Improved Adhesion of the DLC Coating Using HiPIMS with Positive Pulses and Plasma Immersion Pretreatment

Round 1

Reviewer 1 Report

The authors discuss adhesion of DLC coatings to stainless steel substrates as a function of HIPIMS treatment. Prior to publication the following points need to be improved: 

i) Figure quality: Readability of Figures (SEM and graphs) is rather poor.

For all SEM and optical images, descriptions have to be added into the image to facilitate understanding by the reader (e.i. what are we looking at in these images?, indicate layers, delaminations, scratch traces & directions), error bars are hardly readable

For Graphs (e.g. Figure 4a, 12) lines need to be thicker and cannot be distinguised for certain elements at the moment. 

ii) Many Figures are not reffered to in the text (Fig3, 6, 9, ...). References to all Figures have to be added to the relevant sections in the text. 

iii) How was surface roughness of the coatings determined? Please specify in the experimental section

iv) How many scratches were performed per sample? Please specify. 

v) LC1-3: abbreviation needs to be defined the first time it is used in the text

vi) Figure 8 states: sample surface BEFORE scratch test, don't the authors mean after scratch testing?

vii) No LC1 was obtained for adhesion tests on duplex steel compared to HiPIMS with positive pulse, please dicuss

viii) a hardness decrease on duplex samples is related to reduced stress in the coating. How do the authors come to this conclusion? Was the stress measured?

viiii) adhesion is only qualitatively compared in terms of maximum critical failure load LCIII. Other differences in the scratch behaviour (e.g. occurence of LC1 region) is not discussed. Furthermore, scratch testing allows for quantitative adhesion analysis. An example can be found in  https://doi.org/10.3390/cryst11040357. The authors posses all relevant input parameters required, further analysis is highly recommended. 

 

 

 

Author Response

Good Morning,

I am attaching the file with the answers to the questions proposed in the review.

Thank you.

Author Response File: Author Response.docx

Reviewer 2 Report

Manuscript ID: coatings-1338464

Improved adhesion of the DLC coating using HiPIMS with positive pulses and plasma immersion pretreatment

Abstract

1. “DLC coatings are being widely used due to their enhanced tribomechanical performance.”

The application of "DLC" should be emphasized.

DLC should write the full name.

 

2. Compared to other PVD coatings, DLC has limited adhesion, so it is necessary to implement new techniques to overcome this limitation.

Compared with what?

 

3. The results show how……

Only mention the results. The discussion and conclusion should be emphasized.

 

Introduction

1. “Diamond-like carbon (DLC) coatings attract large interest in industrial applications[1–5]. ”

Why? What are the applications?

 

2. Introduction is too simple, the importance of this research should be emphasized! It is recommended to add more narratives in other documents. Describe the current problems in detail, highlighting the importance.

 

Materials and Methods

1. Before subjecting them to the various treatments, a surface mirror polish was carried out on them, with a roughness (Ra) of less than 0.2 microns.

What is the polishing procedure? For example, sequential polishing with water sandpaper?

 

2. Plasma Ion Immersion Implantation. Please add information such as the make and model of the machine.

 

3. Mechanical and tribological tests. Please add information such as the make and model of the machine.

 

4. Do Mechanical and tribological tests comply with the relevant ISO specifications?

 

Results

1. Table 3. Why is the difference between H₃/E₂ (MPa) so obvious?

 

2. Figure 9. Figure 16. and Figure 13. Smoothing should be done.

 

Discussion

1. Should explain why the coating adheres to the stainless steel sample?

 

2. Why does temperature affect?

 

3. “However, the duplex coating showed similar adhesion properties to other techniques studied with thicker coatings [8,34]. It is suggested that the initial cleaning for removal of surface oxides could have caused the appearance of oxynitrides between both coatings, producing a failure point for the adhesion of the DLC on the nitride substrate. ”

 What is the appropriate thickness?

 

Conclusions

1. Specific key points should be put forward.

 

2. Highlighted should not be placed in Conclusions.

Author Response

Good Morning,

I am attaching the file with the answers to the questions proposed in the review.

Thank you.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The quality of Figures and Graphs has improved significantly. 

Some points remaining: 

Line 54: Nitriding treatments have been seen in other studies to improve the adhesion properties of a deposition film [20]. 

What is a depostion film? This sentence has to be made more specific and clear. 

Section 2.4: Operating voltage of the SEM?

General: in many place Figure is written figure, without capital F

Figure 4b: Indications of circles are nice but should not overlap the whole image. I recommend indicating boudnaries only on one half of the image for the reader to still see the original image in the second half. Same for Fig. 11.

 

Fig. 9 COF: Why is the oughness in the COF vs. distance curve of the reference sample higher compared to WC:C. Please exlain in the text. 

 

Figure 11: Why are individual layer thicknesses (Cr, Wc, ..) so different between the three cases (a, b, c)? Please explain and make all images the same scale for better comparison. 

Figure 15 a, c, e are still missing in the text

 

Final statement of the conclusions: The authors claim that HIPIMS has improved the adhesion of the DLC coatings. Technically, adhesion has not really been determined, only critical loads (Lc): To determine adhesion, additional properties (elastic, COF, ... ) have to be considered. The statement should be attenuated to e.g.: HiPIMS with positive pulses has allowed to increase the critical load - indicative for improved adhesion - ... 

Author Response

Good morning,

It has been changed the paper as suggested on your comments.

Thank you.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript has been greatly revised and is very good. However, some problems still need to be improved.

1. “Further studies are necessary to determine the cause of this improvement in wear behavior and to determine the cause of the loss of adhesion of the duplex samples[43].”

It is inappropriate to place the reference in the conclusion, please modify it.

 

2. Figure 13.

It is recommended to change the X-axis to "2 Theta(degree)".
It is recommended to change the Y-axis to "Intensity".

Author Response

Good morning,

It has been changed the paper as suggested on your comments.

Thank you.

Author Response File: Author Response.docx