Development of Thermal Barrier Coating Systems from Al Microparticles—Part II: Characterisation of Mechanical and Thermal Transport Properties
Round 1
Reviewer 1 Report
The reviewed manuscript investigates the mechanical resistance and the thermal insulation potential of previously fabricated thermal barrier coatings made of a foam of hollow alumina particles. The article is made at a good scientific and technical level, and its practical significance is beyond doubt. In order to improve the readability and clarity of the manuscript, some minor concerns need to be addressed before the paper is to be accepted for publishing:
- The abstract requires some quantitative brief results. Abstract is a mini version of manuscript that proceeds. So, include introduction, methodology, results & Discussion and concluding remarks in a precise but effective manner.
- P1 – L30: “….. an aluminide coating after a proper annealing [1–7].” Try to avoid lumped references; a short comment should be included for each reference or two references in the same subject.
- The aim of the current study must be mentioned clearly at the end of introduction part specifying the objective and novelty of this work. The novelty of this research in relation to other thematically similar research papers.
Author Response
Dear reviewer,
Many thanks for your comments and advice. We answer each point you raised in blue font. The major changes made in the revised version of the manuscript are also in blue font. We do hope that we have responded satisfactorily.
Kind regards,
- Boissonnet, J-L. Grosseau-Poussard, G. Bonnet, F. Pedraza
Reviewer’s comments:
Reviewer 1
The reviewed manuscript investigates the mechanical resistance and the thermal insulation potential of previously fabricated thermal barrier coatings made of a foam of hollow alumina particles. The article is made at a good scientific and technical level, and its practical significance is beyond doubt. In order to improve the readability and clarity of the manuscript, some minor concerns need to be addressed before the paper is to be accepted for publishing:
- The abstract requires some quantitative brief results. Abstract is a mini version of manuscript that proceeds. So, include introduction, methodology, results & Discussion and concluding remarks in a precise but effective manner.
The abstract has been revised accordingly and some results were added.
- P1 – L30: “… an aluminide coating after a proper annealing [1–7].” Try to avoid lumped references; a short comment should be included for each reference or two references in the same subject.
The introduction was modified accordingly to add a comment for the references that were put together previously.
- The aim of the current study must be mentioned clearly at the end of introduction part specifying the objective and novelty of this work. The novelty of this research in relation to other thematically similar research papers.
A sentence was added at the end of the introduction for clarity purpose.
Reviewer 2 Report
Have you considered measuring the weight loss of the sample after the scratch test? It would be closer to the wear resistance tests.
Could you explain why do you think DS coating exhibited such a rapid growth after exceeding 650 deg C?
In the reference section you have 1 position from 2021, 1 from 2020 and 2 from 2019, the rest is older. Are there really no recent studies that you could refer to or contrast your studies with? For me, the reference section could be expanded.
All in all the article is very interesting, I enjoyed reading it. Good job!
Author Response
Dear reviewer,
Many thanks for your comments and advice. We answer to each point you raised in blue font. The major changes made in the revised version of the manuscript are also in blue font. We do hope that we have responded satisfactorily.
Kind regards,
Boissonnet, J-L. Grosseau-Poussard, G. Bonnet, F. Pedraza
Reviewer’s comments:
Reviewer 2
Have you considered measuring the weight loss of the sample after the scratch test? It would be closer to the wear resistance tests.
Indeed, this is a good point. We did not carry out such measurements because in all cases a prescan with an applied load of 0.03 N was performed before the different loading between loads (from 0.03 to 10 N). This may fake the overall results and we thus concentrated exclusively on the analyses of the images. Moreover, the remains of the scratch were not fully evacuated from the contact zone and hence of the sample's surface. Therefore, these remains would also fake the measurements.
Could you explain why do you think DS coating exhibited such a rapid growth after exceeding 650 deg C?
The previous article [Boissonnet, G. et al., Development of Thermal Barrier Coating Systems from Al Microparticles. Part I: Influence of Processing Conditions on the Mechanisms of Formation. Surface and Coatings Technology 2019, 380, doi:10.1016/j.surfcoat.2019.125085] describes in a more explicit manner the formation of these coatings:
“Under Ar atmosphere, the Al microspheres tend to release their Al core rapidly while limited oxidation occurs due to the low oxygen and water partial pressures contained in the commercial gas (2 vpm O2 + 3 vpm H2O according to the supplier). Although some Al was still trapped in the smallest particles of the slurry (<3 µm) after the diffusion heat treatment, most of the Al was released towards the substrate and reacted with Ni to form aluminide coatings of ~30 µm thickness following self-propagating high temperature synthesis (SHS) mechanisms…
“When increasing the oxidizing ability of the atmosphere using synthetic air (pO2 ≈0.20 atm), the microspheres tend to keep more Al. As a matter of fact, the threshold for the opening of the microspheres shifted towards larger-sized particles by performing the diffusion heat treatment in synthetic air. This is attributed to the greater peripheral oxidation of Al microparticles in both oxidizing atmospheres than in inert Ar atmosphere…”
“…the further thickening and sintering of the hollow alumina spheres most probably hampered their shrinkage by comparison with the ones formed in Ar. As a result, thicker top coatings were obtained in oxidizing atmospheres…”
That is why, as stated in this paper (lines 298-300) “Delaying the introduction of air from 700°C to 650°C and then to 600°C increases the exposure time to oxidizing conditions, which in turn results in thicker oxide shells and thicker top coatings than with a heat treatment under Ar only…”
and, (lines 304-306) “When air was introduced at 600°C, the thickness of the shells and of the top coatings for both types of particles were greatly improved...”
When we introduce the oxidizing atmosphere at 650°C, the Al starts to melt (Tmelt ≈ 660°C) before a significant thickening of the shells occurs. However, introducing the synthetic air at 600°C allows this shell growth before the melting of the Al and thus results in thicker shells, lesser collapsing and thus, thicker coating.
In the reference section you have 1 position from 2021, 1 from 2020 and 2 from 2019, the rest is older. Are there really no recent studies that you could refer to or contrast your studies with? For me, the reference section could be expanded.
The average age of the works cited is 2013, i.e. less than 10 years old. Please note that these coatings are very specific and therefore have no comparison in the literature in recent years. Therefore, most of the references come from the previous studies made in our research group or by our partners.
All in all the article is very interesting, I enjoyed reading it. Good job!
Reviewer 3 Report
In this manuscript a thermal barrier coating made of alumina particles in form of a hollow foam is investigated. The introduction section is concise and useful. The experimental procedure is described carefully. The results are interesting and expressed appropriately. The discussion is also sound and deep enough. Therefore, I suggest is The manuscript to be published in this journal. A few very small points:.
1. The first sentence of the introduction requires a reference.
2. Table 1. This table is confusing. I suggest the authors to reorganize it. If the heat-treatment is the same for all the samples, it is not necessary to put it in the table. The dividing line at the middle of the table also made reading of the table a bit more difficult. This is, however, a suggestion.
3. Line 108, it is better to remove "while".
4. Dividing the results and the discussion sections, which is a very good practice, is rare these days. It shows the paper is written by professional researchers.
5. I suggest the authors to divide the conclusions section to numbered paragraphs to increase the readability.
Author Response
Dear reviewer,
Many thanks for your comments and advice. We answer each point you raised in blue font. The major changes made in the revised version of the manuscript are also in blue font. We do hope that we have responded satisfactorily.
Kind regards,
Boissonnet, J-L. Grosseau-Poussard, G. Bonnet, F. Pedraza
Reviewer 3
In this manuscript, a thermal barrier coating made of alumina particles in form of a hollow foam is investigated. The introduction section is concise and useful. The experimental procedure is described carefully. The results are interesting and expressed appropriately. The discussion is also sound and deep enough. Therefore, I suggest is the manuscript to be published in this journal. A few very small points:
- The first sentence of the introduction requires a reference.
A reference was added to the first sentence
- Table 1. This table is confusing. I suggest the authors to reorganize it. If the heat-treatment is the same for all the samples, it is not necessary to put it in the table. The dividing line at the middle of the table also made reading of the table a bit more difficult. This is, however, a suggestion.
Table 1 was revised for clarity purposes.
- Line 108, it is better to remove "while".
The sentence was revised accordingly.
- Dividing the results and the discussion sections, which is a very good practice, is rare these days. It shows the paper is written by professional researchers.
- I suggest the authors to divide the conclusions section to numbered paragraphs to increase the readability.
The conclusion was split into bulleted paragraphs to increase readability.
