Research on the Formation Behaviour and Tribological Service Mechanism of Ni-Based Composite Coatings Prepared by Thermal Spraying Assisted with Alternating Current Magnetic Field

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript investigates the use of an alternating current (AC) magnetic field-assisted device to enhance supersonic plasma spraying coatings, making it suitable for submission to the Coating journal. Five coatings were prepared at voltages of 0V, 100V, 150V, 200V, and 220V, and their microstructural, mechanical, and tribological properties were analyzed. However, the reviewer would like to provide the following comments:

1. The authors must clarify which composition of ceramic-like compounds containing boron (B) and silicon (Si) is applied in this study.
2. Why does the 100V AC magnetic field show limited improvement in the spreading quality of the lamellar structure compared to higher voltages?
3. How does electromagnetic stirring caused by the AC magnetic field affect the densification of the coating and the removal of gas holes?
4. How does the redistribution of the Cr element strengthening phase contribute to the mechanical and functional properties of the coatings?
5. How does the texture orientation of the coating change with varying AC magnetic field intensities, and what implications do these changes have for the coating's performance?
6. What mechanisms explain the significant improvement in internal bonding quality and defect reduction observed at 200V, and how does this translate into better tribological performance?
7. Why does the crystal size within the coating become increasingly finer with increasing AC magnetic field intensity, and what mechanisms explain this phenomenon?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript is focused on studying the influence of applying a magnetic field on the ultrasonic plasma spraying jet. The technology is demanded and the problems of adhesion, microstructure and mechanical behavior of the plasma-sprayed Ni-based coatings are relevant.

I find the manuscript good-written, the research design is consistent and the methods are adequate. However there are some recommendations that may help to improve the work:

1. Figure 2. A scalebar is not observed.
2. Figures 3, 5. Higher resolution is appreciated. No legend can be read.
3. Figure 2. The thickness of the coatings is different. Were spraying conditions (time, distance, etc.) apart from magnetic field equal? Please, provide.
4. Figure 1a. Check if there is a typo in Powders.
5. Was the surface of the substrate treated somehow before spraying?
6. Figure 7. What star symbols stay for?
7. 7.Figure 10. The capture should be informative.

I recommend minor revisions.

Thank you.

Comments on the Quality of English Language

English is fine, style could be improved.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1. The abstract lacks conciseness and needs a more quantitative description of key results. Terms like "higher," "lower," "inferior," and "superior" should be replaced with specific numerical values or measurable comparisons for clarity and impact.
2. The need for supersonic plasma spraying in the introduction is vague and not clearly justified. If conventional techniques like APS, VPS, HVOF, and newer methods like cold spray already exist to produce dense coatings, the specific advantages and necessity of this technology should be clearly explained to the audience.
3. The introduction focuses excessively on explaining magnetic field technology, occupying 90% of the section, while failing to establish a clear connection between the coating materials and their intended applications. As a result, it gives the impression that the article is primarily a comparative analysis of magnetic field technology in plasma spraying rather than a study on coatings for corrosion or wear protection. The introduction should be restructured to clearly highlight the relevance of the coating materials and their functional benefits in the intended application.
4. The spray parameters are important in a thermal spray paper; hence must be tabulated in the paper , and can not be cited to a previous study.
5. Fig 1 b-d the legends are barely readable.
6. The characterization section lacks sufficient procedural details, making it unclear for the audience. The methodologies should be explicitly described, including specific testing conditions, parameters, equipment used, and analysis techniques. Providing clear, step-by-step descriptions will enhance transparency and ensure reproducibility of the results.
7. There is no logical explanation or justification for selecting the tribological parameters, such as a 30N load, 30-minute loading time, and 5mm reciprocating distance. The intended application of these conditions must be clearly stated—why such a high load was chosen and how it relates to real-world scenarios. Additionally, the impact of these parameters on material properties should be discussed, including potential wear mechanisms and failure modes. Have Hertzian contact stress calculations been conducted for this configuration? Furthermore, the type of counter ball material used should be specified, as it significantly influences the wear behavior and results. Providing this information is essential for scientific clarity and reproducibility.
8. Figure 2 is not acceptable at all. The image quality is extremely poor, making it difficult to extract any meaningful information. The scale bar is barely visible, rendering any microstructural analysis unreliable. Additionally, the description claims a "better microstructure at 100V," which is factually incorrect based on the visible defects. In reality, interface debonding is evident across all coatings, yet the authors fail to acknowledge this critical issue. The lack of clarity and accuracy in both the figure and its explanation must be addressed seriously. No microstructural features could be explained unless a clear image at representative low to high mags are provided.
9. If the coating thickness is described as increasing or decreasing with voltage, it must be clearly quantified or presented in a table. Vague statements without numerical values lack scientific rigor and make it difficult to assess trends accurately. Providing specific measurements, along with statistical variation if available, will enhance clarity and allow for proper comparison.
10. Again, Figure 3 is completely unacceptable—the image quality is so poor that nothing can be properly read. The elements are indistinguishable, making the EDS analysis virtually meaningless. The figure needs to be significantly improved with higher resolution, properly labeled elements, and a visible scale bar to ensure meaningful interpretation. Presenting data in this state severely undermines the study’s credibility.
11. How can the authors justify this statement when Figure 1 clearly shows interface debonding? The claim that increasing AC magnetic field intensity enhances bonding strength contradicts the visible evidence of poor adhesion. If the interface truly exhibited improved particle movement, better wetting, and stronger mechanical interlocking, there should be no visible signs of interface debonding. The authors need to explain this discrepancy
12. The tribological data completely lacks clarity and proper explanation, making it difficult to validate the claims made in this section. Several statements are baseless and unsupported, with no proper citations or references to justify them. For example, the assertion that "the better the tribological performance, the more superior the internal quality of the coating" is overly simplistic and ignores the complexities of wear mechanisms, which depend on multiple factors beyond just defect distribution. Additionally, the claim that the AC magnetic field significantly enhances internal bonding quality and reduces defects is speculative without quantitative evidence such as porosity measurements, hardness data, or microstructural analysis. The statement that the coating shows no damage or failure behavior under the same friction load is misleading—where is the surface morphology analysis to support this? Fig 9 profiles are also unreadable which questions the integrity of data reporting. This section reads more like a story than a scientific discussion. Without proper experimental validation, numerical comparisons, or supporting references, these conclusions are unsubstantiated and should be revised to align with rigorous scientific standards.

Comments on the Quality of English Language

The English language is clear and generally well-structured, but the manuscript lacks the necessary technical depth and proper references to support key claims, reducing its scientific credibility.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Figure 6 does a great job of capturing how the alternating magnetic field influences hardness distribution through the depth from the bonding interface. This hardness gradient is particularly relevant when considering Hertzian contact stresses in rotating components under bearing loads, where the peak contact stress often occurs slightly below the surface. A direct comparison between these hardness variations and the expected subsurface stress distribution in real-world applications (e.g., rolling contact fatigue scenarios) would add valuable context.

While the study effectively highlights the role of alternating current (AC) magnetic fields in refining microstructure and improving bonding, it could further discuss how variations in coating hardness influence localized wear mechanisms. Given that harder regions typically exhibit lower plastic deformation but higher brittleness, examining whether the magnetic field introduces inhomogeneous wear rates or crack initiation sites would strengthen the tribological assessment.

The manuscript provides residual stress measurements but could better explain how compressive vs. tensile residual stresses influence fatigue and wear resistance. Since residual compressive stress can help resist crack initiation under cyclic loading, discussing whether the observed stress distributions align with improved fatigue performance would provide a more complete picture of coating durability.

Comments on the Quality of English Language

N/A

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Figures 3 and 9 are still unreadable. The elements in EDS spectrum cant be seen after zooming it out to 200%. Same is the case with wear line profiles from the profilometry in Fig 9. The authors  need to provide magnified better quality images.

Author Response

Thank you for your letter and the reviewers’ comments on our manuscript. The main corrections are in the manuscript and the responds to the reviewers’ comments are as follows.

Comments 1: [Figures 3 and 9 are still unreadable. The elements in EDS spectrum cant be seen after zooming it out to 200%. Same is the case with wear line profiles from the profilometry in Fig 9. The authors  need to provide magnified better quality images.]
Response 1: As the reviewer suggested, we have re-formatted Figures 3 and 9, particularly the positions of the elements in EDS and the distribution of the wear marks. We have also uploaded the high-definition versions of the images in the attachment. I'm sorry that the problem of blurry pictures still exists.

Please see the attachment for other materials

Author Response File: Author Response.pdf