Thermal Expansion of Yttria Stabilized Zirconia

Kurzfassung

Today the state of the art material for Thermal Barrier Coatings (TBCs) is Electron Beam Physical Vapor Deposition (EB-PVD) Yttria Stabilized Zirconia (YSZ). As shown in the phase diagram by Scott different polymorphs of YSZ can be obtained by varying the Yttria content. Thereby monoclinic Stabilized Zirconia crystallises in space group P21/c, tetragonal Partially Stabilized Zirconia (PSZ) in space group P42/nmc and cubic Full Stabilized Zirconia (FSZ) in space group Fm3m. In most cases, far from any phase transitions, the linear approximation for thermal expansion turned out to be an adequate approach. In the monoclinic phase (crystal class 2/m) zirconia exhibits four independent tensor coefficients, whereas in the tetragonal (4/mmm) and the cubic phase (m3m) there are only two and one coefficients, respectively. It is remarkable, that in the literature only little is known about the tensor coefficients of thermal expansion in YSZ. Moreover, existing data sets of thermal expansion of the different zirconia polymorphs are partial inconsistent.