High-Temperature Hot Corrosion Resistance of CrAl/NiCoCrAlY/AlSiY Gradient Composite Coating on TiAl Alloy

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The author should be congratulated for conducting a comprehensive and interesting study on the hot corrosion resistance of composite coatings. The study explores the behavior of composite coating, TiAl substrate, NiCoCrAlY coating, and CrAl/NiCoCrAlY/AlSiY coating under high-temperature corrosion conditions. The findings provide valuable insights into hot corrosion mechanisms and the protective effects of different coatings. However, several revisions are necessary to enhance the clarity and impact of the manuscript. The reviewer comments are provided below:

- The abstract should include critical data such as the duration of corrosion exposure as this is an essential parameter that significantly impact the study's findings

- The choice of a 75% Na2SO4 and 25% NaCl composition and a testing temperature of 950°C needs to be justified. Elaborate on why these specific conditions were selected and discuss how they correlate with real-world applications or other studies in the literature.

- Considering that HVOF produces dense coatings and using multiple technologies increases manufacturing costs and may induce impurities or adhesion between layers, it is intriguing why HVOF wasn't used for the final AlSiY layer.

- It is stated that the generally accepted temperature range for engine components is 550-800°C. However, the tests were conducted at 950°C. Explain the reasoning behind choosing this temperature. Is it related to a specific type of engine or application?

- Please include images showing the surface morphology of the samples.

- In the EDS analysis results (e.g., Figs. 3, 6, 7, 8), specify whether the analysis was conducted on points or micro-areas. This will provide clarity on the resolution and scope of the elemental analysis.

- There should be a more thorough correlation and comparison of the results obtained in this study with existing data from the literature. Discussing similarities and differences with other studies will highlight the novelty and significance of your findings.

- The novelties of the present contribution should be better underlined in the introduction part of the manuscript 

- The conclusion section should also include suggestions relevant to the industry and research groups, outlining potential directions for further research and practical applications of the coatings studied.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript is devoted to the investigation of the microstructure and hot corrosion resistance of TiAl alloy with CrAl/NiCoCrAlY/AlSiY gradient composite coating. The authors performed a detailed comparison of the corrosion properties of the conventional NiCoCrAlAlY coating and the CrAl/NiCoCrAlAlY/AlSiY gradient composite coating on TiAl substrate. As a result, the high efficiency of gradient coating has been demonstrated. The manuscript is a coherent and detailed study, with all results clearly presented and discussed by the authors. The conclusions are supported by the results obtained in the paper.

I have a few minor comments on the manuscript:

Table 2. Table 3. Table 4. Table 5. The EDS results. For example, Ni content is 28.22. This is a very high accuracy for the EDS analysis method. I think it would be better to use one decimal place after the dot and it would be 28.2.

Figure 6e-i. Figure 7h-l. Figure 8e-o. EDS maps do not contain scale marks.

Conclusions. “The prepared CrAl/NiCoCrAlY/AlSiY gradient composite coating is dense with 432 10 μm, 45 μm, 5 μm of CrAl layer, NiCoCrAlY layer, and AlSiY layer, respectively.” The thickness of the layers is presented here. I think the authors should clarify and indicate the confidence intervals for the measurements presented, and state them in the results.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf