Study of Non-Transformable t’-YSZ by Addition of Niobia for TBC Application

Abstract

The high toughness of zirconia is paving the way for the development of new materials for application in TBC for gas turbine blades. The main aim of this work was the obtainment of tetragonal zirconia polycrystalline (TZP) with high density, from mixtures of high-purity powder of zirconia, yttria, and niobia with different compositions (14.5 to 21 mol%), through the processes of cold pressing by uniaxial pressing and by isostatic pressing, followed by air sintering processes at 1550 °C for 1 h. The samples were characterized for phase composition by X-ray diffraction, Rietveld analysis, and morphology by transmission electron microscopy and energy dispersive spectroscopy analyses. Mechanical and tribological resistance was evaluated by fracture toughness and nanoindentation tests as well as Weibull statistics. The incorporation of yttria and niobia resulted in relatively denser ceramics with stabilization of the tetragonal phase which was confirmed by detailed X-ray diffraction analysis. Modified ceramics for TBC with 17.5 mol% of yttria and niobia showed higher hardness and fracture toughness, 16.16 GPa and 173.38 GPa, respectively. Through nano hardness measurements, it was possible to verify the effect of the samples’ ferroelasticity. Thus, the addition of niobia and yttria to zirconia represents an opportunity for the development of new materials with increasing mechanical and tribological resistance for TBC application.