Abstract
A Finite-Element Model (FEM) for thermal-barrier coatings was employed to elaborate the temperature distribution on yttria-stabilized zirconia (YSZ) free surface during cracks coalescing, then the influence of sintering of YSZ induced by heat-transfer overlapping on energy release rate was quantificationally evaluated. A three-dimensional model including three layers was fabricated. Two types of cracks, with and without depth variations in YSZ coating, were introduced into the model, respectively. The temperature rise of YSZ coating over the crack is independent of each other at the beginning of crack propagation. As crack distance shortens, the independent temperature-rise regions begin to overlap, while maximum temperature is still located at the crack center before crack coalescence. The critical distance that the regions of temperature rise, just overlapping, is the sum of half lengths of two coalescing cracks (i.e., a1 + a2), which is independent of cracking path. The maximum temperature in YSZ sharply increases once cracks coalesce. Compared with one delamination crack, the effective energy-release rate induced by heat-transfer overlapping increases in the range of 0.2%–15%, depending on crack length and crack distance, which is on some level comparable to that of deterioration of thermal expansion misfit induced by temperature jump between crack faces.
Highlights
The thermal barrier coatings (TBC) are fabricated via the ceramic material coated on the superalloy to protect the superalloy components and increase gas temperature, thereby significantly increasing the efficiency of the gas turbine [1,2,3,4]
The temperature overlap partly affected the durability of TBC via the increasing isothermals, and the maximum temperature corresponded to the center of the crack
A three-dimensional Finite-Element Model (FEM) was established to evaluate the influence of multicracks on temperature temperature distribution characteristic in plasma-sprayed thermal-barrier coatings
Summary
The thermal barrier coatings (TBC) are fabricated via the ceramic material coated on the superalloy to protect the superalloy components and increase gas temperature, thereby significantly increasing the efficiency of the gas turbine [1,2,3,4]. The delamination cracks in this system generate at interfaces and/or TGO/YSZ interface, which locate at different depths in ceramic topcoat [26,27,28,29]. The temperature distribution affected by coalescing cracks with different depths in YSZ coating needs, to be taken into account in addressing the driving force of cracking. The cracks located at different depths in YSZ coating were drawn into the model to analyze the characteristic of temperature under the interaction of cracking modes. How this interaction affects the sintering of the YSZ coating was addressed, the driving force of cracks was sketched via quantitative evaluation of the increasing rate of energy release
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