Corrosion Degradation Behaviors of Ti6Al4V Alloys in Simulated Marine Environments

Round 1

Reviewer 1 Report

Before presents a recommendation to improve of an interesting scientific article, I would like to present the following summary statements on the topic. Based on my long-term research and transfer profile in the field of holistic perception of the issues of innovative materials I consider the evaluated scientific article to be extremely topical and fully convergent with the following author's research and educational premise. Industry products should be constructs from materials designed, built, managed, maintained, recycled (decomposed) at a reasonable price, in reasonable quality, respecting the relevant requirements of users, residents and sustainable development. However, based on a detailed study of the reviewed manuscript, I evaluate it more as a conference paper than an article in a renowned scientific journal. In order for a paper to be accepted as a scientific article in a journal, the following mandatory requirements must be incorporated.

Mandatory requirements:

LNSA (Line number of the scientific article) 27-32...Titanium alloys have several considerable characteristics, such as high specific strength, light mass, excellent corrosion resistance and formability [1, 2], which make them a promising candidate material of these hot end components (e.g., blades) in the submarine and gas turbine sectors [3-9]… Indicate the specific areas of industry where these alloys have already been used more widely.

LNSA 41-42… after approximately 400 h salt spray exposure (LNSA 68..400h..The same notation must be used throughout the article, with or without spaces between numbers and physical units.

LNSA 63 ... 2. Materials and Methods. You must remove the period at the end of the title to make the title compatible with others chapter name.

LNSA 70-71… The solution in the salt spray chamber was… It is necessary to add a photo of the salt spray chamber or to specify it in more detail, a similar recommendations apply to other parts of the article.

LNSA 96-280… 3. Results and discussion ... this chapter, which makes up 62% of the text under consideration, without consideration of references, needs to be divided into several chapters. I recommend working on a separate chapter Discussion.

LNSA 124… Figure 1. Spray powder morphology and energy spectrum analysis… It is necessary to adjust the figures so that the numerical data for the scales used are visible.

LNSA 138… What does arb. units on Figure 3. XRD patterns of all tested samples?

LNSA 306-329… The conclusions need to be reworked, the abstracted knowledge must also be quantified numerically. I recommend the authors to avoid too general statements such as .... ...this alloy showed a satisfactory resistance to salt spray corrosion...suffered from a slight pitting ... during long period salt spray ... during high temperature ... ... in a severe weight loss....

LNSA 310-392… In the scientific articles I had the honor of reviewed for the MDPI publishing house, similar to my publishing activities, I am used to putting a dot at the end of references. Based on these facts, I would like to ask the authors to supplement this punctuation mark.

Facultative recommendations:

LNSA 2-3… I would like to recommend the authors change the name "Comparison on degradation behaviors of Ti6Al4V alloy in 2 simulated environments" for example to Corrosion degradation behaviors of Ti6Al4V alloys in simulated marine environments.

LNSA 10-22... For Abstract, I would like to present similar recommendations as I stated for the Conclusions, although in this part of the scientific contribution their incorporation is not so necessary, but it can be beneficial for readers. It would certainly be worth considering incorporating numerical or ratio quantifications of interesting findings of the authors. 

LNSA 64-69 ... The (α + β) type Ti6Al4V alloy was as the samples. The length, width and thickness of this sample were 15 mm, 15 mm and 5 mm, respectively ... For better clarity, it would be appropriate to give photos of used samples of titanium alloys.

LNSA 127 Fig. 3 shows the XRD patterns of all tested samples ... For each first use of an abbreviation (XRD) that is not generally known, it is necessary to explain what it represents.

LNSA 248-249... In addition, the significant difference in thermal expansion coefficients between the oxide layer and substrate.… It would be appropriate mathematically quantified ... he significant difference in thermal expansion.

The authors presented the scientific research results of the corrosion behaviours of Ti6Al4V alloys in simulated marine environments. In my opinion, the presented results contribute could contribute to the scientific credibility of the mentioned innovative material technology in the field of marine engineering. As already presented, the paper addresses an interesting scientific issue, but needs improvements in several parts, including the extension of the scope (one table in the whole article, 297 lines are fo me insufficient, ...), the composition and organization of the article also require significant changes. I present the minimalist requirements for improving the quality of the contribution as Mandatory recommendations. Despite several shortcomings, the evaluated article "Comparison on degradation behaviours of Ti6Al4V alloy in simulated environments" has a potential for its improvements. In case of incorporation of comments, or relevant justification of their non-incorporation, I am able to process a repeated review within 3 days.

Author Response

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Reviewer 2 Report

I have two remarks.

1. There is no information about the results of the XRD study in the Conclusion.

2. According to the XRD study (Figure 3), the diffraction peaks of sample H1 have the same position for TiO2 or Ti2O or alfa-Ti or (alfa+beta) phases. Why do the authors claim that in the H1 sample all of these phases, not one or two or three phases, are indeed presented, 

Author Response

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Reviewer 3 Report

The following issues must be addressed:

1. The last paragraph for Introduction must be improved in order to outline what is new and innovative in this work;
2. The weight percentage composition of each element in the alloy should be clarified;
3. Explain in more details the mechanism of degradation reactions during the hot salt - water vapour exposure;
4. There is any evidence of bulk degradation during the experiments?;
5. What about the stability of Ti2O product?;
6. Provide the XPS measurements to have a better evaluation of the products.

Author Response

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Reviewer 4 Report

In the manuscript under review, the authors raise an interesting issue concerning the corrosion degradation of Ti6Al4V alloys in the marine environment. It was found during the research that in the high-temperature oxidation test, an oxidation reaction occurs, resulting in an oxide layer appearing. The oxidation and degradation reactions simultaneously occurred during the high-temperature hot salt test. Analysis of received results allowed the proposed corrosion mechanism, which assumes hydrochloric acid (HCl) formation, further degraded the matrix metal and consequently led to a severe weight loss.
In my opinion, the manuscript can be accepted for publication in Coatings after major revision.

In my opinion, the paper requires the following amendments:

3. Results and discussion:

1) line 191-195: These are the oxides of Ti(IV) and Ti(II), and what about the oxide of Ti (III), i.e. Ti₂O₃. XPS studies of the passivation layer produced on the surface of the Ti6Al4V alloy indicate that it is formed by TiO₂-Ti₂O₃-TiO₂-Ti_(surface), respectively.
2) No XPS results. They are necessary for this type of research.
Best regards.
3) Has the formation of volatile chlorides somehow been confirmed?
4) Has the formation of degradation products (14)-(16) been confirmed?

Author Response

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Round 2

Reviewer 1 Report

Based on the incorporation of the changes recommended by me, I allow myself to rate the assessed second version of the scientific paper as follows. Reviewed contribution Corrosion degradation behaviours of Ti6Al4V alloys in simulated marine environments (Original title Comparison on degradation behaviours of Ti6Al4V alloy in 2 simulated environments), I rate it as excellent. Based on my experience in the assessed issue and subsequent deepening of my knowledge, I am pleased that the submitted 2nd version of the article meets all my essential requirements for a quality scientific article.

I am fully satisfied with the implementation of the required changes and recommendations and I hope that I have contributed a little to improving the quality of the assessed scientific contribution. In the final version of the article, it would be appropriate to remove the following minor formal deficiencies:

LNSA (Line number of the scientific article) 73...Table 1 Chemical composition of the original sample ( Wt. %)... From the aspect that in the scientific community in which I work it is not common to write the abbreviation ( Wt. %), I recommend authors consider spelling it out, or spelling out the whole word when using the abbreviation for the first time.

LNSA 79… Table 1 Chemical composition of the original sample ( Wt. %)… I recommend reformatting the text so that the entire table is on one page.

LNSA 96... and 10 °C /min...I recommend changing it to the format of writing physical units in the entire article, that is C/min.

In conclusion, I would like to sincerely congratulate the authors on an excellent scientific article and thank the publisher for the opportunity to expand my scientific knowledge. At the same time, I keep my fingers crossed for the authors in continuing their, for me, very current research, clarifying sustainable, circular economics in the fields of aerospace, biomedical and marine industries.

Based on the incorporation of the changes recommended by me, I allow myself to rate the assessed second version of the scientific paper as follows. Reviewed contribution Corrosion degradation behaviours of Ti6Al4V alloys in simulated marine environments (Original title Comparison on degradation behaviours of Ti6Al4V alloy in 2 simulated environments), I rate it as excellent. Based on my experience in the assessed issue and subsequent deepening of my knowledge, I am pleased that the submitted 2nd version of the article meets all my essential requirements for a quality scientific article.

I am fully satisfied with the implementation of the required changes and recommendations and I hope that I have contributed a little to improving the quality of the assessed scientific contribution. In the final version of the article, it would be appropriate to remove the following minor formal deficiencies:

LNSA (Line number of the scientific article) 73...Table 1 Chemical composition of the original sample ( Wt. %)... From the aspect that in the scientific community in which I work it is not common to write the abbreviation ( Wt. %), I recommend authors consider spelling it out, or spelling out the whole word when using the abbreviation for the first time.

LNSA 79… Table 1 Chemical composition of the original sample ( Wt. %)… I recommend reformatting the text so that the entire table is on one page.

LNSA 96... and 10 °C /min...I recommend changing it to the format of writing physical units in the entire article, that is C/min.

In conclusion, I would like to sincerely congratulate the authors on an excellent scientific article and thank the publisher for the opportunity to expand my scientific knowledge. At the same time, I keep my fingers crossed for the authors in continuing their, for me, very current research, clarifying sustainable, circular economics in the fields of aerospace, biomedical and marine industries.

Author Response

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Reviewer 3 Report

The manuscript can be published in the present form.

Author Response

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Reviewer 4 Report

I propose to accept this paper in present form.

Author Response

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