Tribocorrosion Behavior of γ′-Fe4N Nitride Layer Formed on Mild Steel by Plasma Nitriding in Chloride-Containing Solution
Round 1
Reviewer 1 Report
In this paper, thr tribocorrosion performance of mild steel was improved by using nitriding technology. The paper is well written and could be accepted after following questions are addressed.
1. Why wear from synergism between wear and corrosion is not included the equation 1?
2. Ref 22 is not relvent to the equation 1.
Author Response
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Author Response.pdf
Reviewer 2 Report
A well-written and organized manuscript, but the quality of figures can be improved. Based on the fact that the tribocorrosion performance of the γ’-Fe4N layer is significantly reduced by its local corrosion, the corresponding statements in the manuscript need modification. Minor revision is recommended.
1. Abstract. revise the sentence “The results show that at a cathodic potential, where mechanical wear is predominant, the total material removal (TMR) from the γ’-Fe4N layer is 37% smaller than that from the untreated MS, and at open circuit potential, TMR from the layer is 35% smaller than that from the untreated MS, while at an anodic potential, the γ’-Fe4N layer can reduce TMR from mild steel by 87%.” Be precise.
2. Provide the data to support the statement “X-ray diffraction analysis confirmed that the “white layer” at the surface was composed of γ’-Fe4N phase”. Fig.1 only presents optical images, it is not convincing.
3. Fig.2, mistakenly presents the “potentiodynamic scan rate 1 mV/s” in 2b, moving to 2a.
4. Fig. 3d-f, corrosion pit with large size, max width over 100 micrometers, depth over 15 micrometers. The thickness of the coating is around 5 micrometers. The local corrosion penetrates both the γ’-Fe4N layer and the diffusion layer. So, the conclusion that “the γ’-Fe4N layer is beneficial to the tribocorrosion” is inappropriate. Modification is recommended for part #5 of the conclusions, only state “but there is a concern” seems not respect the fact.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The article has a scientific character. The article deals with tribocorrosion properties of gamma'-Fe4N nitride layer formed on mild steel by plasma nitridi. The Authors applied correct research methods and used the appropriate measuring equipment. The content of the work is logically written, but they did not properly analyze the results obtained. The manuscript contains 13 figures and 4 tables. Figures and tables aren't properly prepared. Authors cited 37 literature sources, but among them there are no basic items on tribocorrosion, e.g. works by Mishler or Landolt. The authors presented an interesting work, but it requires numerous improvements to be of satisfactory quality.
1. The authors must clearly indicate the novelty of the work compared to the current state of the art.
2. Specify the data of the apparatus in the article in the following order: device designation, manufacturer's name, city, country.
3. In general, improve the discussion of the results obtained
4. Line 73 - the description of the carbon content in AISI 1020 mild steel is insufficient, provide the chemical composition in a separate table, enter the temperatures of the heat treatment used
5. Fig. 1 add the course of hardness depending on the distance from the surface
6. Line 91 "raw specimens" - this is normalized material and you should mark it as such throughout the work; "raw" - this is not an adequate term
7. Table 1 add the uncertainty of hardness determination and give the grain size for the structure
8. line 106 - explain in the text why you used a 1% solution instead of the often used 3.5% concentration; also explain how to select the parameters of the tribocorrosion test,
9. Line 127 describe the details of the tribotester used
10. Line 145 You repeated the test twice - why?, the uncertainty of determination for n-1=1 degrees of freedom according to the Student's test can give large error values.
11. Table 3 You must enter the wear rate in mm/yr or g/yr for the corrosion test
12. Chapter 3.2 Did you use a 1% NaCl solution in the Cathodic potential tests? It is not precisely described.
13. Fig. 11 Add error bars.
14. Formula 1 (line 378) is wrong, you have not taken into account the synergy component of corrosion and mechanical wear. The Watson model is commonly used to describe the tribocorrosion process. It is presented in the form: V_tribocorrosion=V_mechanical wear + Vcorr + Delta_V. Delta_V is a component of synergy. According to your formula 1 Vchem is actually Vcorr + Delta_V. You need to correct formula 1 and determine the Delta_V parameter.
15. Table 4 Vmech for nitrided and normalized steels is very similar, but these steels differ significantly in hardness. You haven't discussed this issue at all
15. Figures 5 and 6 Values in mm3 refer to volumetric wear? If so, mark it clearly in the drawing.
16. After the cathode potential test, you determined Vmech but the results between Fig. 5 and Tab. 4 are different.
Summary of comments
In general, you determined the mechanical and tribocorrosive wear correctly. In your work, however, you did not take into account the synergy effect, which may cause greater wear of the surface by oxides that are hard and intensify the wear process getting into the wear zone. You need to rethink chapter 4 and improve it. Re-submit your conclusions based on it. The current ones are not correct. Emphasizing the role of corrosion is wrong in my opinion. In your work, you did not mention the use of nitrided layers as anti-corrosion protection. You also did not analyze the consumption products.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Thank you for considering my comments. I will recommend the publication of the manuscript.
