Multi-layered Ruthenium-modified Bond Coats for Thermal Barrier Coatings

Diffusional approaches for fabrication of multi-layered Ru-modified bond coats for thermal barrier coatings have been developed via low activity chemical vapor deposition and high activity pack aluminization. Both processes yield bond coats comprising two distinct B2 layers, based on NiAl and RuAl, however, the position of these layers relative to the bond coat surface is reversed when switching processes. The structural evolution of each coating at various stages of the fabrication process has been and subsequent cyclic oxidation is presented, and the relevant interdiffusion and phase equilibria issues in are discussed. Evaluation of the oxidation behavior of these Ru-modified bond coat structures reveals that each B2 interlayer arrangement leads to the formation of α-Al 2 O 3 TGO at 1100°C, but the durability of the TGO is somewhat different and in need of further improvement in both cases

Noncontact methods for measuring thermal barrier coating temperatures

Three noncontact, optical methods for measuring temperature are reviewed with an emphasis on their application to the measurement of temperatures of thermal barrier coatings (TBCs). The methods are: infrared pyrometry, Raman spectroscopy, and photo-stimulated luminescence from lanthanide-doped coatings. Although each has the capability of measuring temperatures pertinent to monitoring TBCs, the finite thickness of typical coatings together with the optical properties of zirconia place severe restrictions on the depth from which the temperature sensing can be obtained. Some of these limitations can be circumvented using photo-stimulated luminescence with coatings containing dopants at specific locations. To illustrate this, it is demonstrated that by depositing coatings with a lanthanide dopant, such as Eu3+, at specific locations, for instance in contact with the metallic alloy, temperature sensing can be performed with much higher spatial resolutio

Correlation Between the Microstructure, Growth Mechanism and Growth Kinetics of Alumina Scales on an FeCrAlY-Alloy

The microstructural development of an alumina scale formed on a model FeCrAlY alloy during oxidation at 1200 degrees C was characterized for up to 2000 hours of growth. Quantitative scanning electron microscopy (SEM) studies revealed that the scale had a columnar microstructure, with the grain size being a linear function of the distance from the scale/gas interface. For a given fixed distance from the scale/gas interface, there was found to be no change in the oxide grain size for exposure times ranging from 24 to 2000 hours at 1200 degrees C, up to 100 hours at 1250 degrees C. Thus, there was no significant coarsening of existing grains in the scale. Through oxygen tracer experiments, the scale-growth mechanism was shown to be predominated by inward oxygen diffusion along the oxide grain boundaries. Electron backscatter diffraction (EBSD) analysis further revealed that a competitive oxide-grain growth mechanism operates at the scale/alloy interface, which is manifested by a preferential crystallographic grain orientation. The scale-thickening kinetics were modeled using the experimentally-derived, microstructural parameters and were found to be in excellent agreement with converted thermogravimetric (TG) measurements. The model predicted a subparabolic oxidation rate, with the time exponent decreasing with increasing exposure time. The values of the time exponent were shown to be approximately 0.35 to 0.37, at oxidation times commonly reached in the TG experiments, i.e., a few tens of hours. At longer oxidation times of a few thousand hours and with a constant rate of average oxide-grain size increase, the time exponent was predicted to approach 0.33. corresponding to an ideal cubic oxidation rate

Examining heterogeneity in implied equity risk premium using penalized splines

Equity risk premium, Penalized splines, Subject-specific curves, Linear mixed models, Nonparametric estimation,