Oxidation and Corrosion Resistance of NiCr-Re and NiCr-Re-Al₂O₃ Materials Fabricated by Spark Plasma Sintering

Round 1

Reviewer 1 Report

In Figure 2 caption is indicated that the different elements are defined by different colors but the micrographs look are in grayscale. Please check.

Author Response

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Reviewer 2 Report

Good afternoon, dear collegues

I thik, this work may be accepted for publication.

Author Response

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Reviewer 3 Report

The paper “Oxidation and corrosion resistance of Ni-Cr based materials fabricated by spark plasma sintering” reports on the experimental results of the influence of NiCr based material composition on the microstructure and phase changes during the oxidation and corrosion process. The performed studies are very interesting, but unfortunately, the authors did not provide complete information about the formation of the phase composition of materials and some of their properties. Therefore, there are a number of comments.

• The SEM and EDX micrographs of powders used for sintering process are presented in the Figure 2. But there are no color in the figure, so the distribution of elements is unknown.
• The Authors wrote that densities of the samples were measured by the Archimedes method. What device was used for these measurements and what is the experimental error?
• One of the goals of this research work was to obtain thermally stable materials. However, the temperature coefficient of linear expansion of corundum and nichrome 80Ni–20Cr is about 6.5·10^-6 and 18 10^-6 °C^-1, respectively. Thus, nichrome expands upon heating and shrinks upon cooling three times more intensively than corundum. Therefore, the question is what happens to material containing 90% NiCr and 10% Al₂O₃ during heating and cooling? Does its destruction occur?
• Why in the Figure 5 presented the SEM micrographs of the samples after the oxidation resistance tests only and there are no the images of the samples before the tests? There is no possibility to carry out a comparative analysis.
• In the lines 215–216 the Authors wrote “Due to the low penetration ability and inability of metals to show Raman bands this technic is sensitive selectively to the impurities and oxides formed on the surface.” Then why did the Authors use this research method?
• A study of the phase composition of the materials before and after heat-treating was not carried out in the work; therefore, the results are not sufficiently complete.

Author Response

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Reviewer 4 Report

This manuscript reports on investigation of the oxidation and corrosion resistance of Ni-Cr based materials fabricated by spark plasma sintering. Manuscript is well-structured and related to an interesting topic, but there are some flaws in introduction and discussion parts. Thus, I recommend a major revision.

Specific comments referring to parts of the paper, line numbers, tables or figures.

1. Title of the manuscript should be modified since addition of Re and Al2O3 was investigated
2. Abstract should be rewritten. First part should be reduced and more results should be summarized.
3. In introduction significant part is about erosion and wear resistance. However, in paper there is no information about them. In conclusion it is mentioned again: “wear resistivity”. Where did you measure it and how estimated?
4. Furthermore, is irritating in introduction and results part about coatings, especially at the end of the manuscript. How is it related to the current work? Plasma sprayed coating will have totally different problems related to CTE mismatch and adhesion problems, which are not applicable to SPS produced.
5. Introduction is very short for such a work. I did not understand why ref.24 was used in this work. There is no rhenium addition in this work. Please delete it. At the same time there is a lot of research which should be mentioned and used in this work related to this topic, for example:

https://doi.org/10.1016/j.actamat.2006.08.027

https://doi.org/10.1016/j.surfcoat.2005.10.037

https://doi.org/10.1016/j.actamat.2006.08.024

https://doi.org/10.1016/j.actamat.2007.12.010

https://doi.org/10.1016/j.msea.2017.05.052

Please provide sufficient literature overview

6. Next question is related to the previous one. Re addition was already investigated in a different work, but why do you need to add Re and Al2O3 at the same time and what will be if there is no Re added in this alloy?
7. Please unify all figures. In Figure 1 and 2 different magnifications were used. Please check if in the case of Figure 1a the right scale bar was used. Otherwise difference between powders was significant.
8. Captions of figures 1 and 2 are the same. However, in case of Figure 2 it is not a powder. Furthermore, it is EDX mapping in the case of figure 1 and where is EDX in Figure 2? I think that it is just BSE mode of SEM.
9. Results in table 1 and figure 2 do not correlate with each other. The relative density of sample 2с cannot be higher than that of sample 2b.
10. Figure 4: how could you explain the mass decrease of NiCr-Re as well as NiCr-Re-Al₂O₃ starting at approx. 900°C? In text it is written that “it was assumed that at 550°C some of the oxides from the surface could evaporate, and then a new layer is formed”. What kind of oxide could be formed? In this work, EDX of the cross-section or GDOES should be performed to explain this phenomenon. FTIR explanation is not sufficient.
11. EDX of the surface after oxidation should be also added to the manuscript.
12. In Figure 5 and 6 double capture (a), (b) … is used. In figure 6b what is “as-received” and “heat-treated” material? Is it initial powder and sintered material?
13. In table 2 it is difficult to understand how and why these materials were taken into consideration. Why porous (https://doi.org/10.3390/ma12152405) or monolithic nitinol (10.1016/j.msec.2015.06.051), or widely used Ti-based alloys were not presented.
14. Overall discussion is too short and obvious. Please expand it.
15. Figure 8 is not related to the current work.
16. Please rewrite conclusion. Current version is not acceptable. Please check information given in this part.

Kind regards,

Author Response

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Round 2

Reviewer 3 Report

The authors tried to provide comprehensive answers to the comments and improved the manuscript. The article can be published as presented.

Reviewer 4 Report

Paper could be accepted in the presented form.