Effect of pretreated microstructure on subsequent sintering performance of MgAl2O4 ceramics

Abstract

Pore-grain boundary separation at the final stage of pressureless sintering was successfully suppressed via limiting grain growth in MgAl2O4 ceramics. A pretreatment process by spark plasma sintering (SPS) was utilized to obtain a homogeneous porous body with relative density of 88%, small pores (~28 nm) and uniform grains (~230 nm). The subsequent pressureless sintering results shows that the SPS-ed sample exhibited superior densification with limited grain growth, in contrast to the sample pretreated by pressureless sintering. Coble's model for intermediate stage of sintering was applied to correlate the densification behavior with the instantaneous grain size. It was demonstrated that the densification process could be promoted significantly by maintaining small grain size. In the final stage of sintering, the grain growth mechanism is pore displacement controlled by lattice diffusion. After final densification by hot isostatic pressing, transparent ceramics possessing fine-grained microstructure and acceptable transmittance had been fabricated. Average grain size of the transparent ceramics was 1.9 µm, which enhanced its Vickers hardness (13.9 ± 0.2 GPa).