The Effectiveness of Diamond-like Carbon a-C:H:Si Coatings in Increasing the Cutting Capability of Radius End Mills When Machining Heat-Resistant Nickel Alloys

Round 1

Reviewer 1 Report

I kindly ask to read the attached file and propose a new version

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 1 Comments

 

Dear reviewer,

Thank you very much for your kind evaluation of our work. We do agree with all your proposals and comments and have modified the manuscript according to them. The revised fragments are marked green.

We hope that with your comments the manuscript will be suitable for publishing in Coatings and will attract many potential readers of the journal.

 

Kind regards,

Authors.

 

Point 1: A wide work, some point needs serious rework, coating technology is well explained but not the machining issues. Ref 1 for example is not well induced, many people worked before about Inconel 718.

 

Response 1: Thank you! Additional links are added in the first paragraph. Please confirm that the authors correctly interpreted your kind comment.

 

Point 2: I humbly ask to make a better version, because I was studying the topic over the last 5 years, and some aspects are not logic: state of the art (poor) discussion (weak)..a new version is really needed. Some projects in China are making some results with ball-end milling tools, but flank milling could be also used.

 

Response 2: Thank you! We have tried to revise it. We hope that in the current version it looks better. In any case, we are open to follow further suggestions.

 

Point 3: Why ball-end is important here. Ball-end it is not common in Inconel, with the exception of blades or IBR, please check ASME journal about IBRs in Journal of Manufacturing Science and Engineering…for instance. Integral blade rotors are made in In718, some people like Urbikain are proposing barrel-shape tools, this is quite new.

 

Response 3: Thank you, we agree with the reviewer that the cutters used in the job are not the most common in the industry for nickel-based superalloys, but they are not rare either. The proportion of shaped and curved surfaces in aviation products made of nickel alloys is significant (where our cutters can potentially be used). Here we rely on the data of fundamental works in authoritative publications, for example:

1. Wang, B., Liu, Z. Influences of tool structure, tool material and tool wear on machined surface integrity during turning and milling of titanium and nickel alloys: a review. Int J Adv Manuf Technol 98, 1925–1975 (2018).
2. Ulutan D, Özel T Machining induced surface integrity in titanium and nickel alloys: A review. Int J Mach Tools Manuf 51(3), 250–280 (2011)

Fundamentally important, revealing the features and demonstrating the prospects of Inconel milling with ball end mills is the work of:

3. Sonawane, H.A., Joshi, S.S. Modeling of machined surface quality in high-speed ball-end milling of Inconel-718 thin cantilevers. Int J Adv Manuf Technol 78, 1751–1768 (2015). https://doi.org/10.1007/s00170-014-6759-6

The most typical example of use is processing the feather of the blades of gas turbine engines, where profile milling is necessary, which involves multi-axis processing of curved surfaces. In recent years, the range of end mills produced by the tool industry has become so broad that enterprises have an alternative in terms of tool selection to solve any technological problem. The barrel-shaped (conical barrel-shaped geometry that smoothly transitions into a spherical head) mentioned by a respected reviewer is indeed a very progressive and promising tool, but it is a more expensive tool and is intended exclusively for finishing still. End mills with a spherical cutting part are more affordable today, and the scope of their technological application is wider. Spherical cutters, similar in design and geometry to those used in this paper, are available for semi-finishing and finishing milling and can be found in the catalogs of most reputable carbide tool manufacturers (high-temperature nickel alloys are listed as one of the applications), for example:

1) GUHRING is the most reputable German company, a recognized world leader in the production of axial cutting tools

https://webshop.guehring.de/en/frsen/hpcradiusfrser/3026

2) Karnasch Professional Tools - German manufacturer of professional metal cutting tools https://karnasch.tools/mediafiles/blaetterkatalog/katalog_gk34/160/

3) KYOCERA SGS Precision Tools is the largest manufacturer of fine-grain carbide axial cutting tools in the US

https://www.kyocera-sgstool.com/uploads/products/downloads/KSPT_Performance_Endmill_PDF.pdf

4) Dormer Pramet is a UK-based global manufacturer and supplier of cutting tools for mechanical engineering, including milling tools.

https://www.dormerpramet.com/Downloads/Dormer_EndMill_Brochure_EN.pdf

Taking into account the remark made by the reviewer, we have added the following to the test of the article (1. Introduction, at the end of the second paragraph):

“In recent years, the range of carbide end mills produced by the tool industry has been so broad that enterprises have an alternative tool selection to solve any technological problem.

A variety of end mills with a spherical cutting part is a conical barrel-shaped geometry that smoothly turns into a spherical end. It is an advanced and promising tool for finishing curved surfaces, which, like the classic ball end mills, should not be deprived of the attention of specialists.”

As for the works of one of the authoritative specialists in the field of Inconel 718 alloys machining, Dr. Urbikain Gorka from the University of the Basque Country, mentioned by the reviewer, we carefully studied his works. He is a prominent scientist in this field who has done a lot for the development of science. We added his seminal work to the list of references:

4. Pérez-Ruiz, J.D.; López de Lacalle, N.; Urbikain, G.; Pereira, O.; Martínez, S.; Jorge B. On the relationship between cutting forces and anisotropy features in the milling of LPBF Inconel 718 for near net shape parts. Int. J. Mach. Tools Manuf. 2021, 170, 103801

In addition, we have added the following fundamental papers regarding the experience of authoritative scientific groups with materials such as Inconel 718:

5. Wang, B.; Liu, Z. Influences of tool structure, tool material and tool wear on machined surface integrity during turning and milling of titanium and nickel alloys: a review. Int. J. Adv. Manuf. Technol. 2018, 98, 1925–1975
6. Ulutan, D.; Özel, T. Machining induced surface integrity in titanium and nickel alloys: A review. J. Mach. Tools Manuf. 2011, 51, 250–280

 

Point 4: Please discuss this important point.

• Natural thermocouple: the idea is Good. How much is the resolution and the calibration procedure?

 

Response 4: Thank you, we do agree and these points were clarified. We have described in more detail the methodology and the calibration procedure in paragraph 2.5 of the article (the first paragraph to subsection 2.5).

“The natural thermocouple method is one of the simplest and most accurate methods for experimentally estimating the temperature under the cutting conditions compared to the methods of artificial and semi-artificial thermocouples. When the workpiece and the cutter are combined into a closed electrical circuit, the magnitude of the thermoelectromotive force occurring in the thermoelement is proportional to the temperature of the sliding "junction" of the formed thermocouple. A thermocouple "junction" can be presented as a large number of parallel-connected thermocouples with internal resistance. It is important to note that the temperature in the contact stabilizes within 5 seconds from the start of cutting, and further, it allows us to estimate the average temperature of the cutting zone without focusing on one of the contact surfaces with an error of no more than 6 °C.”

 

We have added to Figures 4(a) and 4(b) another Figure 4(c), which explains in detail the principle of natural thermocouple calibration. In addition, we have added an appropriate description in the text as follows:

Figure 4. Functional diagram of a system based on a turning-milling machine for measuring the average cutting temperature (a), and visualization of the temperature distribution at the cutting edge and adjacent layers of tool material (b) and calibration diagram of a natural thermocouple (c).

 

“The study of the temperature on the contact pads during cutting was carried out by the method of a natural thermocouple (the average temperature during milling was estimated) [52-55]. Figure 4 (a) shows a functional diagram of a system for measuring the cutting temperature, implemented based on a turning-milling machine. Visualization of the temperature distribution at the cutting edge and adjacent layers of tool material is shown in the Figure 4 (b). During the experiments, the part and the end mill were isolated from each other in order to eliminate errors from the so-called "parasitic" thermo-EMF. Thermo-EMF was measured in the range of 5.0-5.5 min after the start of cutting at the stage of the steady-state process (after the running-in stage). Mercury current collectors and a recording device of the Endim 622 model (VEB Messapparatwerk, Германия) were used to register and record the thermo-EMF value. Experimental data were received and processed in an information processing and control rack.”

 

AND

 

“The application package TemPole (Ufa Aviation State Technical University, Ufa, Russia) was used to process the array of data on the measurement of thermo-EMF. An original system was used for calibrating natural thermocouples based on a differential heating scheme and a model of local contact of a single microroughness of the tool and processed materials to convert the obtained values of thermo-EMF during cutting into temperatures. A distinctive feature of this approach is that the natural thermocouple was calibrated at different pressures at the contact during loading and unloading, and heating was carried out by an electro-contact method. Figure 4 (c) shows the calibration scheme for a natural thermocouple. The calibration process was based on a differential scheme. A model of local contact of a single microroughness of a tool is used as a hot junction of a thermocouple. It was made in the form of a two-sided spherical indenter made of tool material under a normal load, embedded in plane-parallel samples of a nickel alloy. In this case, the indenter was given a rotational motion, and the lower sample was heated by the electrocontact method using a regulating transformer. Specially made samples from the material to be machined and indentors from the tool material, including those with coatings, were used. The actual contact temperature was recorded with a control chromel-alumel thermocouple with a diameter of 0.03-0.05 mm and the Endim recording device, on which the thermo-EMF of a natural thermocouple was recorded. The heating temperature was changed due to a change in the strength of the transmitted electric current, the regulating transformer. The contact zone was heated by an electrical installation, which is a step-down and control transformers. The readings of the thermo-EMF of the control thermocouple during cooling and various modes of loading and unloading of the contact zone were recorded, and then they were converted to the corresponding temperature values according to the calibration tables. Comparison of temperature values during machining nickel alloy in a wide range of cutting speeds, and visualization of the temperature distribution on the cutting edge and adjacent layers of tool material, was carried out using a specialized module based on the Deform 3D software package from SFTC (USA).”

 

Point 5: • Figure 5 b…is it the square a defect…did you eliminate droplets after coating method.

Did you check the issues cited by some people in Enhanced performance of nanostructured coatings for drilling by droplet elimination

 

Response 5: The respected reviewer is right since defects in the form of microdroplets are observed in its structure during the TiAlN coating deposition (Fig. 5b). These microdroplets are a distinctive feature of the coatings' deposition from a stream of multicomponent plasma of a vacuum-arc discharge containing microdroplets of the evaporated material (especially during the evaporation of aluminum target). Large microdroplets can reduce the adhesion strength of the coating and cause delamination of coating areas during operation. Various filtration systems are used to minimize them. It should be noted that it is impossible to completely eliminate microdroplets during TiAlN deposition, but it is possible to minimize them by the more expensive the filtration system of the vacuum plasma installation. At the same time, the diameter of the tool is significant. Microdroplets are critical for small-sized tools and cutters with a diameter of no more than 3 mm, and manufacturers use expensive plasma purification systems. In our case, A more simplified plasma filtering system can be used for a reasonably large tool (end mills with a diameter of 12 mm). It will already allow reducing the size and number of microdroplets. Below we have specifically compared the surface of cutters with TiAlN applied under filtration conditions and the surface of test samples with TiAlN coatings applied without filtration (some difference is observed). The coating we obtained is quite efficient on cutters of large diameter, and we did not observe pronounced delamination. Note that the structure of the purchased tool with TiAlN coatings is similar to our technology.

We have added the following phrase from the first paragraph of subsection 3.1 (before the sentence “The TEM image of the surface layer structure of hard alloy samples coated with CrAlSiN-DLC….) to emphasize it:

“It is noticeable that individual microdroplets are encountered on the surface during the deposition of the TiN-AlN-TiAlN coating, even despite the presence of a filtration system in the vacuum-plasma installation. These microdroplets are a distinctive feature of the deposition of coatings from a stream of multicomponent plasma of a vacuum-arc discharge (especially during the evaporation of aluminum). Available experience shows that forming a small amount of microdroplets is not critical for a sufficiently large tool (which includes milling cutters with a diameter of 12 mm) because it does not have a pronounced effect on the strength of the adhesive bond between the coating and the carbide substrate.”

 

Point 6: • 4. Discussion is the poorest point, because the references used were somewhat old. Too many from Grigoriev, in some cases not very well linked with paper content.

 

Response 6: Thank you for your refined evaluation of our work. We have reworked it according to your comments. We hope that it looks better in the current version.

 

Point 7: • CrAlSiN-DLC: did you work with special cutting-Edge treatments like blasting or drag grinding? Some people in Materials and Manufacturing Processes 32 (6), 678-686 gave the real influence in that, because coatings for Nickel alloys are very tricky.

 

Response 7: Thank you for your proposal. Our reviewer is correct that the surface condition of a carbide tool plays a crucial role in the operation of the tool properties and significantly when cutting difficult-to-machine alloys. We have seen excellent work related to the advent of inkjet technologies and the abrasive effect on a potentially dangerous tool. Nevertheless, we wanted to influence precisely the DLC films on the speed tool when milling nickel alloys within our research framework. Therefore, we excluded the influence of any other factors and used the tool with the expectation presented on the market, to begin with. If we encountered coatings, then there would be an effect on the surface of the hard alloy, that means on the soil, which would make it difficult for us to develop the contribution of one or another process. Therefore, we consider using various inkjet technologies and aggressive impact as a development of our work.

 

Point 8: • Line 486: the temperature near the cutting edge is the parameter that limits the cutting ability of ball end mills in cutting nickel alloys of the Inconel 718, …OK but you missed the good approaches in the last 5 years by: Polvorosa, Suarez, Wretland, and others in J manufacturing processes, in In718, Waspaloy and Haynes. This is unacceptable, because the review was really poor. Really is out of any logic not to discuss at the light of the proposed knowledge.

 

Response 8: Thank you very much for pointing this work. We have met it before and now once again looked at the most outstanding results of the authors. The presented results of face-turning for two alloys (including nickel alloy) using cooling at 6 and 80 bar shows that large grain alloy structure leads to higher notch wear when the smaller grain one leads to higher flank wear. We should add that we have not investigated the influence of cooling in the cutting conditions but the influence of the developed coating in the cutting conditions. However, the mentioned idea will be considered in our further research.

The mentioned sentence was rewritten as follows:

The experimental studies showed that the temperature near the cutting edge is the parameter that limits the cutting ability of diamond-like carbon a-C:H:Si coated ball end mills in cutting nickel alloys of the Inconel 718 type to a greater extent (in the conditions of the dry milling).

 

Point 9: • Recently there were works published in IJ Machine Tools and Manufacture about On the relationship between cutting forces and anisotropy features in the milling of LPBF Inconel 718 for near net shape parts and the consequences in the Journal Mechanical Systems and Signal Processing 168, 108675

 

Response 9: Thank you very much for pointing out this article. It was included in the introduction.

 

Point 10: •In last words: please make a better version or please withdraw the paper, in 2022 we have to propose complete discussed works.

 

Response 10: Thank you for your thorough review of our work and your experience with difficult-to-machine alloys, which we greatly appreciate. The article has been revised based on your very helpful comments. We sincerely hope that this version of the article can be considered for the next round of peer review.

Author Response File: Author Response.docx

Reviewer 2 Report

The presented article is prepared at a high scientific level. However, there are some minor issues, which I recommend to check and/or make a correction:

• Line 13: An acronym DLC means Diamond-Like Coating. However, according to references [34, 35, 36, 37, 38, 39, 40, 44, 45, 46] DLC means Diamond-Like Carbon coating. Please, check the real meaning of the DLC acronym.
• Lines 14, 73, 106, 113, 134, 135, 136, 229, 242, 329, 334, 345, 348, 351, 352, 357, 360, 368, 427, 455, 491, 495: I believe the proper term for “hard alloy” (or “hard-ally”; or “hard metal”) is “carbide” (or “sintered carbide” or “wolfram carbide”). Please, check the correct term.
• Lines 69, 129: Perhaps you want to write “mill’s” instead of “mills´”.
• Line 82: I am confused by the term “forces´ work”. Perhaps you want to write “working force”. Please, check this term.
• Lines 111-124: The last paragraph of the introduction is very similar to the abstract (lines 12-25). I do not consider this as a problem, but perhaps it would be better to make it more original.
• Line 127: The term “curved surfaces” is not wrong, but usually is used the term “free-form surfaces (FFS)”.
• Table 1: It is not necessary to use italic only for one “ISO 3878”.
• Table 1: Letters “I” and “C” in KIC should be in a lower index (K_IC).
• Table 1: The unit for crack resistance probably should be “MPa.m^1/2”. Please check it.
• Table 2: Please identify the type of percentage – wt.%? Or at.%? Or vol.%?
• Line 183: Perhaps you want to write “sample’s” instead of “samples´”.
• Line 184: Is it possible to quantify the amount of repetition? If so, you should write the exact number.
• Line 212: You should add the acronym “SEM” behind “Scanning electron microscopy”.
• Line 223: You should add the acronym “TEM” behind “transmission electron microscopy”.
• Line 240: Please, check if the word “wells” is correctly used.
• Line 248: Perhaps it would be better to use units “mm/s” instead of “cm/s” for sliding speed.
• Lines 255, 257, 258, Fig.3a: The speeds should be labelled by lower-case “v” (“v” for velocity; “V” for volume).
• Lines 255, 258, Fig.3a: The feed should be labelled as “f” (or “f_z“ for feed per tooth; or “v_f” for feed rate).
• Lines 255, 258: “given cutting depth” should be referred to as “depth of cut” and labelled as “a_p” (“t” usually refer to “thickness”).
• Figure 3b: The parameter “h_f” were not described in the text above, nor in the figure description. It should refer to tool wear on the flank face, but this parameter is usually labelled as “VB”.
• Lines 263, 517: There should be specified the “speed” as “cutting speed”.
• Line 267: There should be explained why were reported maximum value of the tool wear instead of the average value.
• Line 269: I am not sure if “chamfer” is the correct word.
• Line 292: Is there any “Latin alphabet equivalent” to word “Германия”?
• Figure 10: Perhaps there could be profilograms for cutting speeds 200 and 250 m/min as well. However, if you were limited by a number of pages, I consider cutting speed 150 m/min as the most important representant.
• Figure 11: Perhaps there could be conditions for cutting speeds 150 and 200 m/min as well. However, if you were limited by a number of pages, I consider cutting speed 250 m/min as the most important representant.
• Lines 540-542: You kept the instruction for acknowledgement. Please correct or delete the acknowledgement.
• Line 582: It seems there is number “1” instead of the lower-case letter L in 6Al-6V-2Sn.
• Line 656: It seems there is upper-case i instead of the lower-case L in Ti6Al4V.

Author Response

Response to Reviewer 2 Comments

 

Dear reviewer,

Thank you very much for your kind evaluation of our work. We do agree with all your proposals and comments and have modified the manuscript according to them. The revised fragments are marked yellow.

We hope that with your comments the manuscript will be suitable for publishing in Coatings and will attract many potential readers of the journal.

 

Kind regards,

Authors.

 

Point 1: Line 13: An acronym DLC means Diamond-Like Coating. However, according to references [34, 35, 36, 37, 38, 39, 40, 44, 45, 46] DLC means Diamond-Like Carbon coating. Please, check the real meaning of the DLC acronym.

Response 1: Thank you for noticing it. It’s modified.

Point 2: Lines 14, 73, 106, 113, 134, 135, 136, 229, 242, 329, 334, 345, 348, 351, 352, 357, 360, 368, 427, 455, 491, 495: I believe the proper term for “hard alloy” (or “hard-ally”; or “hard metal”) is “carbide” (or “sintered carbide” or “wolfram carbide”). Please, check the correct term.

Response 2: Thank you for pointing it out. To be more precise, the manuscript was modified as proposed.

Point 3: Lines 69, 129: Perhaps you want to write “mill’s” instead of “mills´”.

Response 3:Thank you, it is revised.

Point 4: Line 82: I am confused by the term “forces´ work”. Perhaps you want to write “working force”. Please, check this term.

Response 4: Thank you, the correct form will be “work of forces” (https://en.wikipedia.org/wiki/Work_(physics)). It is revised.

Point 5: Lines 111-124: The last paragraph of the introduction is very similar to the abstract (lines 12-25). I do not consider this as a problem, but perhaps it would be better to make it more original.

Response 5: Thank you for your attention to the details. We have tried to make it different.

Point 6: Line 127: The term “curved surfaces” is not wrong, but usually is used the term “free-form surfaces (FFS)”.

Response 6: Thank you, it is revised.

Point 7: Table 1: It is not necessary to use italic only for one “ISO 3878”.

Response 7: Thank you, it is corrected.

Point 8: Table 1: Letters “I” and “C” in KIC should be in a lower index (KIC).

Response 8: Thank you, it is modified.

Point 9: Table 1: The unit for crack resistance probably should be “MPa.m1/2”. Please check it.

Response 9: Thank you, it is an absolutely correct remark. The standard unit in SI is MPa·m^1/2. It is revised.

Point 10: Table 2: Please identify the type of percentage – wt.%? Or at.%? Or vol.%?

Response 10: Thank for the question. Traditionally, the chemical composition is indicated in mass fractions (wt.%), corrected in the table.

Point 11: Line 183: Perhaps you want to write “sample’s” instead of “samples´”.

Response 11: Thank you, it is corrected in the text.

Point 12: Line 184: Is it possible to quantify the amount of repetition? If so, you should write the exact number.

Response 12: Thank you for pointing it out. It is difficult to understand it from the context, but it is about the developed principle of the designed setup operation. For multilayer coating, the process repeats many times. The exact number of repeats depends on the designed structure of the coating and its thickness. It is corrected in the text.

Point 13: Line 212: You should add the acronym “SEM” behind “Scanning electron microscopy”.

Response 13: Thank you, it is modified.

Point 14: Line 223: You should add the acronym “TEM” behind “transmission electron microscopy”.

Response 14: Thank you, it is modified.

Point 15: Line 240: Please, check if the word “wells” is correctly used.

Response 15: Thank you for your proposal; indeed, “holes” sound better in this context.

Point 16: Line 248: Perhaps it would be better to use units “mm/s” instead of “cm/s” for sliding speed.

Response 16: Thank you for your exquisite sense of scientific writing style. It is modified.

Point 17: Lines 255, 257, 258, Fig.3a: The speeds should be labelled by lower-case “v” (“v” for velocity; “V” for volume).

Response 17: Thank you, corrected in the text.

Point 18: Lines 255, 258, Fig.3a: The feed should be labelled as “f” (or “fz“ for feed per tooth; or “vf” for feed rate).

Response 18: Thank you, it is revised.

Point 19: Lines 255, 258: “given cutting depth” should be referred to as “depth of cut” and labelled as “ap” (“t” usually refer to “thickness”).

Response 19: Thank you, it is revised.

Point 20: Figure 3b: The parameter “hf” were not described in the text above, nor in the figure description. It should refer to tool wear on the flank face, but this parameter is usually labelled as “VB”.

Response 20: Thank you, it is revised.

Point 21: Lines 263, 517: There should be specified the “speed” as “cutting speed”.

Response 21: Thank you, it is revised.

Point 22: Line 267: There should be explained why were reported maximum value of the tool wear instead of the average value.

Response 22: Thank you, it was a technical mistake. Of course, the average value was taken into account. It is revised.

Point 23: Line 269: I am not sure if “chamfer” is the correct word.

Response 23: Thank you, it is revised.

Point 24: Line 292: Is there any “Latin alphabet equivalent” to word “Германия”?

Response 24: Thank you, there was mentioned Germany. It is revised.

Point 25: Figure 10: Perhaps there could be profilograms for cutting speeds 200 and 250 m/min as well. However, if you were limited by a number of pages, I consider cutting speed 150 m/min as the most important representant.

Response 25: Thank you for your advice. The authors fully agree with you. The profilograms are only shown for 150 m/min to avoid overloading the article.

Point 26: Figure 11: Perhaps there could be conditions for cutting speeds 150 and 200 m/min as well. However, if you were limited by a number of pages, I consider cutting speed 250 m/min as the most important representant.

Response 26: Thank you once again. The authors fully agree with you. The SEM-images are only shown for 250 m/min to avoid overloading the article.

Point 27: Lines 540-542: You kept the instruction for acknowledgement. Please correct or delete the acknowledgement.

Response 27: Thank you for pointing it out. It is deleted.

Point 28: Line 582: It seems there is number “1” instead of the lower-case letter L in 6Al-6V-2Sn.

Response 28: Thank you for your attention to the details. It is revised.

Point 29: Line 656: It seems there is upper-case i instead of the lower-case L in Ti6Al4V.

Response 29: Thank you for your attention to the details. It is revised.

Author Response File: Author Response.docx

Reviewer 3 Report

 

The authors presented an article « The Effectiveness of Diamond-like a-C:H:Si Coatings in Increasing the Cutting Capability of Radius End Mills When Machining Heat-Resistant Nickel Alloys ».

• Abstract

Please provide the main quantitative and qualitative research core findings.

• In the last paragraph of the introduction section

What is the scientific novelty of the paper? What is the practical value? What makes this approach different from other researchers?

• Material and Methods

The texts on Figure 1 can be given more clearly.

The contents of some elements (C, Si, S, P) in Table 2 are not given. The content of these elements should be given or removed from the table 2.

How did you determine the cutting parameters?

How many repetitions of measurements are used?

• Results and Discussion

Figure 11 should be explained in more detail in the text.

It is useful to add explanations of parameters to the results obtained. At least five sentences for each Figures.

The results obtained should be explained by supporting the literature. It is useful to add explanations of phenomena to the results obtained.

• Conclusions

The conclusions need to be improved. What is the novelty of the article? What is the practical significance? What are the differences from previous works?
Please provide the main quantitative and qualitative research findings.

 

Authors should carefully study the comments and make improvements to the article step by step. All changes should be highlighted in color. After minor changes can an article be considered for publication in the "Coatings".

Author Response

Response to Reviewer 3 Comments

 

Dear reviewer,

Thank you very much for your kind evaluation of our work. We do agree with all your proposals and comments and have modified the manuscript according to them. The revised fragments are marked blue.

We hope that with your comments the manuscript will be suitable for publishing in Coatings and will attract many potential readers of the journal.

 

Kind regards,

Authors.

 

Point 1: The authors presented an article « The Effectiveness of Diamond-like a-C:H:Si Coatings in Increasing the Cutting Capability of Radius End Mills When Machining Heat-Resistant Nickel Alloys ».

Abstract

Please provide the main quantitative and qualitative research core findings.

 

Response 1: Thank you, the abstract is revised.

 

Point 2: In the last paragraph of the introduction section

What is the scientific novelty of the paper? What is the practical value? What makes this approach different from other researchers?

 

Response 2: Thank you, I would like to thank the reviewer for the made remark. If such a question arose, it means that the purpose of the work was not clearly presented, and the novelty was not correctly explained. There are only a few examples of technological studies where DLC coatings were produced in the conditions of a real cutting process similar to production ones, and the effectiveness was evaluated for tool protection in machining nickel alloys specifically. Mainly published works are devoted to cutting non-ferrous metals. Until recently, it was believed that the heat stress of milling Inconel-type alloys is excessive for thin films based on DLC, and they cannot provide high wear resistance under such conditions. Numerous works are devoted to using nanocomposite TiAlSiN/TiSiN/TiAlN-, and TiAlN-coated. Extended research in the field of DLC coatings for milling nickel alloys is presented in the works:

1. Ucun I, Aslantas K, Bedir F The performance of DLC-coated and uncoated ultra-fine carbide tools in micromilling of Inconel 718. Precis. Eng. 2015, 41, 135–144 (this work is devoted to microcutters with a diameter of 760 µm);
2. Grigoriev SN, Volosova MA, Fedorov SV, Okunkova AA, Pivkin PM, Peretyagin PY, Ershov A. Development of DLC-Coated Solid SiAlON/TiN Ceramic End Mills for Nickel Alloy Machining: Problems and Prospects. Coatings 2021, 11(5), 532 (this paper focuses on 10 mm diameter end mills made of innovative cutting ceramic instead of cemented carbide).

We have added clarifications to the last paragraph of the introductory part:

“The aim of the work was to study the ability of DLC coatings based on aC:H:Si with a CrAlSiN nitride sublayer to withstand thermal loads in a wide temperature range (varied by choosing a different speed milling mode such as 150, 200, and 250 m/min). The efficiency of DLC-coating deposed to cemented carbide ball end mills was evaluated compared to uncoated ball end mills and the samples coated with the well-proven multi-layer gradient TiN-AlN-TiAlN coating under high-temperature conditions (at 20, ~550, ~650, ~850 °C). During the experiments, the particular focus was on assessing temperature in the cutting zone as the most important and, in many ways, informative parameter. The thermo-EMF (electromotive force) was recorded, which was converted into temperature values according to the corresponding calibration charts using the method of natural thermocouple in the cutting zone. For the first time, the authors compared the behavior of CrAlSiN-DLC and TiN-AlN-TiAlN coatings deposed to ball end mills under operating conditions at different cutting temperatures with the results of high-temperature tribological tests on a friction machine. New experimental results on the assessment of the cutting ability of cemented carbide ball end mills with CrAlSiN-DLC coatings at different levels of thermal loads, as well as establishing the effect of coatings on the state of the machined surface of a nickel alloy part, can be a step towards expanding the areas of technological application of DLC-coatings and implementation based on new technical solutions for the needs of the aviation industry.”

 

Point 3: Material and Methods

The texts on Figure 1 can be given more clearly.

 

Response 3: Thank you for your kind comment. It is revised. We hope that in the current version it looks clearer.

 

Point 4: The contents of some elements (C, Si, S, P) in Table 2 are not given. The content of these elements should be given or removed from the table 2.

 

Response 4: Thank you for pointing it out; it is revised.

 

Point 5: How did you determine the cutting parameters?

 

Response 5: Thank you once again. The cutting conditions in this work were similar to those assigned in real operating conditions of ball end mills and those recommended by world manufacturers of cutting tools that produce spherical cutters of a design identical to that used in work such as KYOCERA SGS Precision Tools, Dormer Pramet. We should note that the feed was not varied during experiments since it has a much smaller effect (compared to the cutting speed) on the level of thermal loads.

In paragraph 2.4. at the end of the first paragraph (before figure 3), the following phrase was added:

The cutting conditions were chosen based on the need to provide a wide range of thermal loads on the cutting part of end mills with DLC-coatings and taking into account the recommendations of the leading manufacturers of cemented carbide ball end mills for cutting hard-to-cut alloys such Guhring and Karnasch Professional Tools (Germany) and others.

 

Point 6: How many repetitions of measurements are used?

 

Response 6: Thank you for the question. There were at least 10 repetitions for each type of coating and ball end mill in the determined cutting conditions. The relevant data is added in the text of the manuscript.

 

Point 7: Results and Discussion

Figure 11 should be explained in more detail in the text.

 

Response 7: The reviewer's comment is correct. We should have originally illustrated Figure 11 differently and Figure 10, which are essentially correlated.

In Figure 10, we have added profiles of the cutting edge of ball end mills, which immediately give a clear visual representation of an important conclusion such as intense sticking of nickel alloy on the cutting edge of the cutter that sharply worsens the condition of the machined part. In Figure 11, we have added contrast SEM-images of the distribution of nickel (particles in red) on the working surfaces of the end mills. Supplementary images immediately make it possible to evaluate the differences in coating effect under increased thermal loads (at a cutting speed of 250 m/min).

 

Point 8: It is useful to add explanations of parameters to the results obtained. At least five sentences for each Figures.

 

Response 8: Thank you for your kind suggestion. The volume of the description was enlarged and placed in the section of the Discussion.

 

Point 9: The results obtained should be explained by supporting the literature. It is useful to add explanations of phenomena to the results obtained.

 

Response 9: Thank you. We have seriously revised section 4 Discussion, as it was in the recommendations of a respected reviewer.

The results obtained on the increase in the resistance of the cemented carbide with coatings to abrasion (Figure 6) demonstrate expected trends since the formed TiN-AlN-TiAlN and CrAlSiN-DLC coatings significantly increase the microhardness of the contact areas of the specimens. Lower abrasion of CrAlSiN-DLC coating over most of the test distance have similar character since the resistance to abrasive wear is determined not only by the microhardness of the contacting surfaces but also mainly by the friction coefficient on the contact pads. Optical analysis of worn holes shows that the rotating sphere quickly wipes through both variants of the coatings under the study, but the CrAlSiN-DLC coating is able to restrain the development of a wear center for a longer time. The noted can be explained by the so-called "edge effect", when the coating remaining along the edges of the hole is capable of reducing the wear rate to a certain point. A similar mechanism was observed by various authors when studying the behavior of PVD coat-ings, in particular [69].

69. Mo, J.L.; Zhu, M.H.; Leyland, A.; Matthews, A. Impact wear and abrasion resistance of CrN, AlCrN and AlTiN PVD coat-ings. Surf. Coat. Technol. 2013, 215, 170–177.

However, the data on resistance to abrasive wear are not sufficient in predicting the coatings behavior directly in cutting under the influence of increased temperature loads typical for milling nickel alloys. The results of tribological tests on a friction machine (Figure 7) were obtained at different levels of thermal impact on the contact zone of two coun-ter bodies, such as tool hard alloy and processed nickel alloy, which are of greatest re-search interest. Figure 7 (a) shows that nitride coatings are obviously and noticeably inferior to DLC-coating at room temperature, which was predictable, taking into account the experimental results previously obtained by the authors of the work in the study of the frictional behavior of various coatings in contact with a nickel alloy [70].

70. Volosova, M.A.; Fedorov, S.V.; Lyakhovetskiy, M.A.; Mustafaev, E.S.; Melnik, Y.A. Effect of PACVD deposition of nitride and Si-containing amorphous hydrogenated carbon films on the tribological characteristics of SiAlON ceramics. Proceedings of SPIE 2021, 11802, 118020T.

The results of tribological tests when exposed to high temperatures such as 550, 650, and 800 ˚C (Figure 7b–c) can explain the effectiveness of the CrAlSiN-DLC coating in terms of increasing the tool cutting ability in milling at cutting speeds of 150 and 200 m/min (1.5 and 1.4 times). However, in milling at speeds of 250 m/min (Figure 8) when elevated temperatures act on the cutting edge, the coating did not show any effect. For example, when analyzing the measured average temperatures at the contact pads of ball end mills with CrAlSiN-DLC coating (Figure 9), it can be seen that they are of 530, 620, and 870 ˚C at cutting speeds of 150, 200, and 250 m/min, respectively. As follows from authoritative works [8-10,17], the prevailing wear mechanism is the adhesive in such temperature conditions, which occurs due to continuous and repetitive gripping processes (cold welding) of the workpiece material and the tool. An increase in temperature promotes an increase in the adhesion component of the friction coefficient, intensifies the gripping processes, and increases the gripping area of the contacting surfaces and the amount of heat released during friction. Thus, when the temperature in the contact zone of two materials rises, an increase in the contact surfaces' friction force and wear rate is expected. In this work, such conclusions were made for the machined material of an Inconel 718 type alloy, but the observed patterns are valid for a broad class of materials. The authors of [71] drew similar conclusions for machining AISI 316 L stainless steel.

71. Parthasarathi N.L.; Borah U.; Albert S.K. Effect of temperature on sliding wear of AISI 316 L(N) stainless steel—analysis of measured wear and surface roughness of wear tracks. Mater. Des. 2013, 51, 676–682.

As long as the CrAlSiN-DLC coating exhibits a lower coefficient of friction at cutting speeds of 150 and 200 m/min, which corresponds to cutting temperatures of 530 and 620 ˚C, respectively, it contributes to the already described significant reduction in the intensification of adhesive gripping processes. The effect of CrAlSiN-DLC coating at milling speeds of 150 and 200 m/min and the average cutting temperatures corresponding to these conditions of about 530 and 625 ˚C (Figure 9) can be considered significant since the milling time to critical wear increases by 1.5 and 1.4 times. Furthermore, it immediately affects the condition of the surfaces in contact. Under these conditions, minimal stuck material on the surface of the machined part and the working surfaces of ball end mills. As can be seen in Figure 8c, the cutting ability of ball end mills under such conditions increases only 1.1 times, which is insignificant.

The coefficient of friction on the contact surfaces significantly depends on the level of thermal exposure and predetermines the wear intensity of the cutting part of the ball end mill in machining nickel alloys and affects the state of the machined surface of the part.

The data presented in Figure 9 at a cutting speed of 150 m/min demonstrate a critical pattern such as higher temperature and friction coefficient on the working surfaces of ball end mills without coating and with TiN-AlN-TiAlN coating contribute to intense sticking of the nickel alloy to the active part cutting edge and directly onto the machined surface of the part, significantly worsening its condition. Many authors, particularly in the review, noted increased adhesion of the nickel alloy to the carbide tool and workpiece when using nitride coatings at cutting speeds up to 150 m/min [72]. In the case of the CrAlSiN-DLC coating formed on the working surfaces, lower temperatures and friction coefficients are observed in the cutting zone, and there are barely noticeable deposits on the cutting edge. In this case, the surface condition of the part is significantly improved.

The higher cutting temperatures that occur at high milling speeds (250 m/min) and the increased coefficient of friction on the contact surfaces observed for ball end mills without coating and with CrAlSiN-DLC coating contribute to the sticking ("spreading") of the nickel alloy on cutting edge and flank face of the tool (Figure 10). In addition, the pre-sented SEM images of the distribution of nickel (particles of red color) on the tool's work-ing surfaces make it possible to visually evaluate the differences between cutters without coating and with two coating options.

72. Fan, W.; Ji, W.; Wang, L. et al. A review on cutting tool technology in machining of Ni-based superalloys. Int. J. Adv. Manuf. Technol. 2020, 110, 2863–2879.

 

Point 10: Conclusions

The conclusions need to be improved. What is the novelty of the article? What is the practical significance? What are the differences from previous works?

Please provide the main quantitative and qualitative research findings.

 

Response 10: Thank you for your kind suggestions. It is revised. The main quantitative and qualitative research findings are highlighted. We hope that in the current version it corresponds to the requirements of the reviewer.

 

Point 11: Authors should carefully study the comments and make improvements to the article step by step. All changes should be highlighted in color. After minor changes can an article be considered for publication in the "Coatings".

 

Response 11: Thank you for your thorough review of our work and your experience in the research topic, which we greatly appreciate. The article has been revised based on your helpful comments. We sincerely hope that this version of the article can be considered for the next round of peer review.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

VERY GOOD WORK.  Some Little things must be improved.

Minor changes:

• The first references 1-5 are introduced without a brief explanation of each one. The same happens with [57–63];
• 3. Evaluation of the Coated: in tis section you repeat a lot the SEM brand, you can reduce the section introduction by half

Section 2.4: if both piece and tools rotates, there will be a results cutting speed much more that of milling….or perhaps the rotation of the part is much slower. You need to define this.

Figure 9: what is this? A simulation by FEM??

Author Response

Response to Reviewer 1 Comments

 

Dear reviewer,

Thank you very much for your kind evaluation of our revision. We do agree with all your proposals and comments and have modified the manuscript according to them. The revised fragments are marked red.

We hope that with your comments the manuscript will be suitable for publishing in Coatings and will attract many potential readers of the journal.

 

Kind regards,

Authors.

 

Point 1: VERY GOOD WORK.  Some Little things must be improved.

Minor changes:

The first references 1-5 are introduced without a brief explanation of each one. The same happens with [57–63];

 

Response 1: Thank you for your kind proposal. The fragments are revised.

 

Point 2: 3. Evaluation of the Coated: in tis section you repeat a lot the SEM brand, you can reduce the section introduction by half

 

Response 2: Thank you, it is modified. There are 9 lines instead of 15 ones in the previous version of the manuscript.

 

Point 3: Section 2.4: if both piece and tools rotates, there will be a results cutting speed much more that of milling….or perhaps the rotation of the part is much slower. You need to define this.

 

Response 3: Thank you for this question. We have also discussed during the experiments with our research team and wanted to add up these speeds. There was 250 m/min for a ball end mill and about 2 m/min for a workpiece. However, such a difference does not make a significant impact on the temperature. The relevant sentence is added:

“During the experiments, the research team discussed adding up the speeds for summary value taking into account v_w. However, such a difference does not show a significant impact on the temperature in the cutting zone.”

 

Point 4: Figure 9: what is this? A simulation by FEM??

 

Response 4: Thank you for your attention to detail. It was mentioned in the section of Materials and Methods, subsection 2.5 (highlighted with red). The software module offers EMF data, converts it to temperature using calibration tables, and visualizes it in the Deform (SFTC, USA). The relevant software module is mentioned in the title of Figure 9.

Author Response File: Author Response.docx