Cohesive Strength and Structural Stability of the Ni-Based Superalloys

Round 1

Reviewer 1 Report

The manuscript presents an interesting about the determination of cohesive strength of a heat-resistant alloy (Ni based). Moreover, the structural stability is evaluated. However, multiple affirmations aren’t supported by the provided references or the experimental results obtained, and many other issues must be addressed. The paper needs major revisions before it is processed further, some comments follow:

Abstract

The abstract is too long, please reducing the size. Also, has multiple too long sentences, making it difficult for the reader to understand. Please divide it into shorter sentences.

There is no clear purpose of the study in the abstract. Please highlight the novelty of the study.

It is also not clear what tests were performed and what is the final conclusion of the study. The abstract must be reformulated.

 

Introduction section

The introduction section must be significantly improved.

In the introduction section, a comprehensive and exhaustive review of the state of the art in the field of the study must be provided. Please refer to previous works, and highlight the experiments and results published previously. In the current form, the introduction section only provides basic/general information.

Also, the novelty of this study isn’t presented. Please include a sentence, in the last paragraph from the introduction section, to highlight the novelty of this study.

Multiple affirmations aren’t supported by the provided references or by the obtained experimental results. Please introduce the corresponding citation to support the affirmations from the introduction section. E.g.

The affirmations: " To increase the interatomic interaction forces....”; and " For improvement the performance characteristics of polycrystalline alloys, it is necessary to....”. These affirmations aren’t supported by the provided reference or experimental results. – please introduce corresponding citations.

Theoretical Evaluation of the Effect of Alloying on the Bulk and GB Cohesion

From my point of view, many information writed in this section must be moved in the Introduction section. Also, there are too many details already published.

 

Materials and Methods section is missing. Please introduce information about the materials used in this study and also about all the methods used to obtain and characterize the material.

Figure 2. Please note the images with (a) and (b) and change the title of the figure, for example: „Specimens produced via LPBF: (a) coated with a single layer of TiN (jewellery samples) and (b) coated with AlTiSiN using the nanocoating strategy.

Results and discussion

Figure 5. Please note the images with (a) and (b) and change the title of the figure accordingly. The same for Figures 7, 8, 9, 17, 19 and 20

The DPA analysis is not presented in the methods sections, please describe it when you write about GDOES analysis.

Subsection 3.4. I consider that from lines 326 to 346 the text should be moved to the methods subsection.

Figure 15 has no scientific value. Please remove the figure or replace it with a schematic representation of the experimental setup.

Conclusion:

The conclusion section should be concise.

 

Reference section

Please check carefully the correlation between the cited papers and the position of that reference in the manuscript text body. Some affirmations have no background in published literature.

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).

General author's response to the comments of first referee:

We have read with great interest the detailed and useful first referee’s review. Unfortunately, we will not be able to meet all the requirements of the reviewer, since the reviewer implies that we have written a new study, but in fact it is a review of existing and already published results.

Reviewer's comments:

Comment 1:

1. The abstract is too long, please reducing the size. Also, has multiple too long sentences, making it difficult for the reader to understand. Please divide it into shorter sentences.

There is no clear purpose of the study in the abstract. Please highlight the novelty of the study.

It is also not clear what tests were performed and what is the final conclusion of the study. The abstract must be reformulated.

Author's response to the comment:

According to the reviewer's recommendation, we offer a shortened version of Abstract in the following form:

Abstract: The influence of alloying elements on the cohesive strength of metal heat-resistant alloys (HRAs) is analyzed. To characterize the individual contribution of each alloying element to the cohesive strength, special parameters are introduced: the partial molar cohesion energy of the matrix (χ) and the cohesive strength of the GBs (η). These parameters can be calculated by computer modeling based on the density functional theory. The results of calculating the parameters χ and η in nickel HRAs with mono– and polycrystalline structures alloyed with refractory metals are presented. The calculated data are used to select the chemical composition and develop new nickel HRAs with superior creep-rupture properties. It is assumed that a similar approach can be used to search for alloying elements that will contribute to increasing the cohesive strength of additive objects. The resistance of coherent γ-γ' and lamellar (raft) structures in nickel HRAs to the process of diffusion coarsening during operation is analyzed.

Comment 2:

Figure 2. Please note the images with (a) and (b) and change the title of the figure, for example: „Specimens produced via LPBF: (a) coated with a single layer of TiN (jewellery samples) and (b) coated with AlTiSiN using the nanocoating strategy.

Fig. 2. Coherent γ-γ ' microstructures of the KS-1 (a) and KS-3 (b) alloys after complete heat treatment (hot isostatic pressing (HIP) + homoganization + two-step agimg).

Author's response to the comment:

We noted (a) and (b) images of figure 2 according to referee's note and we changed figure 2 caption to:

Fig. 2. Coherent γ-γ ' microstructures of the KS-1 (a) and KS-3 (b) alloys specimens were producing via complete heat treatment included hot isostatic pressing (HIP), homogenization and two-step aging.

Referee’s comments:

• However, multiple affirmations aren’t supported by the provided references or the experimental results obtained, and many other issues must be addressed. The paper needs major revisions before it is processed further, some comments follow
• Introduction section

The introduction section must be significantly improved.

In the introduction section, a comprehensive and exhaustive review of the state of the art in the field of the study must be provided. Please refer to previous works, and highlight the experiments and results published previously. In the current form, the introduction section only provides basic/general information.

Also, the novelty of this study isn’t presented. Please include a sentence, in the last paragraph from the introduction section, to highlight the novelty of this study.

Multiple affirmations aren’t supported by the provided references or by the obtained experimental results. Please introduce the corresponding citation to support the affirmations from the introduction section. E.g.

The affirmations: " To increase the interatomic interaction forces....”; and " For improvement the performance characteristics of polycrystalline alloys, it is necessary to....”. These affirmations aren’t supported by the provided reference or experimental results. – please introduce corresponding citations.

• Materials and Methods section is missing. Please introduce information about the materials used in this study and also about all the methods used to obtain and characterize the material.
• The DPA analysis is not presented in the methods sections, please describe it when you write about GDOES analysis.
• Subsection 3.4. I consider that from lines 326 to 346 the text should be moved to the methods subsection.
• The results of long-term tests of the mechanical properties of samples of KS…

Author's response to referee’s comments:

• Our article does not provide a detailed comparison of the results obtained with the data of other authors, since these data can be found in our other works cited here (see, for example, Razumovskii et al. Mater. Sci. Eng. A 1993,171,163; Interface Science 2003, 11, 41–49; Mater. Sci. Eng. A 2008, 497, 18–24; Acta Mat. 2015, 82, 369–377, and others), and in which the reader can get the necessary information. We hope that our proposed approach to the selection of alloying elements, comprehensively tested on nickel HRAs, will be useful in the development of a new generation of HRAs based on many refractory metals and compounds.

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

Reviewer 2 Report

• The tile of manuscript: Cohesive strength and structural stability of the Ni-based superalloys. Abstract: For the design of metal heat-resistant alloys (HRAs), an approach is proposed according to which the creep-rupture characteristics of alloys with a given microstructure at high temperatures are mainly determined by interatomic bonding given by the cohesive properties of atoms in the matrix and at the grain boundaries (GBs). To characterize the individual contribution of each alloying element to the cohesive strength, special parameters are introduced: the partial molar cohesion energy of the matrix (χ) and the cohesive strength of the GBs (η). These parameters can be calculated by computer modeling based on the density functional theory (DFT). This approach is used for the analysis of the Ni-based single crystal superalloys chemical composition. It is shown that creep rupture characteristics of different alloys correlate with the total gain partial molar cohesive energy due to alloying and found that W, Ta, and Re have the highest values of χ, and should play the major role in providing high-temperature strength of superalloys. Based on this finding, the chemical compositions of several new alloys with superior creep-rupture properties are proposed. In single crystals of Ni-based superalloys, the coherent γ-γ' microstructure that occurs after the decomposition of a supersaturated γ – solid solution quickly transforms under load into a lamellar (raft) structure, the stability of which ensures the operating life of the alloy. A model of the mechanism of diffusion coarsening of the raft structure is proposed, which makes it possible to evaluate the kinetics of the process and the operating life of the material. The results of applying the theory to the study of Ni- base polycrystalline superalloys are presented too. Using the calculated values of the parameters χ and η in nickel alloys alloyed with refractory transition metals (Zr, Nb, Mo, Ru, Rh, Hf, Ta,W, Re, and Ir) the elements Zr, Nb, Hf, and Ta can be distinguished, which were recommended for introduction as “low-alloying” additions in nickel HRAs obtained by P/M and having a fine-grained polycrystalline structure. It was established that the experimental alloy with additions tends to have an improved creep resistance at high test temperatures and long time to rupture. Features of  the microstructure of Ni-based polycrystalline superalloys obtained using additive technologies are considered. To strengthen the set of internal interfaces in additive objects made of nickel HRAs, it is proposed to use low-alloying additives considered in this paper. 36 Keywords: Ni-based superalloys, cohesive strength, ab initio calculations, single- and polycrystals, grain boundaries, raft-structure, segregation, mechanical properties, additive object   
• The authors are great interpretation of the superalloys microstructures with DFT. The additive elements with certain modals for analysis the creep-rupture microstructures. 
•  The followings should be modified:　The figure 2, 8 should be arranged in the middle of the figure captions. The figure 9 should be in the publish format.　 Table 2 should be rearrangement in the same page. The table 3 should be align from right side.

 

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:

•  The followings should be modified: The figure 2, 8 should be arranged in the middle of the figure captions.

Author's response to the comment:

The images 2, 8 were arranged in the middle of the figure captions.

Comment 2:

• The figure 9 should be in the publish format.

Author's response to the comment:

The figure 9 was modified .

Comment 3:

• Table 2 should be rearrangement in the same page. The table 3 should be align from right side.

Author's response to the comment:

The changes have been made.

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

Reviewer 3 Report

This manuscript summarizes and puts forward a method to optimize the properties of HRA alloys from the effect of alloying elements on the cohesion strength. This paper has a good guiding role for the design and development of new high-performance HRA alloys.

1. In the section 6, it is suggested to supplement alloying elements and their effects that can be used to enhance cohesion strength, grain boundary and interface strength.
2. It is suggested to add a part to predict the optimal composition of HRA alloys based on the proposed method in the present manuscript.

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:

1. In the section 6, it is suggested to supplement alloying elements and their effects that can be used to enhance cohesion strength, grain boundary and interface strength.
2. It is suggested to add a part to predict the optimal composition of HRA alloys based on the proposed method in the present manuscript.

Author's response to the comments:

We have added literary references in the section 6 where the reader can read about the influence of elements of the alloying system on the cohesive properties of the alloy:

Alloying elements and their influence on the cohesive properties of alloys are considered in the [50,51]; there are also some examples of the choice of alloying elements in accordance with the predictions of the theory.

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

Round 2

Reviewer 1 Report

The authors addressed most of my suggestions and the article was improved accordingly. However, there is one more recommendation that should be addressed before accepting this paper. The conclusions should be concise (write it in a more quantitative form), moreover, no citations should be introduced in the conclusions, since the data presented in that section results from the entire manuscript. 

Author Response

We would like to thank the reviewer for his valuable comments.

Reviewer's comments:

The authors addressed most of my suggestions and the article was improved accordingly. However, there is one more recommendation that should be addressed before accepting this paper. The conclusions should be concise (write it in a more quantitative form), moreover, no citations should be introduced in the conclusions, since the data presented in that section results from the entire manuscript.

Author's response to the comments:

We have made the following changes to the manuscript 1) The conclusions section has been rewritten in accordance with the reviewer's comments. 2) The section 7 was introduced into the manuscript, which is called "Other examples application of the approach: beyond Ni-based alloys".

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