Microstructure and Mechanical Behavior of Magnetron Co-Sputtering MoTaN Coatings

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review on the Manuscript entitled:

Microstructure and Mechanical Behavior of Magnetron Co-Sputtering MoTaN Coatings

 Dear Editor,

In this article, the authors have investigated microstructure and mechanical properties of ternary molybdenum tantalum nitride, MoTaN, coatings. The effects of composition and microstructure variations on mechanical properties, including hardness, elastic modulus, and wear behavior, are investigated. In general, the MoTaN coatings exhibit a columnar polycrystalline microstructure with MoN(111), Mo₂N(111), Mo₂N(200), TaN(200) and TaN(220) multiple phases and orientations through X-ray diffraction analysis.... In my opinion, the subject of this manuscript is interesting and applicable. I recommend this article for publishing in the Coatings; however, it needs some revisions:

1. “In general, the MoTaN coatings exhibits a columnar polycrystalline microstructure…” should be corrected as: In general, the MoTaN coatings exhibit a columnar polycrystalline microstructure…”

2. Please indicate the novelty of this work at the end of abstract.

3. Please indicate the relation coefficient of the line graphs in Figure 1 & 2 and then describe them.

4. Please re-read the manuscript carefully to correct the grammatical errors, typos or any other mistakes.

5. In Figure 3, the authors didn’t mention the frequency amounts of the X-ray spectrum.

6. It is recommended that authors consider a short paragraph as the final consequence at the end of the Results and Discussion section to give a clear indication to the readers.

7. Please increase the quality and labeling of the Figures in the manuscript.

8. Have the authors achieved thermodynamic parameters such as thermal enthalpy or Gibbs free energy for stability approval? Please explain it.

9. Please indicate the units of all parameters in the Figure 10.

10. “In recent years, binary transition metal nitride coatings, including TiN, MoN, NbN, WN, CrN, ZrN, TaN [5-11] have been intensively studied and manipu-lated with superior mechanical performance.” Please indicate the bulk citations of [5-11] for each compound.

11. Please define the abbreviation for the first time in the manuscript such as SAED, TEM, H–TEM, etc.

Author Response

Reviewer1

1. “In general, the MoTaN coatings exhibits a columnar polycrystalline microstructure…” should be corrected as: In general, the MoTaN coatings exhibit a columnar polycrystalline microstructure…”

Ans: Thanks for the suggestion from the reviewer, the sentence in Abstract is corrected as recommended.

2. Please indicate the novelty of this work at the end of abstract.

Ans: Thanks for the suggestions from the reviewer. The abstract is modified thoroughly with several sentences in the beginning and the end to address the novelty of this work. The first two sentences are added as “In recent years, there has been important development in refractory metal nitride coating, such as MoN, TaN, NbN…etc, for versatile applications. The engineered approaches, including deposition method, microstructure control, structural design, and addition of functional elements, are put into practice for promotion of the coating characteristics.” and the last several sentences are rewritten as “The tuning of input power during deposition plays a critical role in determining the overall performance of the MoTaN co-sputtering coatings. The MoTaN coating with an optimized mechanical property is attributed to the microstructure of multiple phase and fine columnar grain size less than 30 nm.”

3. Please indicate the relation coefficient of the line graphs in Figure 1 & 2 and then describe them.

Ans: Thanks for the suggestion. The relation coefficient of the atomic percentage v.s. input power modulation was calculated and added in Fig.1, as recommended. Several sentences were also inserted in 3.1 section “The dependence of elemental atomic percentage as a function of input power modulation was calculated and indicated. The decrease of Mo and the increase of Ta in the MoTaN coatings show a similar correlation approximately 3.0 and 3.3. This led to a consequence that N was constant in all coatings.” to address this point.

4. Please re-read the manuscript carefully to correct the grammatical errors, typos or any other mistakes.

Ans: Thanks for the suggestion from the reviewer. The entire article was carefully checked with grammar, usage of English, spelling… to make a flawless manuscript. All the changes are marked in red.

5. In Figure 3, the authors didn’t mention the frequency amounts of the X-ray spectrum.

Ans: The information concerning X-ray wavelength is provided in the revised manuscript and the related sentence in Experimental Procedures is modified as “Phase identification of the films was carried out through the X-ray diffraction technique (XRD, Ultima IV, Rigaku, Japan) using a conventional theta-2 theta scan with Cu Kα of λ = 0.1541 nm as the incident source.”

6. It is recommended that authors consider a short paragraph as the final consequence at the end of the Results and Discussion section to give a clear indication to the readers.

Ans: Thanks for the great suggestion. The paragraph to address the critical points and novelty in this work is added in the end of 3. Results and Discussion session.  “In summary, the addition of Ta in the MoTaN films with the modulation of input power showed a monotonic proportion relationship. The MoTaN films with Ta incorporation from 3.7 to 16.8 at.%. The superior hardness, elastic modulus, H/E, H³/E², and wear resistance are recognized for MoTaN coatings with 6.8 to 10.4 at.%Ta and a maximum hardness of 18.0 GPa was found for the MoTaN coating deposited at an input power modulation of Mo/Ta = 150/100 W/W. The multiple phase feature with fine columnar grain size are the reasons for MoTaN coating to reach an optimized mechanical property. The MoTaN thin films are developed for enhanced performance for protective application to elongate the lifetime and strengthen the surface properties of the materials of interests in consideration of sustainability. The effect of input power during deposition plays a critical role in determining the overall performance of the MoTaN co-sputtering coatings.

7. Please increase the quality and labeling of the Figures in the manuscript.

Ans: Quality of several figures and their labels are modified as suggested by the reviewer.

8. Have the authors achieved thermodynamic parameters such as thermal enthalpy or Gibbs free energy for stability approval? Please explain it.

Ans: Thanks for the suggestion. There do have been attempts from the authors to verify stability from a thermodynamic perspective. According literatures, basic thermodynamic parameters, like formation enthalpy, for MoN and TaN are available and could be compared. However the sputtering and the deposition processes are far more kinetic ones. The as-deposited Mo(Ta)N thin films in this study possess a multi-phase feature and evolve with increasing impact input power in the plasma, meaning that it’s more difficult to go on a thermodynamic equilibrium for the process. As for the thermodynamical stability of the microstructure of the films, it is designed as the perspective to research the phase stability of the coatings under annealing treatments.

9. Please indicate the units of all parameters in the Figure 10.

Ans: The units of Fig. 10 are introduced and modified for a better understanding. Since the index “H/E” has no unit, so the authors leave the blank for it.

10. “In recent years, binary transition metal nitride coatings, including TiN, MoN, NbN, WN, CrN, ZrN, TaN [5-11] have been intensively studied and manipu-lated with superior mechanical performance.” Please indicate the bulk citations of [5-11] for each compound.

Ans: The related sentence in the Introduction section has been revised as “In recent years, binary transition metal nitride coatings, including TiN[4], MoN[5], NbN[6], WN[7], ZrN[8], TaN[9] have been intensively studied and manipulated with superior mechanical performance.” as recommended.

11. Please define the abbreviation for the first time in the manuscript such as SAED, TEM, H–TEM, etc.

Ans: All the abbreviations have been defined in the 2^nd paragraph of the 2. Experimental procedures section. 

Reviewer 2 Report

Comments and Suggestions for Authors

The article "Microstructure and Mechanical Behavior of Magnetron CoSputtering MoTaN Coatings" has good potential and is devoted to a rather interesting topic aimed at improving the performance of tool or component parts, such as ball bearing, drilling bit, and cutting tools in the surface engineering industry. However, the results and conclusions made in this work diverge. In my opinion, the authors have not achieved the stated goal.

1. The abstract should indicate which optimal mechanical properties are achieved.

2. The introduction should better explain why the authors used TaN and MoN.

3. Fig. 4, 5, 6 typo - (c)v, there is no signature (c) in Fig. 7. Also, the font of the signatures in Fig. 4, 5, 6, 7, 8 is very small.

4. In Fig. 4-8, the SAED images are very similar. It seems that the authors use one figure for each sample.

5. How does changing the deposition mode affect the structure of the coatings? Does the size of the columnar elements change?

6. The conclusion about the improvement of mechanical properties looks completely unconvincing. The hardness for all samples differs within the error limits. Therefore, the conclusion about the increase in mechanical properties is incorrect. All samples have similar properties.

 

7. The introduction of tantalum practically did not improve the properties of the coatings, which calls into question the purpose of this work.

Author Response

Reviewer 2

1. The abstract should indicate which optimal mechanical properties are achieved.

Ans: The abstract is thoroughly modified and a sentence “The optimized hardness of 18.0 GPa and elastic modulus of 220.7 GPa were obtained.” is inserted to stress the point raised by the reviewer.

2. The introduction should better explain why the authors used TaN and MoN.

Ans: Thanks for the suggestion from the reviewer. Two sentences “The formation of MoO₃ phase was demonstrated to be beneficial for reduction of friction force and promotion of anti-wear performance.” and “The combination of MoN and TaN, or to add Ta into the MoN to form a MoTaN coating could be one attempt toward a new protective coatings system.” are introduced in the Introduction section, as recommended by the reviewer.

3. 4, 5, 6 typo - (c)v, there is no signature (c) in Fig. 7. Also, the font of the signatures in Fig. 4, 5, 6, 7, 8 is very small.

Ans: The labels and the icon indication are improved in the revised manuscript as indicated by the reviewer.

4. In Fig. 4-8, the SAED images are very similar. It seems that the authors use one figure for each sample.

Ans: Thanks for the indication of the duplicated data of selected area diffraction patterns in the TEM analysis. The original Figs. 5b and 7b, which are identical with the Figs, 6b and 8b, respectively, are corrected. This work did work on SAED analysis on the different samples, and the results are shown in the revised paper. The SAED images appear a quite similar fashion could be due to the fact that all the films have a polycrystalline structure, with the main phases being relatively similar. Thanks again for this opportunity to clarify and to correct this point.

5. How does changing the deposition mode affect the structure of the coatings? Does the size of the columnar elements change?

Ans: Changing the input power of tantalum would alter its content. When the Ta content reached 6.8 at.%, TaN(200) began to appear, which subsequently influenced the grain size of Mo₂N(200). This point and other indications concerning the controlling parameter-microstructure-characterization are addressed in 3.3 and 3.4 sessions.

6. The conclusion about the improvement of mechanical properties looks completely unconvincing. The hardness for all samples differs within the error limits. Therefore, the conclusion about the increase in mechanical properties is incorrect. All samples have similar properties.

Ans: Thanks for the comment to this work. Indeed, the performance of the hardness did not exhibit a significant change as a function of input power modulation. Nevertheless, the hardness did show slight increase with Ta power and reached an optimized value. With the consideration of index of H/E and H³/E², which would be much more strongly correlated to power control, the anti-wear performance showed a limited damaged wear characteristics, as indicated in Fig. 11d, as compared. It is believed that the outcome is not overstressed that all the data and results are described in a comparative basis.

7. The introduction of tantalum practically did not improve the properties of the coatings, which calls into question the purpose of this work.

Ans: Thanks for the comments to the motivation of this work. As described in the above point, the combination of the MoN and TaN to form a MoTaN coating system was put into practice using co-sputtering technique and microstructure and mechanical property characterization. This is a comparative work on MoN and MoTaN films. Although the hardness and elastic modulus did not show significant changes against input power modulation, the indications of H/E and H³/E² and related wear behavior showed significant difference and an optimized combination could be deduced. To better address this point, a paragraph was added in the end of 3. Results and Discussion for a better understanding for the potential readers.

Reviewer 3 Report

Comments and Suggestions for Authors

This study investigates the microstructure and mechanical properties of MoTaN coatings deposited by reactive RF magnetron co-sputtering with varying Mo/Ta input power ratios. The observed improved mechanical and tribological properties are attributed to the multiple phase structure and nanocrystalline grain size.

Having that said, I would like to share some suggestions as an opportunity to enhance the manuscript:

 While basic mechanical and tribological properties are evaluated, the study lacks application-specific testing that could demonstrate the potential of these coatings in real-world scenarios. For instance, high-temperature performance, corrosion resistance, or cutting tool evaluations could enhance the practical relevance of the work.

The study does not address residual stresses in the coatings, which can significantly impact mechanical properties and coating adhesion. Incorporating residual stress measurements could offer a more complete understanding of the coating behavior.

The manuscript focuses on as-deposited properties but does not explore the long-term stability or potential degradation mechanisms of the coatings. Studies on thermal stability or performance under prolonged wear conditions could be valuable additions.

 The work is primarily experimental. Incorporating theoretical modeling or simulations could provide deeper insights into phase formation and mechanical behavior at the atomic scale.

 

The study does not address the environmental impact or sustainability aspects of the coating process, which are increasingly important considerations in materials development.

Author Response

reviewer3

This study investigates the microstructure and mechanical properties of MoTaN coatings deposited by reactive RF magnetron co-sputtering with varying Mo/Ta input power ratios. The observed improved mechanical and tribological properties are attributed to the multiple phase structure and nanocrystalline grain size.

Having that said, I would like to share some suggestions as an opportunity to enhance the manuscript:

While basic mechanical and tribological properties are evaluated, the study lacks application-specific testing that could demonstrate the potential of these coatings in real-world scenarios. For instance, high-temperature performance, corrosion resistance, or cutting tool evaluations could enhance the practical relevance of the work.

The study does not address residual stresses in the coatings, which can significantly impact mechanical properties and coating adhesion. Incorporating residual stress measurements could offer a more complete understanding of the coating behavior.

The manuscript focuses on as-deposited properties but does not explore the long-term stability or potential degradation mechanisms of the coatings. Studies on thermal stability or performance under prolonged wear conditions could be valuable additions.

The work is primarily experimental. Incorporating theoretical modeling or simulations could provide deeper insights into phase formation and mechanical behavior at the atomic scale.

The study does not address the environmental impact or sustainability aspects of the coating process, which are increasingly important considerations in materials development.

Ans: Thanks for the suggestions from the reviewer. Indeed, for the hard or protective coating application, journal papers and technical reports frequently worked on characterizations, like hardness, elastic modulus, adhesion strength, residual stress, wear and corrosion resistance, as well as real practice tests, such as drilling, fretting, cutting, sea water test, fatigue etc. And as one who is in this field realizes even one specific test possesses multiple dimensions in testing parameters, not to mention for one property of a material there exists several approaches for evaluation. The authors feel sorry about not being able to provide all kinds of test results for this work, in which the microstructure, hardness, elastic modulus, and wear behavior are focused. The authors also like to thank the suggestions from the reviewer and hopefully in the near future the other mentioned property evaluations will be put into practice and shown in the related papers. The impact for environment of the coating manufacture process or its sustainability are addressed in the new paragraph in the end of the Results and Discussion section, as suggested. Generally speaking, the TaN and MoN coatings are developed with higher durability and thermal stability than conventional transition metal nitrides like TiN and CrN. For example TiN film could withstand a temperature of 550°C without oxidation while CrN could survive a temperature of 650°C in air. TaN and MoN exhibit superior properties and thus are beneficial in reducing environmental impact and helpful in sustainability.

Reviewer 4 Report

Comments and Suggestions for Authors

The authors report the reactive RF sputtering deposition of MoTaN thin films. The report provides details on the microstructure and tribological behavior as a function of deposition parameters. Overall, the study is well structured and the manuscript is well written. My only comment to the authors is to please provide the reference for XRD data (simulated or PDF from literature) that have been used to assign the peak positions. 

Author Response

reviewer4

The authors report the reactive RF sputtering deposition of MoTaN thin films. The report provides details on the microstructure and tribological behavior as a function of deposition parameters. Overall, the study is well structured and the manuscript is well written. My only comment to the authors is to please provide the reference for XRD data (simulated or PDF from literature) that have been used to assign the peak positions.

Ans: The built-in Jade software are employed to identify the XRD peaks for phase identification. Several relevant literatures in this study, like [1,6,9,19] listed in the following, are also referred.

[1] M. Kommer, T. Sube, A. Richter, M. Fenker, W. Schulz, B. Hader, J. Albrecht,. “Enhanced wear resistance of molybdenum nitride coatings deposited by high power impulse magnetron sputtering by using micropatterned surfaces”, Surf. Coat. Technol., 333 (2018) 1-12.

[6] M. Benkahoul, E. Martinez, A. Karimi, R. Sanjinés, F. Lévy,. “Structural and mechanical properties of sputtered cubic and hexagonal NbNx thin films”, Surf. Coat. Technol., 180-181 (2004) 178-183.

[9] D. Bernoulli, U. Müller, M. Schwarzenberger, R. Hauert, R. Spolenak, “Magnetron sputter deposited tantalum and tantalum nitride thin films: An analysis of phase, hardness and composition”, Thin Solid Films, 548 (2013) 157-161.

[19] P. Tan, L.C. Fu, J. Teng, J.J. Zhu, W.L. Yang, D.Y. Li, L.P. Zhou, “Effect of texture on wear resistance of tantalum nitride film” Tribology International, 133 (2019) 126-135.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Review letter

Dear Editor,

Regarding the author’s revision, I am pleased to inform my satisfaction of present form of the manuscript entitled: “Microstructure and mechanical behavior of magnetron co-sputtering MoTaN coatings” for publication in Coatings.

Author Response

Reviewer Comments:

Thanks for the constructive comments from the reviewer.

Reviewer 2 Report

Comments and Suggestions for Authors

I consider the conclusions presented in the article to be unconfirmed. In particular: "According to nanoindentation and wear resistance analysis, the superior hardness, elastic modulus, H/E, H3 /E2, and wear resistance are recognized for the MoTaN coatings with 6.8 to 10.4 at.% Ta and a maximum hardness of 18.0 GPa was found for the MoTaN coating deposited at an input power of Mo/Ta = 150/100 W/W. The optimized hardness of 18.0 GPa and elastic modulus of 220.7 GPa were obtained. in determining the overall performance of the MoTaN co-sputtering coatings. The MoTaN coating with an optimized mechanical property is attributed to the microstructure of multiple phase and fine columnar grain size less than 30 nm."

 

All coatings have the same hardness (Fig. 9). It changes within the measurement error. The introduction of tantalum had virtually no effect on the studied properties of the coatings.

It is necessary to change the conclusions made in this work so that they do not contradict the data obtained

Author Response

Response to the reviewer's comments:

Ans: Thanks the constructive suggestions from the reviewer. Indeed, the hardness and elastic modulus data is within certain deviations. The authors rewrote several sentences in the last paragraph in Results and Discussion and Conclusion to avoid the contradiction, as mentioned by the reviewer.

The modified sentences in the last paragraph in Results and Discussion were read as "Through nanoindentation analysis, the hardness and elastic modulus values of the MoTaN films ranged from and 17.0 to 18.0 GPa and 213.8 to 220.7 GPa, respectively. There was no significant differences between samples. Nevertheless, a maximum hardness of 18.0 GPa and resultant superior H/E and H³/E² were observed at an Mo/Ta input power of 150/100 W/W. The calculated H³/E² values indicated improved wear resistance, as illustrated in Figure 11. In comparison to the MoN film, the MoTaN coatings exhibited superior mechanical properties, attributed to its multiphase structure and fine columnar grain size."

The modified sentence in Conclusion was read as "The better antiwear performance were found for the MoTaN fabricated with input power modulation Mo/Ta of 150/100 W/W and a resultant Ta content of 10.4 at.%."

All the modifications for the 2nd revised manuscript were marked in blue.