Recent Progress with BCC-Structured High-Entropy Alloys

Round 1

Reviewer 1 Report

Dear colleagues, I have reviewed your publication in which you examined the oxidation and corrosion resistance of HEAs, the popular topic of the last period. The publication is written in an understandable and clear way. Correction/addition of the following points in the article will make the article stronger. It is important to make this minor correction for the article to be published. Because FCC structures are subjected to an additional heat treatment due to their low hardness. This is a limitation in terms of additional cost and time. The points that I suggest to be corrected are listed below. 

 

• I do not agree on the following statement.

 "Nowadays, HEAs contain four or more multiple principle metallic elements in equal or near equal atomic percent".

The term four shoul change to five. Because HEA alloys consist of at least 5 elements. 4-elements are referred to as medium entropy alloys. Otherwise, if 4 elements are to be called, Other useful terms may be multi(-principal) component alloys

As a literature survey shows.  (see Jien-Wei Yeh, "Recent Progress in High-entropy Alloys", Annales De Chimie - Science des Materiaux, 31(2006), pp. 633-648).

 

• The following statement is very important.

This finding is important. It should be noted that especially FCC structures are subjected to additional heat treatments when used in tribological conditions, which requires an additional cost.

“In contrast FCC HEAs, BCC HEAs are hard and relatively brittle. For re-fractory HEA systems, it have excellent high-temperature mechanical properties but in-sufficient toughness at room temperature [28,29]”.

 This point can be pointed out by reference to the following articles.

 

Zhang, L. J., Jiang, Z. K., Zhang, M. D., Fan, J. T., Liu, D. J., Yu, P. F., ... & Liu, R. P. (2018). Effect of solid carburization on the surface microstructure and mechanical properties of the equiatomic CoCrFeNi high-entropy alloy. Journal of Alloys and Compounds, 769, 27-36.

Günen, A. (2021). Tribocorrosion behavior of boronized Co1. 19Cr1. 86Fe1. 30Mn1. 39Ni1. 05Al0. 17B0. 04 high entropy alloy. Surface and Coatings Technology, 421, 127426.

 

Nishimoto, A., Fukube, T., & Maruyama, T. (2019). Microstructural, mechanical, and corrosion properties of plasma-nitrided CoCrFeMnNi high-entropy alloys. Surface and Coatings Technology, 376, 52-58.

Karakaş, M. S., Günen, A., Çarboğa, C., Karaca, Y., Demir, M., Altınay, Y., & Erdoğan, A. (2021). Microstructure, some mechanical properties and tribocorrosion 

Author Response

Dear reviewer,

Thanks for your constructive comments. The relevant revisions are as follows:

1. We did agree that you said: In the sentence“Nowadays, HEAs contain four or more multiple principle metallic elements in equal or near equal atomic percent", the term four shoul change to five.”

We replaced it by “Nowadays, HEAs contain five or more multiple principle metallic elements in equal or near equal atomic percent”. 

2. We agree the point that you said “it should be noted that especially FCC structures are subjected to additional heat treatments when used in tribological conditions, which requires an additional cost.”

In the revised draft, we have taken into account and revised the corresponding part as follows:

It should be noted that especially FCC structures are subjected to additional heat treatments (solid carburization, boronizing and plasma-nitrided) when used in tribological conditions, which requires an additional cost. In contrast FCC HEAs, BCC HEAs are hard and relatively brittle. For refractory HEA systems, it has excellent high-temperature mechanical properties but insufficient toughness at room temperature. At present, there are many works to improve the room-temperature toughness and reduce the strength loss as much as possible.

Thanks for your further review.

Kind regards,

Fangfei Liu

Reviewer 2 Report

This work provides insight into the development and application of BCC-structured high-entropy alloys, especially refractory HEAs, through many examples in various aspects, from the manufacturing method to mechanical properties, corrosion, and oxidation. The paper is interesting, but there are still some points which can be further improved.

1. In the caption of Fig. 3, 2 m should be corrected to 2 micrometers.
2. Figures 4-6 do not match the text content. Please write more carefully.
3. In Section 2.2, improvement of room temperature mechanical properties through grain refinement was mentioned for BCC HEAs, and it would be better to deal with high temperature mechanical properties along with grain size as well.
4. On page 6, the authors mentioned “interstitial strengthening” by adding Cr for NbMoTaWVCr alloy. What is the evidence for that?
5. Overall, the resolution of the figures is low, making it difficult to read.
6. In Fig. 13, why is there almost no weight change at 1100 degrees Celsius?

Author Response

Dear reviewer,

Thanks for your constructive comments. The relevant revisions are as follows:

1. In the caption of Fig. 3, 2 m should be corrected to 2 micrometers.

This mistake has been corrected, as shown in the updated documentation.

2. Figures 4-6 do not match the text content. Please write more carefully.

This mistake has been corrected, as shown in the updated documentation.

3. In Section 2.2, improvement of room temperature mechanical properties through grain refinement was mentioned for BCC HEAs, and it would be better to deal with high temperature mechanical properties along with grain size as well.

A description of the effect of grain size on high temperature performance was added.

We supply “However, coarse grain size is conducive to the improvement of high-temperature strength, which is mainly attribute to the fact that the grain boundary is the weak area and play as the flow unit at high temperature.”

4. On page 6, the authors mentioned “interstitial strengthening” by adding Cr for NbMoTaWVCr alloy. What is the evidence for that?

The description of the effect of Cr element in the original manuscript is indeed wrong. It should be that Cr element plays the role of atomic size mismatch and O element plays the role of interstitial solid solution strengthening.

We replace “The enhancement in yield strength of NbMoTaWVCr HEA may result from the combined effects of finer grain size, a homogeneous microstructure and interstitial strengthening caused by the addition of Cr element” by “The enhancement in yield strength of NbMoTaWVCr HEA may result from the combined effects of finer grain size, a homogeneous microstructure and enhancement of atomic size misfit caused by the addition of Cr element and interstitial solid solution strengthening from O (O was inevitably introduced into the mechanically alloyed powders”.

5. Overall, the resolution of the figures is low, making it difficult to read.

We provide clearer pictures, as shown in the updated documentation.

6. In Fig. 13, why is there almost no weight change at 1100 degrees Celsius?

The higher temperature, the greater weight change should be. References and descriptions in this article have been removed until a reasonable explanation is found.

Thanks for your further review.

Kind regards,

Fangfei Liu

Author Response File: Author Response.pdf

Reviewer 3 Report

I have found a review of the HEA with BCC structure very interesting, complete and well written. I think it may be a review with a high number of citations. My advice is the acceptance in the present form

Author Response

Thanks for your review！

Kind regards,

Fangfei Liu

Round 2

Reviewer 2 Report

It seems to have responded appropriately to the reviewer's comments.

Author Response

Dear reviewer, 

Thanks for your further review. 

Best wishes!

Fangfei Liu