Cracking Resistance of Selected PVD Hard Coatings

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This work is interesting. I have some comments as follows:

1. Please avoid the wording "Today, there is no standardized method for determining toughness".

2. In Fig. 2, how did author(s) know the exact sites of the tempered martensite matrix and the carbide inclusion before carrying out the indentation test?

3. In Fig. 2, if author(s) performed the indentation tests more than once, did you think the displacement force curves behave the same? Please provide more detailed discussions.

4. Fig. 7 might confuse readers. Could author(s) provide more detailed explanations?

5. On lines 445-446 ("To avoid the plastic deformation of the substrate material ...", please provide the reference.

6. In Fig. 10, why did fracture toughness KIC of TiAlN hard coating determined for different substrate rotation modes for 1 fold have higher variation than others? Please provide more detailed discussions.

Author Response

 

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This is a very interesting paper with interesting results on cracking resistance of hard coatings. However, some key areas could benefit from further development:

 1. The study would be significantly strengthened by additional in-depth characterization of the coatings—particularly TiAlN, (Cr,Al)N, and TiAlN/VN superlattices. Essential information, including composition and phase distribution, is currently lacking and would provide a more comprehensive understanding of these films.

 2. The authors must note that some of the samples indicated multiple pop-ins in Fig.6.

 3. The current references do not include foundational studies in the field of hard coatings. Progress in materials science 51.8 (2006): 1032-1114; Surface and Coatings Technology 207 (2012): 50-65.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The paper presents experimental results on cracking resistance of TiAlN and nl-(CrAl)N coatings on steel substrates. The topic is interesting, the results are relevant and the methodology is clear. The manuscript is well-structured and the tables and figures are substantially clear. However some clarifications and modifications are needed:

General comments

- Check that units of measurement are reported in all the diagrams. The unit of dx/dF is missing.

Introduction

- The Introduction does not mention fatigue strength as one of the properties the coating must have. The deposition of some PVD coatings, for example on aluminum substrates, has been found to decrease the fatigue strength of components, even if the deposition process is responsible for the introduction of high compressive stresses on the surface. This effect is mainly due to thermal loading, which induces modifications in the substrate. You can find some papers on this aspect in the literature.

Materials and methods

-  Further information on the coating deposition processes should be provided in order to guarantee the reproducibility of the experiments. The chemical and mechanical properties of the substrates should be provided.

- Why are the sizes of the two targets different? Could this aspect affect the results?

Results

- Fig. 3: I think the legend of Fig. 3a is incomplete, because you have four curves but only two items listed.

References

- The most recent references are one from 2023, two from 2022 and five from 2021. More recent references must be included.

Author Response

see attached file

Author Response File: Author Response.pdf