Different Heat-Exposure Temperatures on the Microstructure and Properties of Dissimilar GH4169/IC10 Superalloy Vacuum Electron Beam Welded Joint

Round 1

Reviewer 1 Report

The article is devoted to the study of heat treatment modes  influence on the microstructure of a dissimilar welded joint of GH4169 and IC10 alloys made by electron beam welding.

Joining nickel-based superalloys is an extremely urgent task. These materials are used for the manufacture of parts operating at high temperatures and loads, in particular for the manufacture of gas turbine engines elements.

Understanding the patterns of changes in microstructure and properties depending on heat treatment modes, as well as during the operation of welded structures, is relevant and of great practical interest...

There are some small comments to the text of the article:

1.  In lines 84-86 it is written: “He et al. [19] studied the microstructure of Hastelloy N superalloy brazed joints after heat exposure, and found that M5B3 particles were introduced into the isothermal solidification zone (ISZ) of the joints after thermal exposure, resulting in a reduction of welded joint strength.” The last words should probably be “brazed joints strength”?

2. In lines 90-91 it is written: “the precipitation of grain boundaries η slats hinders crack propagation, resulting in a decrease in the impact toughness of the joints”, apparently there is some inaccuracy here, because an increase in resistance to crack propagation should increase impact toughness rather than decrease it.

3. In lines 196-197 it is written: “columnar crystals growing along a near-vertical direction”, however, it is unlikely that crystals grow in the vertical direction, since in this direction there is practically no temperature gradient, probably meaning that they are oriented in vertical direction.

4. In lines 223, 225, 226 indicate the presence of a carbon-boride phase in the structure, although the alloys do not contain boron.

The article makes a positive impression; it deeply analyzes the processes of evolution of the fine structure of the weld. The results of the work can be used in further research, as well as in assigning heat treatment modes for welded structures.

Author Response

Thank you very much for your valuable comments on our manuscript. We have read your suggestions in detail and responded accordingly, and have made changes in the manuscript accordingly.

We have marked the changes in the manuscript in yellow, and the answers to your questions are given below:

1.In lines 84-86 it is written: “He et al. [19] studied the microstructure of Hastelloy N superalloy brazed joints after heat exposure, and found that M5B3 particles were introduced into the isothermal solidification zone (ISZ) of the joints after thermal exposure, resulting in a reduction of welded joint strength.” The last words should probably be “brazed joints strength”?

Re: Yes, we have made corresponding changes in the manuscript (marked in yellow).

2. In lines 90-91 it is written: “the precipitation of grain boundaries η slats hinders crack propagation, resulting in a decrease in the impact toughness of the joints”, apparently there is some inaccuracy here, because an increase in resistance to crack propagation should increase impact toughness rather than decrease it.

Re: The writing shows a lack of clarity of reference, the decrease in impact toughness is attributed to "coarsening of the γ 'phase, which transforms the γ' phase into the η phase ", and the corresponding modification has been made in the paper.

3. In lines 196-197 it is written: “columnar crystals growing along a near-vertical direction”, however, it is unlikely that crystals grow in the vertical direction, since in this direction there is practically no temperature gradient, probably meaning that they are oriented in vertical direction.

Re: It is true that there is a low temperature gradient near the centre of the FZ, and then the grain growth is mainly controlled by the preferred growth direction of the grains to equiaxial crystals. But our results clearly observe columnar crystals in the vertical direction, which on reflection is thought to be caused by the influence of gravity and solidification solid-liquid phase lines.

4. In lines 223, 225, 226 indicate the presence of a carbon-boride phase in the structure, although the alloys do not contain boron.

Re：In this paper, the alloy chemical composition Table 1 refers to the main chemical composition, boron is often used as a grain boundary strengthening elements will be added to a small amount of nickel-based superalloys, and we have added the boron content of both alloys to Table 1.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper presents using the Vacuum electron beam welding (EBW) to join the precipitation-strengthened  GH4169 superalloy and a new nickel-based superalloy IC10 to fabricate the turbine blade discs. The article is well organized. The quality of the images is acceptable and the results are well analyzed. The main challenge of the innovation article is the purpose of the research and the high percentage of similarity between the text and the literature (30%). So, it requires major revision.

The abstract needs correction. Adding innovation, the purpose of the research, quantitative data and findings is a must.

The article needs general writing and grammar editing.

The novelty and purpose of the research should be clearly stated in the abstract and introduction.

What is the innovation of the article compared to the following source? Much of the text is copied from this article. Even the title. https://www.sciencedirect.com/science/article/abs/pii/S0921509323009851?via%3Dihub

The first paragraph of introduction presented are primarily general information. At the end of the introduction, a suitable summary of the importance of the present issue should be provided.  Also, discontinuity between paragraphs is evident in most of the introduction.

The number of used and reviewed references is very small. It is also suggested to use the sources that have been published in the last few years.

Use the following references to deepen the introduction and discussion. The high temperature flow behavior of additively manufactured Inconel 625 superalloy. Effects of post-weld heat treatment on the microstructure and mechanical properties of laser-welded NiTi/304SS joint with Ni filler. Comparison between laser beam and gas tungsten arc tailored welded blanks via deep drawing. Effect of boron on the structural stability, mechanical properties, and electronic structures of γ′-Ni3Al in TLP joints of nickel-based single-crystal alloys.

The process of selecting welding parameters should be presented. Explain how to choose optimum welding parameters. How is the welding quality checked? Explain more about the welding process.

How is the reproducibility of mechanical properties results checked?

Explain about failure mechanism and failure initiation area.

According to the microhardness results, the hardness value of both alloys becomes the same as the temperature increases. What is the reason? Why exposure time is not considered?

***

Author Response

Thank you very much for your valuable comments on our manuscript. We have read your suggestions in detail and responded accordingly, and have made changes in the manuscript accordingly.

We have marked the changes in the manuscript in yellow, and the answers to your questions are given below:

Q1:The abstract needs correction. Adding innovation, the purpose of the research, quantitative data and findings is a must.

Re: We have modified the Abstract accordingly to emphasize the innovation and purpose of the study.

Q2:The article needs general writing and grammar editing.

Re: We have modified the grammar and statements of the article.

Q3:The novelty and purpose of the research should be clearly stated in the abstract and introduction.

Re: We modified the Abstract and Introduction to make the novelty and purpose of the research get more emphasized.

Q4:What is the innovation of the article compared to the following source? Much of the text is copied from this article. Even the title. https://www.sciencedirect.com/science/article/abs/pii/S0921509323009851?via%3Dihub

Re: The similar article mentioned above (https://www.sciencedirect.com/science/article/abs/pii/S0921509323009851?via%3Dihub), which is also our work, focuses on modulation of post-weld organization and the effect of joint organization on high temperature tensile properties, and this The research objective of the manuscript is to investigate the evolution of the organization of joints during service in different high-temperature environment, and the research objectives of the two articles are not the same.

Q5:The first paragraph of introduction presented are primarily general information. At the end of the introduction, a suitable summary of the importance of the present issue should be provided.  Also, discontinuity between paragraphs is evident in most of the introduction.

Re: Thank you for your suggestion, we realized the problem in the introduction and made a careful revision.

Q6:The number of used and reviewed references is very small. It is also suggested to use the sources that have been published in the last few years.

Use the following references to deepen the introduction and discussion. The high temperature flow behavior of additively manufactured Inconel 625 superalloy. Effects of post-weld heat treatment on the microstructure and mechanical properties of laser-welded NiTi/304SS joint with Ni filler. Comparison between laser beam and gas tungsten arc tailored welded blanks via deep drawing. Effect of boron on the structural stability, mechanical properties, and electronic structures of γ′-Ni3Al in TLP joints of nickel-based single-crystal alloys.

Re: Thanks to your suggestion, your suggestion is very helpful. We have cited more literature to discuss our work and made the paper more rigorous.

Q7:The process of selecting welding parameters should be presented. Explain how to choose optimum welding parameters. How is the welding quality checked? Explain more about the welding process.

Re: The welding parameters obtained in the article were obtained after a large number of welding experiments. The obtained weld is completely welded through or not, the uniformity of the width and the presence of defects such as spatter and macro-cracks is an important basis for us to test the quality of the weld. We also use x-ray flaw detection to test the screened welded joints, which shows the weld quality of the joints under this parameter. As this part is not the focus of the article, we only provide the results after our welding experiments. The following figure shows the metallographs of some of the joints obtained from our welding experiments:

Q8:How is the reproducibility of mechanical properties results checked?

Re: We could ensure the reproducibility of the mechanical performance results. In order to avoid chance in performance testing we performed multiple tests on each set of specimens and used intermediate data for the stress-strain curves.

Q9:Explain about failure mechanism and failure initiation area.

Re: The failure areas of the weldments occurred in both sides of the base material (BM), but the article focuses on the evolution of the fusion zone(FZ) microstructure and does not provide a detailed characterization of the microstructure evolution in the base material, so the failure mechanism is not investigated in depth.

Q10:According to the microhardness results, the hardness value of both alloys becomes the same as the temperature increases. What is the reason? Why exposure time is not considered?

Re: The changes in the hardness of the two base materials in the microhardness test results were not investigated in depth because the two base materials are mature commercial alloys that have already received many studies, study of the base materials may lead to duplication of experiments.The focus of this paper is on the effect of thermal exposure temperature on the joint microstructure, and the differences in the variation and stability of the joints' microstructure at these temperatures were observed, and we will follow up with a study of the effect of exposure time on the joint microstructure, and the results presented in the manuscript will be an important guide for the subsequent studies.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript describes the influence of different heat exposure temperatures on the microstructure and mechanical properties of dissimilar GH4169/IC10 superalloy joints after vacuum electron beam welding.

The are some interesting results in the manuscript. However, the results must be presented and discussed better, and some clarifications are needed.

Overall, I recommend a major revision before considering this manuscript for publication. Below are my comments.

ABSTRACT:

1 – The abstract is too long. I suggest reducing its length pointing out the most important findings of this study. Generally, an abstract is long 200-250 words.

INTRODUCTION:

1- Clarify which features (e.g., strength at high temperature, toughness, and so forth) are negatively affected by the Laves’s phase in the sentence “As a brittle phase, the nature of Laves relative to the molten zone is detrimental [9,10].”

MATERIALS AND METHODS

1- I guess that “electric spark-type wire-cutting machine” means “wire electro-discharge machine”. You could modify the sentence “using an electric spark-type wire-cutting machine” with “through wire electro-discharge machining.”

2- The sentence “…the test force was 3 kg…”. Replace “3 kg” with “3 kgf”.

RESULTS AND DISCUSSIONS

1- I suggest discussing first the microstructures and then the mechanical properties. In this manner, the reader is more aware of the results of the mechanical testing based on the microstructures obtained after the different heat treatments. Therefore, paragraph 3.1 should be moved after 3.2. Moreover, I suggest replacing the title of paragraph 3.1 “ Properties of the Welded Joints” with “Mechanical Properties of the Welded Joints”.

2- The acronyms have already been defined before in the text. Therefore, replace the sentence “…Base metals (BMs), fusion zone (FZ), and heat-affected zone (HAZ)…” With “…BMs, FZ, and HAZ…”

3- Authors state: “During welding, the BM is barely affected on both sides away from the FZ, consistent with the pre-weld microstructure”. The sentence is not clear; for instance, the BM, for its nature, is a region of the joint not affected by welding.

4- I suggest anticipating Fig. 5b before Figure 5a. It is better to have an overview of the joint first and then magnifications.

5- The following sentence is too long and should be rewritten better: “In the FZ, it mainly consists of columnar grains growing in the direction of near-vertical two-side fusion lines (the demarcation line between the FZ, HAZ and FL) towards the center of the FZ (as shown by the red line segments in Fig.5b), and cellular structures appearing near the center of the FZ, and columnar crystals growing along a near-vertical direction also appearing near the center (as shown by the green line segments in Fig.5b).” For instance, the sentence “In the FZ, it mainly consists of columnar grains growing in the direction of near-vertical two-side fusion lines (the demarcation line between the FZ, HAZ and FL)…” could be rewritten as: “The FZ mainly consists of columnar grains growing along a perpendicular direction in respect to the two-side fusion lines, FLs (i.e., the demarcation line between the FZ and HAZ)…”.

6- Fig. 6a: check the extent of HAZ. It seems too narrow considering the extent of the FZ region.

7- Fig. 6a: authors should explain better because the grain size is so different in region I and II of the FZ. Which is the cause?

8- “…where the second phases are distributed in bulk in the BMs near the grain boundaries…”. What means “…distributed in bulk…”? Moreover, from Fig. 7 is not clear that the second phases are most near the grain boundaries.

9- “…The second phases in the FZ are not uniformly distributed (shown in Fig. 7b), showing a continuous or discrete distribution (Fig. 7c)…” What means “…continuous or discrete distribution …”?

10- the EDS analysis provides a semi-quantitative chemical composition. Therefore, the authors’ statement “Combined with the EDS analysis (as shown in Table 2) of the second phases, it is considered that the second phase in IC10 BM is a rich-Cr carbon-boride phase (Point A), the bright second phase in FZ is considered to be a rich-Ni-Cr-Nb Laves phase (Point B), while the darker second phase is a rich-Nb, Ti carbon-boride phase (Point C), the second phase in GH4169 BM is a Ti-rich carbon-boride phase (Point D).” should be supported by literature to identify in more detail the nature of the second phases (as for instance done by citing Kruk et al.).

11- In general, a discussion is needed to explain the results of the Discussion paragraph. Often, the results are only present without discussion.

Many sentences (especially in the discussion paragraph) should be rewritten better, also to clarify the meaning itself of the sentences. Moreover, some misprints throughout the main text should be corrected. An English mother tongue should revise the English grammar of the manuscript.

Author Response

Thank you very much for your valuable comments on our manuscript. We have read your suggestions in detail and responded accordingly, and have made changes in the manuscript accordingly.

We have marked the changes in the manuscript in yellow, and the answers to your questions are given below:

ABSTRACT:

1– The abstract is too long. I suggest reducing its length pointing out the most important findings of this study. Generally, an abstract is long 200-250 words.

Re: It is necessary to describe the experimental results and conclusions in Abstract with more statements in order to present them better. In addition, we have reduced the length of the abstract, as marked in yellow.

INTRODUCTION:

1- Clarify which features (e.g., strength at high temperature, toughness, and so forth) are negatively affected by the Laves’s phase in the sentence “As a brittle phase, the nature of Laves relative to the molten zone is detrimental [9,10].”

Re: The microstructure in nickel-based superalloys is complex, and it is not possible to directly account for the effect of a single Laves eutectic on the material properties while ignoring the effect of other second phases (e.g., γ′, γ″, and carbides, etc.). For example, for the Laves phase in Fig.9c (below)of this manuscript, obvious lattice distortion of the surrounding γ matrix is observed, indicating a more obvious stress concentration near the interface between the Laves phase and the γ matrix phase. And in some of the studies on the tensile properties of GH4169 alloys, a fractured Laves phase is observed in the tensile fracture.

MATERIALS AND METHODS

1-I guess that “electric spark-type wire-cutting machine” means “wire electro-discharge machine”. You could modify the sentence “using an electric spark-type wire-cutting machine” with “through wire electro-discharge machining.”

2- The sentence “…the test force was 3 kg…”. Replace “3 kg” with “3 kgf”.

Re: The above two suggestions are of great significance and have been modified accordingly in the manuscript (highlighted in yellow)

RESULTS AND DISCUSSIONS

1-I suggest discussing first the microstructures and then the mechanical properties. In this manner, the reader is more aware of the results of the mechanical testing based on the microstructures obtained after the different heat treatments. Therefore, paragraph 3.1 should be moved after 3.2. Moreover, I suggest replacing the title of paragraph 3.1 “ Properties of the Welded Joints” with “Mechanical Properties of the Welded Joints”.

Re: Concerning the sequence of the discussion of microstructure and mechanical properties, we have written with the idea that the macro comes first before the micro.The first depiction of the mechanical properties of the macroscopic very intuitively clarify the effect of heat exposure temperature on the properties of welded joints. And the title of section 3.1 we have modified and marked yellow.

2-The acronyms have already been defined before in the text. Therefore, replace the sentence “…Base metals (BMs), fusion zone (FZ), and heat-affected zone (HAZ)…” With “…BMs, FZ, and HAZ…”

Re: Modified and marked yellow in the manuscript.

3- Authors state: “During welding, the BM is barely affected on both sides away from the FZ, consistent with the pre-weld microstructure”. The sentence is not clear; for instance, the BM, for its nature, is a region of the joint not affected by welding.

Re: Not so, in the region closer to the FZ BM will still be affected by some welding heat, the microstructure will also undergo some minor changes, but it is more difficult to observe, in order to be rigorous we use the word "away".

4-I suggest anticipating Fig. 5b before Figure 5a. It is better to have an overview of the joint first and then magnifications.

Re: Thank you for your suggestion, we used a low and then high magnification, so as to better describe the structure of the joints from the macro to the more microscopic structure.

5-The following sentence is too long and should be rewritten better: “In the FZ, it mainly consists of columnar grains growing in the direction of near-vertical two-side fusion lines (the demarcation line between the FZ, HAZ and FL) towards the center of the FZ (as shown by the red line segments in Fig.5b), and cellular structures appearing near the center of the FZ, and columnar crystals growing along a near-vertical direction also appearing near the center (as shown by the green line segments in Fig.5b).” For instance, the sentence “In the FZ, it mainly consists of columnar grains growing in the direction of near-vertical two-side fusion lines (the demarcation line between the FZ, HAZ and FL)…” could be rewritten as: “The FZ mainly consists of columnar grains growing along a perpendicular direction in respect to the two-side fusion lines, FLs (i.e., the demarcation line between the FZ and HAZ)…”.

Re: We have modified the statements in the manuscript and marked the changes in yellow.

6-Fig. 6a: check the extent of HAZ. It seems too narrow considering the extent of the FZ region.

Re: Yes, we obtained narrowed HAZ, which is an advantage of EBW, as we mentioned in the Introduction.

7-Fig. 6a: authors should explain better because the grain size is so different in region I and II of the FZ. Which is the cause?

Re: The difference in grain size between the two zones in the FZ is related to the temperature gradient during solidification of the molten pool, which is influenced by the thermophysical properties of the base material (e.g., thermal conductivity), and therefore the difference in grain size is related to the difference in thermophysical properties between the base materials.

8- “…where the second phases are distributed in bulk in the BMs near the grain boundaries…”. What means “…distributed in bulk…”? Moreover, from Fig. 7 is not clear that the second phases are most near the grain boundaries.

Re: The text is not precise enough at this point and has been modified accordingly (highlighted in yellow)

9-“…The second phases in the FZ are not uniformly distributed (shown in Fig. 7b), showing a continuous or discrete distribution (Fig. 7c)…” What means “…continuous or discrete distribution …”?

Re: Thank you for your suggestion, we did have a misrepresentation here, which we have corrected and marked yellow. It means that some of these second phases are aggregated and some are more discrete, and these two types of distribution characteristics are indeed observed in Fig. 7c, look at the figure below:

10-the EDS analysis provides a semi-quantitative chemical composition. Therefore, the authors’ statement “Combined with the EDS analysis (as shown in Table 2) of the second phases, it is considered that the second phase in IC10 BM is a rich-Cr carbon-boride phase (Point A), the bright second phase in FZ is considered to be a rich-Ni-Cr-Nb Laves phase (Point B), while the darker second phase is a rich-Nb, Ti carbon-boride phase (Point C), the second phase in GH4169 BM is a Ti-rich carbon-boride phase (Point D).” should be supported by literature to identify in more detail the nature of the second phases (as for instance done by citing Kruk et al.).

Re: Thank you for your suggestion, we do need to use references to make our statements more convincing. And also these statements are based on the results of the tests, and in polycrystalline nickel-based superalloys the large-scale second phases are mainly carbides and borides. We have inserted references in the appropriate places and marked yellow.

11-In general, a discussion is needed to explain the results of the Discussion paragraph. Often, the results are only present without discussion.

Re: We have analyzed the formation and evolution of the microstructures in the description of the microstructure characterization of the FZ, and summarized and more recently analyzed in section 3.4. Meanwhile, most of the papers are told separately from the results and the discussion.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Most of the referee's comments have not been considered and have not been applied to the article. The abstract lacks innovation and the purpose of conducting research transparently. The authors' response regarding the same article is not acceptable. The introduction is not well-edited. Suggested resources have not been used. The number of images is large. The analysis and discussion of the results is not enough and most of the sections only report the results.

***

Author Response

We have read and responded to the reviewers' comments in detail and made corresponding changes and markings in the article. The innovation of the manuscript is the study of welding of dissimilar superalloys and the evolution of the microstructure of the welded joints under different heat exposure temperature, so we cite the references in the Introduction to show the advantages of the EBW technology and cite the references about the effects of long-term high-temperature environment on the microstructure and properties of nickel-based superalloy and nickel-based superalloy welded joints to express the necessity of investigating the effects of heat exposure on the microstructure of the welded joints and the last paragraph of the Introduction indicate the purpose of our study. For the issue of similar articles mentioned, the research purpose of the similar article is quite different from that of the present manuscript, which investigates the regulation of the microstructure and properties of the welded joints after welding, while the present manuscript investigates the thermal stability of the microstructure of the joints in a long-term high-temperature environment, and the research purposes of the two articles are totally different. We apologize for overlooking your suggested references at the time, but the article you suggested is of great importance to this manuscript and we have cited it and marked it in the manuscript. We have discussed the experimental phenomena in both the results and the discussion, and we have tried to investigate the elemental diffusion during thermal exposure, but the results were not satisfactory after spending a lot of time and cost on the tests. Nevertheless, we have achieved the objective of the study based on the experimental results and discussed the evolution of the joint microstructure at different heat exposure temperatures in depth.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Accept.