Consolidation enhancement in spark-plasma sintering: Impact of high heating rates

Abstract

Spark-plasma sintering (SPS) provides accelerated densification and, in many cases, limited grain growth compared to regular hot pressing and sintering. Possible mechanisms of this enhancement of the consolidation in SPS versus conventional techniques of powder processing are identified. The consolidation enhancing factors are categorized with respect to their thermal and nonthermal nature. This paper analyses the influence of a major factor of thermal nature: high heating rates. The interplay of three mechanisms of material transport during SPS is considered: surface diffusion, grain-boundary diffusion, and power-law creep. It is shown that high heating rates reduce the duration of densification-noncontributing surface diffusion, this favors powder systems’ sinterability and the densification is intensified by grain-boundary diffusion. Modeling indicates that, besides the acceleration of densification, high heating rates diminish grain growth. The impacts of high heating rates are dependent on particle sizes. Besides SPS, the obtained results are applicable to the broad spectrum of powder consolidation techniques which involve high heating rates. The conducted experiments on SPS of an aluminum alloy powder confirm the model predictions of the impact of heating rates and initial grain sizes on the shrinkage rates during the electric current-assisted consolidation. It is noted, that this study considers only one of many possible mechanisms of the consolidation enhancement during SPS, which should stimulate further efforts on the modeling of field-assisted powder processing.

Electric current activated/assisted sintering (ECAS): a review of patents 1906–2008

“…This is shown by the increasing rate of published journal papers and comprehensive reviews [1,2]. About 2000 papers were published from 1970 to 2006 on SPS (see also figure 2 in [14], and figure 1 in [1]). The number of published papers started to grow exponentially from the early 1990s.…”

“…According to the original patent [68] (figure 8), the mold was clamped between water-cooled electrodes (10,11). The powder mixture (14) was placed in the annular space delimited by the metal disc (5), the punch (7) and the die (2). The grinding wheel was mounted on a (15) heat and pressure allowed both the sintering and welding of the outer ring to the metal disc.…”

The production of advanced fine-grained alumina by carbon nanotube addition

“…SPS is a rapid [34] and CNT-friendly [35] manufacturing technique that allows lower sintering temperatures and shorter dwell durations. Dried composite powder (~4 g) was poured into a carbon die (diameter 20 mm) and cold pressed at 1 ton for 5 s before sintering.…”

In-situ synthesis and sintering of mullite glass composites by SPS

“…This allows the rapid sintering of powders as well as the production of metastable phase compositions. It remains a matter for debate that whether the novel microstructures produced are simply a consequence of the rapid heating or a result of the electric field or current involved [2][3][4][5].…”