Thermal Expansion of Yttria Stabilized Zirconia

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

Analysis of Anisotropic void system in electron-beam physical vapor deposited (EB-PVD) thermal barrier coatings

Thermal barrier coatings (TBCs) deposited by EB-PVD protect the turbine blades situated at the high pressure sector of the aircraft and stationary turbines increasing the combustion temperature and/or diminishing the air-cooling requirements. It is an important task to uphold low thermal conductivity in TBCs during long-term service at elevated temperatures. One of the most promising methods to fulfil this task and to improve the turbine efficiency is to optimize the TBC properties by tailoring its microstructure and/or material. The different kinds of pores in EB-PVD TBCs influence their thermal conductivity according to their size, shape, orientation and volume. These pores can be open (inter-columnar and between feather arms gaps) and closed (intra-columnar pores). Since such pores are located within three-dimensionally deposited columns and enclose large differences in their sizes, shapes, distribution and anisotropy, the accessibility for their characterization becomes very complex and requires the use of sophisticated methods. This work describes the analysis of the anisotropic and nano-sized pores in PYSZ-based TBCs by means of small angle neutron scattering (SANS) method. In order to differentiate and analyse 3D closed and open pores in 400 µm thick coatings, a contrast matching SANS technique has been employed. Thermal derived changes in crystal structure as well as pore size and morphology have been correlated with thermal conductivity

Linear electrooptic effect of the monoclinic polar bismuth triborate, BiB3O6

For the monoclinic (point group 2) nonlinear optical crystal BiB3O6 the linear electrooptic properties (Pockels effect), i.e. the 8 independent coefficients of the linear electrooptic tensor [r(ijk)(o)] (at constant stress s) at the wavelength lambda = 632.8 nm are determined by a method based on Michelson interferometry. The electrooptic tensor is analysed with respect to the longitudinal and transverse effects and a classification of BiB3O6 as electrooptic material is given

Analysis of Anisotropic Void Sytem in Electron Beam-Physical Vapour Deposited (EB-PVD) Thermal Barrier Coatings

Thermal barrier coatings (TBCs) deposited by EB-PVD protect the turbine blades situated at the high pressure sector of the aircraft and stationary turbines increasing the combustion temperature and/or diminishing the air-cooling requirements. It is an important task to uphold low thermal conductivity in TBCs during long-term service at elevated temperatures. One of the most promising methods to fulfil this task and to improve the turbine efficiency is to optimize the TBC properties by tailoring its microstructure and/or material. The different kinds of pores in EB-PVD TBCs influence their thermal conductivity according to their size, shape, orientation and volume. These pores can be open (inter-columnar and between feather arms gaps) and closed (intra-columnar pores). Since such pores are located within three-dimensionally deposited columns and enclose large differences in their sizes, shapes, distribution and anisotropy, the accessibility for their characterization becomes very complex and requires the use of sophisticated methods. This work describes the analysis of the anisotropic and nano-sized pores in PYSZ-based TBCs by means of small angle neutron scattering (SANS) method. In order to differentiate and analyse 3D closed and open pores in 400 µm thick coatings, a contrast matching SANS technique has been employed. Thermal derived changes in crystal structure as well as pore size and morphology have been correlated with thermal conductivity