A physics-based life prediction methodology for thermal barrier coating systems

Abstract

A novel mechanistic approach is proposed to predict the life of thermal barrier coating (TBC) systems. The life prediction methodology is based on a criterion linked directly to the dominant failure mechanism. It relies on a statistical treatment of the TBC's morphological characteristics, non-destructive stress measurements and on a continuum mechanics framework to quantify the stresses that promote the nucleation and growth of microcracks within the TBC. The latter accounts for the effects of TBC constituents' elasto-visco-plastic properties, the stiffening of the ceramic due to sintering and the oxidation at the interface between the thermally insulating yttria stabilized zirconia layer and the metallic bond coat. The mechanistic approach is used to investigate the effects on TBC life of the properties and morphology of the top YSZ coating, metallic low-pressure plasma sprayed bond coat and the thermally grown oxide. Its calibration is based on TBC damage inferred from non-destructive fluorescence measurements using piezo-spectroscopy and on the numerically predicted local TBC stresses responsible for the initiation of such damage. The potential applicability of the methodology to other types of TBC coatings and thermal loading conditions is also discussed.

The role of beam dispersion in Raman and photo-stimulated luminescence piezo-spectroscopy of yttria-stabilized zirconia in multi-layered coatings

“…As a consequence, when undertaking PLPS measurements of stresses within the TGO, lateral spreading of the incident laser beam within the TBC will affect the measurement resolution, which is defined by the diameter of the laser at the TGO surface [35]. This resolution is important, for example, for defining the step size when mapping stress in the TGO through the YSZ layer to avoid overlap of the measurements and thereby provide more reliable stress information [36], [37] and [38]. In this paper, the laser beam spreading and the sampling depth of Raman spectroscopy within the YSZ is investigated.…”

Comprehensive damage evaluation of localized spallation of thermal barrier coatings

“…A number of previous reports were related to the damage by spallation. For example, some lifetime prediction models were developed to prevent accidents [22][23][24], and to repair TBCs on a component with localized spallation [25][26][27][28][29][30][31]. Although these reports presented in detail about how to prevent and repair TBCs in case of spallation, little attention had been drawn on evaluating thermal tolerance of the spalled coating when suffering high temperature in service.…”

An Investigation of the Compatibility of Nickel-Based Single Crystal Superalloys with Thermal Barrier Coating Systems

“…This is despite much progress which has been made to emphasise the micromechanics of the failure mode of TBCs [7,8]. In particular, the approach in modeling TBC failure [9][10][11][12][13] generally relies on the treatment of the oxidation-induced stresses that drive TBC spallation despite the fact that it might reasonably be assumed that the TBC life and the modes of failure (i.e. location of interfacial failure) are also influenced significantly by the inherited chemistry of the underlying superalloys.…”