A Review on Ceramic Matrix Composites and Environmental Barrier Coatings for Aero-Engine: Material Development and Failure Analysis

Round 1

Reviewer 1 Report

This manuscript intends to review the failure modelling of CMC/EBC for high service temperature applications. The topic is interesting and in line with the scope of Coatings. In general, I think the manuscript is well written and understandable. I do only have a few comments.

1-    Line 36-38, there’s two sentences repeating the same idea.

2-    Line 62, there seems to be a typo in ‘kind’.

3-  Line 73, perhaps the authors mean “complex loadings such as those at high temperature and high pressure”.

4-   Line 211, whenever EBCs appear there’s no need to add ‘coating’ since that is implied by the C in EBC.

5- Line 212, perhaps the authors mean “has better oxidation resistance than”.

6-  More than half of the review length focuses on the CMC/EBC systems, manufacturing and failure mechanism. A much less attention is given to failure modelling which should be the main topic according to the title. I would, thus, suggest a modification to the title to better fit the manuscript contents.

Author Response

Dear Reviewer and Editor,

Thank you for your comments and suggestions on our manuscript. We have modified the manuscript accordingly, and the detailed corrections are listed below point by point:

 

Reviewer 1#:

This manuscript intends to review the failure modelling of CMC/EBC for high service temperature applications. The topic is interesting and in line with the scope of Coatings. In general, I think the manuscript is well written and understandable. I do only have a few comments.

1- Line 36-38, there’s two sentences repeating the same idea.

​Re: Following the reviewer’s advice, we have deleted the duplicate sentence.

2- Line 62, there seems to be a typo in ‘kind’.

​​Re: We apologize for the omissions. The spelling mistake has been modified.

3- Line 73, perhaps the authors mean “complex loadings such as those at high temperature and high pressure”.

​Re: We appreciate for your pointing out. This sentence has been modified in the revised version.

4- Line 211, whenever EBCs appear there’s no need to add ‘coating’ since that is implied by the C in EBC.

​​Re: Following the reviewer’s advice, the coating has been deleted in the revised version.

5- Line 212, perhaps the authors mean “has better oxidation resistance than”.

​​Re: This sentence has been modified in the revised version.

6- More than half of the review length focuses on the CMC/EBC systems, manufacturing and failure mechanism. A much less attention is given to failure modelling which should be the main topic according to the title. I would, thus, suggest a modification to the title to better fit the manuscript contents.

​Re: The reviewer’s suggestions are highly appreciated. This title has been modified in the revised version.

A review on ceramic matrix composites and environmental barrier coatings for aero-engine: material development and failure analysis

​Thank you again for the reviewer’s comments and suggestions.

Reviewer 2 Report

The authors proposed a review of the important issue of ceramic matrix composites with environmental ceramic barrier coatings, mainly the material system of SiC fibers reinforced SiC matrix composites, SiC_f/SiC. In addition, the authors reported about the technology of thermal barrier coatings, TBC. The paper is based mainly on the work by Wang et al. (2019) on SiC_f/SiC composites and the work on TBC by Darolia (2013). Important experimental results of failure mechanisms, residual stresses distribution, mechanical properties at high temperatures of SiC_f/SiC and TBC, and testing standards and equipment are not shown, only reported. Thus, this article is a brief review of references with a focus on reporting the composite material design and recent results of SiC_f/SiC and TBC investigations (materials and processing). However, missing important experimental results, mechanical and chemical (fatigue stress corrosion) testing evaluations procedures of mechanical properties, R-curve behaviour, failure mechanisms under residual stresses of SiC_f/SiC and TBC at high temperatures. The article presents only a literal description of the failure models. Only a diagram of general failure mechanism of composite ceramic with TBC in steam environment is presented. No cyclic or thermal fatigue performance investigations and results are reported. No design criteria or damage criterion are discussed or presented and no ceramic or fiber selection design map is presented. Therefore, the presented literature reviews and conclusions are somewhat limited and should be improved.

Please correct for better paper clarity and quality:

1.  Abstract, line 13, I would suggest to change “…promising material solution…”. Also, line 15, please correct “…the effective failure prediction models...”.

2.  Introduction, pg.1, line 32, please correct “… CMC, represented by SiC_f/SiC,…”. Also, correct throughout the text the material composite sytem “SiC_f /SiC”, “C_f/C”, etc..

3.  Introduction, pg.2, line 62, please correct, “…Aero-engines are a kind of reusable…”. Also, pg.3, line 86, “To this purpose, many researchers...”

4.  Development of material system, pg.3, line 104, please correct, “…rapidly after carbon fiber.”

5.  Constituents, SiC_f fiber, pg.3, please include a comparative Table of mechanical properties of SiC, SiC_f fiber (first, second and third generation), carbon fiber, alumina fiber (Al2O3_f), Si3N4 fiber (Si3N4_f), including the elastic modulus, coefficient of thermal expansion, tensile strength, flexural strength, shear strength, thermal shock resistance, fracture toughness, fatigue stress limit and creep resistance at room and high temperatures (~1200 ^oC).

6.  Interphase, pg.4, line 134, please correct, “… the widely used interphases are the fiber treatment by pyrolytic carbon…”.

7.  Development of environmental barrier coatings, pg.5, line 184, please change subtitle to “Development of environmental barrier coatings, EBCs”. Also, line 191, please correct, “because of its good coefficient of thermal expansion, CTE, match…”.

8.  Failure mechanism, pg.6, line 237, please correct “With the increasing static and cyclic loading,…”. Also, please include the comments and the reference,

[ ] P.A. Carraro, G. Meneghetti, M. Quaresimin and M. Ricotta, Crack propagation analysis in composite bonded joints under mixedmode (I+II) static and fatigue loading: experimental investigation and phenomenological modelling. Journal of Adhesion Science and Technology, 2012, p. 1-18.

http://dx.doi.org/10.1080/01694243.2012.735902

9. Failure mechanism, pg.7, line 294, please correct “It was found that the…”

10.  Failure modeling, pg.8, please better explain the “homogenization method” and the representative volume element (RVE) model to analyze the mechanical behaviour of the CMC material.

11.  Failure modeling of environmental barrier coatings, pg. 9, line 360, please correct “… overall, the failure is often attributed to the initiation and propagation of cracks and the associate stress state, cyclic loading and temperature”.

12. Conclusions, consider rewriting and improve the conclusions after the required corrections.

Author Response

Dear Reviewer and Editor,

Thank you for your comments and suggestions on our manuscript. We have modified the manuscript accordingly, and the detailed corrections are listed below point by point:

Reviewer 2#:

The authors proposed a review of the important issue of ceramic matrix composites with environmental ceramic barrier coatings, mainly the material system of SiC fibers reinforced SiC matrix composites, SiC​f​/SiC. In addition, the authors reported about the technology of thermal barrier coatings, TBC. The paper is based mainly on the work by Wang et al. (2019) on SiC​f​/SiC composites and the work on TBC by Darolia (2013). Important experimental results of failure mechanisms, residual stresses distribution, mechanical properties at high temperatures of SiC​f​/SiC and TBC, and testing standards and equipment are not shown, only reported. Thus, this article is a brief review of references with a focus on reporting the composite material design and recent results of SiC​f​/SiC and TBC investigations (materials and processing). However, missing important experimental results, mechanical and chemical (fatigue stress corrosion) testing evaluations procedures of mechanical properties, R-curve behaviour, failure mechanisms under residual stresses of SiC​f​/SiC and TBC at high temperatures. The article presents only a literal description of the failure models. Only a diagram of general failure mechanism of composite ceramic with TBC in steam environment is presented. No cyclic or thermal fatigue performance investigations and results are reported. No design criteria or damage criterion are discussed or presented and no ceramic or fiber selection design map is presented. Therefore, the presented literature reviews and conclusions are somewhat limited and should be improved.

Re: The reviewer’s suggestions are highly appreciated. We agree with the reviewer that several reviewers have been published to discuss the progress in CMC, EBCs and TBC, individually.  As mentioned, Wang et al. (2019) discussed the fabrication, preparation processes, and properties of CMC. Darolia (2013) discussed the materials systems, processes, applications, durability issues, technical approaches and progress for improved TBC, and their understanding of the science and technology.

It should be noted that the damages within the CMC substrate and EBCs coating influence each other. As discussed, most existing research studied the failure modes of CMC and EBCs, respectively. Thus, it is necessary to pay more attention to considering the synergetic effect of coating properties and substrate fibrous architecture when analyzing the failure mechanism of the CMC/EBCs system. And, this is the key point of this review paper. Therefore, the failure analysis for CMC and EBCs were summarized briefly.

Meanwhile, the experimental results, mechanical and chemical (fatigue stress corrosion) testing evaluations procedures of mechanical properties, R-curve behavior, failure mechanisms under residual stresses of SiC_f/SiC and TBC at high temperatures mentioned by the reviewer are not the focus of this article. We agree with the reviewer that the mentioned loading mode and environment factors play important roles in the failure analysis of the composite. So, brief review of references related to these issues have added in the revised manuscript. The details can be found in line 262-270, line312-322, line 421-428.

Please correct for better paper clarity and quality:

1. Abstract, line 13, I would suggest to change “…promising material solution…”. Also, line 15, please correct “…the effective failure prediction models...”.

​​Re: Following the reviewer’s advice, these sentences have been rewritten.

2. Introduction, pg.1, line 32, please correct “… CMC, represented by SiC_​f​/SiC,…”. Also, correct throughout the text the material composite sytem “SiC_f /SiC”, “C​_f​/C”, etc..

​Re: The mentioned issue has been modified in the revised version.

3. Introduction, pg.2, line 62, please correct, “…Aero-engines are a kind of reusable…”. Also, pg.3, line 86, “To this purpose, many researchers...”

​​​Re: We apologize for the omissions. The spelling mistake has been modified.

4. Development of material system, pg.3, line 104, please correct, “…rapidly after carbon fiber.”

​​​Re: This sentence has been modified in the revised version.

5. Constituents, SiCf fiber, pg.3, please include a comparative Table of mechanical properties of SiC, SiCf fiber (first, second and third generation), carbon fiber, alumina fiber (Al₂O_3​f​), Si₃N₄ fiber (Si3N4​f​), including the elastic modulus, coefficient of thermal expansion, tensile strength, flexural strength, shear strength, thermal shock resistance, fracture toughness, fatigue stress limit and creep resistance at room and high temperatures (~1200 oC).

​Re: Following the reviewer’s advice, the key properties of SiC fiber (first, second and third generation) were listed in Table. 1. As the topic of this review is focused on the SiC_f/SiC composite, the properties of other fiber such as Al₂O₃, Si₃N₄ were not included. On other hand, it is difficult to collect the fatigue stress limit and creep resistance at room and high temperatures for these kinds of fibers comprehensively due to the limited of literatures.

6. Interphase, pg.4, line 134, please correct, “… the widely used interphases are the fiber treatment by pyrolytic carbon…”.

​​​​Re: This sentence has been modified in the revised version.

7. Development of environmental barrier coatings, pg.5, line 184, please change subtitle to “Development of environmental barrier coatings, EBCs”. Also, line 191, please correct, “because of its good coefficient of thermal expansion, CTE, match…”.

​​​Re: Following the reviewer’s advice, the subtitle and related sentence have been modified.

8. Failure mechanism, pg.6, line 237, please correct “With the increasing static and cyclic loading,…”. Also, please include the comments and the reference,

[ ] P.A. Carraro, G. Meneghetti, M. Quaresimin and M. Ricotta, Crack propagation analysis in composite bonded joints under mixedmode (I+II) static and fatigue loading: experimental investigation and phenomenological modelling. Journal of Adhesion Science and Technology, 2012, p. 1-18.

​http://dx.doi.org/10.1080/01694243.2012.735902

​Re: The mentioned issue has been modified in the revised version. And the related reference has been added in a paragraph to discussed the influence of loading mode at line 262-270.

As mentioned, CMC is the leading material candidate for the hot section component of aero-engine subjected to the extreme temperature–time–oxidative environment. It is important to figure out the influence of cyclic loading, thermal shock, oxidation, etc. on the failure behavior of the composite. In addition, the composite structures usually serve in mixed-mode loading or coupling environment which induces more complex failure behavior such as crack propagation under fatigue loading and crack healing under an oxidation environment. Lots of efforts have been contributed to illustrate the results of an extensive experimental investigation on the static and fatigue crack propagation, creep behavior, oxidation, and corrosion of composite materials over the past decades [34-37].

9. Failure mechanism, pg.7, line 294, please correct “It was found that the…”

​​​​​Re: We appreciate for your pointing out. This sentence has been modified in the revised version.​

10. Failure modeling, pg.8, please better explain the “homogenization method” and the representative volume element (RVE) model to analyze the mechanical behaviour of the CMC material.

​Re: Following the reviewer’s advice, the section has been modified to explain the homogenization method and RVE model. The revised version can be found at line 358-394.

11. Failure modeling of environmental barrier coatings, pg. 9, line 360, please correct “… overall, the failure is often attributed to the initiation and propagation of cracks and the associate stress state, cyclic loading and temperature”.

​​​​​Re: This sentence has been modified in the revised version.

12. Conclusions, consider rewriting and improve the conclusions after the required corrections.

Re: The reviewer’s suggestions are highly appreciated. The conclusions have been modified according to the reviewer’s advices.

Thank you again for the reviewer’s comments and suggestions.

Round 2

Reviewer 2 Report

The corrected paper is accepted.