Strain-Hardening and Strain-Softening Phenomena Observed in Thin Nitride/Carbonitride Ceramic Coatings During the Nanoindentation Experiments

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study presents the fabrication and mechanical characterization of nanostructured tribological coatings (NTCs) featuring multilayered nitride/carbonitride superlattice structures composed of alternating TiAlSiNb-N/TiCr-CN bilayers, alloyed with refractory metals such as Cr and Nb. Nanoindentation techniques were used to evaluate the mechanical properties and to extract stress-strain field (SSF) gradients and divergences, offering insights into localized microstructural heterogeneities. The analysis of load-displacement data revealed distinct oscillatory behavior, interpreted as alternating strain-hardening and strain-softening cycles, likely induced by structural variations within the coating. This methodological approach provides valuable insights into the complex deformation behavior of multilayer coatings and addresses key limitations of conventional hard carbon and nitride films. I recommend acceptance of this manuscript after appropriate revision. Below are my detailed comments and suggestions for improvement:

1. The manuscript states that the addition of refractory metals (e.g., Cr and Nb) contributes to enhanced nanohardness. However, the underlying mechanisms—such as grain refinement, solid-solution strengthening, or precipitation hardening—should be more clearly described to enhance scientific understanding.

2. The observed undulating superlattice pattern attributed to atomic shadowing and anisotropic diffusion is a fascinating structural feature. It would be valuable to discuss whether these anisotropic morphologies could lead to directional frictional behavior. The authors are encouraged to explore this possibility and refer to relevant studies on friction anisotropy (e.g., Y. Gao et al., Tribol. Lett. 61, 27 (2016); J. S. Choi et al., Science 333, 607 (2011); R. Carpick et al., Tribol. Lett. 7, 79–85 (1999)).

3. While the TiAlSiNb-N/TiCr-CN bilayer structure demonstrates promising performance, the rationale behind choosing this particular combination over other potential nitride/carbonitride systems is not adequately discussed. Providing a comparative analysis or supporting references would strengthen the design rationale.

4. Although the manuscript thoroughly explores mechanical behavior via nanoindentation, it lacks quantitative tribological performance metrics (e.g., wear rate, coefficient of friction) under practical or application-relevant conditions. Incorporating such data would provide a more comprehensive assessment of the coatings' functional capabilities.

Author Response

Please take a look at the attached PDF file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

send comments

Comments for author File: Comments.pdf

Author Response

Please take a look at the attached PDF file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

1. The introduction contains a lot of theoretical knowledge, typical of textbooks. I propose to reduce this and instead provide more examples of results from other researchers.

2. The literature review should reveal the research problem, from which the aim of the work should arise. You have a described aim, but it does not result from the revealed gap in knowledge

3. In Table 1, the results of the friction coefficient tests are entered. How were the deviations calculated? Is the given value an average value? If so, please change the name of the column

4. The caption under the figure should be on the same page as the figure - this applies to Figures 2 and 5

5. Figure 4 shows the penetration into the material. How was it measured? I have performed similar tests and vibrations were always a problem - here the graphs came out smooth, hence my question

6. In my opinion, the summary is too extensive. The most important achievements should be listed there - I recommend changing it.

Author Response

Please take a look at the attached PDF file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors' response to my comments is appropriate, therefore, I suggest the paper be accepted as it is.

Reviewer 2 Report

Comments and Suggestions for Authors

The possible publication is under consideration of the editor. 

Comments for author File: Comments.pdf