time-consuming and complex, as the final geometry and properties of the parts depend heavily on the temperature and the thermal cycle applied. For example, a sintering model makes it possible to determine the temperature and dwell time required to achieve a dense microstructure while limiting grain growth, which is particularly active at the end of the cycle.

Furthermore, large parts—whether thin-walled or featuring cantilevered structures—are particularly prone to deformation. These deformations can result from the parts’ own weight, but also from excessive thermal gradients. A thermomechanical simulation makes it possible to anticipate these phenomena and optimize the cycle to reduce the risk of cracking during the temperature ramp-up. This aspect is crucial for unconventional heating methods, such as microwave sintering or Spark Plasma Sintering (SPS), where volumetric heating,...