Review Reports - Experimental and Simulation Studies on Thermal Shock of Multilayer Thermal Barrier Coatings with an Intermediate Transition Layer at 1500 °C

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Strong points

In this study, three sets of AGAP/YSZ/intermediate layer/bonded coating systems were prepared and subjected to flame thermal shock experiments at 1500 ℃. At the same time, finite element simulations of flame thermal shock at 1500 ℃ were carried out for the AGAP/YSZ/bonded coating system and AGAP/YSZ/intermediate layer/bonded coating system. By analyzing the experimental and simulation results, it was found that introducing an intermediate transition layer can effectively relieve the thermal stress during thermal shock and significantly improve the strain tolerance of the coating. On this basis, the study further modulates the structure of the AGAP/YSZ/intermediate/bonding layer coating system and designs a new coating system for the AGAP/YSZ/EMAP intermediate/bonding layer. The finite element simulation results show that introducing the EMAP structure relieves the thermal stress during thermal shock and increases the strain tolerance of the coating but also improves its thermal insulation performance. The main conclusions of this study are summarized as follows:

1. By analyzing the results of the flame thermal shock experiments on the AYIB coating system at 1500 ℃, the coating's failure mode changes due to the introduction of the intermediate transition layer, and the location of crack generation moves from the interface between the BC layer and the ceramic layer to the interior of the intermediate transition layer.

2. The thermal insulation performance of the coating decreases slightly due to the introduction of the intermediate transition layer. For the AYB system, the temperature of the substrate surface is 1275 ℃ at a high-temperature environment of 1500 ℃. After the introduction of the intermediate transition layers of 60 μm, 80 μm, and 100μm, the temperatures of the substrate surface are 1283 ℃, 1287 ℃, and 1294 ℃, respectively.

3. Compared with the AYB coating system without an intermediate transition layer, the thermal mismatch stresses caused by thermal expansion mismatch in the high-temperature thermal shock experiments are significantly alleviated by adding different thicknesses of the intermediate transition layer in the AYIB coating system. When the thickness of the intermediate transition layer is 80 μm and 100 μm, the maximum thermal stresses are 457.1 MPa and 478.1 MPa, respectively, 15.78% and 12.12% are reduced.

4. The coatings' strain tolerance and thermal insulation properties were significantly improved by introducing the EMAP structure in the intermediate transition layer. When the contents of second-phase embedded particles were 3%, 6%, and 9%, respectively, the maximum thermal stresses inside the coatings were 150.39 MPa, 146.85 MPa, and 99.01 MPa. The temperatures on the substrate surface were 1203 ℃, 1193 ℃ and 1183 ℃, respectively. The increase of the second-phase particle content effectively relieves the thermal stress inside the coating and enhances the thermal insulation performance of the coating system.

12 quality references of co-authors of the article.

The authors have proposed an original solution to introduce an intermediate transition layer.

Weak points

1. Align text to width (Lines 328-332).

2. In Take away the greasiness. (Line 368).

3. Draw a dot. (Line 377).

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This research examines how incorporating an intermediate transition layer can improve the strain tolerance of thermal barrier coatings (TBCs), thereby extending their thermal lifespan. The investigation employs both experimental methods and simulations to assess the impact of this structural modification.

Nevertheless, several aspects require careful consideration to improve the overall quality of the manuscript prior to submission:

1- The manuscript lacks definitions for several technical terms upon their initial use, including GZ, AGAP, EMAP, BG, and AYI(E)B, which may lead to reader confusion.

2- Lines 47 and 82 discuss coating effects on microstructure but fail to address potential YSZ phase transformations during the coating process, requiring further explanation.

3- A citation is missing in line 183 to support the provided statement.

4- The fracture toughness measurement method, including device specifications and experimental setup, is not described in line 223, hindering reproducibility and comprehension.

5- While thickness details for ABAQUS simulations are provided in line 272, other crucial parameters such as boundary conditions, material properties, and mesh size are omitted, necessitating inclusion for improved clarity and replicability.

6- Line 308 lacks mention of the ASTM standard used for tensile stress measurements, which is essential for ensuring methodological consistency and adherence to standard practices.

7- The term "S22" is referenced but cannot be located in any figure or description within the manuscript, requiring clarification or removal if irrelevant.

8- An unnecessary bold formatting of the word "in" in line 368 should be corrected for consistency.

9- The justification for observations in line 382 is unclear and requires additional explanation to support the statement made.

10- Lines 419-420 contain a vague and grammatically unclear sentence: "Test due to thermal expansion mismatch." This should be reworded and expanded for better understanding.

11- The research methodology exhibits a lack of detail in certain aspects, particularly concerning the substrate pre-heating process. The omission of exact temperature values and time frames hinders the ability to replicate the experiments accurately.

12- The description of sample preparation techniques, including surface treatments prior to coating application, is inadequate, which negatively impacts the study's reproducibility.

13- While the finite element analysis (FEA) briefly mentions disregarding thermal radiation, it fails to provide a rationale for this decision. Moreover, crucial information such as boundary conditions, material characteristics, and mesh dimensions is absent and should be incorporated.

14- Although the plasma spray parameters are clearly presented in a table, there is insufficient discussion or context regarding how variations in these parameters affect the outcomes. This additional information should be included to enhance comprehension.

15- The paper presents simulation results but lacks adequate experimental data to confirm the findings. Including a comparison between simulated and experimental results would bolster the manuscript's credibility.

16- While the text briefly touches on aging stresses, it does not offer a thorough analysis of how aging influences the distribution of thermal stress and the long-term performance of the coatings. This oversight needs to be addressed.

17- The paper lacks a detailed explanation of the mechanisms underlying thermal shock and its impact on coatings. A more comprehensive discussion on the development and propagation of thermal stresses would improve understanding.

18- The intermediate transition layer is presented as a solution for enhancing strain tolerance, but the potential drawbacks, such as increased production complexity and higher costs, are not explored. This creates an imbalance in the discussion.

19- Several parts of the text contain grammatical issues, including vague or unclear sentences. For example, the phrase "Test due to thermal expansion mismatch" in lines 419-420 requires revision for clarity.

20- The explanations provided for observations, such as those mentioned in line 382, lack sufficient support. More comprehensive justifications are required to substantiate these claims.

21- The study fails to include comparisons with other thermal barrier coatings (TBC) systems under comparable conditions. Such comparative analyses would help validate the claimed benefits of the proposed system.

22- The manuscript inadequately addresses the practical implications and real-world applicability of the findings, particularly in relation to diverse thermal cycling conditions.

23- There is insufficient discussion regarding the potential effects of the intermediate transition layer on adhesion and other properties, which could significantly impact the overall viability of the system.

Comments on the Quality of English Language

just for example:
Lines 419-420 contain a vague and grammatically unclear sentence: "Test due to thermal expansion mismatch." This should be reworded and expanded for better understanding

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The work related to studies on thermal shock of multilayer TBC with an intermediate transition layer.

1. The work does not clearly emphasize what is new.

2. What about the porosity of coatings?

3. Was it the same for all samples?

4. What was the shape of the pores?

5. Was it similar for all samples?

6. What mechanism caused the increase in resistance to thermal shock of tested samples? It is not explained.

Furthermore:

- no explanations of abbreviations used for the first time in the manuscript - literature items are not written in accordance with the publisher's guidelines