Tribological and Micromechanical Properties of the Nanostructured Carbonitride/Nitride Coatings of Transition Metals Alloyed by Hf and Nb

Round 1

Reviewer 1 Report

coatings-2168457

Tribological and micromechanical properties of the nanostructured carbonitride coatings deposited by advanced PVD technique

Good research work for the present scenario. The authors have done a detailed study on tribological performance and micromechanical properties of nanostructured smart coatings on multilayered alternating carbonitride/nitride bilayer system. The conclusion for the present research is that the multilayered NSC samples showed better performance compared to CN/N composite coatings.

1. Avoid using the term “we” in the technical manuscript. Check the whole manuscript and correct it. What is the reason behind selecting PVD technique and also particular on HiPIPMS for this study?

2. Some of the important literatures related to this study has been given below. Kindly go through and cite it in the manuscript.

https://doi.org/10.1007/s12633-019-00370-8

https://doi.org/10.1063/5.0000042

https://doi.org/10.3139/120.111271

https://doi.org/10.1504/IJMATEI.2019.101963

3. Table 1, Why is the reason behind selecting different thickness, PVD process duration, number of periods, etc for different sample combinations? What is the major inference from this table?

4. Many of the sentences were not clear and unable to understand because of poor language. The manuscript should be rewritten and proofread by the native english speaker.

5. Is there any structural change observed while adding metallic additives? The proof of the same for both the elements will add more value to the manuscript and clearly justify your current study.

6. The findings observed from Figures 1-4 should be explained in detail. More explanation which correlates your observation and technical data should be included in the manuscript.

7. Figure 6, in SEM images, there is no difference identified for batch 1-3 and for the batch 4-6. The markings indicating the changes in microstructure observed from the SEM images should be labelled and this figure should be altered.

8. The conclusion section should be explained more elaborately with major observations and findings from the experimental data. This section should be rewritten.

I, as a reviewer of this manuscript, will accept this manuscript for publication in “Coatings” after implementing the above corrections.

Author Response

Thank You for detailed review! The answers to Your questions are attached in file.

Author Response File: Author Response.docx

Reviewer 2 Report

Please see the enclosed comment file.

Comments for author File: Comments.docx

Author Response

Thank You for detailed review! The answers to Your questions are attached in the file.

Author Response File: Author Response.docx

Reviewer 3 Report

The authors investigated the thin films in order to determine tribological properties, microstructure, roughness and hardness. The main idea of the paper is to report the results of coatings dropped with Hf and Nb. The work lacks originality. The idea of the paper is not precisely stated. This paper failed to demonstrate any appreciable benefit compared to state-of-the-art. Moreover, the utilized research methods are insufficient. I don't recommend the publication.

Detailed comments on:

1. - The novelty of the paper is not sufficiently stated. 
2. - Coatings architecture is unclear, how many layers, the thickness of each layer and composition. Cross-sections of coatings are required. 
3. - Why you called these coatings "nanocomposite"? It must be clarified.
4. - Wear methodology seems inappropriate because the hardness of countersample is lower than coatings. 
5. - You should include the wear tracks (eg. SEM) or show the wear of counterballs.
6. - You should use the nanoindentation method for hardness measurements! Vickers provides to high indentation depth, higher than the thickness of the coating - see figs 1-4 which exceeds the thickness of the coating. 
7. - Table 1 - NSC 2 and 3 have almost similar thicknesses - explain it.
8. - Table 2 - what is "true hardness"? Expalin it. 
9. - table 2 - why is substrate hardness given in HRC unit and changes from 13.8 to 58.7 HRC? It is unacceptable because you have a different hardness of the substrate material.
10. - Paper contains unnecessary explanations of the measurement ideas of basic equipment L107-109; or L254-256
11. - XRD phase analysis should be employed in your research to show the structure of coatings.
12. - Table 3 - RSm paramterer is wroglny written (typo!) Paper contains too many typos.
13. - The scientific discussion of the results is missing - also, the selection of the literature references does not provide sufficient background.
14. - Conclusions summarise the research report and do not provide any new knowledge. 

Author Response

Thank You for detailed review! The answers to Your questions are attached in the file.

Author Response File: Author Response.docx

Reviewer 4 Report

If the question is asked, then please try to answer (or/and to give more information) in the paper.

1.       The English language needs some minor improvement. Examples: Page 1 “such tribological and anti-corrosive properties as hardness and wear resistance, thermal stability, and raised denitrification temperature”;

2.       It is not clear why in the body of paper the coating is named as “carbonitride/nitride” while in the title it is named as “carbonitride”.

3.       Page 1 “As mentioned above TiAlSiN nano composite films were deposited by several different PVD (Physical Vapor Deposition) 37 techniques.” Sorry, I cannot find where was it mentioned.

4.       Page 2. “These thin film coatings were deposited onto bearing steel substrates made of 100Cr6 and 107WCr5 type steels”. Please include this information into Table 1. Have you prepared two sets of samples?

5.       Page 2 “NSC based on carbonitride/nitride constituents (denoted here as {‐CN/‐N}) would theoretically be harder even than diamond‐type …”. Please provide the reference.

6.       Chapter 2.2. It is not clear why such hard coating was tested by much softer steel ball. Usually this leads only to the build-up of the steel layer transferred from ball. Please provide the hardness of the ball. Please provide the sample image of the wear track cross-section scan (2D or 3D).

7.       Page 3. “The wear tests were carried out under the same environmental conditions as the coefficient of friction tests.” Have you done separate tests for wear and for COF?

8.       Chapter 2.3. Please report the hardness loads also in “gf” since later you mention it in the Table 2, for example.

9.       Page 3. If you mention angle of HRC indenter, then please mention the radius as well.

10.   Please indicate in Table 1 same coatings structure as in Table 2. Probably there is no need to repeat structure and thickness in Table 2.

11.   Please provide the deviations of COF and other values.

12.   Table 2. Why hardness of substrate is so significantly different (13.8 vs 58.7)?

13.    Page 4. What is “sliding wear erosion”?

14.   Page 5 “The adhesion of the deposited NSC samples was determined by means of the Rockwell HRC test before tribological testing”. Do you think that it changed after wear test?

15.   Probably Figure 1 and 2 can be omitted if it shows the same information as Figure 3 and 4.

16.   Please improve visibility of text in Figure 5, especially for NSC-6.

17.   Figure 5. Why surface preparation was different? NSC-6 and 5 have deeper scratches. Please add average roughness of substrate into Table 3. Please add the deviations of values.

18.   It is not clear what numbers 761, 731, 7, 2 are meaning in Figures 7-9.

19.   Please rewrite the conclusions. Example: “In current investigation deposited and tested nanostructured thin film coatings (t<6300 nm) on bearing steel.” Probably: “Nanostructured thin film coatings with thickness less than 6300 nm were deposited on bearing steel and tested.”

Author Response

Thank You for detailed review! The answers to Your questions are attached in the file.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I have gone through the revised manuscript and completely not satisfied with the revision. The authors have not carefully addressed all the comments raised. The authors should address all the comments and cite the suggested important publication to add the quality of the manuscript. The manuscript is lagging with technical validation. The author should rework on all the above important aspects and submit the revised manuscript for possible consideration. Therefore, I recommend Major Revision. 

Author Response

Thank you for the second review. All your questions were carefully evaluated, and the answer was given to each one of them. As researchers, we are always open to fair scientific discussion and constructive criticism. We believe that the revised manuscript has been significantly improved, considering your recommendations and comments as well as those from other reviewers. Also, the language in the revised manuscript is significantly improved. We carefully reviewed your recommended articles, and in this specific case, we did not see how citing them would significantly improve the quality of the manuscript. Thus they have been added to our Department's digital library and will be considered as references for our future papers. If you did not see any improvements in our manuscript, maybe you accidentally opened a previous article version. 

Reviewer 2 Report

The amendments are acceptable, and therefore I recommend accepting the manuscript for publication.

Author Response

Thank you for the very useful comments that helped us improve the quality of the article significantly.

Reviewer 3 Report

Dear Authors,

thank you for your responses. Paper has been seriously improved and clarifications.

My comments on your paper and improvements.

1. The introduction has been improved and now shows the novelty. You can mention and point out that an interesting idea for improving the lifetime of steel tools is using a hybrid treatment i.e. combination of steel nitriding and coatings deposition, likewise stated in the following exemplary papers: https://doi.org/10.3390/ma16041594 and https://doi.org/10.3390/ma13214895

2. Q9- thank you for your improvements, I am glad that in the current version, you wrote that Rockwell test is used for stating the adhesion, not for coatings or PVD-covered substrate hardness measurement. 

3. Q10 - XRD could help you to understand the grain size, which may be useful for understanding the  wear results. Please reconsider it in your future works.

4. I hope you will use in future the nanoindentation method which is essential for PVD coatings characterization.

5. To understand tribological results you should combine and discuss the width of wear trace and area of wear identified in the steel counteraball. 

6. In the paper title you included "Tribological performance" but to achieve the goal, you should add the SEM of optical photos of wear traces of PVD coatings and discuss the wear mechanism. I strengthen the paper significantly. 

I hope my comments are useful for you in this and future work.

Author Response

Thank you for the very useful comments that helped us improve the quality of the article significantly.

We looked at the recommended articles on steel nitriding and coatings deposition. Thank you very much for the information, we found the articles really interesting and it is a food for thought for future research.

Yes, we agree that more emphasis should be placed on XRD and nanoindentation in future research in order to be able to fully describe the coatings and their mechanical properties.

We added a small discussion section on wear measurements and possible wear mechanisms. See highlighted text in the revised article. For this reason, we also added friction coefficient curves (see Appendix D) and SEM photos (see Appendix A). Also, in order not to mislead the potential readers of the article, we removed the word - performance from the title.

Thanks again for your constructive criticism and helpful comments/suggestions!