Production of superhard corundum under spark-plasma sintering of aluminum oxide nanopowders

Abstract

In the process of optimization of the conditions of spark-plasma sintering of aluminum oxide powders, the repeated nonuniform distribution of microhardness over the surface of the sintered pellets is ascertained. The microhardness in the volume of the pellets was significantly higher (up to 35 GPa) than that on its surface. SEM microstructure investigations on the cleaved surface of the compact show the presence of zones with an unusual structure in the central regions of the sample. The structure of these zones is composed of randomly oriented flat crystals with the longitudinal size of up to 40 μm. Cavities between the long crystals are filled with small grains of 0.3–0.8 μm in size. The results of microhardness measurements indicate that the zones with anomalous structure have superhigh microhardness values.