Modern Powder Metallurgy: Chemical Composition Design for Improved Heat Resistant Alloys

Round 1

Reviewer 1 Report

While the study is interesting, some controversial aspects exist, which must be considered to enhance the interest of the article and make it more attractive:

- Throughout the document there are ideas and parts written in the first person.

- Most of the bibliography included is the authors' own, as well as the figures and results presented. This information should be completed with studies and information carried out by other authors, since it is the essence of writing a review paper that is as complete as possible.

- There is not a complete bibliographic study on the application of this study in additive manufacturing technologies. A more in-depth and related study of the first part of the document with the last one must be done so that everything together makes sense and fits better in the special issue to which it is addressed.

Author Response

Dear Editors,

We would like to thank the referees for the thorough analysis of the manuscript, for carefully checking ours and literature data presented there, and for a number of useful suggestions with which we mostly agree as detailed below (in bold).

Reviewer's comments:

Comment 1:

While the study is interesting, some controversial aspects exist, which must be considered to enhance the interest of the article and make it more attractive:

- Throughout the document there are ideas and parts written in the first person.

Author's response to the comment:

We consider this form of presentation of the material acceptable, we use it in our works, although not often – as in this article (see, for example, Razumovskii IM (1980) Fiz met metallogr 50:650-652; Razumovskii IM et al (1992) Acta Metall. Mater. 40:2707-2716; Razumovskii IM et al (1998) Philosophical Magazine A 77:465-474; Razumovskii IM et al (2003) Interface Science 11: 41-49; Razumovskii IM et al (2011) Scripta Materialia 65:926–929; Razumovskii IM et al (2015) Acta Materialia 82: 369-377). At the same time, if the editors insist, we are ready to make such an edit.

Comment 2:

- Most of the bibliography included is the authors' own, as well as the figures and results presented. This information should be completed with studies and information carried out by other authors, since it is the essence of writing a review paper that is as complete as possible.

Author's response to the comment:

A detailed comparison of the results of our calculations of the parameters of GB segregation of impurities with the data obtained by other authors is presented by us in our works cited here (see, for example, Razumovsky IM et al (2015) Acta Materialia 82: 369-377), from which the reader can get the necessary information. In this paper, we want to draw the attention of our colleagues who are engaged in additive technologies to the achievements in the field of alloying theory (issues of cohesive strength) and processing (HIP) of traditional powder metal alloys.

Some experimental data on segregation of transition metals to HRAs interfaces are given in section 4, lines 246-257.

We believe that this information can be useful for choosing the chemical composition and processing technologies of additive objects.

Comment 3:

- There is not a complete bibliographic study on the application of this study in additive manufacturing technologies. A more in-depth and related study of the first part of the document with the last one must be done so that everything together makes sense and fits better in the special issue to which it is addressed.

Author's response to the comment:

We did not set ourselves the task of a deep and comprehensive discussion of the issues of additive manufacturing technologies, believing that other specialists would do it in a special issue dedicated to AT. We have limited ourselves to discussing the results of several works that, in our opinion, are of great interest, but are little known to a wide scientific audience.

That Note: corrections made are highlighted in blue in the manuscript.

Reviewer 2 Report

I am sending comments on the article.

1) Figure 10b - the scale is missing.

2) The title of the article does not correspond to the content of the article.

3) The article looks more like a review.

4) Of the 36 cited sources, more than half are self-citations (citations of the authors' team). This is not allowed. It is necessary to discuss the results with other authors.

5) The abstract needs to be rewritten, it is not clear from it what was examined and how.

6) The conclusion needs to be rewritten and the results achieved clearly mentioned.

Author Response

Dear Editors,

We would like to thank the referees for the thorough analysis of the manuscript, for carefully checking ours and literature data presented there, and for a number of useful suggestions with which we mostly agree as detailed below (in bold).

Reviewer's comments:

Comment 1:

• Figure 10b - the scale is missing.

Author's response to the comment:

Scale added.

Comment 2:

• The title of the article does not correspond to the content of the article.

Author's response to the comment:

We have changed the title of the article and offers this:

Modern powder metallurgy: chemical composition design and technological application.

Comment 3-4:

• The article looks more like a review.
• Of the 36 cited sources, more than half are self-citations (citations of the authors' team). This is not allowed. It is necessary to discuss the results with other authors.

Author's response to the comment:

Indeed, this is a brief review of some important achievements in the field of traditional powder metallurgy, which can be useful to specialists who are engaged in AT. The theory of alloying of GВ with surfactant transition metals in relation to heat-resistant alloys is developed in our works, in which a detailed comparison of our results with the literature data is carried out, and it is these works of ours that are cited here. We would not like to artificially expand the bibliographic section of our brief review.

Comment 5:

• The abstract needs to be rewritten, it is not clear from it what was examined and how.

Author's response to the comment:

Abstract has been rewritten; a new version has been proposed:

Abstract:  The modern approach to the design of heat–resistant alloys (HRAs) is analyzed, according to which the creep-rupture characteristics of an alloy are mostly determined by the strength of interatomic bonding at grain boundaries (GBs) and in the bulk of a matrix phase. The main attention is paid to the concept of "low alloying additions" to polycrystalline alloys with transition metals, because of which the cohesive strength of the GBs and the cohesion energy of the alloy matrix are increased. This approach is especially important in relation to alloys obtained by powder metallurgy, which in the compacted state are fine-grained polycrystals. The methodology for calculating the key parameters of the theory (the energy of impurity segregation to the grain boundaries E_gb and to the free surface E_fs, as well as the values of the partial molar energy of the cohesion of the alloys) from the first principles is given. Тhe results of applying the theory to the study of Ni-, Cr- and Ti-based alloys and the development of new HRAs based on them are presented. Typical defects of the microstructure of objects obtained using AT and the application efficiency of standard methods of processing powder alloys (HIP, heat treatment) to improve the microstructure and increase mechanical properties are considered.

Comment 6:

-The conclusion needs to be rewritten and the results achieved clearly mentioned.

Author's response to the comment:

The conclusion has been rewritten; a new version has been proposed:

6. Conclusion.

To obtain additive objects from HRAs, alloys developed for production using traditional metallurgical technologies are currently used. Considering the developed network of internal interfaces in AT objects, it seems appropriate to develop special alloys for AT, in the chemical composition of which surface-active elements will be introduced that strengthen the interfaces and increase the creep resistance of HRAs. In traditional powder metallurgy, this type of materials includes nickel alloy NGK-6 and titanium alloy ST-6U, tables 1, 2 . At the same time, several traditional methods of processing powder materials are also effective for processing additive objects.

That Note: corrections made are highlighted in blue in the manuscript.

Reviewer 3 Report

Dear Author,

it is not clear to me the paper structure. there are many mixed new and literature data that are confusing me. I believ ethat you should short the paper, without the unnecessary figures, trying to put in evidence th eactual experimental work you have done. Add and "experimental  activities" chapter.

You pass form th eintroduction, to the "Theoretical evaluation of the effect of alloying on the GB and bulk cohesion" to the " Results of the experimental verification". But what experiments do you have carried out?

Please, try to eliminate any rooth of confused data mixture.

Some suggestions:

Some interesting results are discussed, but why  creep a 800°C for Ti alloys?

What means 11 figures reprinted from other papers? Are those really all necessary?

Line 14: I completely agree with the authors, the transition metals, represents a valid method for the “grain boundary“ strengthening …. But could be useful add some deeper justification. This is generally valid for all the paper: there are many concept that are presented, without deep discussion as for a technical report.

Line 45: Please add some references, because I am not completely sure that this fact is true for every alloy: i.e., some hard intermetallics alloys have low grain boundary resistance.

Line 93: quote the formula

Line 98: as above etc for the other formulas

Line 148-153: Please ad a table with the chemical composition of all the Ti-alloys discussed

Line 150:, Please delete  “well-known” from the “well-known titanium HRAs VT18U” sentence. In fact, it is not worthing if this alloy is well known or not.

Line 188: add a table for the chemical composition (and ranges) and from all the further alloys discussed: insert all the chemical composition discussed in form of table.

Line 274, please check,  I see some unknown characters. Quote the formula. There are other unquoted formulas , please check and quote.

General comment:

Line 428-429_: this two lines are not a conclusion, seems more an introduction.

Line 429 -430: interesting statement: but where are the recall to the experimental results that permitted you to arrive at this conclusion?

 

Author Response

Dear Editors,

We would like to thank the referees for the thorough analysis of the manuscript, for carefully checking ours and literature data presented there, and for a number of useful suggestions with which we mostly agree as detailed below (in bold).

 

Reviewer's comments:

Comment 1:

• it is not clear to me the paper structure. there are many mixed new and literature data that are confusing me. I believ ethat you should short the paper, without the unnecessary figures, trying to put in evidence th eactual experimental work you have done. Add and "experimental  activities" chapter.

Author's response to the comment:

We tried to take this comment into account as follows. 1) We have shortened the article, eliminating section 5. 2) In section 4, we have added the results of several experimental works on the study of grain-boundary segregation of impurities. 3) In section 4, we have added the results of our studies of additive objects made of titanium alloys.

Comment 2:

 

- You pass form th eintroduction, to the "Theoretical evaluation of the effect of alloying on the GB and bulk cohesion" to the " Results of the experimental verification". But what experiments do you have carried out?

Author's response to the comment:

We did not talk in the introduction about experimental studies of the effect of alloying elements on the GB and bulk cohesion. To avoid erroneous interpretation of our goal, we have changed the name of one of the sections: instead of "Results of the experimental verification" in the new version of the article, we use the name “Results of the technological application”.

Comment 3:

• Some suggestions:
• Some interesting results are discussed, but why  creep a 800°C for Ti alloys?

Author's response to the comment:

If we are talking about the information on line 164, the temperature of 800°C is the extremely high operating temperature of titanium HRAs, which is usually not achievable for most such alloys.

Comment 4:

• What means 11 figures reprinted from other papers? Are those really all necessary?

Author's response to the comment:

We have given Figure 11 because it is a good confirmation of the statement given in the article: «The "healing" of pores and microcracks in the protective coating area with the help of HIP is accompanied by an improvement in the fatigue strength of the gas turbine engine blades, Figure 11».

Comment 5:

- Line 14: I completely agree with the authors, the transition metals, represents a valid method for the “grain boundary“ strengthening …. But could be useful add some deeper justification. This is generally valid for all the paper: there are many concept that are presented, without deep discussion as for a technical report.

Author's response to the comment:

We have specifically included in the paper section 2 “Theoretical evaluation of the effect of alloying on the GB and bulk cohesion” to justify the method we use to estimate the value of GB strengthening. It seems to us that the information presented here and the links provided are sufficient to introduce one to the problem.

Comment 6:

• Line 45: Please add some references, because I am not completely sure that this fact is true for every alloy: i.e., some hard intermetallics alloys have low grain boundary resistance.

Author's response to the comment:

We do not touch upon the issues of intermetallic alloys in our article. We have emphasized this fact in the new version of Abstract: The modern approach to the design of heat–resistant metal alloys…

Comment 7:

- Line 93: quote the formula

Author's response to the comment:

Formula number added.

Comment 8:

- Line 98: as above etc for the other formulas

Author's response to the comment:

Formula numbers added.

Comment 9:

- Line 148-153: Please ad a table with the chemical composition of all the Ti-alloys discussed

Author's response to the comment:

Tables with Ti-alloys chemical compositions have been added.

Comment 10:

- Line 150:, Please delete  “well-known” from the “well-known titanium HRAs VT18U” sentence. In fact, it is not worthing if this alloy is well known or not.

Author's response to the comment:

Agree: deleted

Comment 11:

- Line 188: add a table for the chemical composition (and ranges) and from all the further alloys discussed: insert all the chemical composition discussed in form of table.

Author's response to the comment:

Tables with Ti-alloys chemical compositions have been added. The chemical compositions of chromium-based alloys are given in the text.

Comment 12:

- Line 274, please check,  I see some unknown characters. Quote the formula. There are other unquoted formulas , please check and quote.

Author's response to the comment:

All formulas in the text are numbered

General comment:

- Line 428-429_: this two lines are not a conclusion, seems more an introduction.

- Line 429 -430: interesting statement: but where are the recall to the experimental results that permitted you to arrive at this conclusion?

Author's response to the comment:

The conclusion has been rewritten; a new version has been proposed.

That Note: corrections made are highlighted in blue in the manuscript.

Round 2

Reviewer 2 Report

Thank you for your response. 

Author Response

Thank you for your consideration!

Reviewer 3 Report

The paper is greatly improved and now it is more clear. Only one question: it is an article or a review paper?

I suggest a review paper.

Author Response

Thank you for your consideration!

Reviewer's comment:

The paper is greatly improved and now it is more clear. Only one question: it is an article or a review paper?

I suggest a review paper

Author's response to the comment:

we agree, the changes have been made.

Author’s note: corrections made are highlighted yellow in the manuscript.