Microstructural Characteristics and Mechanical Properties of an Additively Manufactured Nickel-Based Superalloy
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
The authors report an interesting research work and analysis related to the manufacturing of nickel-based turbine discs using additive manufacturing. The mechanical properties and defects are optimized under the selective melting additive process.
While the experimental approach should be added to better clarify how the authors chose the process parameters and how the process was carried out.
The following are some suggestions/comments.
Major comments:
Introduction: need to provide a rational and reasonable comparison with the pertinent literature. Need to present the outline of the manuscript
Line 24: the keywords, except the first one, are too general. Please, rewrite them by using something more specific.
Section 2: what are the experimental parameters the authors choose? List them. How did the authors choose their experimental parameters? Explain in this section. Did they perform preliminary investigations? Suggested adding a new section or subsection highlighting this particular comment.
Section 4: add future research direction
Minor comments:
Line 51: Avoid these γ’ and γ’’notations using the words they stand for.
Line 105 Figure 2 .. .Title needs to be rewritten with details of .. (a).. (b) .. so on
Line 126 Figure 3 title is same as Figure 2 (refer line 105), need correction with details of subfigures.
Line 128 Table 2, what are the units of measurements adopted for (L) and (W)? Mention it in the respective column
Author Response
Reviewer 1:
The authors report an interesting research work and analysis related to the manufacturing of nickel-based turbine discs using additive manufacturing. The mechanical properties and defects are optimized under the selective melting additive process.
While the experimental approach should be added to better clarify how the authors chose the process parameters and how the process was carried out.
Response: Thank you very much for your kind works. We have revised the paper according to your good suggestions.
The following are some suggestions/comments.
Major comments:
Introduction: need to provide a rational and reasonable comparison with the pertinent literature. Need to present the outline of the manuscript
Response: Thank you for the nice comment. According to your suggestions, both the comparison with the pertinent literature and the outline of manuscript were added in the introduction section of the new submission. “For instance, Liu et al. [10] found that both the strength and ductility of stainless steel could be improved by introducing the special dislocation network by SLM. Lee et al. [12] further proposed that the preferential precipitation along dislocation cell boundaries would deteriorate the resistance of hydrogen embrittlement in AM Inconel 718 alloy, which could be eliminated by suitable post heat treatments.” “Zhang et al. [15] examined the influence of a standard heat treatment on the micro-structure and mechanical performance of a SLM-manufactured superalloy. Further, Wang et al., [16] found that the SLM-fabricated Inconel 718 sample showed different creep performance and the fracture behaviour from the as-forged and as-cast ones due to the unique microstructure.” “In the following section 2, the experimental materials and methods was presented. In section 3, the microstructural characteristics of as-printed and heat-treated samples were shown first. Then, the tensile properties and fracture surfaces of as-printed and heat-treated nickel-based superalloy samples were given. The effect of heat treatment on the evolutions of microstructure and mechanical properties were discussed. Finally, the conclusions were summarized in section 4.”
Line 24: the keywords, except the first one, are too general. Please, rewrite them by using something more specific.
Response: Many thanks for your good suggestion. The keywords have been revised as: “Additive manufacturing; Nickel-based superalloy; Solution and aging treatment; Dislocations; Precipitates; Tensile properties”.
Section 2: what are the experimental parameters the authors choose? List them. How did the authors choose their experimental parameters? Explain in this section. Did they perform preliminary investigations? Suggested adding a new section or subsection highlighting this particular comment.
Response: Thank you the careful comment. It was true that numerous preliminary investigations were carried out to obtained the optimized processing parameters. In the revised manuscript, we explained how the experimental parameters were chosen. “During SLM process, the range of various testing parameters were firstly determined based on previous publications [3, 12-23]. Then, the selected parameters (listed in Table 2) were tested by numerous orthogonal experiments based on density measurement and defects examinations (e.g., pores, internal cracks, un-melted areas and spheroidi-zation) by using OM. Finally, the optimized processing parameters of layer thickness, hatch spacing, laser power and scan speed were 30 μm, 0.11 mm, 175 W, and 825 mm/s, respectively. The density of the printed samples was about 8.17 g/cm3 which was very close to the theoretical result of 8.19 g/cm3.”
Table 2. Lists of testing parameters for obtained the optimized processing parameters during SLM process.
|
|
Layer thickness (μm) |
Hatch spacing (mm) |
Laser power (W) |
Scan speed (mm/s) |
|
Testing parameters |
26, 28, 30, 32, 34, 36, 38, 40 |
0.5, 0.7, 0.9, 0.11, 0.13, 0.15 |
100, 125, 150, 175, 200, 225, 250 |
800, 825, 850, 875, 900 |
Section 4: add future research direction
Response: Thank you so much for your good suggestions. The future research direction was added in the revised paper: “Further works were called to investigate the interrelation between process, structure, properties and performances (e.g., fatigue, creep resistances, and mechanical behaviours under dynamic loading and high temperature) such additively manufactured nickel-based superalloys [1, 19]. In addition, the in-situ heat treatment was also promising approach to processing nickel-based superalloys more efficiently [5].”
Minor comments:
Line 51: Avoid these γ’ and γ’’notations using the words they stand for.
Response: Thank you very much for your comment. The above notations have been widely used in previous publication, and also explained in details in the revised paper: “form γ’ (generally a face-centered cubic Ni3Al with L12 structure) and γ’’ precipitates (normally a body-centered tetragonal Ni3Nb with D022 structure)”.
Line 105 Figure 2 .. .Title needs to be rewritten with details of .. (a).. (b) .. so on
Response: Thank you very much. The details in the figure illustration were added: “(a) OM (b) EBSD of XY plane, (c) OM (d) EBSD of YZ plane and (e) OM (f) EBSD of XZ plane”
Line 126 Figure 3 title is same as Figure 2 (refer line 105), need correction with details of subfigures.
Response: Many thanks. The figure illustration for Fig. 3 have been revised: “Figure 3. The OM and EBSD microstructures for different planes of the heat-treated nickel-based superalloy specimen: (a) OM (b) EBSD of XY plane, (c) OM (d) EBSD of YZ plane and (e) OM (f) EBSD of XZ plane.”
Line 128 Table 2, what are the units of measurements adopted for (L) and (W)? Mention it in the respective column
Response: Thank you very much. The units have been added in the respective column of Table 2 according to your suggestions.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors have studied microstructural characteristics and mechanical properties of an additively manufactured nickel-based superalloy. The research is well designed and presented clearly. A good comparative analysis of existing publications concerning the tasks set in the work is performed. The methodological section of the manuscript is presented in sufficient detail. A heat treatment/aging technique was adopted to dissolve Laves phase into the matrix with formation of the fine γ´ and γ″ phases precipitates. The effect of such a treatment on the subgrain evolution and improvement of yield and tensile strengths was substantiated. The explanation for the microstructure evolution in the as-printed and heat-treated nickel-based superalloy samples is reasonable. However, some minor shortcomings should be corrected to make the manuscript acceptable for publication in Crystals.
(1) In the abstract and main text, the phrase “fine substructures with size” is confusing as the authors use in this case “substructures” (in plural) as components of microstructure. This should be corrected.
(2) Line 70: the word “closed” should be replaced with “close”.
(3) Lines 70–72: Appropriate references (or a wider explanation) should be added when specifying a heat treatment route.
(4) Lines 78–80: The authors should substantiate in details whether the machining process allowed to avoid residual stresses in such a small tensile sample.
(5) Lines 101–103, the following description is incorrect: “The grains of the XY plane are relatively equiaxed and evenly distributed, while the grains of the remaining two sides (YZ and XZ planes) grow along the Z-axis direction”. In my opinion, it may be as follows: “It appears in the XY plane that the grains are relatively equiaxed and evenly distributed, while in the YZ and XZ planes the grain growth along the Z-axis direction is observed”.
(6) Lines 113–114: The statement “the grains are grown to some extent (especially for the large grains) due to … grain growth” is confusing.
(7) In Table 2 (the last row), the authors should replace “XY plane” with “XZ plane”.
(8) In the caption to Fig. 5, the authors should replace “(b)-(f)” with “(d)-(f)”.
(9) Lines 142–143: Once again (see also Comment 1), “In Fig. 5(a), clear cellular subgrain microstructure with fine size” of what? If “size of subgrains”, then the authors should write “with fine subgrains” without “size”. The same concerns “The average size of cellular substructure is …” (Lines 145–146): It seems that “subgrains” should be used instead of “substructure”.
(10) Fig. 5: It would be good if the authors indicate by arrows and appropriate text the micro/nanostructural features (a few subgrains and subgrain boundaries, Laves phases, dislocations, etc.) in the figure body in positions (b) and (d); the same concerns nano-sized precipitates in position (e).
(11) Line 153: It seems that “with ~4 nm” should be replaced with “width ~4 nm”.
(12) Throughout the manuscript, the authors should check the word form “was/were” for the singular/plural cases.
Author Response
Reviewer 2:
The authors have studied microstructural characteristics and mechanical properties of an additively manufactured nickel-based superalloy. The research is well designed and presented clearly. A good comparative analysis of existing publications concerning the tasks set in the work is performed. The methodological section of the manuscript is presented in sufficient detail. A heat treatment/aging technique was adopted to dissolve Laves phase into the matrix with formation of the fine γ´ and γ″ phases precipitates. The effect of such a treatment on the subgrain evolution and improvement of yield and tensile strengths was substantiated. The explanation for the microstructure evolution in the as-printed and heat-treated nickel-based superalloy samples is reasonable. However, some minor shortcomings should be corrected to make the manuscript acceptable for publication in Crystals.
Response: Thank you very for your nice comments.
(1) In the abstract and main text, the phrase “fine substructures with size” is confusing as the authors use in this case “substructures” (in plural) as components of microstructure. This should be corrected.
Response: Many thanks for your careful suggestion. Such incorrect expressions have been revised in the new submission.
(2) Line 70: the word “closed” should be replaced with “close”.
Response: Thank you for the comment. The word “closed” was replaced with “close” in the revised paper.
(3) Lines 70–72: Appropriate references (or a wider explanation) should be added when specifying a heat treatment route.
Response: Thank you very much for the careful comment. The appropriate references have been added in the revised manuscript: “a heat treatment route of 1040 oC/1 h (solid solution treatment) and 700 oC/84 h (aging treatment) according to previous publications [13-16, 19].”
(4) Lines 78–80: The authors should substantiate in details whether the machining process allowed to avoid residual stresses in such a small tensile sample.
Response: Many thanks for the comment. In this study, the as-printed sample was related small and the residual stresses in as-printed sample were not clear. To avoid residual stresses during machining process, wire-electrode cutting was adopted. And a double-stage machining process was used: a flat piece with thickness of 1.5 mm were firstly cut, then the tensile sample were cut from the flat piece. Such explanations were also added in the new submission. “…machined by wire-electrode cutting from the as-printed and heat-treated alloy block parallel to the building direction. To avoid residual stresses during machining process, a double-stage machining process was used: a flat piece with thickness of 1.5 mm were firstly cut, then the tensile sample were cut from the flat piece.”
(5) Lines 101–103, the following description is incorrect: “The grains of the XY plane are relatively equiaxed and evenly distributed, while the grains of the remaining two sides (YZ and XZ planes) grow along the Z-axis direction”. In my opinion, it may be as follows: “It appears in the XY plane that the grains are relatively equiaxed and evenly distributed, while in the YZ and XZ planes the grain growth along the Z-axis direction is observed”.
Response: Many thanks for your good suggestion. You are right and we are sorry for the incorrect statements. The above sentence has been revised as you suggested in the new submission.
(6) Lines 113–114: The statement “the grains are grown to some extent (especially for the large grains) due to … grain growth” is confusing.
Response: Thanks for your nice comment. The confused statement has been revised: “the initial grains in as-printed sample (especially for the primary grains with larger size) are grown to some extent due to that partial recrystallization or grain growth happened during solid solution treatment [15, 18, 21].”
(7) In Table 2 (the last row), the authors should replace “XY plane” with “XZ plane”.
Response: Many thanks and we are sorry for the mistakes. The incorrect“XY plane” have been replaced by “XZ plane” in Table 2.
(8) In the caption to Fig. 5, the authors should replace “(b)-(f)” with “(d)-(f)”.
Response: Thank you very much. We checked the caption of Fig. 5. Fig. 5 (a)&(b) indicated the microstructures of as-printed specimen. And Fig. 5 (c)-(f) showed the typical microstructures in heat-treated nickel-based superalloy sample.
(9) Lines 142–143: Once again (see also Comment 1), “In Fig. 5(a), clear cellular subgrain microstructure with fine size” of what? If “size of subgrains”, then the authors should write “with fine subgrains” without “size”. The same concerns “The average size of cellular substructure is …” (Lines 145–146): It seems that “subgrains” should be used instead of “substructure”.
Response: Many thanks for your careful suggestion. In the new submission, “subgrains” was used instead of “substructure”. And the incorrect expressions were revised.
(10) Fig. 5: It would be good if the authors indicate by arrows and appropriate text the micro/nanostructural features (a few subgrains and subgrain boundaries, Laves phases, dislocations, etc.) in the figure body in positions (b) and (d); the same concerns nano-sized precipitates in position (e).
Response: Many thanks for your careful suggestion. The typical microstructures of subgrain (boundary), Laves phases, dislocations and nano-sized precipitates were marked in the new submission.
Figure 5. TEM images showing the substructures and precipitates of (a)&(b) as-printed and (c)-(f) heat-treated nickel-based superalloy samples.
(11) Line 153: It seems that “with ~4 nm” should be replaced with “width ~4 nm”.
Response: Thank you so much for the comment. We are sorry for the mistake and the incorrect“with ~4 nm” was replaced by “width ~4 nm”.
(12) Throughout the manuscript, the authors should check the word form “was/were” for the singular/plural cases.
Response: Many thanks. The word form “was/were” for the singular/plural cases has been checked carefully throughout the manuscript.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Once again, the typos should be corrected throughout the manuscript.
All the reviewer’s comments were taken into account by the authors. The manuscript can now be accepted for publication.
