Transparent alumina ceramics densified by a combinational approach of spark plasma sintering and hot isostatic pressing

In order to increase the in-line transmission of fine transparent alumina in visible light the grain growth during sintering of alumina ceramics was supressed using a combined densification process. This process combines presintering of a green body by spark plasma sintering with final hot isostatic pressing. The presintering by spark plasma sintering provided bodies with a substantially smaller grain size than pressureless presintering. It is shown that the fine-grained presintered microstructure could be retained during final hot isostatic pressing and alumina ceramics doped with spinel and zirconia nanoparticles in particular could be sintered to full density with only minor grain growth during final hot isostatic pressing. The novel combined densification process enhanced by the unique nanoparticle doping approach provided fully dense alumina ceramics with an average grain size of 237 nm and an in-line transmission of 76.2% at a wavelength of 632.8 nm and a sample thickness of 0.8 mm.