A Direct Laser Sintering Approach for the Electrophoretic Deposition Overlay of Yttria-Stabilized Zirconia on the Surface of a Thermal Barrier Coating System
Round 1
Reviewer 1 Report (New Reviewer)
This manuscript analyzes the application of a direct laser sintering technique to the electrophoretically deposited overlay of yttria-stabilized zirconia on the surface of a thermal barrier coating. The research is well designed but presented not very clearly. A good comparative analysis of existing publications is carried out, but some issues should be fixed. The methodological section of the manuscript is presented in sufficient detail. The authors used modern equipment for the preparation and testing of samples. They also utilized the equipment for visualization and assistance in the interpretation of the obtained results. The authors found that the direct laser sintering process can provide promising results when implemented in one step, rather than performing two steps of sintering in a furnace and subsequent laser surface modification, thus shortening the application time while improving the performance.
However, some shortcomings should be corrected to make the manuscript acceptable for publication in Coatings.
(1) In the Introduction section, the first two sentences should be corrected. Actually, it should be a single sentence.
(2) In the Introduction section, the abbreviations APS and EPD should be explained when they are first mentioned.
(3) In the Introduction section, in the sentence “High porosity may be desired for thermal barrier coatings, since porosity reduces the coating’s thermal conductivity [10], while the performance aspects of these coatings, such as their corrosion resistance, toughness, and hardness, may be diminished with a high degree of porosity [add References].” the authors should add more references for substantiation of these disadvantages of porous YSZ ceramics. They can use the following articles in which a comparatively wide range of sintering temperatures for YSZ ceramics is analyzed in terms of the optimization of microstructure and mechanical properties: https://doi.org/10.1016/j.matdes.2023.111908, https://doi.org/10.3390/ma15155212. This will increase the weight and significance of the research.
(4) The explanation for (CLA) is given for the first time in sub-section 2.4 and there is no need to repeat this in sub-section 3.2.
(5) In the captions of Table 1 and Table 5, the parentheses should be removed. Throughout the manuscript, “the (CLA) roughness” should be replaced with “the CLA roughness”.
(6) The font size in Figures 4, 12, 13, and 14 is too small to be recognized. These figures are of poor quality. The authors should fix this issue.
(7) The font size in Figures 2(b,c), 16(b,c), and 17(b,c) is too small to be recognized. The authors should fix this issue.
(8) The authors state that “At a low magnification, Figure 6a shows a smooth appearance and a network of segmented cracks distributed throughout the whole laser-treated surface.” It is unclear why they present an optimized laser treatment mode as their achievement if a surface of poor quality with microcracks about 100 μm in size was obtained.
(9) The authors state that “One can clearly observe the increase in the roughness values after the modification of the thermal barrier coating surfaces via EPD overlaying and the following laser sintering process.” It seems that this is a mistake and should be “One can clearly observe the decrease in the roughness values …”
(10) In the phrase “…a spray distance of 100 mm were around 8.6 m [27]”, the measurement unit should be corrected, namely “around 8.6 μm [27]”.
(11) Figure 18 is of poor quality. The size of markers of separate phases should be increased.
(12) In the Conclusions section, Conclusion (7), the measurement unit should be provided for the hot corrosion rate.
(13) In the References section, position 20, the names of the authors should be corrected as follows:
Baufeld, B.; van der Biest, O.; Ratzer-Scheibe, H.-J.
In my opinion, the English language of this manuscript should be slightly improved.
Author Response
Thank you for your comments
Author Response File: 
Author Response.docx
Reviewer 2 Report (New Reviewer)
In this paper, the author used The laser sintering process and modification of yttria-stabilized zirconia (YSZ) coatings subjected to electrophoretic deposition (EPD) on YSZ air-plasma-sprayed (APS) thermal barrier coatings (TBCs) were investigated. This study will help to improve the TBC characteristics of YSZ coatings. However, the paper needs to be revised as follows before publication:
1. On page 4, the author noted that Figure 1 clearly demonstrated a rough appearance, a non-uniform and uneven distribution of open porosity. It is suggested that the author should mark unmelted particles and semi-melted particles in Figure 1.
2. On page 6, the author noted that frequency and pore size distribution of (a) as-sprayed coating (b) EPD overlay surface in figure 4,it is suggested that the author should improve the quality of the images so that readers can view the data.
3. On page 9, the author noted that Figure 9a and c FE-SEM for the direct laser sintering region showing the surface modification. The author should explain why different microscopic results appear in the same region?
4. On page 11, the author noted that One can clearly observe the increase in the roughness values after the modification of the thermal barrier coating surfaces via EPD overlaying and the following laser sintering process. But This result does not match the result in the figure, the author should explain whether the roughness has increased or decreased.
5. On page 13, the author noted that the (CLA) roughness value decreased to 0.99 μm after the laser sintering process, while the AFM results showed that the roughness decreased to 2.48 nm. The author should explain reason in detail.
6. On page 13, the author noted that the attack by corrosion salts (V2O5 + Na2SO4) was greater in the case of plasma-sprayed YSZ coating without surface modification than in the case of direct laser sintering of the EPD overlay. The author should indicate the basis for judging the size of the erosion ratio.
7. In this paper, it is suggested that the author should check the clarity of the pictures, so that increase the quality of the article.
revise
Author Response
Thank you for your comments
Author Response File: Author Response.docx
Reviewer 3 Report (Previous Reviewer 2)
I had previously assessed the manuscript under review, but regrettably, it did not meet the acceptance criteria at that time. However, in this updated version of the manuscript, the issues and criticisms I raised during my initial evaluation have been thoughtfully addressed. As a result, the manuscript has undergone a significant improvement in overall quality. Moreover, upon a thorough reevaluation of the document, notable enhancements have been made in terms of the clarity of language, description of experimental procedures and conclusions.
The English language is signifficantly improved however minor editing is required.
Author Response
Thank you for your comment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report (New Reviewer)
All of the reviewer’s comments were taken into account by the authors. The manuscript can now be accepted for publication in Coatings.
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.
Round 1
Reviewer 1 Report
Ms. Ref. No.: coatings-2508016
Title: Direct laser sintering approach for electrophoretic deposition overlay of YSZ on the surface of thermal barrier coating system
My comments:
It seems that the manuscript is written well. This reviewer had no major problems with it however certain revisions are required so its quality will improve further. Please address the comments below:
1- The plasma spray parameters for coatings should be added to the manuscript.
2- The composition of the substrate should be added to the manuscript.
3- Please remove the additional data on SEM images. for example date and etc.
4- The authors should provide details about the equipment used in the study.
5- Would it be possible for the authors to present a magnified version of Figure 3? or a fracture cross-section ...
6- The figures are often of poor quality.
7- Would it be possible for the authors to include the X-ray diffraction analysis results of the samples?
Author Response
No comment.
Regards
Author Response File: Author Response.docx
Reviewer 2 Report
Please find attached the comments.
Comments for author File: Comments.docx
The English language must be improved, there are sentences/paragraphs whose meaning is not clear. This is a barrier for the reader to comprehend the work done.
Author Response
No comment
Regards
Author Response File: Author Response.docx
Reviewer 3 Report
Dear authors, please explain the action of iodine as a catalyst.
In figures 5,6,11 small inscriptions do not allow to see the picture
In table 3 there is no decoding of physical quantities
The article does not compare the properties and characteristics of coatings with those already known. Sparse discussion of the results of the study.
Author Response
No comments
Regards
Author Response File: Author Response.docx
Reviewer 4 Report
Review of manuscript
Direct laser sintering approach for electrophoretic deposition overlay of YSZ on the surface of thermal barrier coating system
The TBC structure and properties examination is very important to increase their performance. So, the topic is hot. The application of such an EPD-Laser sintering combined technology for YSZ TBCs looks promising. However, the paper looks like a scientific report without any explanations of structure formation mechanisms and proof of the positive effect of the EPD laser-sintered layer on the YSZ TBC performance (thermal conductivity, fracture toughness, durability, etc.). English is very poor. Authors need to make an additional examination of the structure, fracture toughness, porosity, and nanohardness of the EPD laser-sintered layers. So, I cannot recommend the manuscript for publication.
Some comments are below.
Lines 22-23: English is improper (underlined): “….Which is better than the direct laser on plasma-sprayed coatings”. What does it mean “better”? What about thermal conductivity?
Lines 26- 27: English is not proper: “…Gas turbine engines are now designed such that the heat-resistant superalloys operate at temperatures very close to their melting, so current strategies for performance improvement are centered on thermal barrier coatings”
Lines 28- 29: English is not proper: “…Ceramic coatings are often used to improve the surface behavior of metals in high-temperature applications such as thermal barrier coatings (TBCs)”
Lines 34-35: The sentence “…Atmospheric plasma spray is a technique of deposition for the systems presented to extend turbine lives and to improve engine efficiencies for instance” is difficult to understand. What is the “system presented”? The authors did not present a system.
Lines 46-47: English is not proper: ”…And to reduce surface roughness of top coat, increase surface hardness 47 and seal open pores [11].”
Lines 56-57: English is not proper:” …Conventionally, Coating needs to be densified after EPD using an electrical furnace, yet the high temperatures necessary for sintering may be detrimental to the metal.”
Lines 63-64: English is not proper: “..Spark-plasma sintering, two-step-sintering, and laser sintering [19 ].”
Lines 71-72: English is not proper: “…Surface modification of plasma-sprayed YSZ thermal barrier coatings was successfully carried out by deposition overlay layer using the EPD technique which densified by direct laser sintering with a pulsed Nd: YAG solid-state laser.”
Line 120: There is no detailed explanation and description of structure formation during EPD and laser sintering in p. 3.1. Microstructure of direct laser sintering and modification.
Lines 121-122: The sentence “… In order to understand the microstructure of the coating after the laser sintering process, it’s necessary to make a comprehensive description of the coating before that” is not needed because this statement is well known.
Line 125: The authors’ statement “… The lack of pores was also observed” is discussible. Fig.2 show images with a small magnification, and the real porous structure cannot be defined at these magnifications.
Line 126: the sentence “…, and this is important in preventing the plasma coating from penetrating harmful substances during the services” is not clear.
Lines 132-133: The statement “…The use of iodine as a dispersant in suspension enhances the formation of free protons according to the reactions between I2 and the ethanol solvent” is not explained and proven.
Line 148: Authors did not determine surface densification parameters (porosity, pores distribution) and adhesion strength. So, the statement “…High-quality surface densification and adhesion, precise depth, and width can be produced” is speculation.
Lines 155: English is not proper: “….The cross-sectional FE-SEM micrograph of the green EPD overlay coating after laser sintering has been illustrated in Fig. 6. Laser beam led to produce of remelted overlay with a densified microstructure and a network of segmented cracks, which are perpendicular 157 to the surface. The penetration melted depth measured was approximately 41 µm depth 158 (thickness of the remelted layer) [9]. FE-SEM micrograph of the interface between YSZ EPD overlay and direct laser sintering is presented in Figure 7 showing the contrast. It can be seen that the laser sintering track is clearly distinguishable because of the different contrasts between the regions. The heat input produced by the laser beam 13.75 J/mm was enough to sinter the green EPD 163 overlay.”
Line 212: Authors state that “…Surface modification by means of the laser beam is effective as a possible post-processing treatment… for the purpose of reducing surface roughness” and densification. However, they show a lot of microcracks generated in the sintered layer. Moreover, the authors did not define the fracture toughness of the coating. Thus, the authors’ statements are not proven.
Line 221: Authors did not measure thermal conductivity which is the main parameter of TBC
English is poor.
Author Response
No comment
Regards
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
After reading through the revised manuscript and the revisions introduced by the authors, I have found that the manuscript has been improved although Figures 8 and 9 have low quality.
Author Response
Thank you for your comment
Author Response File: Author Response.docx
Reviewer 2 Report
Dear authors,
Thank you for revising your manuscript and addressing all the provided comments.
Author Response
Thank you for your comment
Reviewer 3 Report
All my comments have been removed. The article can be recommended for publication. In table 1, you need to add mole percentages and correct molybdenum.
Author Response
Thank you for your comment
Author Response File: Author Response.docx
Reviewer 4 Report
Comments for author File: Comments.docx
N/A
Author Response
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Author Response File: Author Response.docx
