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

Abstract

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.

Dog-bone copper specimens prepared by one-step spark plasma sintering

“…The potential of SPS for near-net-shaping has been recognized and some studies have reported the formation of complex-shaped samples, with more or less pronounced deviations from the cylindrical symmetry, for materials as diverse as porous silica monoliths [3], oxide composites [4], silicon carbide [5], coatings on Ni-based superalloys [6], and TiAl alloys [7]. However, so far there are only a few studies addressing the problem theoretically [8][9][10], investigating the impact of the sample geometry, size and heterogeneous stress states on the non-uniformity of temperature, relative density, and grain size spatial distributions. The aim of this paper is to investigate the direct preparation by SPS of copper samples with the so-called dog-bone shape used for tensile tests specimens.…”

Numerical model for sparking and plasma formation during spark plasma sintering of ceramic compacts

“…The SPS process can be applied to metallic as well as to ceramic powder compacts; however, the manner the current flows through the powder-die assembly strongly depends on the electric conductivities of the powder and the surrounding die. Previous thermal-electrical model simulations have shown that for insulating powders almost all the current flew through the conductive graphite die [1][2][3][4]. In the case of oxides, only a small current portion is believed to flow through the dielectric powders.…”