Improvement of Mechanical Properties and Adhesion of Ti-Al-Si-N Coatings by Alloying with Ta
, Evgenii D. Kuzminov 1, Yuriy A. Garanin 1,2, Alexey V. Panin 1,2 and Andrey I. Dmitriev 1,3,*
Round 1
Reviewer 1 Report
Comments in the attach document.
Comments for author File: 
Comments.pdf
Author Response
We thank the Reviewer for the careful reading of the manuscript and valuable comments that helped us to improve and clarify it. Please find below a detailed point-by-point response to all comments. The comments have been also addressed in the revised manuscript. All the changes made in the revised manuscript have been highlighted in yellow.
0. English language and style are fine/minor spell check required
Response: English language was polished through the text.
1. Description, state of the art and in general the introduction content is clear. The reading of the section is pleasant and simple; however there not approach to real sectors. Results are not entirely clear because there are no strategies to compare with those currently used by the industry. What is the real application of this kind of coatings in industry?
Response: Thank you for this relevant comment. Ti-Al-N-based coatings are widely used to protect cutting tools, stamps, gas turbine engine blades, etc. Ti-Al-Ta-Si-N coating appear to be more promising since it presents excellent mechanical and tribological properties, thermal stability and oxidation resistance. The information about common industrial applications of the coatings was included in Section I “Introduction” of the revised manuscript.
2. The paper focuses on the effect of Ta on quaternary coating; however, I consider that it is necessary a wide analysis of the Tantalum effects on the microstructure and chemistry comparing with the reference coating. Please consider a revision of these topics in introduction section.
Response: Indeed, to improve the mechanical behavior of protective coatings, it is required to undergo the detailed examination their microstructure and chemistry. The Tantalum effects on the microstructure and properties of Ti-Al-N-based coatings has been widely analyzed in our previous works (40,41 and 44).
1) Shugurov, A.R.; Kuzminov, E.D.; Kasterov, A.M.; Panin, A.V.; Dmitriev, A.I. Tuning of Mechanical Properties of Ti1−xAlxN Coatings through Ta Alloying. Coat. Technol. 2020, 382, 125219. https://doi.org/10.1016/J.SURFCOAT.2019.125219.
2) Eremeev, S.V.; Shugurov, A.R. Chemical Bonding Analysis in Ti1–x–yAlxTayN Solid Solutions. Coat. Technol. 2020, 395, 125802. https://doi.org/10.1016/j.surfcoat.2020.125802.
3) Shugurov A.R., Panin A.V., Kasterov A.M. Effect of Ta alloying on isothermal oxidation behavior of DC magnetron sputtered Ti1-xAlxN coatings on titanium substrate // Surf. Coat. Technol. – 2021. – V.421. – 127488.
Information about the effect of Ta on the properties of the Ti-Al-N coatings was included in Section I “Introduction” of the revised manuscript.
3. In line 107, is not specified the number of silicon inserts used in the TiAl target. What is the relation between Si inserts and silicon composition? The silicon content was kept at 5 at.%, these results are reproducible? Which was the methodology to obtain this percentage?
Response: We used from 10 to 13 Si inserts in order to maintain the constant Si content 5 at.% in the coatings. So, the total area of the Si inserts was increased step-by-step by 10 % compared with their initial area. The reproducibility of the results was confirmed by obtaining the coatings with the same chemical compositions at a certain number of the Si inserts.
4. In line 115, the Bragg Brentano (BB) technique was used for the coating phase identification, authors can assure the absence of substrate influence? There are some methodologies (not instrumental) to avoid substrate effect using BB configuration? If yes, include it in the manuscript.
Response: We didn’t use any additional methods of analysis to avoid the substrate response, because the Ti substrates used in this work provided only separate XRD peaks, which didn’t overlap with the coating peaks.
5. In line 125, hardness measurements, methodology and conditions are missing. How many indentations were done? Load Vs displacement curves were analyzed? How and which penetrations depths were used? The lack of these test conditions is serious at this research level.
Response: Thanks for this important comment. The loading and unloading times were set at 20 s with 10 s dwell time at the maximum load and 60 s dwell time at 90% unloading for thermal drift correction. The maximum applied load was set at 20 mN to ensure penetration depths below 10% of the coating thickness in order to exclude the substrate effect on the measured mechanical characteristics. 20 indents were made for each coating, and the results obtained were averaged. The hardness (H) and Young’s modulus (E) of the coatings were determined from load vs. displacement curves using the Oliver-Pharr method. This information was included in Section II “Materials and Methods” of the revised manuscript.
6. In relation with XRD results and considering the comments of materials and methods section, it is important to review lattice parameter, phase identification, and peaks position. At the technical and research level, the article is interesting. This involves mechanical and microstructural characterization and also adhesion strength. Is evident the influence of Ta in that properties; however, no surprises were found in the results associated with microstructural, mechanical, and adhesion behavior. In this sense and intending to increase the impact and rigor of the article, I recommend including a quantitative chemical analysis of the coatings, since the detector limit of the EDS technique is in the order of 1-10 wt%.; additionally, it is known that EDS error, affected mainly by the surface quality and morphology is around 2-5%. Taking into account the narrow and close values of Ta contents in coatings I consider relevant quantitative analysis such as XPS. Effect of Ta content in the target to evaluate coating performance.
Response: According to the available information, the experimental error in EDS is usually about 1-2 %. Moreover, we have performed additional investigations of the elemental composition of each type of the coatings using the wavelength dispersive spectroscopy, which provides significantly higher accuracy than EDS. In all cases, the deviation between the two methods was less than 0.5 at.%.
7. Lines 192 to 194: SEM images of the coatings are not enough to affirm a dense non-columnar finegrained microstructure, to consider this STEM FIB or TEM micrographs are necessary. How fine are the grains of the coatings? There were not measured. The analysis of the results should be done based on observations and measuring.
Response: Indeed, STEM FIB and TEM are more applicable to study the microstructure of the coatings. Nevertheless, SEM images of fracture cross-sections are commonly used to characterize coatings microstructure (see e.g. Tillmann, W.; Dildrop, M. Influence of Si Content on Mechanical and Tribological Properties of TiAlSiN PVD Coatings at Elevated Temperatures. Surf. Coat. Technol. 2017, 321, 448–454. https://doi.org/10.1016/j.surfcoat.2017.05.014; 30.; Li, G.; Li, L.; Han, M.; Luo, S.; Jin, J.; Wang, L.; Gu, J.; Miao, H. The Performance of TiAlSiN Coated Cemented Carbide Tools Enhanced by Inserting Ti Interlayers. Metals 2019, 9, 918. https://doi.org/10.3390/met9090918). The non-columnar microstructure of the coatings can be clearly seen from the presented SEM micrographs. The average grain size in the coatings has been estimated from the XRD patterns by determination of the average size of coherently diffracting domains, which is the lower limit of the grain size. According to these results, which are presented in Fig. 4, the grain size in the coatings varies within 8-12 nm. It should be noted that the present study mainly deals with investigation of the mechanical and tribological properties as well as adhesion of the Ti-Al-Ta-Si-N coatings, which are of primary interest for the readership of Lubricants. However, currently we are performing detailed investigations of the microstructrure of the Ti-Al-Ta-Si-N coatings using TEM and HRTEM. These results will be presented in our next manuscript.
8. In relation with nanohardness measurements, similarly I mentioned in XRD results, an excellent and detailed methodological description ensures the validity and reliability of the results. Please consider my comments in line 125
Response: The detailed methodological description of the hardness measurements was given in Section II “Materials and Methods” of the revised manuscript.
9. In line 254, according to authors, poor adhesion is related to high residual compressive stress and, therefore high hardness and probably reduced crystallite size. There are some experimental alternatives to improved adhesion? Why no consider thermal treatments, substrate surface modifications, etc?
Response: Of course, there are different other methods to improve adhesion of the coatings, including substrate pre-treatment, deposition of adhesion layers, gradient coatings, etc. There are other studies, which are devoted to these issues, including those cited in Introduction. However, the present work focuses on the elaboration of a new kind of the Ti-Al-Si-N-based coatings with improved mechanical properties and adhesion strength.
Reviewer 2 Report
Review of the manuscript ‘Improvement of Mechanical Properties and Adhesion of 2 Ti-Al-Si-N Coatings by Alloying with Ta’ by Artur R. Shugurov, Evgenii D. Kuzminov, Yuriy A. Garanin, Alexey V. Panin and Andrey I. Dmitriev.
Comments to the Authors
This paper requires corrections and after that is publishable in Lubricants. However, in light of the following concerns, I recommend making major modifications to this paper before reconsidering.
The reviewer would like to address the following issues:
1. The literature analysis is not good enough, because the articles are not up to date
2. How many scratches did authors make?
3. Why authors used the specified amount of Ta?
4. Authors should add the errors bars on the graphs.
5. Why did not Authors show the results of EDS analysis?
Besides the aforementioned, the reviewer advised to check the language, maybe by a certified professional.
Author Response
We thank the Reviewer for the attentive reading and valuable comments. They have allowed us to improve the manuscript a lot. Please find the replies below. We have made some changes in the manuscript according to comments and suggestions. All the modifications were marked in yellow in the revised manuscript.
1. The literature analysis is not good enough, because the articles are not up to date.
Response: Section I Introduction and List of references were modified and more recent papers were included into consideration.
2. How many scratches did authors make?
Response: Two samples of each coating were used for scratch testing. Three scratches were made for each sample.
3. Why authors used the specified amount of Ta?
Response: The specified contents of Ta in the coatings were used because the earlier investigations reported that these contents provided the best combination of the protective properties (see e.g. Seidl, W.M.; Bartosik, M.; Kolozsvári, S.; Bolvardi, H.; Mayrhofer, P.H. Influence of Ta on the Fracture Toughness of Arc Evaporated Ti-Al-N. Vacuum 2018, 150, 24–28. https://doi.org/10.1016/j.vacuum.2018.01.028; Hollerweger R., Riedl H., Paulitsch J., Arndt M., Rachbauer R., Polcik P., Primig S., Mayrhofer P.H., Origin of high temper-ature oxidation resistance of Ti–Al–Ta–N coatings // Surf. Coat. Technol. – 2014. – V. 257. – P. 78–86. doi:10.1016/j.surfcoat.2014.02.067).
4. Authors should add the errors bars on the graphs.
Response: According to the reviewer’s suggestion, the error bars were added on the graphs.
5. Why did not Authors show the results of EDS analysis?
Response: The results of the EDS analysis were presented as chemical compositions of the coating studied. It seems that the EDS spectra could be superfluous, because they do not provide any additional information to the readers.
6. Besides the aforementioned, the reviewer advised to check the language, maybe by a certified professional.
Response: The manuscript was subjected to careful proofreading by a native English speaker.
Reviewer 3 Report
The authors have systematically investigated the Mechanical Properties and Adhesion of Ti-Al-Si-N Coatings by Alloying with Ta. The authors deserve appreciation and the article can be accepted for publication.
Author Response
Thank you very much for the careful reading of our manuscript. We have also made some minor changes in the manuscript according to the comments and suggestions of other reviewers. All the modifications were marked in yellow in the revised manuscript.
Round 2
Reviewer 1 Report
I want to express thanks to authors for response my comments, suggestions and clarify research and technical aspects. I am confident that the construction of science, technology through research articles is an interesting and enriching process that makes us better researchers. Therefore, I consider this discussion scenarios fundamental for improved our skills in the field of research.
The authors answer my questions related to the experimental details, which in turn, is useful for the questions done in the results section. With these clarifications, I consider that the document responds in terms of the quality required both by the level of Lubricants journal and for the scientific community expects.
Despite this, reading again the document arise a new concern: in line 109-110 appears “The Ta-free coatings were sputtered using a compound TiAl (55/45 at.%) target with Si inserts 125 mm in diameter “ it is 125 mm in diameter correct for Si insert? Note that in the next lines (110-112) is mentioned “The deposition of the Ta-alloyed coatings was performed by co-sputtering using the Ti/Al/Si 111 target and a Ta (99.99%) target 100 mm in diameter” I think that Si inserts measurements are wrong. Please explain or correct that.
I look forward to the article that the authors are preparing on the microstructural characterization of Ti-Al-Ta-Si-N coatings using TEM and HRTEM. It will be a useful and valuable complements to current article
Author Response
We thank the Reviewer for the careful reading of the manuscript and its positive assessment. About the comment. Yes, it was a misprint. The correct sentence is:
“The Ta-free coatings were sputtered using a compound TiAl (55/45 at.%) target 125 mm in diameter with Si inserts.”
The misprint was fixed in the revised manuscript.
Reviewer 2 Report
Thank you for the answers.
Author Response
We thank the Reviewer for the positive assessment of our manuscript.
