Microstructure and Properties of MAO-Cu/Cu-(HEA)N Composite Coatings on Titanium Alloy
Round 1
Reviewer 1 Report
This paper describes an approach for coating titanium alloys with a compost coating. They use magnetron sputtering and add differing amounts of CuSO4 to prepare the coatings. They then test the films for anti-wear and anti-microbial behavior. A focus is on the use of seawater. There are some issues to address before acceptance.
Define Cu-(HEA)N in the abstract and in the paper. I do not know what this is.
For Figure 4, add vertical error bars.
For table 3, add error bars and discuss accuracy. Can they measure weight loss to 0.014%? Also I doubt it is a rate of weight loss if it is a percent. A rate is change per time.
Line 198 weightlessness rate makes no sense at all.
Figure 8. add vertical error bars.
More discussion of how Cu2O and how it kills bacteria is needed.
More information on how CuSO4 improves the coating, and its behavior is needed. What is the CuSO4 doing to generate the Cu2O? Expand the conclusions on this aspect of the work.
Author Response
1. Thanks to the reviewer for the reminder, and apologies for not first explaining the nomenclature of Cu-(HEA)N films, which stand for thin films formed on the surface of titanium alloys by simultaneous sputtering of Cu and high-entropy alloy nitrides. I have explained in line 65 of the text.
2. Thanks to the reviewers for the comment, I have added vertical error bars as shown in Figure 4.
3. Thanks to the reviewers for suggestions，I have added error bars in table 3. It is percent of weight loss, I have made the appropriate changes in the article and table.
4. Thanks to the reviewer for the reminder, I have replaced the weightlessness rate with the weight loss percent in line 198. The current position of weight loss percent is in line 206.
5. Thanks to the reviewers for the comment, I have added vertical error bars as shown in Figure 8.
6. Thanks to the reviewers for the comment. I have added an explanation of how Cu2O kills bacteria in lines 292-298 of the text. Expressed as “Studies have shown that reactive oxygen species (OH, H2O2 and O2-) produced by Cu2O may interact with bacterial cell membranes and promote bacterial permeation...”
7. Thanks for this advice of the reviewer. We have added the information on how CuSO4 improves the coating in lines 170-174.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Figure 9 d what are the defective structures here
What is the reason for abrupt behavior figure 8
For a General reader, figure 7 is not very clear
Please explain figure 6 with scientific logic
Table 3 data are not consistent
Figure 5 data are not clear. There is so much noise in it
What is the reason for the first increasing, remaining constant and decreasing behavior of figure 4
Figure 2 data are not consequential
Author Response
1. Thanks to the reviewer's question. We speculate that this may be due to the fact that as the copper sulphate concentration increases, the conductivity of the electrolyte increases, resulting in higher energy during the micro-arc oxidation reaction, thus changing the form of copper present in the coating to a more stable form of copper oxide or copper monomers, neither of which are as effective as cuprous oxide in inhibiting bacterial growth.
2. Thanks to the reviewer's advice. Figure 7 showed the macroscopic appearance of bacteria that have been cultured on the surface of the coating after being inoculated on the surface of the solid medium for a further 24h. The intensity of bacterial growth was representative of the bactericidal ability of the coating.
3. Thanks to the reviewer's comments. The explanation of the abrasion pattern of the coating has been added to the text in lines 227 to 232. Expressed as “The surface of the composite coating without the addition of CuSO4 has more micropores and larger bumps, with a large degree of wear on the grinding balls…”
4. Thanks to the reviewers for the suggestions，it is percent of weight loss, I have made the appropriate changes in the article and table.
5. Thanks to the reviewer's advices，and we have retested and plotted the friction coefficient curve for TC4 in figure 5.
6. Thanks to the reviewers for the suggestion. The addition of CuSO4 concentration promoted the creation of discharge channels, but the continued increase in CuSO4 concentration above 10g/L weakened the electrolyte and reduced the growth rate of the coating.
7. Thanks to the reviewers for the suggestion. The surface micromorphology of the coating is of some significance for a more complete interpretation of the coating.
Author Response File: Author Response.docx
Reviewer 3 Report
Dear Authors,
In this manuscript, the authors discusses about Microstructure and Properties of MAO-Cu/Cu-(HEA)N Composite Coatings on Titanium Alloy in which the wear resistance and antibacterial ability of the substrate in simulated seawater is enhanced. I have few comments to authors before considering further.
Please find my comments
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In Fig. 7, there is no bacteria visible in (b) and (c) and few bacteria are visible in (d) and (e). The authors claims that the antibacterial activity enhances with CuSO4 concentration or the antibacterial activity is almost same for all the CuSO4 samples?
Please use good quality figures so that the few bacterial colonies visible in (b) and (c). or the authors can count the bacterial colonies in each plates and draw a plot.
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The authors claims that increasing CuSO4 concentration causing the surfaces to be flat and smooth. Please provide any proof for this. May be surface roughness?
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Some issues in the XPS fitting of Cu 2p. The original spectra is missing at CuO peak region.
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Why the optical density increases for 10g/L than 5g/L? The authors claiming that the optical density decreased significantly with increasing CuSO4 concentration? Please justify
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Fig. 8 and 9 are contradictory. Fig 9 says that the bacterial attachment decreases with increasing CuSO4 content.
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Please add XPS fitting details.
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The peak value of the O 1s peak was detected at 530.45 eV and 532.09 eV in Fig. 3(c), confirming the existence of TiO2 and Cu2O. Please provide a reference.
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Is there any reason for less thickness for MAO coatings with high CuSO4 concentrations than 5g/L?
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Figure 1 needs to modified. Use different colours for TC4, MAO coating and MAO-Cu/Cu-(HEA)N composite coatings. You can simplify the MAO coating by showing the battery/cell on top.
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It seems that you are supplying DC voltage for the coating process? Please change the to AC supply if I am correct? How you connected the voltage supply?
Author Response
1. Thanks to the reviewers for the suggestion. The bacteria did not grow significantly on the surface of the solid medium after incubation on the surface of the coating containing CuSO4, indicating that the addition of CuSO4 had improved the antibacterial properties of the coating and that the bacteria had lost their activity after incubation on the coating and did not continue to reproduce and grow, at which point the effect of CuSO4 concentration was not significant.
2. Thanks to the reviewers for the suggestion. The surface of the solid medium in Fig. 7 (a) showed a large number of yellowish colonies, while other bacteria cultured on the surface of the coating are hardly present on the surface of the solid medium, so the surface of the solid medium show transparent.
3. Thanks to the reviewer's the advice, pores are a significant factor in the roughness and unevenness of the coating. The surface morphology of the coating showed that there were fewer holes in the surface of coatings after the addition of CuSO4 than without in figure 2, which may account for the smoothness of the coating.
4. Thanks to the reviewer's comment, I have modified the XPS fitting of Cu 2p in Fig. 3.
5. Thanks to the reviewer's question. We speculate that this may be due to the fact that as the copper sulphate concentration increases, the conductivity of the electrolyte increases, resulting in higher energy during the micro-arc oxidation reaction, thus changing the form of copper present in the coating to a more stable form of copper oxide or copper monomers, neither of which are as effective as cuprous oxide in inhibiting bacterial growth.
6. Thanks to the reviewers for the suggestion. Figure 9 focuses more on the morphology and distribution of the bacteria, while the optical density is more representative of the concentration of bacteria, as it is known that microscopic tissue can be observed more locally, we consider the optical density to represent the antibacterial effect of the coating.
7. Thanks to the reviewers for the advice. We have added XPS fitting details in lines 151-159. Expressed as “The XPS fit was carried out using advantage software, and the peak of C1s was used to calibrate the peak of each element….”
8. Thanks to the reviewers for the question, and We have cited the literature in line 162.
9. Thanks to the reviewer for the question. The addition of CuSO4 to the electrolyte promoted the creation of discharge channels, but the continued increase in CuSO4 concentration above 10 g/L weakened the electrolyte and reduced the growth rate of the coating.
10. Thanks to reviewer for the good advice, and we have used different colours and structures for TC4, MAO coating and MAO-Cu/Cu-(HEA)N composite coatings in figure 1.
11. Thanks to the reviewers for the question. In the micro-arc oxidation process, DC pulsed constant current mode is used. We have made additions to the text in lines 77-78.
Author Response File: Author Response.docx
Reviewer 4 Report
The observations of the article are:
1. In case of Titanium, it is useful in dental implant. Can this composite be applicable in dental implant in relation to osseointegration, biofilm formation protection and soft tissue integration. I think this application should be highlighted.
2. In case of marine application, different corrosion tests are required with details image and figures.
3. In Figure 2, the morphology is not clear and well structural trend. Beside this, there are some nanoporous conditions. If there is nanoporosity, in my opinion, this will not efficient for marine technology.
4. FTIR, AFM, XRD, TGA analyses are required. In case of XRD, what is the trend of coating, either it is crystalline or amorphous? How this character effect on marine technology.
5. The novelty of the work is not clearly defined in relation to other research. A comparison table is required to validate the results.
6. Why Titanium alloy with coating is used as we know now light weight material especially composite is effectively considered as promising material in marine field.
7. Correlate the different sea water conditions with this materials
8. What is the condition of slurry erosion and erosion corrosion? It sholud be tested.
8. Include the following references:
(i) Chowdhury, Mohammad Asaduzzaman, Nayem Hossain, Md Abdus Shahid, Md Jonaidul Alam, Sheikh Monir Hossain, Md Ilias Uddin, and Md Masud Rana. "Development of SiC–TiO2-Graphene neem extracted antimicrobial nano membrane for enhancement of multiphysical properties and future prospect in dental implant applications." Heliyon (2022): e10603.
(ii) Chowdhury, Mohammad Asaduzzaman, Nayem Hossain, Abdullah Al Masum, Md Sakibul Islam, Mohammad Shahin, Md Imran Hossain, Md Bengir Ahmed Shuvho, Md Ramjan Ali, AKM Foysal Ahmed, and Mr Rajib Nandee. "Surface coatings analysis and their effects on reduction of tribological properties of coated aluminum under motion with ML approach." Materials Research Express 8, no. 8 (2021): 086508.
Author Response
1. Thanks to the reviewer's the advice, I have added the application of titanium alloys in the field of medicine and implants in the text at lines 25 to 28.
2. This is a very good advice. We have carried out electrochemical tests in simulated seawater, but due to the high presence of Cu in the coating, the corrosion resistance of the composite coating is slightly worse than that of TC4, and our subsequent work programme will aim to improve the corrosion resistance of this composite coating. The results of the electrochemical experiments have been presented in the annex.
3. Thanks to the reviewer's comments, the coating was grown directly on the substrate with good metallurgical bonding despite the many nanopores on the surface of the micro-arc oxide coating, and the coating has better wear and corrosion resistance and antibacterial properties than the titanium alloy substrate, which was more beneficial for marine applications.
4. This is a good advice, we have performed XPS analysis on the coatings but adding FTIR, AFM, XRD, TGA analyses is difficult due to a number of factors and we hope you will understand.
5. Thanks to the reviewer's comments. Most of the titanium alloy coatings focus more on wear resistance and corrosion resistance, we also made a study on antibacterial properties in the paper. Micro-arc oxidation coating and high entropy alloy coating composite coating research is rare, and the combination of the both for the development of the field of composite coatings to increase the scope.
6. Thanks to the reviewer's comments, although light weight material was promising materials, light weight material was always exposed to wear and damage in practical applications, so it is necessary to develop coatings on its surface and also to beautify and modify the surface of the alloy.
7. Sincerely thanks to the reviewer for the reminder, but due to experimental factors it is difficult to carry out experimental comparisons in different sea water conditions at the moment, but this is our next work plan.
8. Thanks to the reviewer's suggestion, the focus of the test conditions in this thesis is biased towards seawater, slurry erosion and erosion corrosion will be in our next work plan, thank you for your good advice for the richness of the thesis.
9. Thanks for the reviewer’s good advice, and we have cited the above literature in lines 26 and 185 of the text.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
can be accepted
Author Response
Thank you for your comments!
Reviewer 3 Report
Dear Authors,
In the response of my Q.3, the author's statement about surface roughness is not correct. Please measure the surface roughness either using some image software or by AFM/profilometry. otherwise include a proper reference. We cannot just make a statement with out any proof.
Author Response
Many thanks to the reviewers for the suggestions. Micro-arc oxidation holes are created by the reaction of the base metal in the channel to form oxides, which are formed after melt ejection-cooling-solidification-phase change under the action of high temperature, high pressure as well as electric fields. According to the literature, volcano-shaped holes can lead to a rough surface of the coating, the relevant literature citations are in line 205 of the text.
Reviewer 4 Report
Although the part of the suggestions are incorporated with the results and according to the suggestions, some new experimentations were required, after logical justification of the authors, the article can be accepted in present form. But the suggestions should be incorporated in a subsection of results as Future Prospect and Challenges.
Author Response
Thanks to the reviewers' suggestions, and we have added future research directions and perspectives on coatings in lines 326-329.
