Intensive particle rearrangement in the early stage of spark plasma sintering process

Abstract

a b s t r a c tThe densification behaviors of 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) ceramics during spark plasma sintering (SPS) were analyzed both using the master sintering curve (MSC) approach and by evaluating the temperature dependent evolution of density and densification rate. It was found that densification curves could hardly be fitted using one apparent activation energy value by MSC conception, by which it indicated that more than one densification mechanisms were involved in SPS. Moreover, dependent neither on applied pressure (20-100 MPa) nor heating rates higher than 50 • C/min, the maximum densification rate had always been observed at rather similar ∼78% of theoretical density (TD) accompanied with negligible grain growth. An intensive particle rearrangement mechanism was proposed to dominate the rapid densification to 78% TD in early stage of SPS process, by which it yielded the considerable faster densification rate than those achievable by diffusion-related processes.

Microstructure and phase composition of steatite ceramics sintered by traditional and spark plasma sintering

“…These changes are normally taking place at approximately 1100 °C, but 950 °C can be accepted as the initial temperature of sTab. enstatite formation [28,30], which was indicated by the change in shrinkage rate at ca 1000 -1050 °C in Fig. 4 .…”

“…Since the steatite is primarily based on talc, its thermally induced behavior should be determined by the dehydration of talc mineral. Namely, talc incorporates adsorption water and hydroxyl groups situated in the space lattice elements [28]. In pure talc, water is normally eliminated in three stages: 115-200 °C; 350-500 °C, and 600-1050 °C [29].…”

“…1), the quantity of quartz is moderate and the resulting effects on the thermal curves are expected to be relatively small. Certain changes can be expected at 800 °C when the crystallization of magnesium metasilicate takes place as talc decomposes into magnesium oxide and silica due to the liberation of constitution water [28,30]. The onset of shrinkage on the dilatometric curves at 800°C can be therefore addressed to crystallization magnesium metasilicate.…”

Considering the use of niobium and titanium to enhance electrical and mechanical properties of copper at higher operational temperature application

“…However, in conductive powder, heating of the particles are mainly due to the Joule effect and for the non-conductive powder like Ti, heating occurs through heat transfer from the die and compressive punches [35]. The Joule effect will initiate rapid heating which can effectively suppress particle coursing and thus favors intensive particle rearrangement [36]. However, densification by particle rearrangement takes place rather rapidly because grains rather than atoms act as the migrating units [36], shrinkage rate of the powdered particle is governed by capillary forces developed in the grain boundary [37], and this information may clarify the observed confirmation of significant higher shrinkage rate and sharp peak found in Cu, Cu-2wt% Nb and Cu-5wt% Nb.…”

“…The Joule effect will initiate rapid heating which can effectively suppress particle coursing and thus favors intensive particle rearrangement [36]. However, densification by particle rearrangement takes place rather rapidly because grains rather than atoms act as the migrating units [36], shrinkage rate of the powdered particle is governed by capillary forces developed in the grain boundary [37], and this information may clarify the observed confirmation of significant higher shrinkage rate and sharp peak found in Cu, Cu-2wt% Nb and Cu-5wt% Nb. This outcome showed that the presence of Cu and Nb as conductive path allows a faster particle rearrangement during the spark plasma sintering at 650 °C.…”