Parameters Optimization and Repeatability Study on Low-Weldable Nickel-Based Superalloy René 80 Processed via Laser Powder–Bed Fusion (L-PBF)
, Antonio Sivo 1,2, Flaviana Calignano 2,3,4, Emilio Bassini 1,2,4, Sara Biamino 1,2,4 and Daniele Ugues 1,2,4Round 1
Reviewer 1 Report
The paper 'Parameters optimization and repeatability study on low-weldable Nickel-based superalloy René 80 processed via Laser Powder-Bed Fusion (L-PBF) ' aims to reduce porosity and hot cracking of the L-PBFed René 80 alloy via process optimization. René 80 alloys are susceptible to hot cracking during laser processing, which is why it is very important to decrease the cracks density and improve the mechanical properties of the alloy. The study described in this paper may also prove very useful. Although the writing was good, some questions should be added:
1. In section 3.2, were the date (cracks density of samples) in Figure 7 obtained from one sample or the average of five samples? If it is the average of five samples, the error bar should be marked.
2. In page 9/18, ‘Figure 7 shows six samples 1, 4, 6, 7, 8, and 15 having crack density lower than 100 µm/mm2…, as represented in Figure 8, and only sets 4, 6, 7, 8 and 15 were kept for further optimization’, if the authors does not provide the process parameters, such as laser power, scanning speed, hatching distance, etc., it is difficult for us to determine what the normal process parameters are for these specimens of 1-18.
3. There is a threshold value of crack density of 100 m/mm2 in this paper; what is the criteria for determining this value?
4. In page12/18, ‘Figure 14 shows the microstructure observed with the secondary electrons in SEM. The image presents the material's cellular structure, with carbides in the intercellular region’. From SEM, it is difficult to determine that the intergranular compounds are carbides, therefore the author should provide an EDS map.
5. In section 4, the authors have analyzed the crack generation induced by residual stress caused by temperature gradient and rapid cooling, but the liquation cracking caused by γ/γ′ phase is also the main hot crack. The authors should present the distribution of elements around the crack in Figure 9 and discuss it.
Author Response
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Reviewer 2 Report
1. The conclusions of the powder characterization tests should be described in detail in the methodology section of the manuscript.
2. The manuscript should include a table of thermal physical parameters of the material.
3. The recorded values range from 30 to almost 300µ m/mm² and from 0.02 to 0.12% in terms. On page 8 of the manuscript, the symbols are missing, and there are many other cases like this, so I hope the author will proofread it again.
4. Page six, Page eleven and Page thirteen of the manuscript contains multiple grammatical errors and contains statements that should not appear.
5. The analysis of crack density and pore area fraction for different samples on page 10 of the manuscript should dig deeper into the intrinsic causes of instability rather than just interpreting the data.
6. In the microstructural analysis of René 80 on page 12 of the manuscript, the common features of the said L-PBF should be marked in Figure 13.
7. The color scheme of Figure 4 is suggested to be modified, the colors are similar and difficult to distinguish.
8. On page 14 of the manuscript, the authors suggest that tensile stresses occur in the top layer and compressive stresses in the bottom layer during the cooling process. However, Figure 15 does not clearly show this phenomenon.
Author Response
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Reviewer 3 Report
1. This sentence "Furthermore, the intra-print repeatability was studied by producing three specimens’ repetitions for each optimal set of parameters in the same build." should not be put in the abstract. It should be put in Section 2.
2. In the last paragraph in the Introduction section, it is suggested to mention the research procedure and used methods briefly not a simple conclusion.
3. There are many "dirty" things adhered on the powder particles in figure 1. What are they? It may be negative for the additive manufacturing process due to reduction of the flowability.
4. The full DOE parameter constipations (18 groups) must be provided in Table 1 and mark them with corresponding numbers. The whole manuscript only mentions the number. It is impossible to recognize the corresponding parameters.
5. Why two batches are provided? Does the difference between these two batches in the element contents influence the repeatability of this study?
6. Please give a detailed description on the intra- and inter-print repeatability.
7. Why was the repeatability done on the full DOE parameter combinations? That will provide a higher credibility.
8. Actually, the error bars in Figures 10 and 11 are very large. Will this still suitable for verify the repeatability?
9. It is suggested to compare the L-PBFed microstructure with the conventional one.
10. The authors should provided the best optimized parameter combination as the title is about "parameter optimization....."
Author Response
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Author Response File: Author Response.pdf
Reviewer 4 Report
Error of references fount at page 6, page 11 and page 13. Authors could explain the DOE results interferences between variables used.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Authors addressed most of my concern, it is ready for publication.
Author Response
Dear reviewer,
thank you again for the time and effort spent in improving this work.
Pietro Antonio Martelli
