Microstructure, Microhardness, Fracture Toughness, and Abrasive Wear of In-Situ Synthesized TiC/Ti-Al Composite Coatings by Cold Spraying Combined with Heat Treatment

Round 1

Reviewer 1 Report

In submitted manuscript the authors anlaysed the titanium carbide as the reinforcing phase which can significantly improve the mechanical property, wear resistance, and heat-resistance stability of TiAl intermetallic compounds.Therefour in this paper the authors the Ti(Al, C) mixture powders were deposited on 316L stainless steel substrate by cold spraying at gas temperature of 250 ℃, 450 ℃, and 550 ℃, and then annealed at temperatures of 650 ℃ for different time, and following holding at 1100 ℃ for constant time equel 3h. The experimental results showed that the coating sprayed at gas temperature of 550 ℃ has the highest microhardness and the lowest weight loss.  Whereas the average porosity of the annealed coating (as-sprayed at gas temperature of 450 ℃) was the lowest. It was also found that the annealed coating (as-sprayed at gas temperature of 450 ℃) has the highest microhardness, fracture toughness, and wear resistance properties after annealing at 1100 ℃ for 3h.

The manuscript is interesting, but some issues need to be supplemented. The submited manuscript requires a some correction as per comments below:

1. Provide a scheme for the production of the coatings.
2. On what basis the parameters used in the microhardness measurement tests were determined. Is this type of coating measured under load 2.94 N and dwell time 20 s?
3. The authors presents the results of fracture toughness but did not present the microstructure after those tests. For the selected coating, please provide a photo of the microstructure with indentation crack length.
4. XRD patterns presented in Figure 16 are a bit unreadable. Please present pictures 16a-16c one below the other.
5. Conclusia are way too long.Please present them in several points.
6. The authors wrote "However, the shortcomings of 45 TiAl intermetallic compounds, such as poor fracture toughness, low ductility, and ex-46 treme brittleness at room temperature, limit their practical applications [7-9]." On the basis of their research, the authors could be provide the possibilities of using such coatings in the broadly understood industry. I see in manuscript that the one of the authors works at the Laboratory of Materials Technology and Application for Intelligent Manufacturing. Perhaps it would be worth mentioning the use of such coatings? If there is one?

Author Response

Dear Editor and Reviewer:

Thank you for your letter and for the reviewer’s comments concerning our manuscript (Coatings-1353643). Those comments are all valuable and very helpful for revising and improving the quality of the manuscript. Based on your suggestions, we have studied comments carefully and have answered the questions in detail one by one. Revised portion are marked in red in the paper. The responds to the reviewer’s comments are as following:

According to the attached iThenticate report，we rewritten some sentences in the revision.

1. Provide a scheme for the production of the coatings.

Thanks very much for your thoughtful suggestion. We provided a schematic diagram of cold spray system (as shown in Figure 3) in the revision.

2. On what basis the parameters used in the microhardness measurement tests were determined. Is this type of coating measured under load 2.94 N and dwell time 20 s?

Thanks very much for your thoughtful suggestion. The microhardness measurement tests were carried out according to GB9790-1988 national standard in this study. Therefore, all of the coatings were measured under load 2.94 N and dwell time 20 s.

3. The authors presents the results of fracture toughness but did not present the microstructure after those tests. For the selected coating, please provide a photo of the microstructure with indentation crack length.

Thanks very much for your thoughtful suggestion. We are sorry for no photo of the microstructure with indentation crack length. The indentation crack was directly measured during shooting SEM micrographs at that time, just like Knoop hardness indentation measurement. We hope to get your understanding. Thank you very much.

4. XRD patterns presented in Figure 16 are a bit unreadable. Please present pictures 16a-16c one below the other.

 Thanks for your very thoughtful suggestion. You are right. According to your suggestion, we presented pictures 16a-16c one below the other.

5. Conclusions are way too long.Please present them in several points.

 Thanks for your very thoughtful suggestion. You are right. According to your suggestion, we revised the conclusion and presented them in several points. The detail revisions could be found in the revised version.

6. The authors wrote "However, the shortcomings of 45 TiAl intermetallic compounds, such as poor fracture toughness, low ductility, and ex-46 treme brittleness at room temperature, limit their practical applications [7-9]." On the basis of their research, the authors could be provide the possibilities of using such coatings in the broadly understood industry. I see in manuscript that the one of the authors works at the Laboratory of Materials Technology and Application for Intelligent Manufacturing. Perhaps it would be worth mentioning the use of such coatings? If there is one?

 Thanks for your very thoughtful suggestion. Your suggestion for us is very valuable. Such coatings are still in the laboratory research stage, and we will try our best to promote this research to the corresponding industry in the future, which is also what we have been planning.

Special thanks to you for your good comments. We hope that these revisions are satisfactory and that the revised version will be acceptable for publication in Coatings.

Thank you very much for your work concerning our paper.

Your sincerely,

Xiao Chen

Corresponding author:

Name: Xiao Chen

E-mail: chenxiaoxyxy@126.com

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript presents an experimental thorough investigation regarding the reinforcement of the intermetallic TiAl with titanium carbide (TiC) to improve the mechanical properties, wear resistance, and heat-resistance stability of the arisen coating.

Overall the experimental study is well written and presented.

Some minor points should be taken into consideration before publication.

Please explain the novelty of the study in the introduction.

Have authors used specific standards to perform their experimental tests and measurements?

Which are the exact benefits of the proposed material components in comparison with relevant coating technologies.

Some comparisons regarding for example the fracture toughness of the proposed coatings with more standard ones would be very interesting for the reader.

In the conclusions section, please highlight the ideal way for producing the most superior type of TiC/Ti-Al Composite Coating considering the present measurements.

Author Response

Dear Editor and Reviewer:

Thank you for your letter and for the reviewer’s comments concerning our manuscript (Coatings-1353643). Those comments are all valuable and very helpful for revising and improving the quality of the manuscript. Based on your suggestions, we have studied comments carefully and have answered the questions in detail one by one. Revised portion are marked in red in the paper. The responds to the reviewer’s comments are as following:

According to the attached iThenticate report，we rewritten some sentences in the revision.

1. Please explain the novelty of the study in the introduction.

Thanks very much for your thoughtful suggestion. According to your suggestion, we explain the novelty of the study in the introduction. The novelty of the study is as follow: 1. in order to avoid the oxidation of spraying materials and the generation of thermal stress in the coating, cold spraying technology was adopted in this study; 2. based on the characteristics of cold spraying technology, Ti-Al intermetallic phases and TiC were in-situ synthesized in the coatings by heat treatment.

2. Have authors used specific standards to perform their experimental tests and measurements?

 Thanks very much for your thoughtful question. All of the experimental tests and measurements were completed under national standards.

3. Which are the exact benefits of the proposed material components in comparison with relevant coating technologies.

Thanks very much for your thoughtful question. The material composition ratio of Ti and Al in the study is order to generate TiAl phase in the study, and the content of C is determined according to some references.

4. Some comparisons regarding for example the fracture toughness of the proposed coatings with more standard ones would be very interesting for the reader.

Thanks very much for your thoughtful suggestion. You are right. We supplemented relevant contents in the revision.

The fracture toughness of the annealed coating (as-sprayed at 450 ℃) was lightly higher than that of sintered TiAl intermetallic compound(12.1 MPa∙m^-1/2), but lower than that of sintered TiC-TiAl composite material (16.8 MPa∙m^-1/2) [55].

[55] Yue, Y.L. Investgation on the synthesis and performance of TiC particulates reinforced TiAl intermetallic matrix composites. Degree of Master of Engineering, Jinan University, 2003.05.

5. In the conclusions section, please highlight the ideal way for producing the most superior type of TiC/Ti-Al Composite Coating considering the present measurements.

Thanks very much for your thoughtful suggestion. You are right. We supplemented relevant contents in the revision.

Cold spraying combined with heat treatment is a good and feasible method to prepare TiC/Ti-Al composite coating during controlling the process parameters.

Special thanks to you for your good comments. We hope that these revisions are satisfactory and that the revised version will be acceptable for publication in Coatings.

Thank you very much for your work concerning my paper.

Your sincerely,

Xiao Chen

Corresponding author:

Name: Xiao Chen

E-mail: chenxiaoxyxy@126.com