This collaborative study between IRCER and CEA Le Ripault aims to characterize and
model the sintering behavior of porous silica-based ceramic structures produced by additive
manufacturing. These silica-based refractory structures are designed as thermal insulators
for high temperature applications. Once the part is printed, it undergoes a thermal treatment
of debinding at low temperature, then sintering at higher temperature. Therefore, it is
important to control the heat treatment parameters (heating rate, temperature and duration
of the isothermal dwell) as they affect the final microstructure of the ceramic object and
obviously its thermal and mechanical properties.
The sintering process involves complex phenomena such as rigidification,
densification or granular coarsening, which depend on the initial organization of the granular
packing but also have a reverse effect on it. A key scale to understand these complex
phenomena is the meso-structure, which includes a few thousand particles interacting with
each other through mechanical contact, allowing the formation of bridges between particles
during the sintering cycle. In order to ensure the quality and the repeatability of the
manufactured parts, it is important to optimize the sintering cycle. Analytical modeling and
numerical simulation of the physical phenomena occurring in the densification process
should help to succeed this optimization and will be the focus of this work.
The first part of this work aimed to characterize the physical and chemical properties
of the selected micrometric silica powder. The thermal behavior of the silica powder was
examined by STA (Simultaneous Thermogravimetric Analyzer) in order to determine the glass
transition and crystallization temperatures. Moreover, after shaping by uniaxial pressing, the
shrinkage kinetics of granular compacts were explored by dilatometry, while varying the
heating rate and the dwell temperature. The analytical aspects of the densification kinetics
have allowed us to verify a viscous flow densification mechanism over the selected
temperature range and to estimate the associated apparent activation energy.
The second part consists in adapting the solid phase sintering model available in the
literature in order to be applied to the case of viscous flow sintering in the discrete element
method.