Effect of Temperature on the Structure and Tribological Properties of Ti, TiN and Ti/TiN Coatings Deposited by Cathodic Arc PVD
, Andrea Giraldo 2, Jorge Andrés Cardona 2, Alexander Ruden 2, Guillermo César Mondragón 1, Juan Pablo Trujillo 2, Arturo Gómez Ortega 1, Juan Manuel González-Carmona 1,* and Edgar Adrián Franco Urquiza 1Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIt seems that the fitting lines in Fig. 15 make no sense.
In Fig. 13, there is a distinct fluctuation on the friction coefficient curve for Ti/TiN bilayer. The authors should give an explanation.
In Figs. 8, 10, 12 and 14, the length scales should be unified, and each image only requires one length scale.
The EDS image is recommended to be given in Fig. 6b.
Regarding as using grazing incidence X-ray diffraction technology to analyze coating structure, there is a literature as below on this topic. The authors can cite it to enrich the Introduction section: https://doi.org/10.1016/j.jare.2021.05.006 .
Author Response
Best regard,
We appreciate the time and dedication provided by the team of reviewers. We have responded to each of your comments constructively and we believe that we have answered all the kindly asked questions.
Please check the answer in the attached file.
Sincerely,
Authors
Author Response File: 
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Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper describes a study of the structure and tribological behaviour of three coatings (Ti, TiN and Ti/TiN) deposited by physical vapour deposition (PVD). The authors used X-ray diffraction (XRD) to identify the phases present at a range of temperatures from ambient (~25 °C) to 800 °C. The tribological behaviour was studied using pin-on-disc tests over the same temperature range and the friction coefficients and wear rates compared as a function of temperature.
The paper is well written, and its subject matter is interesting. I have a few suggestions for improvement before it can be accepted for publication, details of which are given below.
1. I suggest a sight change to the paper’s title to “Effect of temperature on…coatings deposited by cathodic arc PVD” so that it is immediately clear what method was used to deposit the coatings.
2. Introduction (line 33): it would be worth including a brief reminder of the nominal composition of M2 steel for the benefit of people less familiar with this grade.
3. Materials and Methods (line 85): it is not clear what is meant by “micro deformations”. This parameter, which is expressed here as a percentage, is discussed in the Results and Discussion section (see Figures 2 and 4). Is this the percentage strain (as a result of a residual stress) in the coating or change to the coating lattice parameter? The authors should provide a brief explanation of this and what it tells us.
4. Materials and Methods (line 91): a small typographical error (should be “Dektak”).
5. Materials and Methods (line 102): please state how the wear volume was determined.
6. Results and Discussion: the XRD patterns in Figures 1a and 5a show Si peaks. What has caused these to be present?
7. Results and Discussion (line 218): I was surprised by the author’s statement that “Ti is considered a solid lubricant metal”, given that it is traditionally regarded as a poor tribological material, particularly in sliding conditions with high and unstable friction coefficients. Indeed, in unlubricated tribo-systems it transfers and deforms badly; it is also susceptible to fretting damage and exhibits poor abrasion resistance (see, for example, Budinski, Wear, 151 (1991), 203-217; see also Dong and Bell, ref. [36] of the current paper). The authors need to reconsider this statement.
8. Table 1: are those surface roughness values correct? The table lists the Ra values of between 65 and 110 µm! The coatings are only 5 µm thickness. Should the units be in nm instead? In section 2, it states that, prior to deposition, the substrates were polished to 0.1 µm alumina solution.
9. The micrographs (Figures 8, 10, 12 and 14) show the wear tracks overlaid with EDS O maps showing the formation of oxide layers. However, these images do not show the worn surfaces very well, making it hard to see if the coatings have been penetrated, or to see the wear mechanisms. These figures need improving.
10. The authors discuss wear rates in various locations of the paper. Have they done any surface profilometry of the wear tracks? If so, it would be worth including these in the paper to show the differences in wear track depths, as well as show whether the coatings have been penetrated.
11. Conclusions (line 323/324): the authors state that “Significant changes in the lattice parameter…were observed starting at 800 °C”. Where is the evidence for this? There do not appear to be any lattice parameter measurements in the paper.
Comments on the Quality of English Language
1. Introduction (line 38): please change to “These processes result…”
2. Results and Discussion (line 231): please change to “These particles are responsible…”
Author Response
Best regard,
We appreciate the time and dedication provided by the team of reviewers. We have responded to each of your comments constructively and we believe that we have answered all the kindly asked questions.
Please check the answer in the attached file.
Sincerely,
Authors
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors1. Please be more specific with the study of the references in 1. Introduction. Please, present qualitative and quantitative results regarding the tribological and structure properties of the Ti, TiN, Ti/TiN coatings. Please include references by presenting the methods and devices/test rigs and test parameters which offer results that allow to identify the lack of information in the area, in order to define the scientific aim of the paper. Tribological properties are referring, generally, on friction, lubrication and wear so define which of these properties will be investigated in your paper. These investigations should be in linked to the state-of-art presented before.
2. Please present and describe the pin-on-disc tribometer used in your tests (properties, pictures). There is no information about a running-in test. At least, the friction coefficients should be stabilised during tests so a running-in it would be compulsory. Please explain how have been established the test parameters (temperature, distance, speed, load).
3. Figure 7 shows that the friction coefficient for Ti/TiN (at 25 C) is not stabilised. So the test should continue until this parameter is stabilised, otherwise, there are no scientific conclusions regarding that coating.
4. Please explain for figure 15 why the wear rate is decreasing with the increase of the temperature. What about the melting or the plastic deformation in that case?
5. Please compare the results obtained in the paper with similar works from the literature. What is the scientific add-on of your paper?
Author Response
Best regard,
We appreciate the time and dedication provided by the team of reviewers. We have responded to each of your comments constructively and we believe that we have answered all the kindly asked questions.
Please check the answer in the attached file.
Sincerely,
Authors
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe revised manuscript can be accepted.
Author Response
Best regard,
We appreciate the time and dedication provided by the team of reviewers. We have responded to your comments constructively and believe we have answered all the kindly asked questions.
Please check the answer in the attached file.
Sincerely,
Authors
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsI would like to thank the authors for making the revisions to their manuscript. It can be accepted for publication once they have made a few additional minor changes, details of which can be found below.
1. Section 2 (line 80): There is a missing word. I suggest it is changed to “…in an Ar (278 sccm) atmosphere…”
2. Section 2 (line 110): Please state the diameter of the Al2O3 pin.
3. In their reply to my previous review, the authors commented that they used Si substrates to study the crystallographic changes to the coatings as a function of temperature. It would be useful if they could include this statement (“These substrates were used exclusively for the determination of the crystalline structure at RT and at high temperature, because the oxidation of silicon is homogeneous, its behaviour is known and it does not contribute noise to the analysis”) in Section 2 to inform the reader why Si substrate were used as well as steel.
Author Response
Best regard,
We appreciate the time and dedication provided by the team of reviewers. We have responded to your comments constructively and believe we have answered all the kindly asked questions.
Please check the answer in the attached file.
Sincerely,
Authors
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThank you for the revised paper
Author Response
Best regard,
We appreciate the time and dedication provided by the team of reviewers. We have responded to your comments constructively and believe we have answered all the kindly asked questions.
Please check the answer in the attached file.
Sincerely,
Authors
Author Response File: Author Response.pdf
