Tribological and Mechanical Properties of the Nanostructured Superlattice Coatings with Respect to Surface Texture
, Janis Lungevics 1, Uldis Kanders 1, Armands Leitans 1, Guna Civcisa 1, Oskars Linins 1, Karlis Kundzins 1,2 and Irina Boiko 1
Round 1
Reviewer 1 Report
In this manuscript, the authors analyze the correlation between the tribological and mechanical properties of ceramic nanostructured superlattice coatings and their surface texture parameters and, at the same time, propose a rational procedure for measuring and evaluating coating properties and surface texture. The manuscript is informative and well organized and is recommended for acceptance.
Author Response
Dear Reviewer,
Thank you very much for the positive assessment! We improved the clarity of language and figures in the paper (attached PDF file).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The work shows an adequate methodology, the test parameters and the parameters of the coating process are clearly presented. The results are presented quantitatively and are conclusive.Author Response
Dear Reviewer,
Thank you very much for the positive assessment! We improved the clarity of language and figures in the paper (attached PDF file).
Author Response File: Author Response.pdf
Reviewer 3 Report
In the paper, authors studied the correlation dependence between tribological and mechanical properties of the NSC and their surface texture parameters. Although the topic is interesting it could be considered as a reference, several aspects must be improved to take into account this work for publication.
1. The introduction section is too long and should be more concise.
2. It is important to clarify which type of tribometer was used in this study, the pin-on-disc tribometer was described in the Tribology tests section, but the steel ball -100Cr6 was used as the counterpart, while the results in Tables 5 and 6 were based on pin material-100Cr6.
3. The conclusion section should be detailed.
Author Response
Dear Reviewer,
Thank you for the comments/suggestions! We tried to take them into account in order to raise the quality of the paper.
- We agree that perhaps the introduction section is longer than usual for paper articles, but we feel that, considering that the article includes metrology, hardness measurements, tribology, and in addition, the rationale of the article and the coating application technology should also be described. Reducing the introduction volume, we fear there might be a lack of clarity for some readers. If you still strongly suggest that shortening is required, then perhaps the part about the comparison of 2D and 3D surface texture parameters could be reduced, leaving “Given the current state of technology, it is already known that 3D texture measurements should be used instead of 2D for more accurate surface characterization.”.
- Yes, sorry for the confusion! A ball-on-disc tribometer was used in these experiments. We made changes to the text accordingly.
- Thank you, we made the conclusion section more detailed: “Microhardness measurements in the applied force range from 0.1 to 6.0 N allow the integrated hardness changes to be evaluated depending on the applied force. As the applied indentation force increases, the impact of the coating on the result of the microhardness measurement decreases. At 6.0 N applied force, the measured microhardness values of the coated samples start to converge with the microhardness value of the substrate (the difference is less than 8 %).
The surface roughness significantly impacts the results using the visual microhardness measurement method. As the roughness increases, the accuracy of microhardness measurements decreases. The standard deviation decreased approximately two times as applied force increased from 0.2 to 0.5 N, and the standard deviation was almost three times higher for the rougher surface (Sa 0.1 µm) compared to the polished one (Sa 0.04 µm).
High correlation dependence between the steady-state friction coefficient and the amplitude (correlation coefficient above 0.8 in 94 % of cases) and functional (correlation coefficient above 0.8 in 67 % of cases) surface texture parameters of tribo-track surface were obtained.”
The language were checked and improved as well as the quality of the figures (Fig.2, Fig.4, Fig.6, Fig.7).
We attached the improved version of the article.
Thank you again for the comments and hopefully, we were able to integrate them in the paper fully!
Author Response File: Author Response.pdf
Reviewer 4 Report
"Abstract", WHY → This section usually contains texts mainly defining what is the objective of the study or this work was done.
"Introduction", Test method of Tribological and Mechanical Properties is suggested to added (https://doi.org/10.1080/17480272.2022.2119432)
Figure 1 The title is too cumbersome. It is recommended to rewrite.
Provide the model of experimental detection equipment。
There is no space between the Numbers and Celsius units, 21±1 °C.
From the graph (see Fig. 7)→From Figure 7.
Provide more explaination for the conclusion (the value and standard deviation of reuslts increased with the increase of wear).
Provide the reason for the selection of experimental parameters.
The pixels of some pictures are too low. It is recommended to provide pictures with high pixels
In general, it is suggested that this manuscript can be accepted after minor revision.
Author Response
Dear Reviewer,
Thank you for the comments/suggestions! We tried to take them into account in order to raise the quality of the paper.
The Abstract section was prepared based on the instructions for the authors, including the necessary sections: Background, Methods, Results, Conclusions (https://www.mdpi.com/journal/lubricants/instructions). We tried to emphasize the WHY aspect in the abstract text “Improving the material properties using nanocoatings for such a widely used material as, for example, bearing steel 100Cr6 makes it possible to improve the service life of machine parts. In this paper, the correlation dependence between tribological and mechanical properties of the NSC and its surface texture are considered to determine how much surface texture will affect tribological performance of the coated workpieces, as well as the measuring and evaluation procedure of the nanocoatings are presented.”.
Unfortunately, Riga Technical University does not have access to the Taylor and Francis publications database, so we could not fully familiarize ourselves with the recommended article. We certainly noted the existence of this article and will try to get access to it in the near future.
We created a shorter description to Fig. 1, corrected the editorial spaces in the paper and tried to make it more readable and clear. Fig.2, Fig.4, Fig.6 and Fig.7 were improved so that the images have higher quality. The tribometer model were added as well.
An explanation was given for the conclusion that the standard deviation increases with increasing wear: “This can be explained by the fact that as the total worn area increases, the numerical value of the standard deviation also increases proportionally, as well as for a material or coating with low wear resistance, wear debris impact and separation of layers is possible in specific places, which accordingly affects the size of the wear cross-sectional area and standard deviation”.
The experimental settings for tribo-measurements were chosen based on the recommendations in standard ISO 18535 (Diamond-like carbon films – Determination of friction and wear characteristics of Diamond-like carbon films by ball-on-disc method), also we improved the text in paper for clarity. Accordingly, the experimental settings for the microhardness measurements were chosen based on technological availability and to cover the widest possible range of forces. At the lowest applied force (0.1 N), the hardness of the coating (the indentation depth does not exceed 10% of the thickness of the coating) was measured, not the integrated hardness, thus the microhardness value of the coating was obtained. Surface texture were analysed according to ISO 25178 (Geometrical Product Specifications (GPS) – Surface texture: areal) standard.
We attached the improved version of the article.
Thank you again for the comments and hopefully, we were able to integrate them in the paper fully!
Author Response File: Author Response.pdf
