Thermal Barrier Coating Life Prediction Model Development

Abstract

A thermal barrier coated (TBC) turbine component design system, including an accurate TBC life prediction model, is needed to realize the full potential of available TBC engine performance and/or durability benefits. The objective of this work, which was sponsored in part by NASA under the Hot Section Technology (HOST) Program (Contract NAS3-23944), was to generate a life prediction model for electron beam-physical vapor deposited (EB-PVD) zirconia TBC. Specific results include EB-PVD zirconia mechanical and physical properties, coating adherence strength measurements, interfacial oxide growth characteristics, quantitative cyclic thermal spallation life data, and a spallation life model.

Modelling of microstructural evolution in multi-layered overlay coatings

“…For oxidation, the model proposed by Meier et al for a Ni-Co-Cr-based bond coat was used [26]. The model assumes that only Al is oxidised at the coating surface and the diffusion of elements within the oxide was not considered in the current model.…”

“…The model assumes that only Al is oxidised at the coating surface and the diffusion of elements within the oxide was not considered in the current model. For isothermal oxidation, the boundary condition at the oxide/coating interface is given in [26] as the rate of Al consumption, where the thickness d of the oxide scale in is given by Eq. (2)…”

“…The time step for the simulations was varied in accordance with stability criteria for the explicit finite-difference solution scheme, e.g. [26]. The density of the outer coating layer and partial molar volume of Al in the coating were assumed to be 7754 kg/m 3 and 7.1 9 10 -6 m 3 /mol.…”

“…In the model, the differential terms in (1) were replaced by their finite-difference (F-D) equivalents as detailed in [26]. The explicit scheme was used to solve for concentrations of all elements.…”

“…The F-D grid zones were expanded dynamically into the coating layers (or substrate) as the concentration fields extended with time [26]. The interface between the outer coating layer and the oxide scale was treated as a moving phase boundary, using the scheme suggested in [28].…”