Why the authors used two different precursor for deposition of SiC in two different samples, Si powder and Methyltrichlorosilane? How Methyltrichlorosilane was introduced to the CVD system? What do the authors mean in "NANOVEA company of America"? The name of the country is the USA. And just the name of the company is enough. "The micron indentation" can be rewritten as Micron scale indentation or micro indentation. Figures should be presented right after they are explained in the text. " It can be revealed that the crystalline of ZrC coating is good because of the sharp ZrC peaks". What is good for a coating? Please use more specific terms to explain something instead of general descriptions. Any results for thickness of coatings? Figure 10, 11 caption: Please introduce each figure in the caption, what is a, b, c and d?

Author Response

To reviewer 1 #:

Thank you for your comments, which are all valuable and very helpful for revising and improving our paper. We have considered comments carefully and have made correction. Revised portion are marked in the blue color in the revised manuscript.

1:Why the authors used two different precursor for deposition of SiC in two different samples, Si powder and Methyltrichlorosilane?

Thank you for your comment. In this work, we mainly aimed to investigate the differences of ablation behaviour between ZrC/SiC double-layer coating and ZrC-SiC coating. After attempts, if the inner SiC layer of ZrC/SiC double-layer coating was deposited with silicon powder, the free silicon, as impurity phase, would easily appear in the coating. On the other hand, using Methyltrichlorosilane as the precursor for the deposition of SiC phase in ZrC-SiC coating is difficult to control. Besides, free carbon tends to occur in coating systems. Meanwhile, it is reported that SiC phases fabricated below 1800 ^oC are almost 3C-SiC. To ensure the stability of the experiment and the phase purity in the coating system, we used Si and MTS as precursor for deposition in ZrC-SiC coating and ZrC/SiC double-layer coating, respectively.

2:How Methyltrichlorosilane was introduced to the CVD system?

Thank you for your question. The Methyltrichlorosilane (MTS) was introduced by volatilization at low pressure and constant temperature (30 ^oC). The diagram of this equipment is shown in the figure below. The introducing method has been added. (Page 3, Line 101-102)

3:What do the authors mean in "NANOVEA company of America"? The name of the country is the USA. And just the name of the company is enough.

Thank you for your suggestion. The “NANOVEA company of America” has been modified. (Page 4, Line 126)

4:"The micron indentation" can be rewritten as Micron scale indentation or micro indentation.

Thank you for your comment. The expression has been modified. (Page 4, Line 125)

5:Figures should be presented right after they are explained in the text.

Thank you for your suggestion. The position of the figures in the revised manuscript has been changed.

6:" It can be revealed that the crystalline of ZrC coating is good because of the sharp ZrC peaks". What is good for a coating? Please use more specific terms to explain something instead of general descriptions.

Thank you for your question. The meaning we wanted to present is “Judging from the narrow peaks of ZrC (pdf: 65-4932) peaks in Fig. 2 of two patterns, the ZrC phases in two coating presented high crystalline.” The sentence has been changed in revised manuscript.

7:Any results for thickness of coatings?

Thank you for your question. The thickness changes of two coatings were quite different. The part about the results for thickness of coating before and after ablation has been added in the revised manuscript. “Ignoring the gap, the thickness of ablated ZrC/SiC double-layer coating decreased a lot compared with Fig.3(b). Meanwhile, the thickness decreasing of ZrC-SiC coating is less than that of ZrC/SiC double-layer coating illustrating that the mechanical erosion of ZrC-SiC coating was slighter than that of ZrC/SiC coating during ablation process.”(Page 9, Line 229-232)

8:Figure 10, 11 caption: Please introduce each figure in the caption, what is a, b, c and d?

Thank you for your suggestion. The captions of Fig.11 and Fig.10 have been completed. (Page 10, Line 267-269) (Page 11, Line 283-284)

Author Response File: Author Response.doc

Reviewer 2 Report

A brief summary outlining the aim of the paper and its main contributions.

The paper fits to the scope of “Coatings” journal and presents ZrC-SiC double-phase coating fabricated by one-step chemical vapor deposition at a relatively low temperature to increase its thermal protective ability, as well as a new assistant method for characterizing its thermal protective effect by the change of hardness and elastic modulus of carbon-carbon (C/C) composites substrate before and after ablation. The proposed methods for the fabrication of coatings and estimates of their thermal efficiency contribute to the development of cheaper methods for the manufacture of ZrC-SiC double-phase coatings with high ablation resistance, a dispersive microstructure, and satisfactory mechanical properties for applications in the aerospace industry and may be of interest to a wide range of researchers in the field of thermal protecting coatings.

Broad comments highlighting areas of strength and weakness.

Overall, the presented experimental study is original, its novelty is clearly defined and the results give progress in current knowledge.

The introduction provides sufficient background and includes relevant references, however this section should be revised to improve English and, possibly, add or clarify some references.

Thus, on the first page of the manuscript on line 40 should be "studied" instead of "study", otherwise the sentence «Wang S. et al..." on lines 39-40 is grammatically inconsistent.

On the second page, lines 61-62, there is the lack of references after the sentence "Few works are reported about the ablation behaviour of ZrC-SiC double-phase coating fabricated by one-step CVD method", these few works should be indicated.

The meaning of the text in lines 62-70 is not entirely clear, since it contains both grammatical inaccuracies and some inconsistency. In particular, it is difficult to understand the meaning of the sentence in lines 67-70: “It is very likely that the poor inhibiting oxygen diffusion ability of the coating would lead to the obvious increase of oxidation products and the obvious weight loss of C/C substrate, resulting in mass ablation rate of the coated C/C substrate is not obvious”. It should be clarified what exactly are the problems with the study of ablation resistance of thermal protective coatings, so that the setting of the goals of the authors' studies would be more clear.

At the section 2 “Material and methods” the materials and methods are adequately described, with sufficient details to allow another researcher to reproduce the results. However, some minor amendments are required. The line 82 “2.5D C/C substrates” - it is not entirely clear what was meant by the designation of 2, 5 D: 2D Carbon/Carbon Composites and substrates? This should be explained in the text. Line 83 contains the symbol Ф (a dimension of Փ30×6 mm³), is this necessary? Line 109 gives reference to the journal article [20] (the lines 344-345), while the manuscript mentions the use of the ablation standard of China. If the cited paper [20] describes the mentioned standard, then it is better to indicate this in the text of the manuscript. In line 128 (scan electron microscope (SEM, Tescan VegaⅢ), it is better to use the Arabic numeral 3 instead of the Roman III.

At the section 3 “Results and discussion” the data and analyses presented appropriately, and the results are interpreted appropriately. The results are significant and conclusions are justified and supported by the results. The disadvantages of this section are, firstly, its design, and secondly, the lack of speculation.

The figures presented in this section have good image quality, but there is a significant drawback in how they are embedded in the text. As a rule, a figure is placed after it is mentioned in the text of the manuscript. This document should be revised so that this requirement is met. In addition, line No. 272 on the 11th page of this paper erroneously indicates the number of figure 10, while a description of figure 11 is given there.

To make the significance of this study more understandable to readers, it would not be out of place to discuss the relevance of the results to hypotheses and add a few assumptions on how the results of this study can be applied by other researchers, how this research will develop in the future and in what area it will contribute.

The “Conclusions” section contains a typo on line 209: "doule-phase", should be "double-phase" This section could be somewhat expanded to attract more readers by emphasizing exactly what the reader of this paper can learn, and what contribution this study makes.

English Level

Some sentences are too long for the idea to be expressed clear (see the last sentence of the abstract, for example, lanes 67-70)

The line 16 of Abstract instead “effect about coatings” should be “effect of coatings”

The use of tenses is often inconsistent like in lanes 96-97, 104-105

Subject-verb agreement also needs revision (see lanes 101-102, 136, 183, etc.)

There are some cases of annoying reiteration (can reveal – can be revealed; cleaned – cleaning, etc.)

Some sentences contain double verb (is – can be found in lane 145, 185, etc.)

The insufficient use of definite article should be reviewed.

There is occasional misuse of grammar forms as in line 172

Sometimes grammar errors make it difficult to get the meaning of a statement (see lanes 224-225 for example)

There are also some spelling mistakes.

Taking into consideration all the above it is highly recommended that the paper should be thoroughly revised from the point of view of the English language usage.

Author Response

To reviewer 2 #:

Thank you for your recognition of our work. Your comments are all valuable and very helpful for revising and improving our paper. We have considered comments carefully and have made correction. Revised portion are marked in the blue color in the revised manuscript.

1: The introduction provides sufficient background and includes relevant references, however this section should be revised to improve English and, possibly, add or clarify some references.

Thus, on the first page of the manuscript on line 40 should be "studied" instead of "study", otherwise the sentence «Wang S. et al..." on lines 39-40 is grammatically inconsistent.

Thank you for your comments. The tense of the verb “study” has been changed to “studied” . (Page 1, Line 40) The reference about the ablation behaviour of ZrC-SiC double-phase coating prepared by one-step CVD method has been added in the revised manuscript. (Page 2, Line 63) The sentences in Lines 63-70 have been polished and modified. (Page 2, Lines 63-71)

“Linear and mass ablation rate are common methods for characterizing ablation resistance of thermal protective coatings. Nevertheless, the ablation process is often accompanied with the generating of oxidation products^[24] resulting mass increase of the coating materials, which could influence the judgement of mechanical erosion during ablation. Thus, the oxidation of coating materials leads to mass gain; but the mechanical erosion of the coating and oxidation of C/C substrate results in mass loss. Therefore, it is difficult to analyze the reasons for mass changes of specimens after ablation. It is also confused to judge the ablation resistances of protective coatings for C/C composites just from mass ablation rates.”

2: At the section 2“Material and methods”the materials and methods are adequately described, with sufficient details to allow another researcher to reproduce the results. However, some minor amendments are required.

The line 82“2.5D C/C substrates”- it is not entirely clear what was meant by the designation of 2.5 D: 2D Carbon/Carbon Composites and substrates? This should be explained in the text.

Line 83 contains the symbol Ф (a dimension of Փ30×6 mm3), is this necessary?

Line 109 gives reference to the journal article [20] (the lines 344-345), while the manuscript mentions the use of the ablation standard of China. If the cited paper [20] describes the mentioned standard, then it is better to indicate this in the text of the manuscript.

In line 128 (scan electron microscope (SEM, Tescan VegaⅢ), it is better to use the Arabic numeral 3 instead of the Roman III.

Thank you for your comments. On line 82, what we trend to express is that the Carbon/Carbon Composites would be used as substrate for depositing coatings. And the sentence has been changed. (Page 2, Line 83)

Because the shape of the samples are circle plate. The symbol “Փ” means diameters of the samples. The thickness of the specimens is 6 mm.

The parameters of the ablation standard was described in the manuscript on lines 112-118. And the expression of the sentences was also modified (Page 3, Line 112-118)

On line 128, the Roman “III” has been changed with “3” in revised manuscript. (Page 4, Line 133)

3: At the section 3“Results and discussion”the data and analyses presented appropriately, and the results are interpreted appropriately. The results are significant and conclusions are justified and supported by the results. The disadvantages of this section are, firstly, its design, and secondly, the lack of speculation.

In addition, line No. 272 on the 11th page of this paper erroneously indicates the number of figure 10, while a description of figure 11 is given there.

Thank you for you suggestions. According to your comment, the positions of all figures in this section have been placed after the corresponding text in revised manuscript. The wrong number of the figure has been delete in the manuscript. (Page 10, Line 282)

According to the suggestion, the “Expectation” has been added. (Page 12, Line 304-311)

Expectation

C/C composites are potential thermal structure materials in aerospace field. Various kinds of coatings for protecting C/C composites under oxidation and ablation environment have been reported in recent years. However, traditional judging standard (linear and mass ablation rates) could not accurately characterize the protective effects of the coatings gradually. Basing on this problem, the new assistance method introduced in this paper can effectively and accurately judge the ablation resistance of coatings under the condition of low cost. It also might be a new standard to judge the ablation resistances of coatings for protecting C/C composites in the future.

4: The“Conclusions”section contains a typo on line 209: "doule-phase", should be "double-phase"

This section could be somewhat expanded to attract more readers by emphasizing exactly what the reader of this paper can learn, and what contribution this study makes.

Thank you for your comments. The spelling problems have been corrected. (Page 12, Line 318) The “Conclusions” section also has been polished and modified. (Page 12, Lines 319-320; 322-323; 327-329; 331-332)

5: Some sentences are too long for the idea to be expressed clear (see the last sentence of the abstract, for example, lines 67-70)

The line 16 of Abstract instead “effect about coatings” should be “effect of coatings”

The use of tenses is often inconsistent like in lines 96-97, 104-105 Subject-verb agreement also needs revision (see lanes 101-102, 136, 183, etc.)

There are some cases of annoying reiteration (can reveal–can be revealed; cleaned–cleaning, etc.)

Some sentences contain double verb (is–can be found in lane 145, 185, etc.)

The insufficient use of definite article should be reviewed.

There is occasional misuse of grammar forms as in line 172

Sometimes grammar errors make it difficult to get the meaning of a statement (see lanes 224-225 for example) There are also some spelling mistakes.

Taking into consideration all the above it is highly recommended that the paper should be thoroughly revised from the point of view of the English language usage.

Thank you for the suggestions. According to the comment, the long sentences which are hard to understand have been taken apart to shorter sentences. (Page 1, Lines 20-23) (Page 2, Lines 67-70)

The phrase “effect about coatings” has been changed to “effect of coatings”. (Page 1, Line 16)

The tense use in Lines 96-97 has been modified. (Page 3, Lines 96-98; Lines 104-108)

The subject-verb relationships have been corrected. (Page 4, Line 103-104; 137; 194; 202; 204; 221; 237; 264)

The cases of annoying reiteration have been corrected in the revised manuscript. (Line 84; 137)

The sentences containing double verb have been corrected. (Line 148-149; 170-171)

The use of definite article has been modified. (Line 21; 242; 243; 253)

The grammar forms in the manuscript have been checked and modified. (Line 228; 230; 235-236; 254)

Spelling mistakes have been checked and corrected.

The manuscript has been checked carefully according to the comments.

Reviewer 3 Report

The manuscript can be accepted in its present form.

Author Response

To reviewer 3 #:

Thank you very much for your recognition and support of our work.

Reviewer 4 Report

1. Good work overall. The hypothesis are well supported by the experimental work.

2. English needs major revision. Certain words and sentences need to be framed better. Spelling mistakes have been noted as well.

3. Additional references for previous work in the Introduction section need to be added.

4. The evidence provided for the predicted behavior (as shown in the models) of the two different types of coatings could be further elaborated through characterization.

Author Response

To reviewer 4 #:

1: Good work overall. The hypothesis are well supported by the experimental work.

Thank you very much for your approval.

2: English needs major revision. Certain words and sentences need to be framed better. Spelling mistakes have been noted as well.

The English language has been polished. Meanwhile, the mistakes have been checked and corrected. (Line 16; 20-23; 67-70; 96-98; 103-104; 106-108; 137; 194; 202; 204; 221; 237; 264; 318, etc)

3: Additional references for previous work in the Introduction section need to be added.

The reference about the ablation behaviour of ZrC-SiC double-phase coating prepared by one-step CVD method has been added in the revised manuscript. (Page 2, Line 62-63)

References:

He Q.; Li H.; Wang C. et al. Microstructure and ablation property of gradient ZrC SiC modified C/C composites prepared by chemical liquid vapor deposition, Ceram. Int. 2019, 45, 20414-20426. Liu T.; Niu Y.; Pan X. et al. Laser ablation behaviors of vacuum plasma sprayed ZrC-based coatings, J. Am. Ceram. Soc. 2019, 102, 4247-4258. Liu Q.; Liu J.; Luan X. Preparation of ZrC-SiC composite coatings by chemical vapor deposition and study of co-deposition mechanism. J. Mater. Sci. Technol. 2019,https://doi.org/10.1016/j.jmst.2019.07.005

4: The evidence provided for the predicted behavior (as shown in the models) of the two different types of coatings could be further elaborated through characterization.

Thank you for your comment. The further explanation was added in the revised manuscript. (Line 292-299; 302-303; 305-311)

“Moreover, the oxidation of ZrC is accompanied with CO gas escaping and the generation of porous ZrO₂ structure during ablation process. Then the cohesion of outer ZrO₂ becomes weak resulting in serious mechanical denudation under high speed airflow and particles scouring. These explanation can be confirmed from Fig.6(c) and Fig.7(a). After that, the damages were generated. And the damages could be new paths for oxygenated gas diffusing into inner C/C substrate, which leads to the reduction of its hardness and elastic modulus. The CO and CO2 gases generated from the oxidation of C/C substrate would accelerate the damages of ablated ZrC/SiC coating.”

“On the contrary, the ZrC-SiC coating fabricated by one-step chemical vapor deposition is different.”

“Secondly, oxygen diffusion blocking effect of Zr-Si-O glass would protect the inner coating from further oxidation; and the adhension effects could inhibit the powdering oxidation of ZrC, trap ZrO₂ grains and reduce depletion of coating materials. So, the decrease of the cohesion of the coating would be inhibited effectively.”

“;and the inner C/C substrate was prevented from oxidation. Without oxidation and damages, the hardness and elastic modulus of C/C substrate would maintain well. And these explanation can be supported by Fig.3(c) and (d), Fig.4, Fig.7, Fig.9 and Fig. 10.”

Round 2

Reviewer 1 Report

The authors addressed my concerns in an appropriate way.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

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A New Assistant Method for Characterizing Ablation Resistance of ZrC-SiC Dispersive Biphasic Coating on C/C Composites

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