Review Reports

Round 1

Reviewer 1 Report

Referee report on mabuscript “Predicting the Residual Stress of amorphous Al2O3-Y2O3 Nano-laminated Deuterium Permeation Barrier under Thermal Cycles”

This is a quite interesting and very good paper, which is of great interest for fusion community, so that certainly can be recommended for publication, but clarifying and detailing some parts of the text.

1.     Line 7 looks as an error.

2.     In the introduction, in order to increase the visibility of the article for a more wide range of readers, it is important to note other fusion applications of such ceramics on the base on Al₂O₃.  Namely, Al₂O₃ is of great interest and importance as one of highly radiation resistant material for optical and dielectric windows:

Ehrhart, P., et al.  Radiation Effects and Defects in Solids, 1995, 136(1-4), pp. 169–173.

Popov, A. I., et al. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2018, 433, 93-97.

3.     Fig.1. Was there any degradation/aging of the studied samples during the SEM measurements and how it was checked?

4.     Right part of Fig.3. Not all letters are clearly distinguishable.

5.     The same for Fig.4.

6.     Fig. 5. The data on this figure needs an error bars.

7.     Fig. 6 allow needs strong improvement, because most of the information is hardly distinguishable.

8.     The same for Fig.8.

9.     Before conclusion, it is important to discuss the role of point defects. What is their role in the formation and stability of such structures, including interfaces?

 In general, the manuscript is interesting and can be recommended for publication after constructive reflection on the above comments.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The article deals with safety problems at fusion facilities where tritium, the fuel of a fusion reactor, is radioactive and can easily penetrate through structural materials such as 316L stainless steel, leading to fuel leakage and hydrogen embrittlement of the structure and thus threatening the safe operation of the fusion reactor. Multilayer Al₂O₃/Y₂O₃ coatings that can be used in fusion reactors to prevent fuel leakage and radiological hazards are considered. It is shown that the thermal mismatch between amorphous Al₂O₃ and Y₂O₃ is so large (large difference in thermal expansion coefficients) that it becomes the main factor determining the thermal residual stress in the coating system, which can lead to the destruction of the multilayer coating. The article is relevant, but at the same time there are serious drawbacks.

A fundamental comment on the content of the article:

(1) It is demonstrated that the use of a Y₂O₃ sublayer in a Y₂O₃/Al₂O₃ multilayer coating is optimal, which leads to a reduction in stresses. It is also shown that the use of a four-layer Y₂O₃/Al₂O₃/Y₂O₃/Al₂O₃ structure reduces the thickness of the multilayer structure with reduced mechanical stresses.

Here we can draw an analogy with the creation of multilayer heterostructures in microelectronics and multilayer X-ray mirrors in X-ray optics, where the number of layers increases as their thickness decreases, buffer layers are introduced, which allows to reduce the mismatch of thermal expansion coefficients:

- it is necessary to show the tendency of stress reduction in multilayer coating with increasing number of layers and decreasing their thickness (do not stop at two and four layers, show, for example, for 10 and 20 layers),

- consider the introduction of buffer layers, which occupy an intermediate position in terms of thermal expansion coefficient between Y₂O₃ and Al₂O₃ and allow to reduce mechanical stresses.

(2) Table 2 shows the values of densities and elastic parameters for calculating the stresses in the multilayer system. If for stainless steel the density value is not in doubt, in magnetron sputtering the densities of the layers differ significantly. Here it is necessary to use the method of X-ray diffractometry, which allows to unambiguously determine the densities of Y₂O₃ and Al₂O₃ layers. This method also makes it possible to determine the thickness of the sprayed layers, the presence of transition layers at the Y₂O₃/Al₂O₃ boundary

Technical comments on the content of the article:

(1) a comma is necessary after the expression (2): {∆?} = {?}{?}^e,

Line 90 (with a small letter and no indent from the beginning of the line): where {?} is the strain matrix.

(2) a comma is necessary after the expression (3): {∆?^??} = {?}{∆?^??}

Line 92 (with a small letter and no indent from the beginning of the line): where {?} is the elastic matrix for any given material that defined by its elastic modulus, E, and Poisson’s ratio, ?, at a given temperature.

(3) a comma is necessary after the expression я (4): {∆?^?ℎ} = {?}∆T,

Line 96 (with a small letter and no indent from the beginning of the line): where ? is the thermal expansion coefficient.

(4) In Figure 4, you need to change the background (e.g., white) or change the color of the grid on the dark background (e.g., white). At the moment, the color scheme of the figure is not optimal for perception.

(5) In Figure 6, you need to change the color of the grid on the dark background (e.g., white). At the moment, the color scheme of the figure is not optimal for perception.

(6) a comma is necessary after the expression (9): ?_? = ?/?_? , ? < ?₀,

Line 210 (with a small letter and no indent from the beginning of the line): where ?₀ is the vicinity zone of the stress singularity, and ? is the stress intensity factor.

(7) In Figure 8, you need to change the color of the grid on the dark background (e.g., white). At the moment, the color scheme of the figure is not optimal for perception.

(8) a comma is necessary after the expression я (10): ,

Line 247 (with a small letter and no indent from the beginning of the line): where E is the Young’s modulus, ? is the Poisson’s ratio, ? =  is the moment of inertia for bending, and K is the bending curvature.

(9) a comma is necessary after the expression (11): ,

Line 250 (with a small letter and no indent from the beginning of the line): where B =  is the biaxial modulus of the layers.

 

Authors should make appropriate additions and corrections to the text of the article.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The paper deals with the potential to apply multilayers Al2O3-Y2O3 coatings instead of monolayers ones in fusion reactors for attaining better tritium permeation resistance considering the developed thermal stresses due to different thermal expansion coefficients. It’s an interesting computational work. My main remarks are the following:

 

1.         Figures 4,5,6,7,8 are too small and they can’t be read. The letter’s fonts have to be enlarged.

2.         The authors have to describe the direction of the calculated principal stresses using a sketch. Are these stresses compressive or tensile?

3.         Τhe authors have to comment if the developed thermal stresses in the examined cases are critical for a static or a dynamic failure and thus, such coating architectures have to be avoided.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have constructively improved their original manuscript, so now it can be certainly be recommended for publication.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have made technical corrections to the text of the article.

Однако остается ряд замечаний:

(1) In Figure 4, it is highly recommended to make a white background.

 

(2) The authors presented an X-ray diffraction spectrum in their answers, which enables us to determine the phase composition of the layers.

The authors were recommended to measure by X-ray diffraction the reflectivity curve from the layered structure, which allows to determine the density, roughness, thickness of the damaged layer, thikness of the layers, the presence of the interface between the layers.

The figure shows the calculated reflectivity curve of a 4-layer Al2O3/Y2O3/Al2O3/Y2O3 structure with the thickness of each layer 150 nm. In the experiment the authors should get something close to it.

 

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The submitted paper can be accepted for publication after an extensive improvement of the English usage.

Author Response

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Author Response File: Author Response.pdf