Subsurface evaluation of hydrothermal degradation of zirconia

The objective of this work is to study the subsurface microstructure and mechanical response of hydrothermal degraded yttria stabilized tetragonal zirconia polycrystals (3Y-TZP). Samples of 3Y-TZP have been subjected to accelerated degradation for different times and several techniques are used to analyse the surface degraded layer: Raman spectroscopy, X-ray diffraction, nanoindentation, atomic force microscopy and transmission electron microscopy (TEM). Results show that there is a non-lineal gradient in the in-depth distribution of monoclinic phase determined by Raman spectroscopy, while the drop in elastic modulus and hardness recorded by nanoindentation is attributed to the extensive microcracking produced by the large shear strain of the first martensite plate formed during the transformation. Moreover, it is shown that the monoclinic layer is thicker than the layer in which microcracks are detected. Finally, TEM analysis of the degraded layer shows a clear orientation of the twin-related monoclinic variants and microcracks with respect to the surface.