Spark Plasma Sintering Kinetics of Pure α‐Alumina

Abstract

The microstructure development of sintered alumina at different stages in the spark plasma sintering process has been investigated. Based on classical kinetics laws and adapted Coble creep models of hot pressing, the densification and grain growth kinetics were analyzed as a function of various parameters such as heating rate, sintering temperature, and dwell duration. It is found that sintering kinetics are greatly influenced by heating rates. The local temperature gradients at interparticle contacts during high heating rate can be from three to 10 times higher than in low heating rate cycles. Plastic yield might lead to instantaneous densification at an early stage of sintering. However, grain-boundary diffusion probably dominates at low heating rate whereas grain coarsening, in respect of thermal equilibrium establishment, is unavoidable with high heating rate during the initial-stage sintering at low temperatures. During the final-stage sintering, fast grain growth mechanisms such as surface diffusion and pore-controlled grain-boundary migration may dominate over densification controlled by grain-boundary sliding or lattice diffusion. The grain size-density trajectory corroborates that low heating rate is much favorable to achieve near full density with fine grain size at low sintering temperatures.

Pore closure in spark plasma sintered alumina studied by variable energy positrons

“…For the samples sintered at the low heating rate closed porosity is initiated at 1050ºC (Figure 6a) and its relative contribution to the total porosity seems to increase with the sintering temperature but it is not detected at lower sintering temperatures (Figure 6b). This is in agreement with the findings that sintering kinetics is greatly influenced by heating rates [11].…”

“…The powder was sintered using an SPS apparatus type HD P 25/1 (FCT Gmbh, Germany). Preparation details can be found elsewhere [11,12]. Mechanical pressure of 80 MPa was applied uniaxialy all over the heating and dwell step.…”

“…Alumina, a widely used ceramic material, has been extensively studied as a model material, and for which the sintering mechanism has been ascribed to grain boundary diffusion during intermediate stage of SPS [10,11]. The objective of this study is therefore to obtain a better understanding about the influence of SPS heating rates and the sintering temperatures on the stability of the interconnected open pores.…”

Effects of the nature of the doping salt and of the thermal pre-treatment and sintering temperature on Spark Plasma Sintering of transparent alumina

“…The heating rate has been found to be a critical parameter in obtaining such a material. According to Aman et al [20], grainboundary diffusion probably dominates at low heating rates whereas grain coarsening, in respect of thermal equilibrium considerations, is unavoidable at high heating rates during the initial stages of low temperatures sintering. According to Kim et al [1], when sintering at under 1250 8C, rapid heating creates high defect concentrations inducing dynamic grain growth and thus decreasing the transparency of the material.…”

“…SPS is a processing technique that has been widely used over the past decades [1,5,[17][18][19][20]. It was shown that dense, finegrained materials can be developed at low temperatures and short sintering times compared to conventional techniques such as hot isostatic pressing (HIP).…”