Research on Titanium Ion Etching Pretreatment Process on Cemented Carbide Before DLC Film Deposition

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript I reviewed was subject to a previous review. This is evidenced by modifying the manuscript title and the yellow indications in the text. Unfortunately, I do not know the last reviewer's significant comments. The manuscript reflects a particular research effort of the co-authors in demonstrating the purposefulness of using plasma curing preceding the formation of the coating. While the results of the studies resulting from this are a fact, their interpretation raises doubts. They are primarily concerned with the phase composition of the coating material. In this area of ​​their research, the authors limited themselves exclusively to Raman spectroscopy in its most simplified form and, in the same very simplified form, formulated the interpretation of the obtained Raman spectra after their deconvolution in the context of the content of sp3 hybridization. Judging from the determined parameters of the spectra, one can expect a relatively low content of sp3 bonds (primarily high values ​​of Id/Ig) in the material of the obtained coatings. A reasonable question arises whether the produced layer contains DLC characterized by carbon-carbon bonds or whether the synthesis product is a hydrocarbon polymer.
Additionally, the obvious question arises about the presence of titanium carbide since the coating was produced in an atmosphere with the participation of acetylene under the sputtering of a titanium target. Variable process parameters, such as those used by the authors, should affect the share of TiCx in the phase composition of the product. A more detailed (and, in fact, obvious) analysis of the phase composition of the produced layer could also be helpful in the way the authors interpret the role of cobalt in shaping the phase composition of their carbon layer (lines 367-378). Suppose the authors had considered the presence of the carbide phase (dependent on the synthesis conditions) in the phase composition of their layers. In that case, the title of their manuscript should be modified. For minor remarks, I would mention the following: 
1. Broader development in the Introduction, based on the literature, of the topic of Ti-DLC composites (properties, production) in the context of the purposefulness of their proposed research; 
2. A more precise description of the technology by describing the magnetrons used (the technological parameter is the current density, not its absolute value!) and the geometry of the experiment; 
3. Adding the value of the laser radiation wavelength in the Raman study; 4. Provide the full names of all authors of the cited works in the list of references.

Author Response

The manuscript I reviewed was subject to a previous review. This is evidenced by modifying the manuscript title and the yellow indications in the text. Unfortunately, I do not know the last reviewer's significant comments. The manuscript reflects a particular research effort of the co-authors in demonstrating the purposefulness of using plasma curing preceding the formation of the coating. While the results of the studies resulting from this are a fact, their interpretation raises doubts. They are primarily concerned with the phase composition of the coating material. In this area of their research, the authors limited themselves exclusively to Raman spectroscopy in its most simplified form and, in the same very simplified form, formulated the interpretation of the obtained Raman spectra after their deconvolution in the context of the content of sp3 hybridization. Judging from the determined parameters of the spectra, one can expect a relatively low content of sp3 bonds (primarily high values of Id/Ig) in the material of the obtained coatings. A reasonable question arises whether the produced layer contains DLC characterized by carbon-carbon bonds or whether the synthesis product is a hydrocarbon polymer.

Additionally, the obvious question arises about the presence of titanium carbide since the coating was produced in an atmosphere with the participation of acetylene under the sputtering of a titanium target. Variable process parameters, such as those used by the authors, should affect the share of TiCx in the phase composition of the product. A more detailed (and, in fact, obvious) analysis of the phase composition of the produced layer could also be helpful in the way the authors interpret the role of cobalt in shaping the phase composition of their carbon layer (lines 367-378). Suppose the authors had considered the presence of the carbide phase (dependent on the synthesis conditions) in the phase composition of their layers. In that case, the title of their manuscript should be modified.

Answer： Thank you very much for your valuable suggestions. The research object of this paper is the etching treatment of the substrate by titanium ions. Our objective is to optimize the process parameters of the etching treatment through experiments. Besides, to identify the main factors that affect the properties of the DLC film. The preparation process parameters of the Ti-DLC film came from the previous research of the co-authors. We directly used this process. Therefore, the content of sp³ bonds in Ti-DLC and the existence of titanium carbide were not discussed in this paper. In our previous research, the sp³ content in Ti-DLC was relatively high, and there was about 2% TiC_x. However, due to the relatively long time span, we cannot determine the reason for the high I_D/I_G in this article. It may be caused by the etching treatment, or it may be due to equipment aging and other reasons. Therefore, we cannot provide further discussion on this.

Regarding the issue of Co, it is true that our manuscript lacks sufficient analysis in this regard. Your suggestion is right on the mark. We have analyzed the existing data and referred to relevant research findings to make some modifications to the section on Co content. As for carbides, in our previous research, no carbide residues were found on the interface between etched surface and DLC films. The relevant content has been published in our previous paper. (Li C, Huang L, Yuan J, et al. The influence of Ti plasma etching pre‐treatment on mechanical properties of DLC film on cemented carbide. DOI: 10.1002/sia.7053)

For minor remarks, I would mention the following: 

1. Broader development in the Introduction, based on the literature, of the topic of Ti-DLC composites (properties, production) in the context of the purposefulness of their proposed research; 

Answer：We have revised the Introduction and added the content about DLC films.
2. A more precise description of the technology by describing the magnetrons used (the technological parameter is the current density, not its absolute value!) and the geometry of the experiment; 

Answer：The Ti targets used were two rectangular targets, each with a length of 300 mm, a width of 72 mm, and a thickness of 5 mm. Due to equipment limitations, only the absolute value of the magnetron current can be set, so the absolute values are used throughout the text. At a current of 4.0 A, the current density was 18 mA/cm² and the power density was 11 W/cm². The corresponding description has been added to the Experimental details section.
3. Adding the value of the laser radiation wavelength in the Raman study;

Answer：The wavelength of the Raman spectroscopy was 514nm. It has been added to the discussion about Table 1.

4. Provide the full names of all authors of the cited works in the list of references.

Answer：Thanks for your reminder. We have revised all the references.

In summary，thank you again for your comments. Your comments have been of great help in revising our manuscript. They also provide valuable guidance for us to improve our experimental results and explore new research directions in the future. We have also made some revisions based on the comments from other reviewers. We hope you will approve of our research findings and the manuscript.

We hope you can provide your new comments as soon as possible. We are in great need of this paper. Thank you so much.

Kind regards

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors investigate the effect of a pretreatment using Ti targets in mid-frequency pulsed magnetron sputtering on the adhesion and tribological properties of Ti-DLC thin films. While the topic is relevant and potentially valuable for improving the performance of DLC thin films, the manuscript has several significant issues that need to be addressed before it can be considered for publication.

General Comments:

1. The motivation and novelty of the study are not clearly addressed in the introduction. The authors should clarify why this specific pretreatment method was chosen and how it improved the adhesion compared to existing approaches.
2. The introduction lacks a thorough review of previous studies in this area. Relevant works on DLC film deposition and etching pretreatment using metal ions should be discussed to establish the state of the art and the specific gap that this study aims to fill.
3. There is insufficient evidence to support the claim that mid-frequency magnetron sputtering produces Ti ions for etching. The results presented do not convincingly demonstrate that the substrate was etched by Ti ions rather than by highly ionized Ar ions in the working atmosphere.
4. In its current form, the manuscript does not provide sufficient evidence to support the conclusions drawn.

 

Introduction:

• In the first paragraph, the authors describe the sputtering process and the formation of thin films. However, the claim that the sputtered species are ionized is not entirely correct. In direct current (DC) and mid-frequency magnetron sputtering, the majority of sputtered species remain neutral. In contrast, high-power impulse magnetron sputtering (HiPIMS) achieves higher ionization degrees, although some species remain neutral. This should be clarified.
• The authors should consult the article “A structure zone diagram including plasma-based deposition and ion etching” by André Anders and incorporate relevant information on metal ion etching.
• The transition from the first to the second paragraph is abrupt. The discussion on metal ion formation and etching should be separated from the discussion on Ar ion etching, as these are distinct processes.
• The advantages and disadvantages of noble gas ion etching versus metal ion etching should be more thoroughly discussed. A brief comparison of different methods for generating metal ions, such as HiPIMS and cathodic arc evaporation, would enhance the context and clarify the connection to thin film adhesion.
• Since the study focuses on DLC thin films, the introduction should better reflect previous research on the effect of different etching pretreatment methods on DLC properties.
• The rationale for using Ti ions should be explained more clearly. For example, the study “Improved adhesion of carbon nitride coatings on steel substrates using metal HiPIMS pretreatments” by Bakoglidies shows that Ti²⁺ ions can degrade the interface between the substrate and thin film. The authors should address whether this potential effect was considered in the study design.

 

Experimental Details:

• The peak power density of the Ti cathodes should be provided, as it directly correlates with the ionization degree of the sputtered species.
• The method used to measure the etching depth is not clearly described and should be specified in more detail.

 

Results and Discussion:

• The authors need to provide direct evidence that Ti ions, rather than Ar ions, are responsible for substrate etching. What data supports this conclusion?
• SEM micrographs of the surface after etching should be included to highlight structural changes. For cemented carbide, it is known that the Co binder is more susceptible to etching than WC grains. This effect should be addressed through SEM analysis.
• Cross-sectional SEM or TEM images should be provided to determine whether a dense Ti layer formed or if the substrate was genuinely etched by Ti ions.
• A comparison with a substrate etched purely with Ar ions would clarify whether the proposed pretreatment improves adhesion.
• A Raman spectrum should be included to confirm the presence of C-H stretching bonds (2600–3200 cm⁻¹) when ethyne is used as a reactive gas. The study “Effects of acetylene flow rate and bias voltage on the structural and tribo-mechanical properties of sputtered a-C:H films” by Tillmann provides relevant reference spectra.
• The authors’ statement that Ti-DLC films contain sp³-hybridized carbon is not entirely accurate. Since C-H bonds are also sp³-coordinated, it would be more precise to state “sp³-hybridized bonds” rather than “sp³-hybridized carbon.”
• The hardness of the Ti-DLC thin films should be reported, as it would provide insight into the impact of the etching treatment.
• The discussion on the chemical composition of the cemented carbide should be presented earlier, before discussing the properties of the Ti-DLC thin films. If no correlation between the C/W ratio and Ti-DLC properties was found, the authors should clarify why Figure 14 was included and why such a correlation was expected.
• Energy-dispersive spectroscopy (EDS) is not sufficiently precise to determine C content in WC-Co cemented carbide. The authors should reconsider the reliability of these data.

 

Conclusion:

The manuscript presents an interesting approach to improving the adhesion and tribological properties of DLC thin films through Ti ion etching. However, the study suffers from several weaknesses, including a lack of evidence for Ti ion generation, insufficient characterization of the etched surface, and limited discussion on the motivation and novelty. Therefore, I recommend rejection. However, the authors are encouraged to address the comments, mprove the study's quality, and resubmit a revised version for reconsideration.

Author Response

The authors investigate the effect of a pretreatment using Ti targets in mid-frequency pulsed magnetron sputtering on the adhesion and tribological properties of Ti-DLC thin films. While the topic is relevant and potentially valuable for improving the performance of DLC thin films, the manuscript has several significant issues that need to be addressed before it can be considered for publication.

General Comments:

The motivation and novelty of the study are not clearly addressed in the introduction. The authors should clarify why this specific pretreatment method was chosen and how it improved the adhesion compared to existing approaches.

The introduction lacks a thorough review of previous studies in this area. Relevant works on DLC film deposition and etching pretreatment using metal ions should be discussed to establish the state of the art and the specific gap that this study aims to fill.

There is insufficient evidence to support the claim that mid-frequency magnetron sputtering produces Ti ions for etching. The results presented do not convincingly demonstrate that the substrate was etched by Ti ions rather than by highly ionized Ar ions in the working atmosphere.

In its current form, the manuscript does not provide sufficient evidence to support the conclusions drawn.

Reply: Thank you for your helpful suggestions. I would like to provide some explanations here. We discovered this etching method by accident during our experiments. We prepared DLC films on surfaces etched with Ti ions, surfaces etched with Ar ions, and on the Ti transition layer surface, respectively. We found that the Ti etching method has a significant advantage in enhancing film adhesion. We once published a paper based on these results, but did not delve further into it. Recently, we wanted to explore this area more, which led to this article. In our previous research, we had already confirmed that it is feasible to use medium-frequency magnetron sputtering to generate Ti ions for etching the substrate. The etching rate can reach 600-1000 nm/h, while under the same conditions, the etching rate of Ar ions is less than 20 nm/h. We have added a brief explanation in the introduction. You can refer to this paper for the detailed information: Li C, Huang L, Yuan J, et al. The influence of Ti plasma etching pre‐treatment on mechanical properties of DLC film on cemented carbide. DOI: 10.1002/sia.7053.

Introduction:

1. In the first paragraph, the authors describe the sputtering process and the formation of thin films. However, the claim that the sputtered species are ionized is not entirely correct. In direct current (DC) and mid-frequency magnetron sputtering, the majority of sputtered species remain neutral. In contrast, high-power impulse magnetron sputtering (HiPIMS) achieves higher ionization degrees, although some species remain neutral. This should be clarified.

Answer: We have added the relevant explanations in the Introduction as per your suggestions.

2. The authors should consult the article “A structure zone diagram including plasma-based deposition and ion etching” by André Anders and incorporate relevant information on metal ion etching.

Answer: Thank you for the reference you provided. We plan to further theorize the etching treatment and obtain more universal conclusions through simulation and modeling in our subsequent research. The article you provided is very helpful for our future work, but we may need more time to fully digest it.

3. The transition from the first to the second paragraph is abrupt. The discussion on metal ion formation and etching should be separated from the discussion on Ar ion etching, as these are distinct processes.

Answer: We have revised the Introduction section, separating out the part on gas ion etching. We aim to explain the basic principles of ion etching through the discussion on gas ion etching.

4. The advantages and disadvantages of noble gas ion etching versus metal ion etching should be more thoroughly discussed. A brief comparison of different methods for generating metal ions, such as HiPIMS and cathodic arc evaporation, would enhance the context and clarify the connection to thin film adhesion.

Answer: We have revised this part of the content, briefly explaining the characteristics of different etching methods based on other literature.

5. Since the study focuses on DLC thin films, the introduction should better reflect previous research on the effect of different etching pretreatment methods on DLC properties.

Answer: There are not many existing studies. Based on relevant literature and our own previous research, we have made some modifications.

6. The rationale for using Ti ions should be explained more clearly. For example, the study “Improved adhesion of carbon nitride coatings on steel substrates using metal HiPIMS pretreatments” by Bakoglidies shows that Ti²⁺ ions can degrade the interface between the substrate and thin film. The authors should address whether this potential effect was considered in the study design.

Answer: We aim to improve the preparation process of Ti-DLC films, and etching treatment is one of the steps. To avoid introducing other impurity elements, we used Ti ions. In our previous research, we found that there was no residual Ti element on the etched surface, so the influence of Ti²⁺ on the interface is not within our consideration.

Experimental Details:

1. The peak power density of the Ti cathodes should be provided, as it directly correlates with the ionization degree of the sputtered species.

Answer: We have added the power densities corresponding to different medium-frequency currents in the Experimental details.

2. The method used to measure the etching depth is not clearly described and should be specified in more detail.

Answer: It has been added to the Experimental details. We used the step method. Part of the substrate was masked, and then the etching depth was determined by measuring the height difference between the two sides after etching.

Results and Discussion:

1. The authors need to provide direct evidence that Ti ions, rather than Ar ions, are responsible for substrate etching. What data supports this conclusion?

Answer: We conducted experiments on both Ti ion etching and Ar ion etching. For the relevant conclusions, please refer to our published papers.

2. SEM micrographs of the surface after etching should be included to highlight structural changes. For cemented carbide, it is known that the Co binder is more susceptible to etching than WC grains. This effect should be addressed through SEM analysis.

Answer: We added a set of SEM images of the substrate before and after etching, as well as the film, in the form of examples. The SEM images of the etched surfaces were quite similar and could not show differences in morphology. The SEM images of samples with Ar flow 80, 95 and 110 sccm are like these. Therefore, we adopted 3D topography.

  

3. Cross-sectional SEM or TEM images should be provided to determine whether a dense Ti layer formed or if the substrate was genuinely etched by Ti ions.

Answer: In our previous paper, elemental detection did not detect Ti elements on the etched surface. In this experiment, we also performed XPS detection once, and Ti elements were not detected. Therefore, there is no Ti layer on the etched surface.

4. A comparison with a substrate etched purely with Ar ions would clarify whether the proposed pretreatment improves adhesion.

Answer: In the previous paper, we compared the etched surface with the surface etched only by Ar ions and the surface with a Ti layer. The adhesion of the film on the etched surface was significantly improved.

5. A Raman spectrum should be included to confirm the presence of C-H stretching bonds (2600–3200 cm⁻¹) when ethyne is used as a reactive gas. The study “Effects of acetylene flow rate and bias voltage on the structural and tribo-mechanical properties of sputtered a-C:H films” by Tillmann provides relevant reference spectra.

Answer: The range we selected for Raman spectroscopy was from 800 to 2000 cm⁻¹. We don't have time to redo the Raman spectroscopy this time. But we will supplement this experiment.

6. The authors’ statement that Ti-DLC films contain sp³-hybridized carbon is not entirely accurate. Since C-H bonds are also sp³-coordinated, it would be more precise to state “sp³-hybridized bonds” rather than “sp³-hybridized carbon.”

Answer: Thank you for the correction. We have revised the statement according to your suggestion.

7. The hardness of the Ti-DLC thin films should be reported, as it would provide insight into the impact of the etching treatment.

Answer: This was originally one of the tests we planned to conduct. However, unfortunately, after measuring a group of nano hardness, we found that the results had significant errors. After communicating with the experimental personnel, they believed that the maximum peak-to-valley morphology height of the etched surface reached 150 nm, while the film thickness was only about 1 μm. The measurement depth was too small relative to the large surface roughness, rendering the results unreliable. Therefore, we abandoned the hardness testing.

8. The discussion on the chemical composition of the cemented carbide should be presented earlier, before discussing the properties of the Ti-DLC thin films. If no correlation between the C/W ratio and Ti-DLC properties was found, the authors should clarify why Figure 14 was included and why such a correlation was expected.

Answer: As you mentioned, the distribution of content in this paper is indeed somewhat unreasonable. After re-discussing, we believe that the first half of the paper, which focuses on the properties of Ti-DLC films, is too extensive, while the last two sections are actually the key points. We have made significant changes to the structure of the article in order to highlight the logic behind the design of our experiment.

In our previous paper, we had made some inferences about the mechanism by which etching treatment affects film properties. Through XPS and EDS, we found changes in surface elements and clear damage to the grains. Therefore, the C/W ratio was our primary suspect. However, after comparing the data, we found no clear correlation between the C/W ratio and film properties. There are two reasons why we included Figure 14. First, we believe that ruling out the correlation of a suspicious factor is an important part of research. Second, we found a portion of vertically distributed data in Figure 14. We think that within this specific range, there must be another factor that has a more significant impact on film properties. Through comparison, we found that the Co element has a great influence on these samples. Therefore, Figure 14 and the subsequent content are causally related.

9. Energy-dispersive spectroscopy (EDS) is not sufficiently precise to determine C content in WC-Co cemented carbide. The authors should reconsider the reliability of these data.

Answer: You are correct. EDS detection of C elements is not very accurate and has a certain degree of error. However, after comparing the XPS results of three samples, the error is acceptable. Moreover, we mainly focus on the changes in elemental content rather than the absolute values. The EDS results are sufficient to illustrate the changes in elements.

Conclusion:

The manuscript presents an interesting approach to improving the adhesion and tribological properties of DLC thin films through Ti ion etching. However, the study suffers from several weaknesses, including a lack of evidence for Ti ion generation, insufficient characterization of the etched surface, and limited discussion on the motivation and novelty. Therefore, I recommend rejection. However, the authors are encouraged to address the comments, mprove the study's quality, and resubmit a revised version for reconsideration.

In summary，Thank you for giving us the opportunity to revise. We are in great need of this paper. You have provided us with very professional suggestions. Some of these suggestions coincide with many key issues in our previous research. We hope that the revised manuscript will address your concerns.

Kind regards

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The paper deals with the effect of various parameters on titanium ions etching, carried out on substates of YG8 cemented carbide for the deposition of DLC films. The topic could be of interest to a large audience, but the paper is not well organized and there is not a real discussion of the reasons for the role of the different parameters in film formation. In addition, all the parameters are considered separately, with no attempt to verify the best conditions for the films deposition, which could be of interest to the reader. Finally, many of the reported data do not show clear trends, so several statements are not really supported by the data. In conclusion, the paper presents many problems and the most important are reported below.

1. The trend of the data reported in Fig.3 does not match the sp3 carbon content, as stated by the authors (lines 144-147). For example, at a voltage of -1400 V the adhesion force is higher than that at -1200 V, which corresponds to a higher sp3 carbon content. In general, the trends of the different properties with the bias voltages are not so clear and coherent.
2. I do not see a clear negative correlation between the changes in the friction coefficient and those in the film roughness (lines 239-240). Where are the data about film roughness? The only reported data are about substrate surface roughness (Fig. 5) and those data do not show any clear correlation with the friction coefficient.
3. There is no correlation between the film adhesion (Fig. 7) and the sp3 carbon content: why?
4. How do the authors know the presence of graphite crystallites (lines 311-312)?
5. What is the meaning of the sentence of lines 350-360? Why should a vertical alignment of points related to different properties have a particular importance?
6. Why should the Co concentration affect the film characteristics? An explanation should be given.
7. The conclusions are poor. They state only that different deposition parameters could influence DLC film. What are the novelties of the paper?
8. The references should be checked, since some errors are present (see ref. 12, 18 and 30).

As a minor remark, DLC is a well known acronym but, anyway, its meaning should be reported in the text.

Author Response

The paper deals with the effect of various parameters on titanium ions etching, carried out on substates of YG8 cemented carbide for the deposition of DLC films. The topic could be of interest to a large audience, but the paper is not well organized and there is not a real discussion of the reasons for the role of the different parameters in film formation. In addition, all the parameters are considered separately, with no attempt to verify the best conditions for the films deposition, which could be of interest to the reader. Finally, many of the reported data do not show clear trends, so several statements are not really supported by the data. In conclusion, the paper presents many problems and the most important are reported below.

Reply: Thank you very much for your comments. Your comments are very representative. After considering your questions, we realized that the structure of this article is not reasonable. Our basic logic is divided into two steps. The first step is to obtain substrates with different properties by changing the etching process parameters. The second step is to study the influence of the changes in substrate properties on the deposited DLC films. Due to the large amount of experiments, this logic was not clear. We have made significant changes to the structure and order of content in the article, to better present our intentions.

Regarding the issue you raised about all the parameters considered separately, we have tried orthogonal experiments in the past, but the results were not satisfactory. Therefore, we had to use single-factor experiments to uncover some patterns.

Additionally, we have published a paper about Ti ion etching. If you have any doubts about the feasibility of this method, you can refer to this paper. (Li C, Huang L, Yuan J, et al. The influence of Ti plasma etching pre‐treatment on mechanical properties of DLC film on cemented carbide. DOI: 10.1002/sia.7053)

1. The trend of the data reported in Fig.3 does not match the sp3 carbon content, as stated by the authors (lines 144-147). For example, at a voltage of -1400 V the adhesion force is higher than that at -1200 V, which corresponds to a higher sp3 carbon content. In general, the trends of the different properties with the bias voltages are not so clear and coherent.

Answer: The bias mentioned here is the bias for etching treatment, not the bias during film deposition. Therefore, the relationship between bias and film properties is not direct. For each sample, we prepared three in the same batch to take the average value to ensure the reliability of the data. The mismatch between the changes in adhesion strength and the content of sp³ bonds indicates that other factors played a more significant role.

2. I do not see a clear negative correlation between the changes in the friction coefficient and those in the film roughness (lines 239-240). Where are the data about film roughness? The only reported data are about substrate surface roughness (Fig. 5) and those data do not show any clear correlation with the friction coefficient.

Answer: We have added content regarding film thickness and roughness. As for the issue of the coefficient of friction, we believe it is related to the filling of wear tracks by wear debris. We have provided some explanations at the end of the article. In fact, in some of our other experiments, there were also cases where the coefficient of friction did not match the roughness.

3. There is no correlation between the film adhesion (Fig. 7) and the sp3 carbon content: why?

Answer: We have revised the structure of the article and removed this figure. We realized that a single parameter of the etching treatment is not sufficient to explain the changes in the subsequent coating performance. These changes are multifaceted. Therefore, we have integrated these data and reorganized them.

4. How do the authors know the presence of graphite crystallites (lines 311-312)?

Answer: This is mainly based on the results of Raman spectroscopy analysis. It is an inference made from relevant literature and our previous experimental results.

5. What is the meaning of the sentence of lines 350-360? Why should a vertical alignment of points related to different properties have a particular importance?

Answer: In our previous studies, we found that there was a reduction in C elements during the etching process, but Ti elements did not remain on the etched surface. Therefore, when analyzing the results, we prioritized the impact brought about by the change in the C/W ratio. However, we found that there was no obvious correlation between the C/W ratio and film properties. This indicates that other factors have a more significant impact on film properties. After comparing all the data, we believe that the vertically distributed data is meaningful. This suggests that within this specific range, there should be another factor dominating the influence on the film. We have explained this in the paper.

6. Why should the Co concentration affect the film characteristics? An explanation should be given.

Answer: We have added some analysis and inferences in this part. The original analysis of this content was too limited, with only general explanations based on experimental results.

7. The conclusions are poor. They state only that different deposition parameters could influence DLC film. What are the novelties of the paper?

Answer: We have revised the conclusion section. Etching with metal ions is a relatively uncommon method. We proposed this method before. The purpose of this article is to explore the underlying patterns, rather than to introduce a new method.

8. The references should be checked, since some errors are present (see ref. 12, 18 and 30).

Answer: The references have been modified. Upon checking, we found that we had selected an inappropriate style when inserting references.

As a minor remark, DLC is a well known acronym but, anyway, its meaning should be reported in the text.

Answer: Thank you for the reminder. We have provided an explanation for the term DLC the first time it appears in the introduction.

In summary, thank you very much for reviewing our article amidst your busy schedule. We have made revisions according to your suggestions as much as possible. Due to time constraints, some data could not be supplemented in time, for which we apologize. There are many samples in this paper, and each sample was prepared in triplicate in the same batch to obtain the average value. As a result, many data points show some degree of dispersion. We plan to conduct more experiments to address this issue. We hope you can approve the revisions we have made to this article. We are in great need of this paper.

Kind regards

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have introduced significant changes to the text of their manuscript as currently presented. These changes have greatly improved the clarity of the text. The interpretations of the experimental results concerning the effects of etching the carbide substrate with titanium ions seem logical. I appreciate the authors' effort. However, the text fragment contained between lines 362-381, concerning the relationship between the Co content and the number of sp3 bonds in the carbon layer obtained with the participation of acetylene, requires a more detailed analysis. It is good to support the authors' conclusions in this matter with additional literature studies so that the authors' assumptions are less speculative. Regarding interpreting the ID/IG relationship and the content of sp3 bonds, supporting the authors' statements with literature views would also be good. Since the phase composition of the carbon coating obtained with the participation of the Ti target and acetylene, as a component of the gas atmosphere, was already the subject of the authors' previous published studies, it would be good to consider this in their current considerations.

Author Response

The authors have introduced significant changes to the text of their manuscript as currently presented. These changes have greatly improved the clarity of the text. The interpretations of the experimental results concerning the effects of etching the carbide substrate with titanium ions seem logical. I appreciate the authors' effort. However, the text fragment contained between lines 362-381, concerning the relationship between the Co content and the number of sp3 bonds in the carbon layer obtained with the participation of acetylene, requires a more detailed analysis. It is good to support the authors' conclusions in this matter with additional literature studies so that the authors' assumptions are less speculative. Regarding interpreting the ID/IG relationship and the content of sp3 bonds, supporting the authors' statements with literature views would also be good. Since the phase composition of the carbon coating obtained with the participation of the Ti target and acetylene, as a component of the gas atmosphere, was already the subject of the authors' previous published studies, it would be good to consider this in their current considerations.

Reply: We have revised the relevant paragraphs. After consulting more papers, we found some more conclusions that can serve as evidence and have made the appropriate citations.  

In summary, thank you once again for your valuable comments. Due to time constraints, we are unable to provide further direct evidence to perfect this article. We are already planning more experiments to verify our arguments regarding the changes in elements at the coating-substrate interface, especially the role of the Co element. If you are interested in this, we hope you will follow our future research outcomes.

Best regards

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed most of the comments within the short review period and have revised the manuscript accordingly.

While direct experimental evidence of Ti ions could not be provided, the SEM images demonstrate significant etching of the WC-Co surface, which effectively illustrates the etch process.

To ensure the manuscript meets the necessary quality for publication, the authors are encouraged to address the following points:

1. In the revised introduction, references for some newly added sentences are missing. There are already several relevant studies in the field of metal ion etching for DLC coatings, such as Santiago’s “Adhesion enhancement of DLC hard coatings by HiPIMS metal ion etching pretreatment” and Tillman’s “Improved adhesion of a-C and a-C:H films with a CrC interlayer on 16MnCr5 by HiPIMS-pretreatment”, which were not mentioned or cited. The authors should include these or other relevant references to strengthen the context and support the discussion.
2. The order and relevance of the cited sources are not always correct. For example, in the sentence “However, if the particle energy is too high, when the particles bombard the substrate strongly, the released energy will take away the deposited particles and some atoms on the substrate surface [12-14],” the cited sources do not appear to support the statement. Accurate citation is crucial for maintaining scientific integrity. The authors should carefully review the citations and correct any mismatches or inaccuracies.
3. Figure 3 appears to be a screenshot from the Inca software by Oxford. To improve the overall quality of the manuscript, the authors are encouraged to present the data in a high-resolution, self-generated image rather than relying on a software screenshot.

Author Response

The authors have addressed most of the comments within the short review period and have revised the manuscript accordingly. While direct experimental evidence of Ti ions could not be provided, the SEM images demonstrate significant etching of the WC-Co surface, which effectively illustrates the etch process. To ensure the manuscript meets the necessary quality for publication, the authors are encouraged to address the following points:

1. In the revised introduction, references for some newly added sentences are missing. There are already several relevant studies in the field of metal ion etching for DLC coatings, such as Santiago’s “Adhesion enhancement of DLC hard coatings by HiPIMS metal ion etching pretreatment” and Tillman’s “Improved adhesion of a-C and a-C:H films with a CrC interlayer on 16MnCr5 by HiPIMS-pretreatment”, which were not mentioned or cited. The authors should include these or other relevant references to strengthen the context and support the discussion.

Reply: Thank you for the references you provided. We have involved them and appropriately cited other references.

2. The order and relevance of the cited sources are not always correct. For example, in the sentence “However, if the particle energy is too high, when the particles bombard the substrate strongly, the released energy will take away the deposited particles and some atoms on the substrate surface [12-14],” the cited sources do not appear to support the statement. Accurate citation is crucial for maintaining scientific integrity. The authors should carefully review the citations and correct any mismatches or inaccuracies.

Reply: Thank you for your reminder. We have carefully reviewed the references cited in the text to ensure their accuracy.

3. Figure 3 appears to be a screenshot from the Inca software by Oxford. To improve the overall quality of the manuscript, the authors are encouraged to present the data in a high-resolution, self-generated image rather than relying on a software screenshot.

Reply: Figure 3 has been generated based on the EDS data, with the elements corresponding to each peak labeled.

In summary, thank you for acknowledging the revisions we have made to this article. It is thanks to your valuable suggestions that this article has been improved. There are still gaps in many of our experiments, and we will continue to perfect the related research in the future.

Best regards

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The changes carried out by the authors have improved the quality of the paper that now is suitable for publication.

Author Response

The changes carried out by the authors have improved the quality of the paper that now is suitable for publication.

Reply: Thank you very much for your positive feedback on the revised version of our manuscript. We are pleased to hear that the changes we have made have been recognized. Based on the comments from the other reviewers, we have also made some minor revisions to further improve the manuscript. We would like to express our sincere gratitude to you for your constructive input, which has been invaluable in refining our research presentation. Thank you once again for your time and effort in reviewing our manuscript.  

Best regards

Author Response File: Author Response.pdf