Flash Spark Plasma Sintering of 3YSZ: Modified Sintering Pathway and Impact on Grain Boundary Formation

We demonstrate the possibility to prepare porous 3 mol.% yttria stabilized zirconia ceramics thanks to a recently developed method called Flash-SPS, allowing extremely fast densification in just a few seconds. This method allows to reach heating rates up to 200 °C/s, which has a strong impact on sintering mechanisms, both in terms of densification and grain growth. We demonstrate the possible preparation of specimens with 5 to 15% porosity, limited grain growth (< 350 nm) and mechanical properties similar to fully dense ceramic. Through the use of sintering trajectories, but also based on microscopy, mechanical and electrical analyses, we highlight a new sintering mechanism. It appears that densification is largely advanced at grain boundary interfaces, while inter-grain porosity remains present. This phenomenon is particularly supported by the mechanical hardness and impedance spectroscopy measurements, the latter showing a very low impedance contribution from the grain boundaries despite the low density. This opens up opportunities for the fabrication of porous lightweight materials with high mechanical properties, but also presents interests in alternative sintering pathways for refractory ceramics.