Fully coupled thermal-electric-sintering simulation of electric field assisted sintering of net-shape compacts

A fully coupled thermal-electric-sintering finite element model was developed and implemented to predict heterogeneous densification in net-shape compacts using electric field assisted sintering techniques (FAST). FAST is a single-step processing operation for producing bulk materials from powders, in which the powder is heated by the application of electric current under pressure. Previous modeling efforts on FAST have mostly considered the thermal-electric aspect of the problem and have largely neglected the sintering aspect of the problem. A new model was developed by integrating a phenomenological sintering model into a previously established thermal-electric finite element framework to predict the densification kinetics of the sample. The model was used to quantify the effect of specimen geometry on the evolution of thermoelectric gradients and resulting heterogeneous sintering kinetics during FAST processing of a conductive powder. It is shown that the new model which considers sintering kinetics and density-dependent properties provides a substantial increase in accuracy compared to thermal- electric only models. It is also shown that small changes in local resistance due to densification can greatly impact the distribution of thermoelectric gradients during the process, which are exacerbated by heterogeneous stress states induced by sample geometry. Experimental characterization of sintered specimens is used to provide qualitative validation of the model predictions.