Assessment of low-temperature degradation of Y-TZP ceramics based on Raman-spectroscopic analysis and hardness indentation

This paper focuses on the analysis of hydrothermally induced phase transformation of yttria-stabilized tetragonal polycrystalline zirconia (Y-TZP) and its influence on the hardness. Due to the hydrothermal exposure and the accompanied low-temperature degradation (LTD), a micro-cracked transformation zone is generated at the surface and progresses into the subjacent material. Raman-spectroscopic analysis of hydrothermally loaded and cross-sectioned samples revealed complete phase transformation within this zone. Its depth as well as its temperature-dependent growth rate was verified. Raman-spectroscopic measurements at the surfaces were correlated with the progression of the transformation zone. An efficient model, which assumes one extinction coefficient for tetragonal and monoclinic microstructure, enables to determine the depth of the transformation zone from the measured Raman signals. Furthermore, an exponentially decreasing Vickers hardness with increasing depth was determined. Finally, a differently sintered Y-TZP ceramic revealed enhanced resistance against LTD for the same hydrothermal loading conditions.