Innovative Tungsten Coatings for an Application in Modern and Future Fusion Devices
Round 1
Reviewer 1 Report
1 This is an simple experimental study with a clear goal and based on a solid conception.
Some topics still need to be optimized, related both to the testing procedure (avoid contaminations) and to the adhesion of the coating to the substrate. The authors demonstrate to be aware of the improvements needed.
I have some suggestions that I hope will be accepted in order to fix few mistyping and, above all, strengthen significance and discussion of the results.
11) Line 4: the affiliation of the last author is missing
22) Line 30: “its high reactivity” should be modified to “the high reactivity”
33) Line 37: a comment about the need for in-situ coating of the existing divertors and the tools available for such a work (e.g., the MASCOT would be used?) could be useful to frame the study
44) Line 63: a full stop is missing
55) Line 133: how did you measure the oxygen content? In the text EDS oxygen maps are highlighted: those work on a differential base. None the less in Table 5 a numerical value is reported for oxygen content: EDS is not truly quantitative for any element, even more so for “light” elements. Please specify, in order to alert the reader on the value significance
66) Line 229: a comma to be deleted
77) Line 230: please better explain the detrimental impact of tungsten sensitivity to oxygen on the applicability for fusion environments. On the oxidation behavior of tungsten, the work of Karin M. Andersson in the early 2000s could be useful
88) Line 242: the second “rapidly” has to be delated
99) Line 279: “brittle-to-ductile” transition, instead of “brittle-to-tensile”
110) Line 350: “probability” instead of “porbability”
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Editor, metals
Title: “Innovative tungsten coatings for an application in modern and future fusion devices”
Manuscript Number: metals-2222387
In this paper, the authors have studied the effect of changing different parameters during the coring of CFC by tungsten using low pressure plasma spraying using tungsten powder. The authors investigate the effect of the nozzle diameter, carrier gas flow, and scanning speed and spray distance on the porosity, overspray, microstructure, composition and adhesion of the coating. Authors recommended sample 6 processing conditions to be used to reach the best coating layer. It is exciting research however, the reviewer suggests accepting this paper for publication in the metals after a major revision to cover the following comments.
1- Please rewrite the abstract; it must be comprehensive and contain some details about aims, experimental work, results, and correct conclusions.
2- English needs to be corrected throughout the manuscript, for example, in lines 16, 44 and 45…. etc . English needs deep polishing.
3- The objectives of the present work must be clarified.
4- Overspray results did not mean anything. Authors depend on the difference in colors. Moreover, how do authors decide that samples 4 and 5 are better without showing their photos and depend only on table 3 results?
5- On page, the authors speak about the shape and sizes of the coating grains. How were these results obtained, considering that figure 3 needs to be clarified to obtain those results?
6- Why the grain size and shape results for the different samples were not provided in the microstructure part?
7- How the CoNiCrAl inclusions indicated in figure 4 were defined.is using EDS capable of doing that.
8- The adhesive observation by the visual method is too weak to depend on.
9- Authors did not provide a correlation between the results in figure 2 and table 4 and the discussion of the overspray part. It is a misleading discussion.
10- The discussion of the porosity of the coated layer must be enhanced. How do the authors know the increase of the porosity in the interface between the CFC and the coating layer (need to support that with SEM micrographs)? Moreover, SEM of the lower porosity-contained samples, such as samples 6 and 7, must be added.
11- The discussion for the other parts is feeble, and the authors should have supported the results with observations. Can the authors imagine that they did not provide any EDS or even XRD patterns or different microstructure photomicrographs and just provided results that did not rely on accurate observation? Authors must give results to depend on them in the discussion.
12- Please reconstruct the conclusions.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Dear Authors,
I have carefully reviewed your manuscript entitled “Innovative tungsten coatings for an application in modern and future fusion devices”, submitted for publication in the Metals journal.
I must admit that I read this manuscript with great interest. Many researchers are conducting studies on the deposition of tungsten coatings on CFC substrates using various techniques. I think your results are worth publishing and will certainly be helpful to other researchers. The introduction provides a good, generalized background of the topic and the objectives of the study are clearly defined. The results are clearly explained and are presented in an appropriate format. The figures show essential data; some of the data are also summarized in the text. The cited literature is relevant to the study and balanced. To summarize, this well-written manuscript could be accepted for publication after a few editing corrections.
In Tables 1, 3, and 4 please use dots instead of commas. In the English language decimal separator is a dot.
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
The manuscript reports about the study of the process parameters of tungsten coatings manufactured by low pressure plasma spray (LPPS) on CFC graphite 291 substrates.
The manuscript is clear and well written, even though the results are only at a preliminary stage for the selected application. A few specific suggestions to improve manuscript’s quality are reported below:
1) In the Abstract the authors claim that the LPPS setup is designed for in situ application. However, during the discussion of results the applicability of the system for the in situ coating should be more stressed.
2) At line 48, please write “SNECMA Propulsion Solide” instead of “SNECMA propulsion solide”.
3) Please specify the thickness of the tungsten coatings and if all the coatings grown during campaign 1, 2 and 3 have the same thickness.
4) From table 5 it is evident the composition of the W feedstock powder. It is not much clear if the starting powder could contain less impurities in order to avoid the formation of foreign phases in the coating (apart the one coming directly from the LPPS system), or not.
5) Please specify if there is any correlation between the overspray and its composition (presence of impurities), apart from/or in addition to the already given explanations.
6) At lines 275-277, please rewrite the sentences making more clear that the data about thermal conductivity of CFC are taken from the literature. “Orthogonally to the interface surface, 0.5 x 10-6 K-1 was measured. Parallel to the interface surface, it was 1.2 x 10-6 K-1 in one direction and 2.7 x 10-6 K-1 in the other one [27]”.
7) I suggest to add, at the end of the manuscript, some sentences mentioning the future work to be done necessary for coatings’ optimization and characterization. To act as thermal barrier, in fact, some fundamental properties such as adhesion of the coating to the substrate, thermal conductivity, creep, mechanical properties, radiation resistance, etc.. need to be assessed.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The manuscripte can be accepted in the current form
