The Influence of High-Temperature Helium and the Amount of Revert Material on the Material Properties of Inconel 738

Round 1

Reviewer 1 Report

The premises of the article is quite interesting and can be a significant contribution to the scientific community. However, it needs some polishing before publication. The following points need to be addressed by the authors:

1.      The title is verbose. Kindly rewrite the appropriate title.

2.   In the “Introduction” section, the author has reviewed a few pieces of existing literature. However, no prior contributions of researchers were found.

3. The purpose/motivation behind this article is not clear. The author should elaborate on how this article will benefit readers/researchers/industries.

4.      Material selection needs to be justified.

5.      Were obtained microstructures mapped with any standards?

6. Were obtained tensile and hardness values mapped with the standard/permissible values? I didn’t see anything such in the manuscript.

7.     A graphical representation for nanoindentations will add up some more value to the article as well as clarity to the readers.

8.      The discussion section needs more explanation. It is desirable to increase the descriptive part of the article.

9.      Please highlight the contribution of the paper.

10.  Too many paragraphs in the conclusions! Even one, general (main) conclusion should be raised. Currently, in the presented form, the conclusions are too detailed and cannot put the reader in one way (idea). Conclusions should be more concrete and future research directions should be presented.

11.  About the conclusions presented by the authors, is that possible to apply the methodology to another type of material/alloy?

12.  The authors should include the beneficial area as well as the future work/possibilities. The practical and managerial significance of the work must be reported.

Comments for author File: Comments.pdf

Author Response

1. Done - The Influence of High-temperature Helium and the Amount of Revert Material on the Material Properties of Inconel 738.

2. and 3. The purpose of this study is primarily in obtaining new knowledge about the degradation of alloy 738 (with different content of recycled material) in a high-temperature helium environment. There is not much such information in the literature, e.g. most of the experimental data on corrosion in high-temperature helium refer to other alloys. The knowledge is important, among other things, for the foundry, which produces high-temperature components from this alloy. Especially if they will produce, for example, gas turbine components for gas-cooled reactors in the future.

4. added to the article - IN738 was chosen in cooperation with a precision-casting foundry that uses this alloy for most of its production. 

5. and 6. Standards were used to calibrate devices, but no standard was extra-tested to compare its material behavior to IN 738.

Nanoindentation calibration measurements were performed on fused silica calibration standards. The calibration measurement is done to compensate for the changes in tip geometry due to wear.  

7. I don't understand this comment, as there is a graphical performance of indents and their values in Figure 11.

8., 9., and 10. The discussion part was extended and the Conclusion was shortened, hopefully with good highlighting.

11. Yes, the mentioned methodology can also be applied to other alloys, especially those used in casting production, also added to the Conclusion part.

12. Now mentioned in the Conclusion part, but the explanation is similar to point 3. 

Reviewer 2 Report

The paper reported corrosion behavior of Ni-based 738 superalloys under Helium gas atmosphere. Related research is scare and report is new. The pictures are exquisite, and the description is logic. There are only minor misleading parts need to be improved or explained as followings:

1.     Figure 10, please put figures in some sequence such as 50R-received, 50R, 100R, such a heating time procedure.

Author Response

Revision is done - added labeling to the image, to clarify what is which material.
Please see the attachement.

Author Response File: Author Response.pdf

Reviewer 3 Report

Please see review report

Minor corrections

Comments for author File: Comments.pdf

Author Response

1. Abstract has been modified.

2. A real picture was added.

3. Different components, so a deeper explanation was added: In the production of a so-called fusible model using the precision casting method, a large amount of waste alloy is produced. This alloy is returned to production (revert), where it is mixed with a new alloy (virgin material) in a certain ratio. According to various research and empirical findings (obtained in a specific foundry), in order to maintain a stable quality of production, it is necessary to maintain the content of virgin material in the alloy at a level of at least 20% (i.e. the revert content max. 80%).

4. Berkovich-type indenter tip was used because of its availability at our nanoindentation device. Berkovich-type indenter tip is usually used as a default for nanoindentation, as it provides the best possible sharpness due to its three-sided pyramid geometry.

5. I am sorry, I was not able to create this figure now in such a short time for the revision.

6., 7., 8. Done, added.

9. The distance is indicated by a line in the image for each diagram.

10. The difference between YS and UTS is basic knowledge, hard to implement into the article, where many more challenging thoughts are mentioned.

11. Vickers hardness was measured in long and cross sections in bulk material, nanoindentation was measured only in cross-section, 100 um near the surface.
If needed, the schema of microhardness measurements in cross-section and longitudinal directions can be added.

12. This is summarized in section 2.3 of the article. Which additional information should be added?

13. I am not sure what is the idea to mention measurement error. Each method has its own possible errors, but a qualified operator is assumed during the measurement.

14. Oxides on the surface are non-uniform, so there can be a possible area for abrasion and erosion, but no standardized tests were done to support this idea.

15. The Conslusion has been modified. 

Reviewer 4 Report

Dear authors, thank you for the opportunity to review your article.

After reviewing the article I can note that the title quite accurately reflects the content of the study. The abstract gives the motivation, the methodological approach and the statement of the most important findings.

As it is indicated by the title, abstract and introduction part, your paper deals with the topic of ensuring the high mechanical-technological properties of Ni alloys under the challenging operating conditions in high-temperature gas reactors. Due to the reason that the investigated materials are partly or fully made of revert materials, the question of achievable mechanical properties is of a practical importance.

The manuscript is well structured. The methods of investigation are well described. The results are adequately discussed. The graphical material is of good quality.

I have the following comments and suggestions for improvement of the manuscript:

In my view, this sentence on page 1 of the introduction section is unclearly formulated: “A good understanding of metallic materials under high temperature, pressure and corrosive atmosphere is necessary for development of materials with improved performance”. In what context do you mean understanding of metallic materials? Please specify which aspects / properties of the materials are subject to investigation in order to develop materials with improved performance.

Despite the results are described comprehensively and in a well understandable form, I find that Table 4 is rather difficult to analyze. The results of the EDX point analysis are presented as single values. This makes it difficult for the reader to compare the data. My suggestion is to plot the measured values / spectra as bar graphs. This will result in 7 diagrams for the material variant 50R and 7 diagrams for the material 100R. The chemical elements should be marked in different colors. With this way of visualization, the comparison of the measured values can be more conclusive.

please, check if the writing is correct: Page 2 and Page 15: gamma prime γ^’ particles

please, unify the writing of Inconel alloy: IN 738 or IN738?

please, check through the text writing chemical formulas H2, H2O, CH4, CO, CO2, O2 (use a subscript for atom number)

Author Response

1. I tried to rewrite this sentence, but I deleted it finally.

2. Thank you for this recommendation, I converted Table 4 into Diagrams 1 and 2 and it is really better to understand these data.

3., 4., 5. checked and corrected.