Additive Manufacturing of C/C-SiC Ceramic Matrix Composites by Automated Fiber Placement of Continuous Fiber Tow in Polymer with Pyrolysis and Reactive Silicon Melt Infiltration

Round 1

Reviewer 1 Report

Authors should focus on following major comments to improve the quality of the work further so that the work can be published in this journal.

1 1. References (3-10) was mentioned which needs to be changed. Pls mention the references one by one after each property of SiC, so that it is possible to understand which information is collected from which reference sources.

2 2. A new manufacturing process of CMC composite is presented in this work combining PMC AFP and CF-PEEK pyrolysis with RMI processes. The author needs to mention the novelty of this new manufacturing process clearly such as - any obvious benefits or better control on the process etc.

3 3. It was mentioned that CF-PEEK pyrolysis/RMI process is based on expensive tooling. In this context, how does the author justify that the presented new manufacturing process is not based on expensive tools and complex manufacturing processes?

4 4.  How the author selected the pyrolysis conditions? Any reference for this?

5 5. How the author calculated the required silicone content to fill the pores? Also, how the porosity of the developed samples was estimated or calculated?

6 6. For the four-point bending test- what loading rate was used in the test?

7 7. Figure 2 - please point out the cracks/debonding/porosity in the figure.

8 8. Figure 3- The author can consider to include CF-PEEK sample without pyrolysis, just to give the context that the pyrolysis increased the porosity.

9 9. In Table 1 – the porosity (%) was mentioned as 40% for the pyrolised sample while it was mentioned as 30% in the main text. Can you check this?

1 10. Was there any shrinkage or warpage observed for the CMC samples as it was mentioned that the samples were primarily flat with some deviation?

   11. Fig-4- The author can consider to include nail impact for other samples- CF-PEEK with and without pyrolysis.

   12. Fig 5- point out the delamination in the pictures.

 

   13.  Please check the figure numbers in the main text carefully. Such as – Figure 4 was mentioned in the last paragraph at page number 6 instead of figure 6. Also check page number 10 wherein Figure 8D was mentioned instead of Figure 10D.

1 14. Why the author used Weibull statistical analysis? The calculation process was not described in the methodology section. In Weibull analysis- why the modulus and strain failure graphs were not provided? How the Weibull analysis supported the results of this work?

  15.  For four-point bending test- it was claimed that the developed sample showed higher strain to failure, but no data was presented for other samples (CF-PEEK with/without pyrolysis) and that’s why it can’t be compared that the developed CMC is good (or by how much?) in terms of failure strain. Also, the author didn’t cite any reference for the sentence- “Displacement to failure was high, similar to well-formed CMCs”.

P 16. Page 10, please check the description, some information was mentioned twice.

 

  17.   No quantitative test was done for impact toughness analysis.

   18.    Summary should be mentioned separately as a summary of the discussion on results.

   19.    In the summary- damage tolerance term was used. Author can consider replace this term with any other appropriate term that reflects the work.

   20. Please provide a conclusion section point-by-point mentioning the major findings of this work and how they can be used in real-life applications etc.

Author Response

Thank you kindly for your review.

1. We have separated references 3-10 so that it is clearer. We also added another relevant reference.
2. We have added some language
3. This fits in with the last comment, and we have added verbiage to explain the novelty and why no tooling adds to the novelty and time/cost to make a part. This means that all the added benefits of AM are available like rapid part development and changes without making a new tool every time.
4. We used PEEK for the high char yield, and we added a reference.
5. We use areal and Archimedes, and we have added an equation for the amount of Si to add. 
6. The strain rate was 0.01 mm/s at 50 Hz collection rate.
7. We have added arrows to point out the matrix cracks
8. We added a CT scan of the printed Cf-PEEK part.
9. We fixed that in the text.
10. No shrinkage, but there was warpage less than 5%, and we have added that to the manuscript. 
11. We do not find it necessary, so we will leave that out. I think if we wanted to add nail test to all, then we would need mechanical properties of stages, and that is out of the scope. We just want properties of the final composite even though the Cf-C and Cf-PEEK may survive the nail test too.
12. We have added some description and arrows of some features in the figure including delamination, pores, and cracks.
13. We have checked all of our figure call outs and made changes where necessary.
14. Weibull is appropriate for first to "experience" any event. The event is cracking in the matrix, so the stats are on the linear region of the stress vs. strain. Passed that, the crack deflection and load transfer is seen in the stress versus disp. but is not well understood. This is done with CMCs a lot.
15. Since we are comparing to CMCs with ceramic as a matrix, the comparison to Cf-C is not valid. That is why we did not test the Cf-C, and we would have to densify it further with carbon to get good results. We are primarily interested in the ones with SiC. We have added a reference. We used 4-pt bending, so that we could get a lot of samples tested. Tensile testing was not done. Because we use bending, the strain cannot be accurately measured and calculated because of compliance in the machine and fixture, so we are left with displacement data, which correlates to the strain behavior but not with definitive numbers. We add the references and better verbiage to explain this.
16. We have checked this, and we do have direct duplication.
17. That is correct. We do not measure impact, and the study is not about impact. Maybe we can do that later.
18. We have separated discussion and conclusion
19. Exchanged the term with toughness
20. We have updated the conclusions.

Reviewer 2 Report

fine paper

Author Response

Thank you kindly for your review.

Reviewer 3 Report

The paper deals with an interesting and important topic related with the development of a ceramic matrix composites fabrication process for 3D printing technology. In my opinion there are only few points, which should be addressed before further consideration:

1. For a better understanding, the authors could prepare a simple diagram showing the research methodology/individual stages of the research process.

2. Why the authors decided to use PEEK filament? What about the other materials commonly used in FDM/FFF technology? Whether the type of material may affect the achieved fabrication effects?

3. On how many samples were the tests carried out, were the tests repeated?

4. What is the application area for newly fabricated fiber reinforced ceramic matrix composites?

Author Response

1. Thank you for the comment - we have made a diagram to be used with the graphical abstract
2. PEEK is used because of the high char yield. We wanted to have the most carbon we could get in the matrix. Nylon and others can be used, but PEEK was strategic. We have mentioned that now in the manuscript.
3. We tested up to 30 samples across 4 samples, so our data is very statistical. We even show the Weibull stats, which are decent for this new method.
4. The application space for this is very large, but essentially high temperature, tough ceramics for turbines and nuclear shroud.

Round 2

Reviewer 1 Report

Authors worked on my comments and updated them in the revised manuscript. I am overall happy that the quality of the manuscript has been increased and this can be published after adding the responses for the following comments-

1. Please mention/describe  properly different terms  used in the equation 1, such as the meaning of Vcf/c etc. 

2. Author didn't provide any details of the weibull statistical analysis in the methodology section with the four point bending testing details, please provide details how you calculated or at-least the references. 

 

Reviewer 3 Report

After the modifications and explanations introduced, the paper has a sufficient scientific level, therefore I recommend it for further consideration.