Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Editor

 

A paper on the densification of Gd2Zr2O7 for use as a target in the EB-PVD process is submitted for evaluation. The effect of the degree of densification on fracture toughness is also presented. The authors of this paper used commercially available nanopowders and sinterability tests were carried out using different temperatures as well as different annealing times at given temperatures. The paper classically comprises a theoretical introduction, a description of the experiments and a discussion of the research carried out. The paper concludes with a summary. In the reviewer's opinion, the editing of the paper is also adequate, with the exception of the not very legible SEM observations. However, several issues seem questionable in the reviewer's opinion:

1. it would be advisable to include a more detailed description of the powder used: XRD, grain size distribution - what influences densification by sintering
2. why did the Authors subject the starting powder to grinding and drying? Did the Authors introduce any sintering activators into the starting powder? If so, which ones...,
3. It seems that the authors' difficulty in achieving full densification resulting in the need for higher temperatures and thus grain growth could be addressed by using more advanced sintering techniques - HP or even HIP...? As is well known, these techniques also make it possible to significantly reduce sintering temperatures while achieving a very high degree of densification.

4 There is a lack of information as to whether the target sinters produced by the authors are suitable for PVD.

All the above remarks, in the opinion of the Reviewer, do not invalidate the very large amount of work put in by the Authors, but only, in the opinion of the Reviewer, should complete it and, consequently, publish it.

Sincerely

Reviewer

Author Response

Thank you very much for taking the time to review this manuscript. Please find the revisions related to Question 1 in re-submitted files. For Questions 2-4, no detailed amendments have been implemented in the text, and the specific rationale can be located in the following responses.

Comments 1: it would be advisable to include a more detailed description of the powder used: XRD, grain size distribution - what influences densification by sintering.

Response 1: Thank you very much for pointing out the shortcomings in this manuscript. The revised manuscript incorporates the XRD analysis results of the raw materials, along with a concise interpretation of the raw materials. The X-ray diffraction (XRD) pattern of the raw powder exhibits broadened peaks, indicating the presence of typical nanostructural characteristics. As the sintering temperature increases and the holding time is prolonged, the full width at half maximum (FWHM) of the diffraction peaks gradually decreases, suggesting an increase in grain size and a further crystallization process of the nanopowder.

Comments 2: why did the Authors subject the starting powder to grinding and drying? Did the Authors introduce any sintering activators into the starting powder? If so, which ones..

Response 2: Thank you very much for your insightful guidance on the manuscript. To improve the yield of cold isostatic pressing (CIP) , the powder underwent pretreatment. Ball milling was employed to alleviate the agglomeration of the nanopowder. To ensure the purity of the target material, no sintering aids were added in this experiment.

Comments 3: It seems that the authors' difficulty in achieving full densification resulting in the need for higher temperatures and thus grain growth could be addressed by using more advanced sintering techniques - HP or even HIP...? As is well known, these techniques also make it possible to significantly reduce sintering temperatures while achieving a very high degree of densification.

Response 3: Thank you very much for your insightful guidance on the manuscript. For electron beam physical vapor deposition (EB-PVD) technology, highly dense targets are unfavorable for the deposition process. Therefore, the experimental results do not aim for fully dense ceramic targets, and methods such as hot pressing or hot isostatic pressing were not used as the sintering method for the ceramic targets.

Comments 4: There is a lack of information as to whether the target sinters produced by the authors are suitable for PVD.

Response 4: We are thankful for the reviewer’s professional insights, which are also valuable references for our future research. This manuscript focuses on the densification process of targets and the factors affecting fracture toughness, while the related PVD experimental content will be presented in the next manuscript.

Similar Q&A responses like those in the text box can also be found in the following attachments.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper describes the research on fracture toughness of the ceramic material Gd2Zr2O7. It is a significant material being a compound of Gd (rare earth element Gadolinium) that can be applied as thermal barriere. The ceramics is doped with Yb (Ytterbium). 

The research is described clearly. The devices used in the fracture toughness evaluation are described well. 

In particular,  the authors show the predominant ro;le of the grain size and relative density for fracture toughness.

It is a valuable work for the industry.

Author Response

Comments 1: 

The paper describes the research on fracture toughness of the ceramic material Gd2Zr2O7. It is a significant material being a compound of Gd (rare earth element Gadolinium) that can be applied as thermal barriere. The ceramics is doped with Yb (Ytterbium). 

The research is described clearly. The devices used in the fracture toughness evaluation are described well. 

In particular,  the authors show the predominant ro;le of the grain size and relative density for fracture toughness.

It is a valuable work for the industry.

Response 1: We thank you for the patient review and positive evaluation of our work, which greatly encouraged us to improve the manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript “Study on Densification of Gd₂Zr₂O₇-Based Ceramic Target for EB-PVD Application and Its Effect on Fracture Toughness” presents a study on the densification process and its impact on the fracture toughness of ceramic targets based on Gd₂Zr₂O₇. The experimental approach and the analysis of grain growth, pore evolution, and their correlation with the mechanical properties represent a novel contribution compared with previous studies.
It is recommended that the citation and formatting guidelines established by the journal be reviewed in detail. Each reference should be adapted to conform fully to these requirements. This includes aspects such as the order of bibliographic elements (authors, year, title, journal name, volume, pages, DOI, etc.), the correct use of punctuation, and the typographic style required by Coating.
A thorough review of the English text is necessary, particularly with respect to scientific terminology. For example, in the methodology (line 109) the sentence “the phase structure of all tragets targets is of a single fluorite phase” is unclear—specifically, the term “tragets” should be corrected to indicate the intended meaning (presumably “targets”).
The resolution of the SEM images in “SEM of the cross section of ceramic targets under different sintering temperatures (holding time: 3 h)”, corresponding to:
(a) 1200℃; (b) 1250℃; (c) 1300℃; (d) 1350℃; (e) 1400℃; (f) 1450℃; (g) 1500℃; (h) 1550℃; (i) 1600℃
should be improved to enhance clarity.
There is a need to explain the behaviour at 1500°C in greater detail. It is mentioned that the isolated porosity is ‘disruptive’ at this temperature, yet thereafter the trend follows that observed at 1400°C, as illustrated in “Effects of Sintering Temperature on Relative Density, Grain Size, and Porosity of the Ceramic Targets (Holding Time: 3 h)”. This aspect should be clarified.
Similarly, the resolution of the SEM images in “SEM of the cross section of Ceramic Targets under Different Holding Times (Sintering Temperature: 1500℃)” corresponding to:
(a) 1 h; (b) 2 h; (c) 3 h; (d) 4 h; (e) 5 h; (f) 6 h; (g) 7 h
should also be improved.
What changes are observed in the relative density and in the porosity values (both total and isolated) when the sintering temperature increases from 1550℃ to 1600℃?
Which mechanism (for example, volume diffusion) dominates the densification process at this stage, and how is it manifested in the microstructure?
Finally, in what manner do the experimental observations (grain growth, reduction of porosity, variation in density) correlate with the three sintering stages proposed by Kingery?

 

Comments on the Quality of English Language

The manuscript “Study on Densification of Gd₂Zr₂O₇-Based Ceramic Target for EB-PVD Application and Its Effect on Fracture Toughness” presents a study on the densification process and its impact on the fracture toughness of ceramic targets based on Gd₂Zr₂O₇. The experimental approach and the analysis of grain growth, pore evolution, and their correlation with the mechanical properties represent a novel contribution compared with previous studies.
It is recommended that the citation and formatting guidelines established by the journal be reviewed in detail. Each reference should be adapted to conform fully to these requirements. This includes aspects such as the order of bibliographic elements (authors, year, title, journal name, volume, pages, DOI, etc.), the correct use of punctuation, and the typographic style required by Coating.
A thorough review of the English text is necessary, particularly with respect to scientific terminology. For example, in the methodology (line 109) the sentence “the phase structure of all tragets targets is of a single fluorite phase” is unclear—specifically, the term “tragets” should be corrected to indicate the intended meaning (presumably “targets”).
The resolution of the SEM images in “SEM of the cross section of ceramic targets under different sintering temperatures (holding time: 3 h)”, corresponding to:
(a) 1200℃; (b) 1250℃; (c) 1300℃; (d) 1350℃; (e) 1400℃; (f) 1450℃; (g) 1500℃; (h) 1550℃; (i) 1600℃
should be improved to enhance clarity.
There is a need to explain the behaviour at 1500°C in greater detail. It is mentioned that the isolated porosity is ‘disruptive’ at this temperature, yet thereafter the trend follows that observed at 1400°C, as illustrated in “Effects of Sintering Temperature on Relative Density, Grain Size, and Porosity of the Ceramic Targets (Holding Time: 3 h)”. This aspect should be clarified.
Similarly, the resolution of the SEM images in “SEM of the cross section of Ceramic Targets under Different Holding Times (Sintering Temperature: 1500℃)” corresponding to:
(a) 1 h; (b) 2 h; (c) 3 h; (d) 4 h; (e) 5 h; (f) 6 h; (g) 7 h
should also be improved.
What changes are observed in the relative density and in the porosity values (both total and isolated) when the sintering temperature increases from 1550℃ to 1600℃?
Which mechanism (for example, volume diffusion) dominates the densification process at this stage, and how is it manifested in the microstructure?
Finally, in what manner do the experimental observations (grain growth, reduction of porosity, variation in density) correlate with the three sintering stages proposed by Kingery?

 

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions in track changes in the re-submitted files.

Comments 1: A thorough review of the English text is necessary, particularly with respect to scientific terminology. For example, in the methodology (line 109) the sentence “the phase structure of all tragets targets is of a single fluorite phase” is unclear—specifically, the term “tragets” should be corrected to indicate the intended meaning (presumably “targets”).

Response 1: We sincerely appreciate your careful reading and for pointing out the error in the manuscript. We also carefully reviewed the entire manuscript to ensure the accuracy of scientific terminology and have made further language improvements where necessary.

 

Comments 2: The resolution of the SEM images in “SEM of the cross section of ceramic targets under different sintering temperatures (holding time: 3 h)”, corresponding to:

(a) 1200℃; (b) 1250℃; (c) 1300℃; (d) 1350℃; (e) 1400℃; (f) 1450℃; (g) 1500℃; (h) 1550℃; (i) 1600℃

should be improved to enhance clarity.

Similarly, the resolution of the SEM images in “SEM of the cross section of Ceramic Targets under Different Holding Times (Sintering Temperature: 1500℃)” corresponding to:

(a) 1 h; (b) 2 h; (c) 3 h; (d) 4 h; (e) 5 h; (f) 6 h; (g) 7 h

should also be improved.

Response 2: Thank you very much for your valuable and constructive comments, which have helped us improve the quality of the manuscript. We have adjusted the clarity of the SEM images in the manuscript.

 

Comments 3: There is a need to explain the behaviour at 1500°C in greater detail. It is mentioned that the isolated porosity is ‘disruptive’ at this temperature, yet thereafter the trend follows that observed at 1400°C, as illustrated in “Effects of Sintering Temperature on Relative Density, Grain Size, and Porosity of the Ceramic Targets (Holding Time: 3 h)”. This aspect should be clarified.

Response 3:Thank you for taking the time to carefully review our manuscript and provide insightful suggestions.We compared the densification rates and grain growth rates of ceramic targets sintered under temperature and time experimental conditions, and added the sentence "As shown in Figure 4, rapid densification of the ceramic target occurred between 1450℃ and 1550℃. Notably, the grain growth rate exhibited an initial increase followed by a decrease around 1500℃." to emphasize this phenomenon.

 

Comments 4: What changes are observed in the relative density and in the porosity values (both total and isolated) when the sintering temperature increases from 1550℃ to 1600℃?

Response 4: We sincerely appreciate the reviewer’s comments, which have positively contributed to improving the quality of our manuscript. We have provided a detailed description of the variation ranges of relative density and porosity between 1550℃ and 1600℃, and made corrections in lines 163-164 and line 168 of the manuscript.

 

Comments 5: Which mechanism (for example, volume diffusion) dominates the densification process at this stage, and how is it manifested in the microstructure?

Response 5: Thank you very much for pointing out the shortcomings in this manuscript. The manuscript supplements the densification mechanism of targets sintered at 1550℃-1600℃, attributing it to pore shrinkage and volume diffusion.

 

Comments 6: Finally, in what manner do the experimental observations (grain growth, reduction of porosity, variation in density) correlate with the three sintering stages proposed by Kingery?

Response 6: We thank you for devoting time to review our manuscript and for the detailed and constructive suggestions. Kingery proposed a sintering theory based on the contact of spheres during sintering. This manuscript links the observed grain growth and densification processes to Kingery's theory, aiming to better understand the mass transfer mechanisms at different stages of sintering.

Similar Q&A responses like those in the text box can also be found in the following attachments.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The work contains interesting results, presented logically. Some unclear sentences or mistakes listed in the attached file should be corrected.  

Comments for author File: Comments.pdf

Author Response

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions in track changes in the re-submitted files.

Comments 1: Line 15, 18-19,68, 69, 72…: “the target's densification”, “target's relative density”, “a ceramic's crack-resistance”, ”material’s”, “ceramic's “,…and so on. Saxon genitive is not used with objects, in this case “of” is a preferred form.

Response 1: Thank you very much for pointing out the shortcomings in our manuscript. We have carefully reviewed the formatting and expression issues and made the corresponding revisions. For example, “the target’s densification” has been revised to “the densification of the target” for improved clarity and consistency.

 

Comments 2: Abstract should contain a description of the results with short conclusions without analysis and discussion. Please remove unnecessary parts.

Response 2: We greatly appreciate your specific suggestions, which have been carefully addressed in the revised manuscript. We have revised the redundant narration in the abstract section.

 

Comments 3: Keywords (line 39): Please correct “energy; potentially leading to a marked decline in fracture toughness”?

Response 3: Thank you very much for pointing out the shortcomings in this manuscript. We have revised the redundant narration in this section.

 

Comments 4: Line 68: Please replace the short form with the full form: “it's closely”

Response 4: Thank you very much for pointing out the shortcomings in this manuscript. We have explicitly identified the specific referent of "it's" in the text.

 

Comments 5: Line71-72: The sentence contains grammatical errors, please correct it, for example like this “These theories suggest that optimizing the Young's modulus of ceramic materials by controlling the grain structure and sintering processes can increase fracture toughness.”

Response 5: We thank you for pointing out the language issues, and we have thoroughly polished the manuscript accordingly.

 

Comments 6: Line 85: Please use “next” to avoid repetitions.

Response 6: We thank you for pointing out the language issues, and we have thoroughly polished the manuscript accordingly.

 

Comments 7: Line 93: Please add explanation of the abbreviation “CIP” (cold isostatic pressing)

Response 7: We thank you for pointing out the language issues, and we have thoroughly polished the manuscript accordingly.

 

Comments 8: Line 91, 101, 113: There are no spaces at the beginning of sentences and before (a) and (b). There is a double space (line113).

Response 8: Thank you for pointing out the formatting issues in the manuscript.  We have revised this type of formatting in this manuscript.

 

Comments 9: Subsection 3.1.: Please comment briefly on the effect of sintering temperature and holding time on the structure of the targets.

Response 9: We sincerely appreciate the reviewer’s comments. No new phases were formed or phase transitions occurred during the entire sintering process, and similar emphasis has been placed in the manuscript.

 

Comments 10: Fig. 2: Scale bars are not described or descriptions are invisible. Please correct them.

Response 10: Thank you very much for pointing out the shortcomings in this manuscript. I have used image enhancement and magnification to correct the unclear scale bars in the SEM images.

 

Comments 11: SEM analysis line115-119: The sentence “As shown in Figure 2, with the increase of sintering temperature, the porosity decreases and the density increases, and simultaneously grain growth occurs continuously.” is not clear. For example: (1) the porosity of the sample (a) seems to be very low; grain boundaries are invisible; (3) how did the Authors estimate the density difference between images, e.g., (a) and (i)? Please improve the description and explain the origin of your conclusion. Is there any difference between the morphology of the surface layers and the bulk?

Response 11: Thank you very much for pointing out the shortcomings in this manuscript.Following your suggestion, we noticed the low contrast in the images. We have revised phrases like "improved densification" to more intuitive terms such as "particle aggregation," which can be directly observed in the images.

 

Comments 12: Line 127-128, 161-162, 169-170, 194-195, 211-212, 227-228, 229-230: The figure caption was written in capital letters, please correct it.

Response 12: Thank you for pointing out the formatting issues in the manuscript.  We have revised this type of formatting in this manuscript.

 

Comments 13: Fig. 3, 5, 6: Please use the same nomenclature “density ratio” or “relative density”.

Response 13: Thank you for your suggestion regarding the consistent use of terminology. We have unified the description of "density ratio" in both the text and figures of the manuscript.

 

Comments 14: Line 163-165: “the gradual coalescence and reduction of pores and continued grain growth” Please show where you can see the gradual coalescence, reduction of pores and continued grain growth.

Response 14: We appreciate yuor careful and thorough review, as well as the insightful suggestions provided. We have clarified which figures in the manuscript illustrate the phenomenon and revised the description of the phenomenon more intuitively observed in Figure 5 under the isothermal holding time experiment.

 

Comments 15: Fig. 6: The legend is unnecessary. The Authors should keep the same colors as in Fig. 3 and 5 whenever possible.

Response 15: Thank you very much for pointing out the shortcomings in this manuscript. I have corrected the representative color for "average grain size" in the figures to match the colors used in previous figures.

 

Comments 16: Line 201: The temperature of 1600℃ is not exceeded. Correct sentence, e. g. approaches

Response 16: We thank you for pointing out the language issues, and we have thoroughly polished the manuscript accordingly.

 

Comments 17: Line 206-207: “Consequently, crack tip blunting through plastic deformation becomes inhibited, leading to reduced fracture toughness”. Please develop this sentence, taking into account the stress concentration at the crack tip.

Response 17: Thank you very much for pointing out this shortcoming in the manuscript. We have revised the sentence to include the effect of crack tip blunting on stress concentration.

 

Comments 18:Line 213-214: Young's modulus and hardness increase in the entire tested range, not only 1200-1500℃. Please improve the sentence.

Response 18: Thank you very much for pointing out the shortcomings in this manuscript. We have revised this content in this manuscript.

 

Comments 19: Line 223: The word “toughness” is capitalized, please correct it

Response 19: Thank you for pointing out the formatting issues in the manuscript.  We have revised this type of formatting in this manuscript.

 

Comments 20: Line 233: Missing space.

Response 20: Thank you for pointing out the formatting issues in the manuscript.  We have revised this type of formatting in this manuscript.

 

Comments 21: Line233: Fig. 6 shows the fracture toughness with a max at 1500OC (not Fig. 7). Please correct this.

Response 21: Thank you very much for pointing out the shortcomings in this manuscript. We have revised this content in this manuscript.

 

Comments 22: Line 237: The statement “extending the holding time beyond 4 h leads to significant grain growth” is exaggerated. There are no significant changes in the crystallite size between 4 and 6 hours of holding time. Please correct this sentence.

Response 22: Thank you very much for pointing out the shortcomings in this paper. I have rephrased the description of grain growth after 4 hours.

Similar Q&A responses like those in the text box can also be found in the following attachments.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

I concur with the revisions that have been implemented, and based on my assessment, the manuscript meets the standards for publication in the journal.