Quantitative Characterization of the Interfacial Damage in EB-PVD Thermal Barrier Coating

Round 1

Reviewer 1 Report

The cyclic oxidation test was performed through heating for 10 min 286 followed by air cooling for 10 min with a maximum temperature of 1050 °C- author should include the number of cycles. 

Author Response

Thanks very much. This sentence has been modified as follows: “… the cyclic oxidation test was performed with a maximum temperature of 1050 °C. Typical schemas of thermal loads in the test are shown in Figure 6 . Note that each cycle included heating for 10 min followed by air cooling for 10 min, as shown in Figure 6(b).”

Reviewer 2 Report

The authors present a detailed study on the evolution of interfacial damage in thermal barrier coatings. An established method using uniaxial compression to induce buckling is employed; several improvements in the analysis are developed to enhance the generality of the method. Ultimately, the degree of damage is correlated with the thickness of a thermally grown oxide produced during either cyclic or static oxidation conditions.

Overall, the improvement to the existing method is noteworthy. However, in analyzing the results several potential factors are overlooked. Detailed comments on these shortcomings and additional general comments are included here:

- How isotropic are the elastic constants of PWA1484? From the text is appears that the orientation of the single crystal substrate is not tracked (line 303-304), and this is attributed as a source of error. If C11/(C12-C44) is close to 1 then the effect would be minimal; conversely if the ratio is large, then the elastic anisotropy of the substrate may introduce large errors.

- It appears that the residual stress is assumed to be constant throughout the experiments. However, it is possible that factors such as the growth of the TGO or plastic deformation of the bond coat or substrate may act to relieve the residual stress particularly of the cyclic exposure tests.

- The preparation of cross sections for measuring the TGO thickness should be described.

- Where are the parameters in Table 3 taken from? If taken from the literature include the relevant references.

- The analysis of the interaction between damage stemming from cyclic effects and oxidation requires more support. It is stated that changes in TGO morphology might explain the apparent interaction parameter (k) is -1. Since images of all TGO films were collected for the thickness measurements an example of the TGO different TGO morphologies should be included.

- Furthermore, the conclusion that k=-1 appears to stem from empirical fits to the damage-TGO thickness relationship and depends on changes at TGO thicknesses greater than 2.1 μm. Yet the maximum TGO thickness from the cyclic tests is ~2 μm due to the TBC spalling on cooling after 750 thermal cycles (i.e. the critical strain is 0%). How is this extrapolation and resulting conclusions justified when the TBC has already failed due to thermal cycling in this region.

- A few minor typos should be corrected. Line 38: “theTC” needs a space. Line 257 “synchronous” should be synchrotron.

- Overall, the figure captions need to be more descriptive to add the reader in interpreting the figures. Specifically, Figure 1, Figure 2, and Figure 14 would benefit from more detailed captions.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper is related to ‘Quantitative characterization of the interfacial damage in EB-PVD thermal barrier coating’. This paper fits well with the special issue Corrosion, Cracks, and Failure of Advanced Thermal Barrier Coatings. This paper has the potential to be published in this special issue after minor revisions.

1.   Introduction is too long. Authors should link it with issues/shortcomings in the literature that they address in this paper.

 Line 167-169: Why does the thermal mismatch between YSZ and TGO gradually increases with decreasing temperature?

 Mention temperature and time in Fig. 6.

 How different equations given in this manuscript are used in the results and discussion section. Some equations are intentionally added but are not used in this manuscript.

 Line 302: Provide stiffness values of the substrate and coating.

 Schematically show the digital image correlation (DIC) method.

Enlarge the image of Fig.7.

Add References for those equations that are being used from other sources.

Schematically show the experimentation and quantitative characterization that are used in this paper.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

 

I am still not satisfied with the response of the authors to my comments. Authors are once again asked to revise the manuscript accordingly:    1. Introduction is too long. Authors should link it with issues/shortcomings in the literature that they address in this paper. The authors' reply is not satisfactory. They have to link the Introduction with issues and shortcomings in the literature and they have to revise the Introduction part.
  2. How different equations given in this manuscript are used in the results and discussion section. Some equations are intentionally added but are not used in this manuscript. Authors have replied that they have not used all the equations, then they should remove all other equations that are not used in this manuscript or they have to highlight the importance of those equations in this manuscript. The manuscript should be revised according to this comment.     3. Schematically show the digital image correlation (DIC) method. The authors' reply is not acceptable. I once again ask to schematically show the digital image correlations (DIC) method.   4. Add References for those equations that are being used from other sources. Authors should clearly show which equations are taken from References and which equations are derived by authors.  

5.  Schematically show the experimentation and quantitative characterization that are used in this paper. From the authors' reply, it seems they are not interested to revise their manuscript according to reviewers' comments. Please schematically show the experiment and characterization that are used in this paper.

Author Response

Please see the attachment.

Author Response File: Author Response.docx