Effective Ti-6Al-4V Powder Recycling in LPBF Additive Manufacturing Considering Powder History

Round 1

Reviewer 1 Report

My suggestions and feedback: (1) The powder recovery treatment method presented by the author lacks innovation and does not demonstrate significant advancements compared to existing research. For instance, there is no substantial proposal for further processing the recycled powder to enable more frequent recycling and truly support sustainable manufacturing. (2) Since Ti-6Al-4V powder is a relatively costly metal powder, it would be highly beneficial to enhance the recovery, treatment, and reuse efficiency of the powder. Unfortunately, this paper does not achieve this goal. (3) The logical structure of the language is unclear, and the literature review lacks depth. Research in this area has been steadily growing since 2015, and this should be reflected in the paper. (4) The article's organization needs improvement. (5) The quality of several images, such as Figure 2, is subpar. Please consider using professional drawing software to enhance the visual presentation. (6) Figure 3's quality is even worse, as it is directly derived from an SEM image. Please revise it according to the SEM figure in the article. (7) Along with assessing the quality of the powder, the internal properties of the powder should also be characterized. (8) Figures 5 and 6 are of poor quality and do not add value to the paper. (9) The comparison of tensile results for the AM build between the current study and existing literature is unclear and needs to be better presented. (10) Overall, this paper lacks innovation and has limited research significance. Furthermore, there are numerous shortcomings in the writing and illustration quality that need to be addressed.

It is fine

Author Response

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Reviewer 2 Report

Dear authors,

The proposed manuscript is focused on “Effective Ti-6Al-4V powder recycling in LPBF additive manufacturing considering powder history”.

The main is very interesting. Although a novelty is provided, in my frank opinion, a MAJOR REVISON should be provided before its final publication. The main reasons are described below:

Line 136: Is the unit bundled or separate? 50g or 50g? Check the entire text. There are times when the unit appears next to the number and others separately.

Please inform the percentages of each element at the beginning of the experimental procedure. Suggestion for elaborating the topics in the text: Materials, sample preparation and densification

Reference suggestions: https://www.sciencedirect.com/science/article/abs/pii/S0925838819304098

https://journals.sagepub.com/doi/abs/10.1177/00219983211029352

https://meridian.allenpress.com/corrosion/article-abstract/76/12/1109/447822/Silicon-Content-Affecting-Corrosion-Behavior-of?redirectedFrom=fulltext

Although it is not the same theme of the work, this reference can help in structuring the experimental procedure that should be adopted. In my frank opinion, work needs to improve on the experimental procedure.

You can explore further the application of powder metallurgy, for example. When we talk about recycled powders, a manufacturing route in great expansion is powder metallurgy. By developing this theme, the work will become richer, and allow the reader to understand more applications.

Line 171 and 252: What is the error associated with the diameter measurement?

Line 261: Errors must be enclosed in parentheses.

Line 266: The correct one is et al. (with dot).

Figure 5: What is the unit on the y-axis?

Line 380: check the website: https://procopytips.com/et-al/

Figure 9: In my honest opinion the R² values are not good. How were the experimental measurements made? Was it in duplicate? Triplicate?

English must be proofread.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Congratulations to the authors for this comprehensive work!

I only noticed a discrepancy between values of the scale used for R index and BV ratio, more specifically:

1. In figure 2, BV ratio appears on the left side with a maximum value of 0.4 and R index appears on the right side with a maximum value of 0.225;

2. In figures 3b, 4, 5ab, 9c and Table 1 - other values appear for R index (from 0 to max 0.4);

3. Likewise, in the case of graphs c and d from figure 5, other values appear for the BV ratio index (values attributed to R index).

I think these values should be checked and correlated to be the same in all figures and tables!

5. In figure 5 b and f, the Hall flow test - values for flow time are similar to that of BV ratio in figure 2! Is this correct? I expected it to be of the order of seconds;

6. In figure 5 f - How do you explain that the time values obtained for the Hall flow test appear identical to those obtained in figure 2 for the R index (the graph is roughly the same shape)?

7. In my opinion, the conclusions could be improved by introducing numerical values obtained, percentages, trends, etc.

Author Response

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Reviewer 4 Report

The manuscript addressed a meaningful and relevant topic. It is well-structured and has precise details. The review suggests that the manuscript can be accepted after the below comments:

1.     Add the metallurgical effects of the oxygen on Ti-alloy's physical metallurgy in the introduction section.

2.     Considering the powder laser-DED (absence of chamber and controlled atmosphere), can the feedstock (powder) material be reused? The low feedstock material consolidation rate reduces the process efficiency of this process.

3.     The authors related the problems of reusing the powder that comes from LPBF. And for electron beam PBF (vacuum chamber)? Please address this discussion.

4.     Other minor elements (e.g., C, N, H, ...) can also alter the microstructure and behavior of the Ti alloys consolidated via LPBF?

5.     Add a schematic sequence to explain the R factor. It is not easier to understand it.

6.     In section 3.1.2, describe how the D10 tends to increse. If preferable, the authors can add a schematic drawn to demonstrate this.

7.     In Figure 6, add the root mean squared error and the residual normality. Also, compare the build number, R, and Bv, indicating the better factor to represent the increased oxygen content in the recycled powder. This comparison must be performed based on the statistical analysis.

8.     Increase the Figure 8 image quality and add arrows that indicate the alpha and beta phases.

9.     A hardness profile (from the Virgen powder to the recycled powder) will show the real effect of the oxygen content (increase during the recycling cycles) on the final strength.

10.  Add a Figure with the Table 1 data.

11. Perform a similar statics analysis of figure 6 in figure 9.

Author Response

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Round 2

Reviewer 1 Report

I don't think the author has revised it well according to the comments and opinions I raised last time.

This paper does not give more detailed and effective methods of powder recovery and treatment.

The quality of figure in the article is still not very good.

Sample handling and microstructure characterization were not detailed enough.

All in all I don't think the paper has been well revised.

it is ok

Author Response

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Reviewer 2 Report

Dear author,

Thank you for accepting my suggestions and modifications. The work is good!

Author Response

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Reviewer 4 Report

The authors answered all the comments.

Author Response

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