Spark Plasma Sintering of Alumina

Abstract

A systematic study of various spark plasma sintering (SPS) parameters, namely temperature, holding time, heating rate, pressure, and pulse sequence, was conducted to investigate their effect on the densification, grain‐growth kinetics, hardness, and fracture toughness of a commercially available submicrometer‐sized Al2O3 powder. The obtained experimental data clearly show that the SPS process enhances both densification and grain growth. Thus, Al2O3 could be fully densified at a much lower temperature (1150°C), within a much shorter time (minutes), than in more conventional sintering processes. It is suggested that the densification is enhanced in the initial part of the sintering cycle by a local spark‐discharge process in the vicinity of contacting particles, and that both grain‐boundary diffusion and grain‐boundary migration are enhanced by the electrical field originating from the pulsed direct current used for heating the sample. Both the diffusion and the migration that promote the grain growth were found to be strongly dependent on temperature, implying that it is possible to retain the original fine‐grained structure in fully densified bodies by avoiding a too high sintering temperature. Hardness values in the range 21–22 GPa and fracture toughness values of 3.5 ± 0.5 MPa·m1/2 were found for the compacts containing submicrometer‐sized Al2O3 grains.

Enhanced properties of alumina–aluminium titanate composites obtained by spark plasma reaction-sintering of slip cast green bodies

“…As the sintering temperature increases (1300 to 1400) ºC, the alumina grain growth is greater, so that at 1400 ºC an average grain size 1.4 m is observed. This grain size is very small compared to that of monolithic alumina sintered by SPS at 1400 ºC reported elsewhere [32], which is 5.0 m. Therefore, the nanoparticles of the second phase to the aluminium titanate leads to an inhibitory effect in alumina grain growth.…”

Simultaneous Synthesis and Consolidation of Nanostructured MoSi2-NbSi2 Composite by High-Frequency Induction Heated Sintering and Its Mechanical Properties

“…The effect has been explained by rapid heating due to Joule heating at contacts points, the presence of plasma in pores separating powder particles, and the intrinsic contribution of the current to mass transport. [23][24][25][26] Vickers hardness measurements were made on polished sections of the MoSi 2 -NbSi 2 composite using a 5-kg load and 15-s dwell time. The calculated hardness value of the MoSi 2 -NbSi 2 composite was 1180 kg/mm 2 .…”

Fabrication of submicron alumina ceramics by pulse electric current sintering using M2+ (M=Mg, Ca, Ni)-doped alumina nanopowders

“…It was also shown that the sintering behavior and densification rate are strongly dependent on the reactivity of the starting powder on the basis of the results of some 20 PECS-treated different commercially available alumina powders: powders having larger specific surface areas sinter and yield homogenous microstructures more easily than do coarse-grained starting powders [28]. However, PECS studies on different cation doped α-alumina powders have been lacking.…”

“…PECS densification of Mg 2+ (0.1 mass%)-doped α-alumina powders obtained by the impregnation method was reported to be also effective in suppressing grain growth as in the case of conventional sintering techniques, showing that the average grain size of non-doped and Mg-doped samples sintered at 1250°C under 50 MPa was 1.0 m (for a normalized comparison, the reported size is divided by 1.56 [29]) and 0.58 m, respectively [28]. It was also shown that the sintering behavior and densification rate are strongly dependent on the reactivity of the starting powder on the basis of the results of some 20 PECS-treated different commercially available alumina powders: powders having larger specific surface areas sinter and yield homogenous microstructures more easily than do coarse-grained starting powders [28].…”

“…This indicates that the high loading pressure of 80 MPa at the lower temperature of 1250°C employed during the PECS process in this study further leads to a marked decrease in the average grain size. Shen et al [28] pointed out that the applied pressure provides an extra strain energy, promoting diffusion, however, applying a higher pressure also makes it possible to obtain dense specimens at lower temperatures where grain boundary migration is not yet fully thermally activated. Consequently, under a higher loading of 80 MPa, all GA-M powders could be densified at 1250°C by further suppressing grain growth.…”