Microwave Hybrid Sintering of Nanostructured YSZ Ceramics

Abstract

Radiant and hybrid sintering experiments have been performed on dry and wet processed nanocrystalline 3-YSZ using both a conventional single stage and a new two stage sintering cycle. Whilst densities >98.5% of theoretical were achievable by all combinations, a nanostructure could only be retained using the two stage sintering approach. With hybrid heating the average grain sizes for die pressed samples were in the range 70 – 80 nm whilst for the more homogeneous slip cast samples a final average grain size of just 64 nm was achieved for a body with a final density of >99%. It is believed that the primary advantage offered by hybrid heating is the ability to use a much faster initial heating rate, 20 versus just 7oC min-1, without risking damage to the samples. Whilst detailed characterisation of the properties of these nanostructured ceramics is still underway, preliminary results have suggested that neither the hardness or toughness has been improved compared to conventional, submicron-sized 3-YSZ. As a result of detailed crystallographic characterisation this is believed to be due to a grain size dependent shift in the phase boundary composition for nano YSZ ceramics leading to ‘over stabilisation’ at any given yttria content.