Thermal Stability of Microstructure of High-Entropy Alloys Based on Refractory Metals Hf, Nb, Ta, Ti, V, and Zr

Round 1

Reviewer 1 Report

The article is devoted to the study of the thermal stability of high-entropy alloys. This direction is of scientific and practical interest, however, before this article is accepted for publication, the authors should answer a number of questions that arose when reading this work.

1. The introduction is very poorly written, the authors should expand the description of the applicability of these alloys, and also note in more detail the relevance of the study in comparison with other data.
2. An increase in hardness is justified with an increase in the alloy components, however, the authors should explain what exactly such an increase is associated with, what role new components play in increasing strength.
3. New reflections are observed in the X-ray diffraction patterns after annealing; the authors should explain what causes their appearance.
4. SEM images require the provision of better quality and explanation of the presence of a dendritic structure.
5. The authors need to provide detailed explanations for the formation of a dendritic structure that forms near cracks and grain boundaries.
6. The authors should reconsider the concept of the article, as in the presented form it looks more like a report or a dissertation chapter.

Author Response

Please, see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper "Thermal stability of microstructure of high entropy alloys based on refractory metals Hf, Nb, Ta, Ti, V and Zr" describes interesting experimental results about microstructure, hardness and tensile properties of the multi principal element HfNbTaTiVZr alloys. The paper is well written. However, the authors should highlight the scientific novelty of their work. A lot of refractory metals based multi principal alloys with high thermal stability were investigated previously. The works of the other scholars have shown similar results. The manuscript may be accepted for publication after revision accordingly following comments:

1. Most of the references in the paper are too old. It is recommended to consider the last works in this field (e.g. 10.1038/s41467-021-25807-w, 10.3390/cryst11060612, etc.)
2. Not all peaks are recognized in Figures 4 and 9. It is seen that the microstructure of the NbTaTiZr and HfNbTaTiZr alloys consists of more than two bcc phases.
3. It is unclear, why did the authors choose such a low temperature for annealing (homogenization)? Accordingly thermodynamic simulations [Ref 17], the liquidus temperature of the TiZrNbHfTa is about 1850 º It is needed a higher temperature to eliminate the dendritic liquation in the microstructure.
4. How many samples were tested for the determination of the tensile mechanical properties? It is not enough just one sample for each state for the comparison of the mechanical properties (especially, plasticity) due to the high sensibility of the properties to internal defects. The standard deviations should be added to the values of the mechanical properties.
5. The comparison of the obtained mechanical properties with the results obtained by other investigators for similar alloys should be added to the manuscript.
6. It is recommended to add to Table 2 the lattice parameters of all allotropic modifications of the considered metals as well as the values of the polymorphic transformation temperatures.
7. Minor corrections:

• It is unclear, how the authors have made quenching “into water in vacuum”. It is hardly possible to have high temperatures, vacuum and water simultaneously in the same furnace. Additional information is required.
• V should be added to the title of Table 2.
• The language of the manuscript should be improved.

Author Response

Please, see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript entitled “Thermal stability of microstructure of high entropy alloys  based on refractory metals Hf, Nb, Ta, Ti, V and Zr” has investigated the as-cast state and annealing microstructure of NbTaTiZr, HfNbTaTiZr, HfNbTiVZr and HfNbTaTiVZr and compared them. The manuscript was well presented and experimental content is complete. I would like to congratulate the authors for their successful work. However, before the manuscript can be accepted, I have several concerns and questions that need proper attention and should be well addressed.

1. In the abstract line 23 “sold solution” could be “solid solution”. In addition, Hf appears in lines 167 and 177. There is no Hf in NbTaTiZr. Please pay attention to these details and carefully check the manuscript.
2. In the experimental details “Cast ingots have dimensions approx. 100×10×5 mm³”. I want to know whether it is made by casting or suction casting. Please clarify this.
3. The authors are willing to add some latest and relevant references about high entropy alloys (e.g., International Journal of Plasticity 2021, 142, 102997; ACS Applied Materials & Interfaces 13 (2021) 55712−55725) in the appropriate places (e.g., Introduction or Discussion) of this manuscript.
4. In the line of 166, the authors say that Nb and Ta are enriched in the bright regions. However, the results of EDS (line scan) do not lead to this conclusion. The author could display the ordinates in Figure 3(a)(b).
5. The EDS data in the manuscript should come from point scan, but the position of point scan is not marked in the EDS diagram.

Author Response

Comments and Suggestions for Authors

The manuscript entitled “Thermal stability of microstructure of high entropy alloys  based on refractory metals Hf, Nb, Ta, Ti, V and Zr” has investigated the as-cast state and annealing microstructure of NbTaTiZr, HfNbTaTiZr, HfNbTiVZr and HfNbTaTiVZr and compared them. The manuscript was well presented and experimental content is complete. I would like to congratulate the authors for their successful work. However, before the manuscript can be accepted, I have several concerns and questions that need proper attention and should be well addressed.

1. In the abstract line 23 “sold solution” could be “solid solution”. In addition, Hf appears in lines 167 and 177. There is no Hf in NbTaTiZr. Please pay attention to these details and carefully check the manuscript.

Response: The misprints mentioned by the reviewer have been corrected. The whole manuscript has been checked and further misprints and grammar errors have been corrected.

 

2. In the experimental details “Cast ingots have dimensions approx. 100×10×5 mm3”. I want to know whether it is made by casting or suction casting. Please clarify this.

Response: The ingots were made by casting in a water cooled copper mould (not by suction casting). 

 

3. The authors are willing to add some latest and relevant references about high entropy alloys (e.g., International Journal of Plasticity 2021, 142, 102997; ACS Applied Materials & Interfaces 13 (2021) 55712−55725) in the appropriate places (e.g., Introduction or Discussion) of this manuscript.

Response: The references to recent papers related to high entropy alloys mentioned by the reviewer have been added to the revised manuscript. 

 

4. In the line of 166, the authors say that Nb and Ta are enriched in the bright regions. However, the results of EDS (line scan) do not lead to this conclusion. The author could display the ordinates in Figure 3(a)(b).

Response: There was a mistake in labels of EDS elemental concentration profiles in Fig. 3 (labels for Ti a Ta were swapped). This mistake has been corrected in the revised manuscript (Figs. 2 and 3 were merged together so Fig. 3 now corresponds to Fig. 2c,d).  One can see in corrected figure that the concentration of Nb and Ta is enhanced in the bright regions.

 

5. The EDS data in the manuscript should come from point scan, but the position of point scan is not marked in the EDS diagram.

Response: In order to reduce the statistical uncertainty the EDS data about chemical compositions were obtained using average of five EDS point scans taken in regions belonging to the corresponding phases. The position of one of these EDS scans for one and second phase is indicated in the revised manuscript in Figs. 2d, 6b by cross and star symbol, respectively.

Round 2

Reviewer 1 Report

The authors answered all questions, the article can be accepted for publication.

Reviewer 2 Report

The authors have answered the previous comments and made necessary modifications to the manuscript.  The paper may be accepted for publication.

Reviewer 3 Report

I would like to congratulate the authors for their successful work. Nice revised work. In my opinion, it is acceptable now.