Influence of Texture and Thickness of Pyrocarbon Coatings as Interphase on the Mechanical Behavior of Specific 2.5D SiC/SiC Composites Reinforced with Hi-Nicalon S Fibers
Round 1
Reviewer 1 Report
The manuscript entitled: „Influence of texture and thickness of pyrocarbon coatings as interphase on the mechanical behavior of specific SiC/SiC composites reinforced with Hi-Nicalon S fibers” reports a study of 2.5D SiC/SiC composites which can be used for development of generation IV high temperature nuclear reactor core materials.
The main issues addressed by the research article relate to influence of a carbon phase on its microstructure/texture and on fiber/matrix bonding in SiC/SiC composites. The authors of submitted paper explain the aforementioned issues in the context of 2.5D SiC/SiC composites.
The article creates a positive impression in general. The paper is clearly written and well organized. However, the authors should highlight more the originality and the relevance of their work. What are the main contributions? Is it the novelty of some experimental procedures? Or the improvements of the fabrication protocols giving rise to samples with optimized properties or higher reproducibility?Suggest minor revision.
Author Response
Dear reviewer 1,
At first, we would like to thank you for your revision of our paper and for your pertinent comments. The changes are added in revision mode of the manuscript.
F/M bonding is governed by the PyC processing parameters in SiC/SiC composites reinforced by HNS fibers. The major novelty is that PyC thickness is not the only way to control this bonding as observed in previous work. Pyrocarbon microstructure/texture nature (and so PyC processing parameters) is more likely to be used in this goal to generate an adhesive or cohesive failure. Moreover, this is possible without modifying the interphase thickness. This is crucial for applications where PyC interphase thickness needs to be as low as possible (Nuclear applications for example). Conclusion was modified to highlight this work main contribution.
At last, some English expressions have been improved in the revise manuscript to respect reviewers comments.
Thank you for your revision of this manuscript.
Sincerely,
Dr. Cédric SAUDER, expert in composites materials for CEA
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript contains interesting research results. The authors precisely described the research methodology. Moreover, they presented the research results in an understandable way and analyzed the research results. I only have one comment regarding the admission, namely:
Out of 42 references, only 5 are from the last two years. The introduction only cited two items from the last two years. The introduction should be supplemented with the latest literature.
Author Response
Dear Reviewer 2,
at first, we would like to thank you for your revision of our paper and for your pertinent comments. The modifications are in yellow in the article.
Introduction was changed and is now supplemented with the latest literature. Seven recent references have been added in the introduction and discussed.
Thank you for your revision of this manuscript.
Sincerely,
Cédric SAUDER
Reviewer 3 Report
The authors studied the influence of texture and thickness of pyrocarbon caotings in the paper. The results will be interesting for nuclear application. It can be accepted before some English expressions are improved.
Comments for author File: Comments.pdf
Author Response
Dear reviewer 3,
At first, we would like to thank you for your revision of our paper and for your pertinent comments. The changes are added in revision mode of the manuscript and you will find answers to your questions/comments just bellow.
- The texture of the matrix is not a primary concern on the mechanical tensile behavior of SiC/SiC materials reinforced with HNS fibers, especially for the F/M bonding strength. In these materials, the cracks deviation always occurs at the F/I interface (weakest interface) in the F/M area so that matrix has no significant influence on the F/M bonding strength. The influence of the matrix texture should only be visible on the SiC matrix Weibull parameters. Consequently, it may have an influence of the mechanical tensile behavior but not on the F/M bonding strength. Nevertheless, in this study, CVI SiC matrix processing parameters are identical, so that no influence of SiC matrix should be observed between samples.
- As explained in introduction, PyC thickness must be lower than 150 nm for nuclear applications. Only 30 nm and 150 nm thicknesses were explored because no large differences were expected from the literature in this small range of thickness. It is also clear that in this range, as shown in figure 3 and discussed in section 2.2, no difference of thermal residual stresses are observed in the interface for these 2 low PyC thicknesses.
- For our 2.5D composites specimens, PyC thickness was uniform as observed by TEM. That is the main reason for the use of 2.5D samples. This is not always the case, especially for specific specimen, as minicomposites or 1D composites.
- Figure 8 analysis is done in section 3.3.1 but perhaps not clearly enough so we completed discussion of this figure. No main differences are observed for PyCHa between 30 nm and 150nm thicknesses but there is a slight difference for PyCLA. Thicker layer leads to longer fiber pull-out for PyCLA. Anyway, fracture surface analysis did not highlighted significant differences between samples.
Minor revision of line 94 has been corrected (scale of figure 2)
Thank you for your revision of this manuscript.
Sincerely,
Dr. Cédric SAUDER, expert in composites materials for CEA
