FEM of Flash Sintering

Flash Sintering (FS), a recent development in ceramic processing, has the potential to address these two challenges. Using FS ceramics can be densified in a few seconds (rather than hours in conventional sintering) and at much lower temperatures by the application of electric field.

FS is a recent discovery, and thus the underlying mechanisms are still debated. Computational modelling can help in identifying the underlying mechanisms but only a few literature available on the modelling of the FS process. The dog bone sample geometry is the most popular geometry used for FS. But the detailed analysis of the effectiveness or the optimization of the dog bone geometry was never attempted in the literature.

In this work, we have attempted a computational modelling of the FS process for 3 mol% Yttria Stabilized Zirconia (3YSZ) to understand the traits of the dog bone sample geometry and applying that results to optimize the geometry. We have used finite element analysis (FEA) to compute the rise in temperature, heating rate, and thermal gradient in the dog bone sample. 3YSZ material was then compared with other ceramic oxides, namely 8 mol% Yttria Stabilized Zirconia (8YSZ), Zinc Oxide (ZnO), and Titania (TiO₂) owing to its contrasting electrical and thermal properties.

Using FEA, we have shown that there is a significant rise in temperature due to Joule heating during FS. Additionally, we have computed the heating rate and concluded that a limited thermal runaway develops inside the sample during FS. The maximum heating rate during FS approaches 1000⁰C/sec which is four orders of magnitude higher than conventional sintering and can explain the rapid densification. We have also estimated the thermal gradient that can develop in the dog bone sample. Our thermal gradient result can explain the frequent cracking that has been observed in 3YSZ dog bone sample during FS.

We have optimized the dog bone sample geometry with respect to reference dog bone sample geometry in terms of thermal gradient and usable volume of materials. Finally, this study helps in understanding the flash sintering process fundamentally and predicts the optimum shapes for the dog bone geometry, which will prevent cracking thus far observed in the dog bone sample during flash sintering. The quality of the discussion and analysis in the present manuscript, in our opinion, presents a significant advance in the fundamental understanding of the mechanism of FS. Such knowledge is necessary for the industrial applicability of the FS process.