Wear Resistance Behavior of Low-, Mid-, and High-Phosphorus Electroless Ni-P Coatings Heat-Treated in the Air Environment

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript ID: coatings- 2988736-v1

The introduced manuscript under the title of “Wear resistance behavior of low-, mid-, and high-phosphorus electroless NiP coatings heat-treated in the air environment” aimed to improve the wear resistance of electroless NiP coatings deposited on steel substrates, especially in high-temperature conditions. The authors varied the phosphorus content in the coatings and applied heat treatment to determine the optimal combination for enhancing wear resistance.

The following suggestions may improve the proposed manuscript:

Abstract section:  

1.     Specify the actual phosphorus value.

2.     State the substrate type and clarify the NiP coatings' application.

3.     Support the key results with numerical values to validate the improvement and highlight the research's novelty.

Introduction section:

1.     Justify the importance of heat treatment (annealing) for NIP coatings in the intended application.

Results section:

1.     Discuss the impact of Ni and Fe diffusion on coatings-substrate adhesion strength, evidenced by observed Fe and Ni diffusion at the interface (Lines 213-214).

2.     Explore the influence of the Ni3P phase on film hardness, considering chemical bonding. XPS or Raman analysis could provide valuable insights.

3.     For accurate elemental composition determination within coatings, prefer XPS survey analysis, benefiting from surface data compared to EDS, which offers bulk data.

4.     Consider utilizing scratch tests or abrasive powder blasting for adhesion evaluation.

5.     Incorporate friction/wear measurements of the substrate for comparison.

Conclusion:

1.     Enhance the conclusion section by incorporating numerical values and elucidating the mechanisms underlying each change in the properties of NiP coatings.

References:

1.     Please, use more recent references.

Summary:

The manuscript exhibits an engaging and well-organized structure, making it worthy of publication in the coating journal, especially upon incorporating the provided suggestions.

Author Response

Please find attachment for response of reviewer comments

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors presented the results of a series of experimental studies to determine the changes in wear resistance resulting from the heat treatment of electrodeless Ni-P coating layers with low, medium, and high phosphorus content in an oxygen environment. The study involves extensive laboratory work. However, I believe some major deficiencies must be addressed before acceptance.

-The abstract should provide brief and concise information about the characterization methods used. Additionally, it should include numerical results that express the critical findings obtained.

-In the Introduction section, it is important to emphasize which approximate values of P ratios represent low, medium, and high P ratios. Moreover, the literature contains numerous studies on the mechanical and tribological properties of electrodeless Ni-P coatings (with varying P ratios) subjected to heat treatment in oxygen environments at different temperatures. The exact novelty of the current study is not fully apparent. What precisely is lacking in the literature and which gap is being filled? The answer to this question should be clearly provided in the last paragraph of the Introduction section. 

- 2.1 Electroless Ni plating.... I think it is Ni-P plating not Ni plating.

-Give details for the mechanical pre-treatment of the substrate steel. For example, what meshes was it sanded with? Also, provide the chemical composition of the substrate material. Give the molarity of the chemicals used for the electrochemical degreasing process. Also, how did you determine the ratio of chemicals used in coatings containing low, medium, and high P? What is the mechanism for changing the P ratio without changing the reducing agent (sodium hypophosphite) ratio (for low and medium P production)? The use of these chemicals and the determination of the rates for P production at all rates should be shown and explained with reference to the literature in the experimental section.

-Page 3 , lines between 101-108, 'Two categories of heat treatment were performed: (a) at 400 C/1h and (b) at 400 C/1h,.....' and 'The specimens heat-treated at 400 C and 400 C followed by....' 400 and 400 ? What does it mean?'

-How can you only determine the hardness of the coating layer by applying a 100 g Vickers hardness load? At this load, doesn't the hardness tip start to act on the substrate material by piercing or deforming the coating?

-2.5 Tribology and wear test... it describes the same things, 'tribology' and 'wear.' Please use one of them.

-The authors state that the hardness of the steel ball, which is the abrasive counter surface, is 848 HV. They also increased the hardness values of the resulting Ni-P coatings to over 1000 HV. So, doesn't a counterball body with a hardness lower than the coating hardness deform during wear? Shouldn't a counter body harder than the coating layer be used for wear tests? When looking at the wear results, ball wear values are also given because the coatings are harder and corrode the ball. Why wasn't a harder ball used instead? Additionally, harder coatings showed less wear on the ball. How did the harder coating result in lower wear on the softer ball?

-For Figure 1, SEM images rather than optical images should be presented so that the Ni-P nodules can be clearly seen. An image of the substrate surface without coating should also be presented. Morphological images should also be provided for HT400-LP, HT400-MP, and HT400-HP samples.

-Figure 2 should also include the results obtained for the HT400-LP, HT400-MP and HT400-HP samples.

-When examining the results obtained in the study, it is not entirely clear what the uniqueness of the research is. The authors' work seems to demonstrate that the heat treatment at 400°C is the most suitable thermal treatment, as both the wear and mechanical properties are achieved at this temperature. The literature has already reported that heat treatment at this temperature is the most effective. The authors do not understand the purpose of the heat treatment at 650°C. Additional papers addressing this issue should be added; otherwise, I believe the publication would not be accepted.

-Debris examination is one of the most effective and critical characterization methods in determining wear mechanisms. SEM images showing debris examination should be submitted.

Author Response

Please find attachment for response of reviewer comments

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript ID: coatings- 2988736-V2

The following suggestions should be considered to improve the proposed manuscript:

Results section:

1.   Discuss the impact of Ni and Fe diffusion on coatings-substrate adhesion strength, as evidenced by observed Fe and Ni diffusion at the interface (Page 7; lines 243-246). To solidify these claims, it's crucial to base them on your actual measured data. Comparing your results with similar findings in other research would provide strong confirmation and validation.

2.   The provided data suggests that the film might have weak adhesion to the substrate, potentially leading to peeling under certain conditions. This characteristic hinders its practical applicability. To accurately assess the film's adhesion strength, it's recommended to utilize standardized tests like scratch tests or abrasive powder blasting. These techniques provide a more quantitative and reliable evaluation of the film's ability to resist mechanical forces and remain adhered to the substrate.

3. For a comprehensive evaluation, including friction and wear measurements of the bare steel substrate, to clearly demonstrate the tribological improvements achieved by the deposited Ni-P coatings.

Summary:

The reviewer expresses doubts about the quality and characteristics of the deposited coatings, such as adhesion to the substrate and improvement in tribological properties, due to the authors' inadequate response to comments. Therefore, it is crucial to incorporate the provided suggestions before publication.

Comments on the Quality of English Language

The authors are encouraged to enhance the clarity, and readability of the English language used in the manuscript.

Author Response

Please  check attached file 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Thanks for the satisfactory revisions.

Author Response

Thank you for accepting our work

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

Thanks for considering the suggestion.

It is advisable to incorporate the acquired acoustic signals and scratch lines into the main body of the text rather than relegating them to supplementary data. Additionally, for future research endeavors, it is recommended to augment the scratching load from 40N to a value exceeding 60N in order to ascertain the critical load for all samples.

Author Response

Reviewer’s comments and suggestions for authors

Thanks for considering the suggestion.

It is advisable to incorporate the acquired acoustic signals and scratch lines into the main body of the text rather than relegating them to supplementary data. Additionally, for future research endeavors, it is recommended to augment the scratching load from 40N to a value exceeding 60N in order to ascertain the critical load for all samples.

Response to the reviewers’ comments and suggestions:

The authors disagree with the reviewer's recommendation to include the scratch data in the main text rather than have it appear in the supplemental information file. However, the scratch data provide extra evidence to support the findings of the wear behavior of the coatings. Therefore, the scratch results are sufficiently covered in the main body of the manuscript. Seven significant data figures are already included in the manuscript and are integrated into the narrative to ensure a seamless flow. Maintaining the scratch data (figures) in the supplement file does not change the fundamental conclusions about the wear characteristics of the Ni-P coatings. Prospective readers of this work will easily locate the scratch data on the supplement information. Thus, the authors provided scratch data in the supplementary information file.

We appreciate the reviewer’s recommendation of considering the large scratch load (larger than 40 N) for our future works. It will be kept in mind while evaluating the scratch behavior of Ni-based coatings.