Abstract
Elastic properties of a thermal barrier ceramic coating composed of an NiCoCrAIY bond coat and a ZrO2(Y2O3) top coat were measured by a four-point bending rig in the temperature range 20°C–900°C. Different types of specimens (i.e., with bond coat only or with bond coat and top coat, on one side or on both sides) were employed. Test procedures were based on the theory discussed in Part 1 to enhance accuracy and to estimate confidence intervals. In particular, the method employed at high temperature was calibrated at room temperature by comparing the results with those obtained by methods with low sensitivity to layer thicknesses. For the bond coat, Young's modulus was found to be temperature independent up to about 500°C; a decreasing trend was observed above this temperature. For the top coat, a slightly temperature range examined. A possible explanation is given on the basis of phase transformation and the microstructure of the two layers. At room temperature, Poisson's ratio for the bond coat was found to be near 0.3, whereas a near zero value was measured for the top coat.
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Abbreviations
- B :
-
specimen width
- H :
-
total specimen thickness
- L :
-
total specimen length
- S :
-
specimen length subjected to constant bending
- a :
-
spacing between the inner and outer loading pins in the four-point bending test
- E s, Ebc, Etc :
-
Young's modulus of substrate, bond-coat and top-coat materials
- v s, vbc, vtc :
-
Poisson's ratio of substrate, bond-coat and top-coat materials
- h s, hbc, htc :
-
thickness of the substrate, bond-coat and top-coat layers
- g s, gbc, gtc :
-
depth coordinate of the substrate, bond-coat and top-coat centroid, with reference to the geometric center of the specimen
- ζ:
-
ratio of the transverse to the longitudinal strain measured on the external specimen surface
- \(P\varepsilon _s ,P\varepsilon _{bc} ,P\varepsilon _{tc} \) :
-
slope of the experimental regression line correlating the measured load and strain on the substrate, bond-coat and top-coat surfaces
- P w :
-
slope of the experimental regression line correlating the measured load and midsection specimen displacement
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Beghini, M., Benamati, G., Bertini, L. et al. Measurement of coatings' elastic properties by mechanical methods: Part 2. Application to thermal barrier coatings. Experimental Mechanics 41, 305–311 (2001). https://doi.org/10.1007/BF02323923
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DOI: https://doi.org/10.1007/BF02323923