Influence of Gradient Index and Pores on the Properties and Internal Stress of Continuous Transition Ceramic–Metal Coating
Round 1
Reviewer 1 Report
The authors performed the studies on “Influence of gradient index and pores on the property and in
ternal stress of continuous transition ceramic-metal coating”. The research results are interesting in the scientific community. However, the authors need to address the following comments to improve the quality of the manuscript.
- In the Introduction Section, the last para authors need to be rewritten, including the gaps in the existing literature and the need for the present research work and the objective.
- The application of the material GH4099 concerning the coating to be included.
- How the thickness of the coating is selected. Is there any process optimization that has been carried out
- In the Experimental Section, no details about the simulation are included. The procedure can be included
- Section 3.1 presents the Microstructure results, whereas the justification of the results is not explained in detail.
- Why the hardness variation is very high in the traditional coating process. The explanation for the result is not there in the manuscript
- Why authors are not performing the bond strength of the coatings.
- At the beginning of each para, the sentence must start with full words. In a few places, the authors mentioned that Fig. should be replaced with Figure. The same should be checked throughout the manuscript.
Author Response
Reviewer #1: Reviewer's comments:
The authors performed the studies on “Influence of gradient index and pores on the property and internal stress of continuous transition ceramic-metal coating”. The research results are interesting in the scientific community. However, the authors need to address the following comments to improve the quality of the manuscript.
We would like to thank to Reviewer 1 for his valuable and detailed comments.
- In the Introduction Section, the last para authors need to be rewritten, including the gaps in the existing literature and the need for the present research work and the objective.
We agree with your comment. The last para of the manuscript text was revised and polished by the authors, the modification to the manuscript text are highlighted in red.
- The application of the material GH4099 concerning the coating to be included.
We agree with your comment. After consideration, we added the application of the material GH4099 concerning the coating to the first paragraph of Introduction, and this was corrected in the manuscript.
- How the thickness of the coating is selected. Is there any process optimization that has been carried out.
The typical structure of TBCs consist of bond coat (BC) and top coat (TC). The bond coat with a thickness of 50-200 μm provides the oxidation resistance. The Top coat with a thickness of 50-150 μm provides insulation from hot gases. For the convenience of the calculation simulation, the thickness of the continuous transition zone, the bonding coating and the ceramic coating are each 100 µm.
- In the Experimental Section, no details about the simulation are included.
We agree with your comment. We rewritten the Experimental, and then added some important simulation, such as Finite Element Analysis Modelling and Finite Element Analysis way.
- The procedure can be included Section 3.1 presents the Microstructure results, whereas the justification of the results is not explained in detail.
We agree with your comment. After confirmation, we corrected this issue. The transition coating consists of three section: the bond coating, the obvious gradient region between the ceramic coating and alloy bond coating, the outer ceramic coating. At gradient region, CoNiCrAlY splats were inserted into the ceramic region, which made the interface between the top ceramic coating and the alloy bond coating disappear. During the spraying process, the molten droplets formed by ceramic and metal powders are non-uniformly distributed in the flame, resulting in a staggered deposition of ceramic and metal mixed.
- Why the hardness variation is very high in the traditional coating process. The explanation for the result is not there in the manuscript.
The reason for hardness variation is very high in the traditional coating process is that there is no stress buffer between the top coating and bond coating. Ceramics have a higher hardness than metals, so a larger hardness variation occurs near the interface between metal and ceramic. We also explained this issue in the manuscript.
- Why authors are not performing the bond strength of the coatings.
We agree with your comment and explained as follows. Bond strength is an important property of the coating, However, the main motivation of this work has been to investigate the influence of gradient index and pores on the property and internal stress of continuous transition ceramic-metal coating by computer simulation. We will continue to investigate the effect of gradient structure on the bond strength of the coating in our next work.
- At the beginning of each para, the sentence must start with full words. In a few places, the authors mentioned that Fig. should be replaced with Figure. The same should be checked throughout the manuscript.
We agree with your comment and corrected this issue.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The work reported that transition zone was introduced between the ceramic coating and the bonding, then air plasma spraying was prepared traditional coatings and continuous transition coatings, and the Vickers hardness analysis results show that the existence of the continuous transition zone will make the change of the hardness between the ceramic coating and the bonding coating more gradual. However, there are some issues which should be resolved before acceptance as following below.
-Introduction should contains recent method used in coating such as PEO, DCC, PVD, and etc. To understand these method, authors can use recent references such as
Progress. Materials Science 112 (2020) 100663, Electrochemical Acta 379 (2021) 138190, Chemical Engineering Journal 356 (2019) 850-856, Progress in Organic Coatings 163 (2022) 106639, Applied Materials Today. 24 (202) 101142.
-Should clarify the novelty from this work and try to compare with other reports.
-Regarding Figure 1, BC, CT, and 8YSZ should be clearer and make related with EDS mapping.
-Should provide SEM images of surface.
-Could you explain instability in stress as shown in Figure 6 and Figure 8?
-why you thermal stress of coating?
-Does number of pores increase with increasing the thermals stress?
Author Response
Reviewer #2: he work reported that transition zone was introduced between the ceramic coating and the bonding, then air plasma spraying was prepared traditional coatings and continuous transition coatings, and the Vickers hardness analysis results show that the existence of the continuous transition zone will make the change of the hardness between the ceramic coating and the bonding coating more gradual. However, there are some issues which should be resolved before acceptance as following below.
We would like to thank to Reviewer 2 for his valuable and detailed comments.
- Introduction should contain recent method used in coating such as PEO, DCC, PVD, and etc. To understand these method, authors can use recent references such as Progress. Materials Science 112 (2020) 100663, Electrochemical Acta 379 (2021) 138190, Chemical Engineering Journal 356 (2019) 850-856, Progress in Organic Coatings 163 (2022) 106639, Applied Materials Today. 24 (202) 101142.
We agree with your comment. The previous studies show that various methods such as Air plasma spraying (APS), High velocity oxygen-fuel (HVOF), Low-pressure plasma spraying (LPPS), Electron beam physical vapor deposition (EB-PVD), have been developed to fabricate the TBCs. We corrected this issue and cited some literature on the methods for preparing protective coatings.
- Should clarify the novelty from this work and try to compare with other reports.
We agree with your comment. The last para of the manuscript text was revised and try to compare with other reports, the modification to the manuscript text are highlighted in red.
- It Regarding Figure 1, BC, CT, and 8YSZ should be clearer and make related with EDS mapping.
The Fig. 1 was re-marked, as shown below. About the EDS mapping of the coating, we point it in the manuscript.
Figure 1. SEM image and element distribution of traditional coating (a) and continuous transition coating (b).
- Should provide SEM images of surface.
We agree with your comment and explained as follows. About the SEM images of surface, we found the same microstructure on the surface of the traditional double-layer coating and the continuous transition coating, as shown below. Therefore, we study on the different microstructures of the coating cross-sections.
Figure2. SEM image surface of traditional coating (a) and continuous transition coating (b).
- Could you explain instability in stress as shown in Figure 6 and Figure 8?
The instability in stress as shown in Figure 6 and Figure 8 because of the continuous transition ceramic-metal. At gradient region, CoNiCrAl alloy splats were inserted into the ceramic region and eliminated the top coating/bond coating interface, which is present in a traditional multilayer coating system
- why your thermal stress of coating?
The combustion chamber temperature of gas turbine engines can approach 2000°C and the high-pressure turbine inlet temperature can reach 1600°C. Thermal barrier coatings are typically used at temperatures of around 1100℃. A lot of evidences have proved that the failure often occurs at the cooling stage. In order to simulate the service environment of thermal barrier coatings, we applied a temperature load on the upper surface of the ceramic and applied heat dissipation conditions on the base metal coating, the heating rate is 10 K per second, the holding temperature is 1273 K, and the cooling rate is twice the heating rate.
- Does number of pores increase with increasing the thermals stress?
Based on current research, the number of pores in the coating depends mainly on the preparation method and preparation process. The coating produced by APS shows laminal structure containing some un-melted thick particles, oxides and pores. The coating produced by HVOF shows a relatively dense structure. There are a little bit oxides and pores in the bond coat. The densest microstructure of coating is fabricated by LPPS. We think that the pores do not increase with increasing the thermals stress.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Authors made the necessary changes in the manuscript.
Reviewer 2 Report
This form can be accepted in this coatings
