Resistance of PVD Coatings to Erosive and Wear Processes: A Review

Round 1

Reviewer 1 Report

• The paper discusses the current knowledge of the resistance of PVD coatings to degradation and also an influence of the properties of coatings and their structure on such resistance. In the hydraulic machines, damages caused by cavitation erosion and also by the erosion of solid particles results in an increase in the maintenance costs. This paper presents a case of how PVD coatings can help address this problem. 
• This paper provides a good review of the different PVD coatings and the readers can benefit from the learnings and examples mentioned in the paper.
• The paper is well-written, with clear text and easy to read. Also, adequate references have been presented. 
• The conclusions and/or analysis are supported well by the data or by citing references.
• The paper discusses both the improvements brought about by different PVD coatings and also their limitations.

Minor suggestions (optional) that could be done during formatting/final review:

• Suggest authors give abbreviation of the terms hardness (H) and Young’s modulus (E) in the abstract when it is mentioned for the first on Page 1, Line 20. It is mentioned on Page 2 , Line 60 but will be good to have it in the abstract as well.
• Page 1, Line 39: Suggest authors give units of hardness when they say 5 to 45 [10,11]
• Page 2, Line 60: Suggest authors correct H3 and E2, as these are raised to powers such H^3/E^2

Author Response

The paper discusses the current knowledge of the resistance of PVD coatings to degradation and also an influence of the properties of coatings and their structure on such resistance. In the hydraulic machines, damages caused by cavitation erosion and also by the erosion of solid particles results in an increase in the maintenance costs. This paper presents a case of how PVD coatings can help address this problem. 

This paper provides a good review of the different PVD coatings and the readers can benefit from the learnings and examples mentioned in the paper.

The paper is well-written, with clear text and easy to read. Also, adequate references have been presented. 

The conclusions and/or analysis are supported well by the data or by citing references.

The paper discusses both the improvements brought about by different PVD coatings and also their limitations.

Thank you very much for your opinion of my work.

Minor suggestions (optional) that could be done during formatting/final review:

• Suggest authors give abbreviation of the terms hardness (H) and Young’s modulus (E) in the abstract when it is mentioned for the first on Page 1, Line 20. It is mentioned on Page 2 , Line 60 but will be good to have it in the abstract as well.
  The abbreviations of hardness (H) and Young’s modulus (E) have been added in the abstract.
• Page 1, Line 39: Suggest authors give units of hardness when they say 5 to 45 [10,11]
  Thank you for your comment. I have left the unit by mistake. The hardness unit (GPa) has been added.
• Page 2, Line 60: Suggest authors correct H3 and E2, as these are raised to powers such H^3/E^2
  Thank you for your comment. The powers were omitted by mistake. Now, they are corrected and resistance to plastic deformation (H^3/E^2 ratio) is written correctly.

Reviewer 2 Report

Please read the authors guideline of this journal to see if abbreviations are allowed in the abstract section and title and also how to abbreviate a scheme. 

please reconsider the whole MS in order to make sure all sentences which are not the authors views are appropriately cited, e.g.,line 68-71 & 78.

if any of the figures is borrowed for reprint or resketched may need an appropriate license based on journals' policy.

I strongly recommend to reconsider the conclusion section in order to only and clearly summarise the points that have already in the body of the MS. 

 

Author Response

Thanks for all your comments on improving the manuscript. Below are the reviewers' comments and my responses to them:

1. Please read the authors guideline of this journal to see if abbreviations are allowed in the abstract section and title and also how to abbreviate a scheme.
   Thank you for your comment. According to the authors guideline: “abbreviations should be defined in parentheses the first time they appear in the abstract, main text, and in figure or table captions and used consistently thereafter”. The abbreviation of PVD had been defined in the abstract part.
2. Please reconsider the whole MS in order to make sure all sentences which are not the authors views are appropriately cited, e.g.,line 68-71 & 78.
   I suppose that MS means the main submission. All sentences which are not presented my view have been checked to be are cited. In the mentioned lines (68-71) the following sentences have been added: “However, the results of fatigue test also depend on the substrate material. For example, TiN coating deposited on 316L steel and tested at R = -1 and 50 Hz increased about 22% fatigue limit [31], while deposited on Ti–6Al–4V alloy caused about 24 % decrease in fatigue endurance [43]. Testing TiN coating deposited on Cr–Mo–V steel at R=-1 and 10 Hz, the fatigue limit increased about 7% [45].” All citations have been checked.
3. If any of the figures is borrowed for reprint or resketched may need an appropriate license based on journals' policy.
   All borrowed figures for reprint have the appropriate permissions from publisher.
4. I strongly recommend to reconsider the conclusion section in order to only and clearly summarise the points that have already in the body of the MS.
   As the conclusion section was not in the manuscript, I suppose that the reviewer suggested reconsidering the summary section. This section has been greatly expanded. I think that the summary section is much improved in the current version.

Reviewer 3 Report

To improve the manuscript, please perform some changes and provide additional information, as follows:

• the title and Abstract are written in a general manner; the class of materials should be defined along with the PVD methods for obtaining hard PVD coatings; the same observation is for the Introduction section, and the aim of this review;
• on page 1, line 39, define hardness as indentation hardness and put the measurement unit as GPa and specify the coating materials that have these values for hardness;
• on page 2, lines 60-61, and page 6, line 177, at H3/E2 put the numbers as a superscript;
• on page 2, line 76, "Resent investigations..." should be replaced with "Recent investigations...";
• on page 2, line 78, "...test devises" should be replaced with "...test devices";
• for all the figures that are included in this review and are copied from the published articles with protected rights should be obtained from the publisher (e.g. Elsevier) or the Copyright Clearance Center the rights to reuse the figures;
• on page 4, line  139, "Ti6Al4V steel" and in Fig. 4 caption delete "steel" since Ti6Al4V is a Ti-based alloy, not a Fe-based alloy (steel);
• in the Discussion section, the values for the properties of the coatings (e.g. thickness, hardness, etc.), substrate material and size, along with the comparatively properties related to the coatings, as well as the used PVD method should be specified, not only in some examples; 
• in the figures caption should be added material type for coatings and substrate and the PVD method to grow the coatings;
• on page 5, line 155, "...bas voltage..." should be replaced with "...bias voltage...";
• on page 5 - line 165, page 11 - line 347, and page 16 - line 475, check the measurement unit of the thickness of the coatings, which is not "m";
• on page 6, line 181, check NiTi/NiCT coatings, because it is not clear NiCT;
• on page 7, line 219, the thickness of the coatings should be defined instead of "thinner" and "thicker" coating;
• on page 8, line 262, "...young modulus..." should be replaced with "...Young modulus...";
• on page 12, line 368, "... the triboligical test..." should be replaced with "... the tribological test...";
• on Fig. 17 caption, and on page 16, line 479, instead of "the entire tests" should be specified the tribological testing conditions (normal load,  sliding speed, sliding distance, material and size of the counterbody/static partner); however, in the example from the reference [132] it is not clear which is the substrate material, the CoF value of the substrate, as well as when the coatings were delaminated from the substrate because the steady-state of the CoF for the coatings could be owed to the CoF of the substrate due to the high value of CoF (> 0.75); In this respect, I recommend you to provide additional data for this example, and results from other studies on the similar material class of coatings, using comparatively tribological testing conditions;
• on page 14, referring to the example from the reference [136], the sliding distance and the diameter of the balls used in the experimental works should be specified, along with the properties (hardness, and elastic modulus) of Si3N4, Al2O3, and steel balls;
• on page 16, line 484, correct the measurement unit for the wear rate;
• on page 16, referring to the critical loads (Lc), the microscratch testing conditions should be specified;
• on page 16, lines 500-501, "PVD coatings have many defects in the form of micro-droplets, so the surface roughness is relatively high [96,143]", I recommend you to specify the PVD method, the coating materials, the range of surface roughness of the coatings and substrate;
• on page 16, lines 500-512, provide the values for the thickness and surface roughness of the coatings, mention the substrate material and tribological testing conditions, specify how the coating polishing affected the thickness, morphology, chemical composition, and hardness of the coatings;
• in the Discussion and Summary/Conclusion sections, should be specified which are the best PVD methods to obtain hard PVD coatings with a good mechanical and tribological behavior, as well as which are the optimum PVD coatings for various applications, especially in this review were discussed different classes of materials for coatings and substrate, and different properties of these materials were compared; also, the testing conditions were not comparatively; therefore, I recommend you to quantify the results in a table to notice the main properties of the coatings and substrate, PVD method for coating deposition, main findings, as well as the practical applications of the developed coatings.

Author Response

Thank you for all your comments that allow improving my work.

• the title and Abstract are written in a general manner; the class of materials should be defined along with the PVD methods for obtaining hard PVD coatings; the same observation is for the Introduction section, and the aim of this review;
  The abbreviation of “PVD” has been defined.
  
  
• on page 1, line 39, define hardness as indentation hardness and put the measurement unit as GPa and specify the coating materials that have these values for hardness;
  The unit has been added as well as the type of the coatings. Now there is: “Hardness of the coating can be in range of 5GPa for Ti11Mg29Gd2N58 coating to 45 GPa for CrCN/CrN coating with 1 mm thick layer of tetrahedral carbon [10,11]. However, this method also allows producing reflective coatings, e.g. Nb2O5/SiO2 coating, with a hardness even lower than 1 GPa [12].”
  
  
• on page 2, lines 60-61, and page 6, line 177, at H3/E2 put the numbers as a superscript;
  The formation of numbers had been corrected.
  
  
• on page 2, line 76, "Resent investigations..." should be replaced with "Recent investigations...";
  Thank you, the word “Recent” has been corrected.
  
  
• on page 2, line 78, "...test devises" should be replaced with "...test devices";
  Thank you, the word “devices” has been corrected
  
  
• for all the figures that are included in this review and are copied from the published articles with protected rights should be obtained from the publisher (e.g. Elsevier) or the Copyright Clearance Center the rights to reuse the figures;
  All the figures have permission from the publisher (e.g. Elsevier) obtained from the Copyright Clearance Center. To each reused figures the sentence: reprinted from (the title of a journal, e.g. Ultrasonics Sonochemistry, reference number, e.g. Ref. [29]), with permission from Elsevier” has been added.
  
  
• on page 4, line  139, "Ti6Al4V steel" and in Fig. 4 caption delete "steel" since Ti6Al4V is a Ti-based alloy, not a Fe-based alloy (steel);
  Thank you for your comment, It has been corrected
  
  
• in the Discussion section, the values for the properties of the coatings (e.g. thickness, hardness, etc.), substrate material and size, along with the comparatively properties related to the coatings, as well as the used PVD method should be specified, not only in some examples; 
  The tables with detailed data have been added
  
  
• in the figures caption should be added material type for coatings and substrate and the PVD method to grow the coatings;
  In each figure caption material type for coatings and substrate and the PVD method to grow the coatings have been added.
  
  
• on page 5, line 155, "...bas voltage..." should be replaced with "...bias voltage...";
  Thank you, this mistake has been corrected.
  
  
• on page 5 - line 165, page 11 - line 347, and page 16 - line 475, check the measurement unit of the thickness of the coatings, which is not "m";
  Thank you, the unit of the thickness has been checked and corrected.
  
  
• on page 6, line 181, check NiTi/NiCT coatings, because it is not clear NiCT;
  Thank you, the coating name has been checked and corrected
  
  
• on page 7, line 219, the thickness of the coatings should be defined instead of "thinner" and "thicker" coating;
  Thank you, the coating thickness has been added instead of description "thinner" and "thicker"
  
  
• on page 8, line 262, "...young modulus..." should be replaced with "...Young modulus...";
  Thank you, this mistake has been corrected.
  
  
• on page 12, line 368, "... the triboligical test..." should be replaced with "... the tribological test...";
  Thank you, this mistake has been corrected.
  
  
• on Fig. 17 caption, and on page 16, line 479, instead of "the entire tests" should be specified the tribological testing conditions (normal load,  sliding speed, sliding distance, material and size of the counterbody/static partner); however, in the example from the reference [132] it is not clear which is the substrate material, the CoF value of the substrate, as well as when the coatings were delaminated from the substrate because the steady-state of the CoF for the coatings could be owed to the CoF of the substrate due to the high value of CoF (> 0.75); In this respect, I recommend you to provide additional data for this example, and results from other studies on the similar material class of coatings, using comparatively tribological testing conditions;
  All data concerning the test conditions has been added.
  
  
• on page 14, referring to the example from the reference [136], the sliding distance and the diameter of the balls used in the experimental works should be specified, along with the properties (hardness, and elastic modulus) of Si3N4, Al2O3, and steel balls;
  The tests conditions have been added.
  
  
• on page 16, line 484, correct the measurement unit for the wear rate;
  The unit for the wear rate has been corrected to mm³/Nm, which was used in Ref.[136].
  
  
• on page 16, referring to the critical loads (Lc), the microscratch testing conditions should be specified;
  The conditions of the scratch tests has been added.
  
  
• on page 16, lines 500-501, "PVD coatings have many defects in the form of micro-droplets, so the surface roughness is relatively high [96,143]", I recommend you to specify the PVD method, the coating materials, the range of surface roughness of the coatings and substrate;
  
  
• on page 16, lines 500-512, provide the values for the thickness and surface roughness of the coatings, mention the substrate material and tribological testing conditions, specify how the coating polishing affected the thickness, morphology, chemical composition, and hardness of the coatings;
  Detailed information has been added.
  
  
• in the Discussion and Summary/Conclusion sections, should be specified which are the best PVD methods to obtain hard PVD coatings with a good mechanical and tribological behavior, as well as which are the optimum PVD coatings for various applications, especially in this review were discussed different classes of materials for coatings and substrate, and different properties of these materials were compared; also, the testing conditions were not comparatively; therefore, I recommend you to quantify the results in a table to notice the main properties of the coatings and substrate, PVD method for coating deposition, main findings, as well as the practical applications of the developed coatings.
  There is a problem to specify the best method to obtain PVD coating with a good mechanical and tribological behavior, as well as which are the optimum PVD coatings for various applications.

Round 2

Reviewer 2 Report

the author has addressed some of the reviewers concerns. now I think it is publishable in this journal.

Author Response

Thanks for your opinion and accepting the current version of the manuscript.

Reviewer 3 Report

The author performed satisfactorily the revision of the manuscript. However, some amendments are needed:

- referring to the comment “the title and Abstract are written in a general manner; the class of materials should be defined along with the PVD methods for obtaining hard PVD coatings; the same observation is for the Introduction section, and the aim of this review;” the author provided the answer “The abbreviation of “PVD” has been defined.” I have the following observations:

- The class of the studied materials was not defined (at least some examples of nitride coatings discussed in the manuscript should be given in the Abstract) and the PVD methods were not defined (i.e. the ones described in figure captions and in tables); Therefore, the phrase “Up to now, numerous investigations of resistance of coatings produced by physical vapor deposition (PVD) method to cavitation erosion, solid particle erosion and wear have been made.” should be reformulated in one or two phrases to define the nitride coatings and the PVD methods used to deposit this kind of coatings (at least the main ones discussed in this review)”

- at Author Contributions: Since only one author wrote the manuscript I recommend you to put only once “A.K.K. performed………”; also “The author have read…” should be replaced with “The author has read…..”;

- at Conflicts of Interest: “The author declare no conflict of interest.” should be replaced with “The author declares no conflict of interest.”

Author Response

Thank you for all your comments.

- The class of the studied materials was not defined (at least some examples of nitride coatings discussed in the manuscript should be given in the Abstract) and the PVD methods were not defined (i.e. the ones described in figure captions and in tables); Therefore, the phrase “Up to now, numerous investigations of resistance of coatings produced by physical vapor deposition (PVD) method to cavitation erosion, solid particle erosion and wear have been made.” should be reformulated in one or two phrases to define the nitride coatings and the PVD methods used to deposit this kind of coatings (at least the main ones discussed in this review)”
Thanks for your comment. However, according to the instructions for Authors, the abstract should have a total of about 200 words maximum. This was the reason why it was not so much expanded. In its last version, it already had 220 words. Taking into account your comment, the Abstract has been even more expanded and some examples of nitride coatings have been mentioned as well as the techniques of deposition. Now it is: “Up to now, numerous investigations of resistance of coatings, mainly nitride coatings, such as Cr-N, TiN, TiCN, (Ti,Cr)N and multilayer TiN/Ti, ZrN/CrN and TN/(Ti,Al)N coatings, produced by physical vapor deposition (PVD) method using different techniques of deposition, such as magnetron sputtering, arc evaporation or ion plating, to cavitation erosion, solid particle erosion and wear have been made.” The abstract has now 251 words.

- at Author Contributions: Since only one author wrote the manuscript I recommend you to put only once “A.K.K. performed………”; also “The author have read…” should be replaced with “The author has read…..”;
Thank you for your comment. The Author Contribution part has been corrected.

- at Conflicts of Interest: “The author declare no conflict of interest.” should be replaced with “The author declares no conflict of interest.”
Thank you for your comment. The Conflicts of Interest part has been corrected.