Microstructural and Mechanical Characterization of W-CuCrZr Joints Brazed with Cu-Ti Filler Alloy

Round 1

Reviewer 1 Report

The paper presents the microstructural and mechanical characterization of W-CuCrZr joints brazed with Cu-Ti filler alloy. The novelty is good and the paper is well written. The paper can be accepted in the journal.

Author Response

Thank you for the time and consideration

Reviewer 2 Report

The current paper is aimed to find the mechanical properties of brazed joints made from W-CuCrZr joint brazed with an 80Cu-20Ti filler. The authors study the effects of brazing temperature and dwell time on the mechanical properties. Also the microstructure is evaluated for different phase formations. The authors also measured the hardness and shear strength.

Figure 1 should be moved in materials and methods section and not in the introduction, this figure and the discussion about it makes the paper reads more like a chapter from a book.

There is no mention whatsoever about past studies on same or similar topics, the authors must carry out a proper literature review discussing past work and what has been done and what were the most important findings.

In section 2 and 2.1 please combine small paragraphs into bigger ones. The section feels fragmented

All figures and their captions should be centralised

Perhaps add the figure 1 in section 3 to give brief information about the mechanical properties of brazed joints.

Figure 4 c b and d are very poor in resolution, please consider updating them with ones with better resolution, also better use some arrows to explain to the readers what are we looking at here.

Line 174 is requires a reference to support this claim, or how did the authors come to this conclusion.

176 same as line 174

Line 114 do you mean 100gf? Also how many indentations  measurements were made for each of the evaluated in different specimens/surfaces?  

In figure 6 there is a significant variation in the braze region for the value of hardness +/- 200 which is quiet high. Perhaps then it is a good idea to map the hardness at different locations in the braze region and check if there is a trend that can be found of where high and low hardnes exist or is more likely to be.

For the tungsten based material, did the authors use same load to create the indents on the surface? Perhaps a higher load is needed to check if the hardness at inner surface was changed or not.

Figure 8 please use some arrows and texts to explain to us what we are looking at there.

How many tests were carried out overall in this study?

English of paper is well written.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The article was written reliably. Original results of research work are included. The presented results of the structure (SEM) are at a high level.

Methodology question:

• what devices were used for grinding powders (ball mills, atrittor, etc.) and were the obtained fractions of powders separated?

how were the metallographic specimens prepared :

• how were the test samples taken,
• were the standard etching reagents used, or were their concentration selected experimentally? (Ammonia and hydrogen peroxide reactants)

Application question:

• The text shows that the received connector is designed to work in the complex environment (high thermal loads, particle sputtering). So, will the use of a material containing tungsten cause it to crumble during operation? Have such tests been performed or are planned ?
• I kindly ask you to analyze the results of the structural tests and compare them with the results presented in the literature (whether they are analogous or show differences).

The work is very interesting, I believe it requires minor corrections before publication.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

The tungsten-CuCrZr alloy brazed joints, produced using a Cu-Ti filler, were in the focus of the research, described in the present manuscript by J. de Prado, M. Sanchez, D. Swan and A. Urena, entitled "Microstructural and mechanical characterization of W-CuCrZr joints brazed with Cu-Ti filler alloy". By the reviewer's estimation, the topic of the study is highly relevant, and its results are of a fair practical importance. Although the authors recently published several papers on the same subject (references no. 5, 11, 14, 18, 20, 21 in the present manuscript), the reviewer hasn't found that these results have been highlighted ever before. Thus this research may be considered moderately novel.
The manuscript itself generally has a clear and logical structure. The title entirely corresponds with the contents of the manuscript. The abstract does summarize the findings, altough the reviewer recommends to extend the description of the brazing technology. The amount of the completed research allows to get a holistic picture of the object of the study, although the description of the experimental procedure should be expanded. The results themselves are presented in a logical manner, however, their analysis is sometimes too speculative. Conclusions generally correspond with the presented results and their analysis, however, they are sometimes written in a too speculative way. The number of references is sufficient. It is worth noting that 78% (eighteen references out of 23) are from 2017 and later years, what demonstrates the high relevance of this research. At the same time, the number of self-citations could be lower. Language and formatting are generally at a good level, although some corrections are still necessary.
To summarize, this manuscript deserves being published, however, a major revision will be mandatory. The reviewer's comments are listed below.COMMENTS TOWARDS TEXT.

1. Abstract: more details of the brazing process (brazing technology, form of the filler metal, etc.) should be added.
2. Abstract, line 6; Results -> Microstructural characterization of the joint, paragraph 4, line 8: what is meant under the 'Cu phase'? Was it a Cu-based solid solution?
3. Abstract, lines 10-11; Results -> Mechanical characterization, paragraph 7, lines 4-5: there is no evidence that crack propagated along the Cu4Ti grains. Therefore this statement must be deleted.
4. Keywords: 'brazing' and 'brazing joint' actually refer to one and the same issue, therefore the reviewer insists that only one keyword out of two must be left.
5. Introduction: the first three paragraphs and Fig. 1 must be deleted, as the principle focus of this manuscript is on brazed joints, not on mechanical testing.
6. Introduction: the authors must extend the description of the state-of-the-art in the current research field by citing more works, which highlight the same or similar studies. Also the novelty of this research must be stated in a clearer way.
7. Introduction, paragraph 4: may the joint, brazed using the 80Cu-20Ti filler, withstand a high temperature and radiation, which are characteristic to fusion power plants?
8. Introduction, paragraph 5, lines 4-5: what is meant here by [citation] "... some welding defects could be avoided by other mechanisms ..."?
9. Materials and Methods -> Materials, paragraph 1, line 3: 'correspondingly in EN standards and in UNS' must be deleted as non-informative.
10. Materials and Methods -> Materials, paragaph 2, line 2: the parameters of mill mixing should be added here.
11. Materials and Methods -> Brazing tests, lines 5-6: the text [citation] "... which allowed to adjust the sample into the grip of the shear fixture to minimize hte misalignment of the load with respect to the joint interface ..." must be deleted as irrelevant in the present context.
12. Materials and Methods -> Characterization techiques, line 10: g must be recalculated to N (g or gf isn't a SI unit in the present context).
13. Results -> Microstructural characterization of the joint: paragraph 1 must be omitted as non-informative.
14. Results -> Microstructural characterization of the joint, paragraph 2, lines 2-3: the sentence, starting with "The analysis of those figures ..." must be omitted as irrelevant in the present context.
15. Results -> Microstructural characterization of the joint, paragraph 3, lines 1-2: the first sentence in the paragraph must be deleted as non-informative.
16. Results -> Microstructural characterization of the joint, paragraph 3, lines 7-8 and Fig. 4c: in contrast to what is stated here, the traces of tungsten may be observed in the brazed joint.
17. Results -> Microstructural characterization of the joint, Fig. 4, caption: the full stop after 'brazed joint' must be replaced by comma; apparently 'Elemental distribution of Ti, W and Cu', not 'Elemental distribution of W, Ti and Cu'.
18. Results -> Microstructural characterization of the joint, paragraph 5, lines 3-4: 'bottom part of the joint', not 'bottom part of the image'.
19. Results -> Mechanical characterization: the first paragraph must be deleted as non-informative.
20. Results -> Mechanical characterization, paragraph 2, lines 3-6: was the recrystallization phenomenon considered as a reason for a lower hardness of the CuCrZr alloy after brazing?
21. Results -> Mechanical characterization, paragraph 2, lines 6-11: the last three sentences in the paragraph must be deleted as irrelevant in the present context.
22. Results -> Mechanical characterization, Fig. 6, vertical axis: 'Microhardness', not 'Hardness'.
24. Results -> Mechanical characterization, paragraph 5, lines 1-2: the text 'using the fixture described in Figure 2' must be deleted as non-informative.
25. Results -> Mechanical characterization, paragraph 7, line 7: 'strength properties', not 'adhesion properties'.
26. Results -> Mechanical characterization, paragraph 7, lines 7-8: the last sentence in the paragraph must be deleted as irrelevant.
27. Conclusions must be more concise and not contain speculative suggestions about thermal treatment (quenching and ageing) or brittle nature of tungsten.
28. Reference no. 6 seems to be not finished.

COMMENTS TOWARDS LANGUAGE.

1. Results -> Microstructural characterization of the joint, paragraph 3, lines 3-4: 'the heterogeneous microstructure that constituents the braze can be observed', not 'it can be observed the heterogeneous microstructure that constituents the braze'.
2. Results -> Microstructural characterization of the joint, paragraph 4, lines 3-4: the sentence [citation] "... This phase contains a dispersion of homogeneously distributed fine precipitates inside it ..." isn't understandable and must be reformulated.
3. Results -> Mechanical characterization, paragraph 2, lines 2-3: 'in the as-received condition', not 'in as-received conditions'.
4. Results -> Mechanical characterization, paragraph 2, line 6: probably 'to induce precipitation', not 'to produce a proper precipitation mechanism'.
5. Results -> Mechanical characterization, paragraph 3, line 3: 'could' and 'from softer to harder phases,' must be deleted.
6. Results -> Mechanical characterization, paragraph 3, line 4: 'associated with', not 'associated to'.
7. Results -> Mechanical characterization, paragraph 4, lines 3-4: 'Because of the refractory nature of this base material the temperatures reached', not 'The refractory nature of this base material provokes that the temperatures reached'.
8. Results -> Mechanical characterization, paragraph 4, line 5: 'could modify', not 'could modified'.
9. Results -> Mechanical characterization, paragraph 5, lines 5-6: the text [citation] "... Peng et al. also used Cu-Ti filler alloy with Ti richer contents to join also W-CuiCrZr materials obtaining 96 +- 18 MPa ..." isn't linguistically correct and must be reformulated.
10. Results -> Mechanical characterization, paragraph 6, lines 3-4: 'There is no presence', not 'There is not presence'.
11. Results -> Mechanical characterization, paragraph 7, line 1: the words 'a detail of' must be deleted.
12. Results -> Mechanical characterization, Fig. 8: 'c) SEM-BSE image at the CuCrZr side, d) elemental distribution map', not 'c) and d) Detail of the phases at the CuCrZr side, obtained by SEM-BSE detector and EDS elemental distribution map, respectively'.

COMMENTS TOWARDS FORMATTING.

1. Keywords: 'mechanical properties' must be written in the low case.
2. Materials and Methods -> Characterization techniques,
a) line 1: 'scanning electron microscope' must be written in the low case;
b) line 2: 'optical microscopy' must be written in the low case;
c) line 4: 'ammonia' must be written in the low case.
3. Results -> Mechanical characterization, paragraph 6, line 1: the comma after 'that' must be deleted.
4. Results -> Mechanical characterization, Fig. 8: the full stop after 'tungsten side' must be replaced by comma.
5. Reference no. 1: the author's surname must be written in the sentence case.
6. References no. 4, 8, 12: semicolons, separating the authors' surnames, must apparently be replaced by commas.
7. Reference no. 18: the spelling of the authors' surnames should be checked.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have answered all the questions, the paper can be accepted for publication

Author Response

Thank you for your time and effort

Reviewer 4 Report

This is the revised version of the manuscript, entitled "Microstructural and mechanical characterization of W-CuCrZr joints brazed with Cu-Ti filler alloy". The reviewer thanks the authors for the careful attention to his comments and agrees with all the authors' statements. By the reviewer's estimation, this manuscript may now be accepted for publication. However, the reviewer also assumes that few minor changes could be made to the text during the proofreading process:

1. Line 30: 'an acceptable wetting', not 'an acceptable wetting property'.
2. Lines 39-40: 'Tungsten ... acts', not 'Tungsten ... act'.
3. Lines 46-47: the reviewer suggests formulation 'some defects' instead of 'some welding defects'.
4. Line 56: 'copper', not 'cooper'.
5. Lines 56-62: the aims of the study could still be formulated here.
6. Line 68: rpm should be recalculated to s^(-1) (rounds per minute or rpm isn't a SI unit).
7. Line 72: the en dash (not hyphen, as currently) could be used to designate the thickness range.
8. Line 84: 'optical microscopy' should be written in the low case.
9. Line 88: 'ammonia' should be written in the low case.
10. Line 91: probably, 'three indentations were made for each microhardness value', not 'three indentations for each distance were made'.
11. Lines 95-96: 'Pure shear allows', not 'Pure shear allow'.
12. Lines 107-108: 'optical microscopy' should be written in the low case.
13. Lines 170-171: 'due to the fact that fracture has propagated', not 'due to the fracture has propagated'.
14. Line 171: probably 'tungsten grains', not 'tungsten grain'.
15. Fig. 8d: wasn't Cr or Zr meant here insead of Fe?
16. Lines 190-191: the words [citation] "..., which is enough to withstand the load of the tungsten monoblock, which will face the plasma ..." must be deleted, as no actual proof for that is provided.
17. Line 249: the reference no. 17 seems to be unfinished and must thus be corrected.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf