Study of the Effect of Various Heat Treatments and C Addition on the Microstructure and Hardness of CoCrFeNiAl_0.3Hf_0.02 High-Entropy Alloys

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The topic of the research is highly relevant and timely.  The manuscript investigates the microstructural evolution and mechanical properties of the CoCrFeNiAl7Hf0.4 high-entropy alloy (HEA), specifically focusing on the effects of Hafnium (Hf) and Carbon (C) additions combined with various heat treatment protocols. The study addresses the precipitation of Co2Hf phases and Cr23C6} carbides and their subsequent impact on the hardness of the matrix. In summary, while the scientific core of the work is solid and appropriate for the scope of the journal. I recommend a Major Revision to allow the authors to address these critical structural and stylistic deficiencies.

Section 1: Title and General Nomenclature

Comment 1: Regarding the title and throughout the manuscript, it is highly recommended to use the standard high-entropy alloy notation, such as CoCrFeNiAl7Hf0.4 instead of FeCoNiCrAl. This change will significantly improve the article's visibility in search databases. Additionally, since an alloy without Hf was not investigated, the title should be adjusted accordingly. Suggested Title: "Study of Various Heat Treatments and C addition on the Microstructure and Hardness of CoCrFeNiAl7Hf0.4 High Entropy Alloys".

Section 2: Introduction

Comment 2: The citation style must be updated. All references must strictly follow the MDPI formatting guidelines (please refer to the template on the journal’s website).

Comment 3 (Line 32): Please elaborate on the specific advantages provided by these alloys at this point. For instance: high hardness, excellent wear resistance, corrosion resistance, and thermal stability.

Comment 4: The authors should specify the potential application areas for the alloy under consideration and clearly define the problems or challenges that this research aims to solve.

Comment 5: Please justify the choice of this specific alloy system and its elemental proportions in comparison to others, such as medium entropy alloys (CoFeCuNi, FeAlCoCr), 1st generation HEAs (CoCrFeNiMn, AlCoCrFeNi), and 2nd generation HEAs (CoCrFeNiAl0.3, NbMoTaW, Fe50Mn30Cr10Co10). For example, CoCrFeNiAl0.3 is known for high hardness, significant oxidation resistance, and good mutual solubility [see: https://doi.org/10.1016/j.mtcomm.2024.110195; https://doi.org/10.1016/j.jallcom.2025.185642].

Comment 6: Briefly discuss different manufacturing methods for these alloys (e.g., Vacuum Arc Melting (VAM), Spark Plasma Sintering (SPS), Laser Additive Manufacturing (LAM), etc.) and state the advantages of the manufacturing method chosen for this study.

Comment 7: The second paragraph should begin by discussing existing post-casting heat treatment processes. For example: "Currently, to improve mechanical properties and enhance corrosion and abrasive wear resistance, the following types of heat treatment are used: ... []". Please support these statements with relevant references.

Comment 8 (Lines 46–47): The sentence "The emergence of high-entropy alloys was expected to conquer the challenge that traditional alloys are difficult to achieve both strength and toughness" should be moved to the first paragraph.

Comment 9 (After Line 72): The literature review requires a summary or intermediate conclusion. Briefly state the necessity of conducting comparative studies on the effects of heat treatment and the addition of Hf and C on the CoCrFeNiAl7Hf0.4 alloy. This will provide a logical transition to the research objectives.

Section 3: Materials and Methods

Comment 10 (Line 83): Grammatical error: "...and The chamber..." should be corrected (remove the redundant "and" or fix the capitalization).

Comment 11 (Lines 90–93): Please provide a justification for the selected heat treatment parameters. This should be supported either by citing previous publications or by referring to preliminary experimental data.

Comment 12: Please state the manufacturer and their location (city, state abbreviation, and country) for all equipment used in the study.

Section 4: Results and Discussion

Comment 13 (Figure 1): In the caption for Figure 1, change the alloy designations from FeCoNiCrAlHf to CoCrFeNiAl7Hf0.4 and from FeCoNiCrAlHfC to CoCrFeNiAl7Hf0.4C1.2. Apply these corrections consistently throughout the entire text.

Comment 14: Please provide a more detailed description correlating the changes in phase composition from XRD diffraction patterns with the obtained SEM microstructure images for both the base alloy and the C-doped alloy under different processing conditions.

Comment 15 (Figures 2 and 3): Instead of using labels (a, b, c) to denote different magnifications of the same SEM sample, please use indices such as (a1, a2, a3). The same applies to samples from different processes.

Comment 16 (Figure 2): In the title/caption of Figure 2, change the designation from FeCoNiCrAlHf to CoCrFeNiAl7Hf0.4. Ensure consistency throughout the manuscript.

Comment 17 (Figure 3): In the title/caption of Figure 3, change the designation from FeCoNiCrAlHfC to CoCrFeNiAl7Hf0.4C1.2. Ensure consistency throughout the manuscript.

Comment 18 (Figures 4–7): Please clearly indicate the specific regions or points on the figures where the corresponding elemental phase compositions were measured.

Section 5: References

Comment 19: References must be formatted according to the MDPI house style. Please refer to the "Instructions for Authors." Example format: Ulbrich, D.; Kowalczyk, J.; Josko, M.; Sawczuk, W.; Chudyk, P. Assessment of selected properties of varnish coating of motor vehicles. Coatings 2021, 11, 1320. https://doi.org/10.3390/coatings11111320

Comments on the Quality of English Language

Comment 1 (Line 13) In the Abstract, the phrase "The heat treatment did not modified" contains a grammatical error. It should be corrected to: "The heat treatment did not modify".

Comment 2 (Line 14) In the Abstract, the phrase "which remains the FCC structure" is stylistically inaccurate. It is recommended to change it to: "retains the FCC structure".

Comment 3 (Line 26) In the Introduction section, the sentence "Their notable feature origin from" is grammatically incorrect. It should be: "Their notable features originate from".

Comment 4 (Line 108) In the Results section, the phrase "undergo different heat treat-ment processes" should be revised to: "undergoing different heat treatment processes".

Comment 5 (Line 125) The phrase "which is in fact have a skeleton-like manner" is grammatically incorrect. It should be replaced with: "which in fact has a skeleton-like morphology".

Comment 6 (Line 182) Spelling error: "disslsoved" should be corrected to "dissolved".

Comment 7 (Line 212) Spelling error: "formstion" should be corrected to "formation".

Author Response

Comment 1: Regarding the title and throughout the manuscript, it is highly recommended to use the standard high-entropy alloy notation, such as CoCrFeNiAl₇Hf_0.4 instead of FeCoNiCrAl. This change will significantly improve the article's visibility in search databases. Additionally, since an alloy without Hf was not investigated, the title should be adjusted accordingly. Suggested Title: "Study of Various Heat Treatments and C addition on the Microstructure and Hardness of CoCrFeNiAl_0.3Hf_0.4 High Entropy Alloys".

Response 1: We thank the reviewer for this important observation. In the revised manuscript, we have changed the title to “Study of Various Heat Treatments and C addition on the Microstructure and Hardness of CoCrFeNiAl_0.3Hf_0.02 High Entropy Alloys”. And we have replaced all FeCoNiCrAl in the text with the more standard CoCrFeNiAl_0.3.

Comment 2: The citation style must be updated. All references must strictly follow the MDPI formatting guidelines (please refer to the template on the journal’s website).

Response 2: We are very grateful to the reviewer for pointing out this point. We have updated all citation style by referring to the MDPI template on the journal's website to ensure their correct usage.

Comment 3: Please elaborate on the specific advantages provided by these alloys at this point. For instance: high hardness, excellent wear resistance, corrosion resistance, and thermal stability.

Response 3: In the revised version, we have emphasized the excellent properties of high-entropy alloys, such as high strength and high toughness. The changes can be found in Lines 32-37.

Comment 4: The authors should specify the potential application areas for the alloy under consideration and clearly define the problems or challenges that this research aims to solve.

Response 4: Thank you to the reviewer for this suggestion. We have added the potential application fields of the studied alloy in the revised version (refer to Lines 37-39). This study aims to explore the changes in the microstructure and properties of high-entropy alloys at high temperatures, as well as the impact of carbide formation on the alloys.

Comment 5: Please justify the choice of this specific alloy system and its elemental proportions in comparison to others, such as medium entropy alloys (CoFeCuNi, FeAlCoCr), 1st generation HEAs (CoCrFeNiMn, AlCoCrFeNi), and 2nd generation HEAs (CoCrFeNiAl_0.3, NbMoTaW, Fe₅₀Mn₃₀Cr₁₀Co₁₀). For example, CoCrFeNiAl_0.3 is known for high hardness, significant oxidation resistance, and good mutual solubility [see: https://doi.org/10.1016/j.mtcomm.2024.110195; https://doi.org/10.1016/j.jallcom.2025.185642].

Response 5: Thank you very much to the reviewer for the literature recommendations. We have added references to the above-mentioned literature in the revised version (references21,22). In lines 65-81, we have discussed in detail the current research status of CoCrFeNiAl series high-entropy alloys to illustrate that it is reasonable to choose this specific alloy system.

Comment 6: Briefly discuss different manufacturing methods for these alloys (e.g., Vacuum Arc Melting (VAM), Spark Plasma Sintering (SPS), Laser Additive Manufacturing (LAM), etc.) and state the advantages of the manufacturing method chosen for this study.

Response 6: We are very grateful to the reviewers for pointing out this omission. We have already added an introduction and discussion on the mainstream manufacturing methods of high-entropy alloys in the revised version (refer to Lines 40-53).

Comment 7: The second paragraph should begin by discussing existing post-casting heat treatment processes. For example: "Currently, to improve mechanical properties and enhance corrosion and abrasive wear resistance, the following types of heat treatment are used: ... []". Please support these statements with relevant references.

Response 7: Thank you to the reviewer for pointing out this issue. In the revised version, we have adjusted the logic of this paragraph and cited relevant references to explain the influence of heat treatment processes on the properties of high-entropy alloys (refer to Lines 82-98).

Comment 8: The sentence "The emergence of high-entropy alloys was expected to conquer the challenge that traditional alloys are difficult to achieve both strength and toughness" should be moved to the first paragraph.

Response 8: Thank you to the reviewer for pointing out the logical issues in the paper. The above sentences have been adjusted to appropriate positions in the revised version to make the paper's logic more coherent and reasonable (refer to Lines 54-55).

Comment 9: The literature review requires a summary or intermediate conclusion. Briefly state the necessity of conducting comparative studies on the effects of heat treatment and the addition of Hf and C on the CoCrFeNiAl₇Hf_0.4 alloy. This will provide a logical transition to the research objectives.

Response 9: Thank you to the reviewers for pointing out this issue. In the revised version, we have adjusted the logic of this paragraph and cited relevant references to explain the influence of heat treatment processes on the properties of high-entropy alloys (refer to Lines109-114).

Comment 10: Grammatical error: "...and The chamber..." should be corrected (remove the redundant "and" or fix the capitalization).

Response 10: Thank you to the reviewers for pointing out the issues with word choice and grammar. The revised version has been revised to appropriate sentences (refer to Line124).

Comment 11: Please provide a justification for the selected heat treatment parameters. This should be supported either by citing previous publications or by referring to preliminary experimental data.

Response 11: The heat treatment parameters used in the text were obtained from the preliminary experiments and are mentioned at lines 137 to 139.

Comment 12: Please state the manufacturer and their location (city, state abbreviation, and country) for all equipment used in the study.

Response 12: Thank you to the reviewers for pointing out the issues in the paper. The revised version has already indicated the manufacturers of all the instruments used and their locations.

Comment 13: In the caption for Figure 1, change the alloy designations from FeCoNiCrAlHf to CoCrFeNiAl₇Hf_0.4 and from FeCoNiCrAlHfC to CoCrFeNiAl7Hf_0.4C_1.2. Apply these corrections consistently throughout the entire text.

Response 13: We have modified the labels of the high-entropy alloys in the entire text to the more standard versions (such as CoCrFeNiAl_0.3Hf_0.02 and CoCrFeNiAl_0.3Hf_0.02C_0.06) and ensured consistency throughout the text.

Comment 14: Please provide a more detailed description correlating the changes in phase composition from XRD diffraction patterns with the obtained SEM microstructure images for both the base alloy and the C-doped alloy under different processing conditions.

Response 14: We have accepted the reviewer's suggestion. In the revised version, the corresponding analysis section is described in more detail.

Comment 15: Instead of using labels (a, b, c) to denote different magnifications of the same SEM sample, please use indices such as (a1, a2, a3). The same applies to samples from different processes.

Response 15: We have changed the original (a), (b), and (c) labels in Figures 2 and 3 to (a1), (a2), and (a3) labels to represent different magnifications of the same SEM sample (refer to Figures 2 and 3).

Comment 16: In the title/caption of Figure 2, change the designation from FeCoNiCrAlHf to CoCrFeNiAl₇Hf_0.4. Ensure consistency throughout the manuscript.

Response 16: We have modified the labels of the high-entropy alloys in the entire text to the more standard versions and ensured consistency throughout the text.

Comment 17: In the title/caption of Figure 3, change the designation from FeCoNiCrAlHfC to CoCrFeNiAl7Hf_0.4C_1.2. Ensure consistency throughout the manuscript.

Response 17: We have modified the labels of the high-entropy alloys in the entire text to the more standard versions and ensured consistency throughout the text.

Comment 18: Please clearly indicate the specific regions or points on the figures where the corresponding elemental phase compositions were measured.

Response 18: In the revised version, we have detailed the specific locations or areas measured in Figures 4-7, such as lines 179-180 and 219-220.

Comment 19: References must be formatted according to the MDPI house style. Please refer to the "Instructions for Authors." Example format: Ulbrich, D.; Kowalczyk, J.; Josko, M.; Sawczuk, W.; Chudyk, P. Assessment of selected properties of varnish coating of motor vehicles. Coatings 2021, 11, 1320. https://doi.org/10.3390/coatings11111320

Response 19: We have updated all citation style by referring to the MDPI template on the journal's website to ensure their correct usage.

Comment 20:Comments on the Quality of English Language

Response 20: We sincerely apologize for the language issues. The manuscript has now been thoroughly revised by a native English‑speaking colleague with expertise in materials science. All changes in wording and sentence structure are marked in yellow. We believe the readability and clarity have been greatly improved. Highlights of major revisions include: restructuring the methodology section for logical flow and clarifying ambiguous phrases in the discussion.

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript investigates the influence of Hf and C micro-alloying on the microstructure and Vickers hardness of FeCoNiCrAl-based high-entropy alloys (HEAs) across three states (as-cast, solution-treated at 1210 °C/10 h, and aged at 800 °C/24 h). The work uses vacuum arc melting and standard characterization (XRD, SEM-BSE, TEM-EDS/SADP) to show that (i) both alloys retain an FCC matrix with Co₂Hf in the as-cast condition, (ii) solution treatment dissolves Co₂Hf, and (iii) C addition enables intergranular Cr₂₃C₆ precipitation during aging, raising hardness to 224.64 HV (200 g load). The topic is relevant to precipitation-strengthened HEAs for structural applications.

The study directly compares Hf-only vs. Hf+C variants under identical processing/heat-treatment conditions, isolating the role of C in carbide formation. TEM/SADP confirms Cr₂₃C₆ identification (Fig. 8) and shows dissolution of Co₂Hf during solution treatment—consistent with literature on refractory-element stabilization in FCC HEAs. The ~50% hardness increase in the C-containing aged alloy (HfC-a) is quantitatively impressive and attributed to intergranular Cr₂₃C₆, offering a straightforward strengthening route. Combination of XRD (phase identification), BSE-SEM (morphology), and TEM-EDS/SADP (local chemistry/structure) is suitable for the scope.

The scientific core is acceptable, but the manuscript requires substantial rewriting, additional quantitative analysis, statistical treatment, and English editing before it can be considered for publication. I recommend returning it to the authors with the above points explicitly addressed in a point-by-point response. A revised version with corrected data presentation and improved language would likely reach the standard required by Coatings.

Authors should address these weaknesses:

• No volume fraction, size distribution, or inter-particle spacing of Co₂Hf / Cr₂₃C₆ / NiAl phases. Hardness trends (Fig. 9) cannot be rigorously linked to microstructure without these metrics. Use ImageJ or equivalent to report phase volume fractions, average particle sizes, and spacing from ≥10 SEM/TEM fields per condition.

• Hardness values reported as single numbers (Fig. 9) with no error bars, standard deviations, or number of indents per condition. TEM/SEM images are single fields only. Report hardness as mean ± SD (minimum 5–10 indents per sample). Add error bars to Fig. 9.

• XRD shows “weak peaks” for Co₂Hf but no Rietveld quantification. EDS tables (Tables 3–6) list compositions without uncertainty or statistical validation.

• Only Vickers microhardness (200 g); no macro-hardness, tensile/compression, or wear data. Claim of “very remarkable strengthening” is unsupported by broader properties. Add at least one macro-mechanical test (e.g., compression) to support the “remarkable strengthening” claim.

• Why does C promote Cr₂₃C₆ only during aging? No discussion of C solubility, diffusion kinetics, or comparison to literature on C-doped HEAs (e.g., Refs. 20–23). Explain C-driven Cr₂₃C₆ formation (thermodynamics, C solubility limits, grain-boundary segregation). Compare hardness gains with literature on C-doped HEAs. Discuss limitations (e.g., embrittlement risk from intergranular carbides).

• Vacuum arc melting details are vague (“repeatedly melted 6 times”). No ingot size, cooling rate, or homogeneity verification (e.g., multiple EDS scans). Specify exact arc-melting parameters (current, number of flips, crucible type), ingot dimensions, and exact cooling rates. Clarify “air-cooled” vs. “furnace-cooled”.

• No thermocouple calibration, atmosphere control, or cooling-rate data for “air-cooled” and “furnace-cooled” steps.

• XRD scan rate (4°/min) is unusually fast for precise peak fitting; no mention of sample preparation for TEM (electropolishing conditions are given but incomplete). Add scale bars to all micrographs. Provide complete, self-contained captions. Format tables uniformly (include units, uncertainties).

• Heavy non-native phrasing throughout (e.g., “did not modified”, “the HEAs both contains”, “auther: rzliu@imr.ac.cn”, “in-furnace to room temperature”). Many run-on sentences and awkward constructions. 

• Alloy notation varies (FeCoNiCrAlHf vs. FeCoNiCrAl0.3Hf0.02); phase labels inconsistent (Co₂Hf vs. Ni-Hf). Rewrite for grammatical correctness and scientific tone. Use consistent alloy notation (e.g., FeCoNiCrAl₀.₃Hf₀.₀₂ and FeCoNiCrAl₀.₃Hf₀.₀₂C₀.₀₆).

• Some references lack DOIs or full details; several are only marginally relevant. Ensure all are up-to-date and include DOIs where available. Verify accuracy of cited works (e.g., Ref. 9, 10 appear incomplete).

Author Response

Comment 1: No volume fraction, size distribution, or inter-particle spacing of Co₂Hf / Cr₂₃C₆ / NiAl phases. Hardness trends (Fig. 9) cannot be rigorously linked to microstructure without these metrics. Use ImageJ or equivalent to report phase volume fractions, average particle sizes, and spacing from ≥10 SEM/TEM fields per condition.

Response 1: Thank you to the reviewers for pointing out the issue of insufficient verification rigor. In the revised version, the volume fractions corresponding to the Co₂Hf, C₂₃C₆ and NiAl phase analyzed by the Image J software have been added (refer to Lines 174-176, Lines 181-182 and Lines 204-209).

Comment 2: Hardness values reported as single numbers (Fig. 9) with no error bars, standard deviations, or number of indents per condition. TEM/SEM images are single fields only. Report hardness as mean ± SD (minimum 5–10 indents per sample). Add error bars to Fig. 9.

Response 2: In the revised version, we have added detailed instructions for the hardness test. Each sample has 9 indentations, and the average of them is reported. The error bar in Figure 9 has also been added.

Comment 3: XRD shows “weak peaks” for Co₂Hf but no Rietveld quantification. EDS tables (Tables 3–6) list compositions without uncertainty or statistical validation.

Response 3: Thank you to the reviewers for pointing out this issue. However, due to the uneven distribution of Co₂Hf within the alloy, and minor volume of the Co₂Hf phase, the results obtained from quantitative analysis only by XRD have difficulty to quantification for us. The EDS analysis was conducted by Oxford EDS (INCA), the results did not give statistical validation, unlike the results obtained from EDAX EDS. We are very sorry for the uncertainty of the EDS analysis.

Comment 4: Only Vickers microhardness (200 g); no macro-hardness, tensile/compression, or wear data. Claim of “very remarkable strengthening” is unsupported by broader properties. Add at least one macro-mechanical test (e.g., compression) to support the “remarkable strengthening” claim.

Response 4: You are absolutely correct. In the revised version, we supplemented the macroscopic hardness test to measure the macroscopic Rockwell hardness of the alloy (refer to Pages 10-11).

Comment 5: Why does C promote Cr₂₃C₆ only during aging? No discussion of C solubility, diffusion kinetics, or comparison to literature on C-doped HEAs (e.g., Refs. 20–23). Explain C-driven Cr₂₃C₆ formation (thermodynamics, C solubility limits, grain-boundary segregation). Compare hardness gains with literature on C-doped HEAs. Discuss limitations (e.g., embrittlement risk from intergranular carbides).

Response 5: Thank you to the reviewer for pointing out this issue. We have added a detailed analysis of carbides in the revised version (refer to Lines 260-265).

Comment 6: Vacuum arc melting details are vague (“repeatedly melted 6 times”). No ingot size, cooling rate, or homogeneity verification (e.g., multiple EDS scans). Specify exact arc-melting parameters (current, number of flips, crucible type), ingot dimensions, and exact cooling rates. Clarify “air-cooled” vs. “furnace-cooled”.

Response 6: Regard to this issue, in the revised version, we have detailed the melting and casting conditions and processes of high-entropy alloys in lines 121 to 131 of the text.

Comment 7: No thermocouple calibration, atmosphere control, or cooling-rate data for “air-cooled” and “furnace-cooled” steps.

Response 7: The parameter settings and temperature changes during alloy melting and casting have been provided in lines 126 to 130. The temperature data of the subsequent heat-treated specimens are given in lines 135 to 137. Due to the limitations of the test equipment, the cooling rate of the sample cannot be provided in real time; only the time spent on cooling can be offered.

Comment 8: XRD scan rate (4°/min) is unusually fast for precise peak fitting; no mention of sample preparation for TEM (electropolishing conditions are given but incomplete). Add scale bars to all micrographs. Provide complete, self-contained captions. Format tables uniformly (include units, uncertainties).

Response 8: Thank you to the reviewer for pointing out the format issues of the paper. In the revised version, we checked and added scale bars to all microscopic images to ensure the uniformity of the entire text format. We have added some details on the preparation of the films used in the TEM analysis. For the analysis of XRD, we have no plenty of time to conduct it again, and the speed of scan is generally acceptable for normal phase analysis. 

Comment 9: Heavy non-native phrasing throughout (e.g., “did not modified”, “the HEAs both contains”, “auther: rzliu@imr.ac.cn”, “in-furnace to room temperature”). Many run-on sentences and awkward constructions. 

Response 9: We sincerely apologize for the language issues. The manuscript has now been thoroughly revised by a native English‑speaking colleague with expertise in materials science. All changes in wording and sentence structure are marked in yellow. We believe the readability and clarity have been greatly improved. Highlights of major revisions include: restructuring the methodology section for logical flow and clarifying ambiguous phrases in the discussion.

Comment 10: Alloy notation varies (FeCoNiCrAlHf vs. FeCoNiCrAl_0.3Hf_0.02); phase labels inconsistent (Co₂Hf vs. Ni-Hf). Rewrite for grammatical correctness and scientific tone. Use consistent alloy notation (e.g., FeCoNiCrAl₀.₃Hf₀.₀₂ and FeCoNiCrAl₀.₃Hf₀.₀₂C₀.₀₆).

Response 10: Thank you to reviewer for this suggestion. We have replaced all high-entropy alloy notation in the text with the more standard CoCrFeNiAl_0.3, CoCrFeNiAl_0.3Hf_0.02, CoCrFeNiAl_0.3Hf_0.02C_0.06. And we make sure that all the phase labels are consistent.

Comment 11: Some references lack DOIs or full details; several are only marginally relevant. Ensure all are up-to-date and include DOIs where available. Verify accuracy of cited works (e.g., Ref. 9, 10 appear incomplete).

Response 11: We have updated all citation style by referring to the MDPI template on the journal's website to ensure their correct usage. Make sure all cited references are relevant to the paper and include DOIs where available.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The article is well written and can be recommended for publication.

Author Response

Thank you very much for your valuable comments and suggestions on our manuscript (Manuscript ID: coatings-4262570). We have carefully considered all the points raised by the Academic Editor and reviewers. We have revised the manuscript accordingly. Below we provide our point‑by‑point responses. All changes in the revised manuscript have been marked in yellow.

Reviewer 2 Report

Comments and Suggestions for Authors

All the changes made by authors are good and I recommend this manuscript for publication. 

Author Response

Thank you very much for your valuable comments and suggestions on our manuscript (Manuscript ID: coatings-4262570). We have carefully considered all the points raised by the Academic Editor and reviewers. We have revised the manuscript accordingly. Below we provide our point‑by‑point responses. All changes in the revised manuscript have been marked in yellow.