[en] Spallation sensitive as-coated EB-PVD TBC systems on Nimonic 75 substrates were investigated by transmission electron microscopy (TEM). Decohesion was observed within the thermally grown oxide (TGO) layer between NiCoCrAlY bond coat and TBC. The TGOs consisted of unexpected oxide phases. In one case the TGO consisted of stratified layers containing spinel phase and chromia. In another case the TGO contained a vitreous Ca-silicate and a crystalline Y-silicate two-phase interlayer. The generation of the respective oxides is initiated by preceeding processing steps before TBC deposition. Suggestions for the manufacture of more confident TBC systems are presented. (orig.)

[en] The thermal stability of a directionally solidified (d.s.) eutectic CoCrCAl-alloy in a thermal gradient is compared to isothermal conditions. A device has been designed and constructed for examination of d.s. eutectics in high temperature gradients at temperatures above 1300 K in different atmospheres and vacuum. Experiments in this gradient furnace show coarsening of the carbide fibres forming the aligned strengthening phase. A microstructural instability resulting from the transformation of carbide fibres has been observed. These effects are discussed in relation to isothermal conditions and their implications on the applicability of the alloy as high temperature gas turbine blade material. (orig.)

[en] This paper focuses on the combined effects of substrate temperature and rotation during electron-beam physical vapor deposition (EB-PVD) on the columnar microstructure of yttria partially stabilized zirconia (YPSZ) thermal barrier coatings. Diameter and degree of ordering of the columns and the density of the coatings are sensitive to the processing parameters. Results are discussed in the frame of common structural zone models for PVD processes. The models are extended to consider the rotational effect. EB-PVD YPSZ TBCs of different column diameters were deposited on top of an EB-PVD NiCoCrAlY bondcoat on IN 100 superalloy test bars. The performance of the TBCs was investigated in a cyclic oxidation furnace test rig between 1100 C and 130 C and in a burner rig under hot gas corrosion conditions at a maximum temperature of 900 C. Results showed a correlation between cyclic lifetime and the various microstructures of the TBCs. Samples having a non-regular arrangement of columns performed best in both tests. (orig.)

[en] Progression of TGO scale in a NiCoCrAlY/EB-PVD TBC system is monitored via analytical SEM and TEM from the first vacuum anneal of the NiCoCrAlY bond coat through the different processing stages of the EB-PVD Y-PSZ coating (preheating; initial and advanced stages of TBC deposition) and upon cyclic fatigue at T > 1100 C. During the early stages segregation of oxide constituents to the TGO scale is dominated by yttria giving rise to a transient ''off-plane'' mixed zone (Al₂O₃, ZrO₂) microstructure textured perpendicular to the TGO/TBC interface. Subsequently Y-aluminates and spinel are formed. Local phase incompatibility of coexisting oxides is considered critical for the formation of failure-relevant clustered pores, as verified from the bond coat/TGO interface and the TGO mixed zone adjacent to the TBC top layer. (orig.)

[en] ZrO₂-based ingot sources with stabilizing oxides of 6.5 and 20 wt.% Y₂O₃ and 25/2.5 wt.% CeO₂/Y₂O₃ respectively were used to deposit thermal barrier coatings (TBCs) on rotating cylindrical electron beam physical vapour deposition (EB-PVD) NiCoCrAlY-coated IN 100 substrates by reactive high rate EB-PVD. The TBCs were investigated by scanning electron microscopy, X-ray fluorescence and X-ray diffraction. The phases within the TBCs were t' tetragonal for 6.5 wt.% Y₂O₃-ZrO₂ and cubic for 20 wt.% Y₂O₃-ZrO₂ TBCs. The phases found in ceria-stabilized TBCs were t', cubic and monoclinic depending on the compositional fluctuations within the layers. Compositional variations were due to wide differences in the respective vapour pressures of the various oxides in ceria-stabilized ingot sources which become effective in single-source EB-PVD processing. The apparent crystal habits in the TBCs were correlated with process parameters, phases and chemistry and with regard to structural growth models. (orig.)

[en] Purpose: Texture analysis of femur radiographs may serve as a potential low cost technique to predict osteoporotic fracture risk and has received considerable attention in the past years. A further application of this technique may be the measurement of the quality of specific bone compartments to provide useful information for treatment of bone fractures. Two challenges of texture analysis are the selection of the best suitable texture measure and reproducible placement of regions of interest (ROIs). The goal of this in vitro study was to automatically place ROIs in radiographs of proximal femur specimens and to calculate correlations between various different texture analysis methods and the femurs' anchorage strength. Methods: Radiographs were obtained from 14 femoral specimens and bone mineral density (BMD) was measured in the femoral neck. Biomechanical testing was performed to assess the anchorage strength in terms of failure load, breakaway torque, and number of cycles. Images were segmented using a framework that is based on the usage of level sets and statistical in-shape models. Five ROIs were automatically placed in the head, upper and lower neck, trochanteric, and shaft compartment in an atlas subject. All other subjects were registered rigidly, affinely, and nonlinearly, and the resulting transformation was used to map the five ROIs onto the individual femora. Results: In each ROI, texture features were extracted using gray level co-occurence matrices (GLCM), third-order GLCM, morphological gradients (MGs), Minkowski dimensions (MDs), Minkowski functionals (MFs), Gaussian Markov random fields, and scaling index method (SIM). Coefficients of determination for each texture feature with parameters of anchorage strength were computed. In a stepwise multiregression analysis, the most predictive parameters were identified in different models. Texture features were highly correlated with anchorage strength estimated by the failure load of up to R²=0.61 (MF and MG features, p<0.01) and were partially independent of BMD. The correlations were dependent on the choice of the ROI and the texture measure. The best predictive multiregression model for failure load R_adj²=0.86 (p<0.001) included a set of recently developed texture methods (MF and SIM) but excluded bone mineral density and commonly used texture measures. Conclusions: The results suggest that texture information contained in trabecular bone structure visualized on radiographs may predict whether an implant anchorage can be used and may determine the local bone quality from preoperative radiographs.