Microstructural and Hardness Behavior of H13 Tool Steel Manufactured by Ultrasound-Assisted Laser-Directed Energy Deposition

Round 1

Reviewer 1 Report

The authors have outlined an experimental study where ultrasound (US) was used while processing H13 tool steel in a DED Additive manufacturing scenario. Although there were issues with micrcracks, the anisotropy of the samples was removed due to the action of the US on the grain structure.

A few comments:

The authors use the acronym DLD. I believe that the new convention is to use Directed Energy Deposition or DED. To add in the fact that it is laser you could use Laser-Directed Energy Deposition or L-DED. This convention is commonplace in literature.

Line 133: It was stated that hardness was performed on thin samples. How thin? It is well known (ISO 6507-1:Annex A) that the samples must have thickness greater than a minimum value to be valid. Please check this to be the case.

 

line 210-211: please make the numeral superscript when giving the units of density.

line 249: the last sentence 'There is the grain size is larger' seems incomplete or out of place. please revise.

Figures 10, 13, and 14 use bar charts with error bars. what could be useful is a the application of a significance test (student t-test, chi-squared or similar) between results. If the authors could determine if the results are significantly different or not as the case may be, then this would strengthen the article and the findings.  For example, in figure 13 it should be possible to show that the difference in HV due to direction is significant in the original case  but not significant (i.e., no difference) is the US-assisted  case.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Review report on the topic ‘Microstructural and hardness behavior of H13 tool steel manufactured by ultrasound-assisted direct laser deposition’. The work is presented well. The comments to improve the quality of the manuscript are listed below:

 

1. Add the key conclusion of the work at the end of the abstract section.
2. Please add a separate section to discuss the novelty and application of the work.
3. Remove the Fig. 1. The quality is very poor and second thing no need to cite the image of other work in the introductiuon section.
4. Please make a proper bridge between current and previously published work. At the end of the introduction, discuss in brief the gap and objective of the current work.
5. Provide clear description of each tool and material used under the section of Materials and Method.
6. How was the particle size measured and also add EDS spectra for particles.
7. Provide the image of the experimental setup.
8. Quality of the image is very poor. Instead of optical, add an SEM image of good quality to describe the grain structure.
9. In Fig. 6 quality of the image is not clear. Also, in Fig. 6(c-d), cracks are observed. How does this occur? Please discuss the mechanism in detail.
10. During the deposition, the researchers' major problem is the variation in mechanical properties along the direction and at the interface of the substrate and deposited metal. The discussion about the interface of substrate and deposited metal is missing. Add clear discussion about the macrosegragation at the interface and provide the elemental mapping and formation of the unmixed zone at the interface. Also, deposited metal adds a good quality image for starting middle and end pass deposited metal in both directions: https:// doi.org/10.3390/ma14216732; https://dx.doi.org/10.3390%2Fma13214747;https://doi.org/10.1016/j.addma.2020.101293; https://doi.org/10.1016/j.ijpvp.2021.104439;https://doi.org/10.1016/j.fusengdes.2021.112616; https://doi.org/10.1016/j.jmrt.2021.08.060;https://doi.org/10.1016/j.ijpvp.2021.104536; https://doi.org/10.1016/j.pmatsci.2017.10.001.
11. Discuss the significance of the XRD results.
12. It is difficult to get information about porosity from Fig. 9. How was the porosity measured?
13. The role of annealing is not clear. Provide more discussion and add a good quality image to discuss their effect on micrograph.
14. After the HT, an drastic increase in hardness was measured; why?
15. Provide the hardness variation at the interface of the substrate and deposited metal: https://doi.org/10.3390/ma14216591.
16. In US assisted, the decrease in hardness in perpendicular direction was measured; why?
17. The conclusion section is presented well.

Overall, the work is quite good and interesting and can be accepted after minor corrections

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The authors investigate the effect of ultrasounds (US) and heat treatment on resulting microstructure and hardness of H13 steel samples made trough Direct Laser Deposition (DLD). They found ultrasounds able to assist the DLD process ensuring the formation of fully equiaxed structures and improved hardness.

Despite the article is properly organized, the Introduction does not provide a sufficient background on the DLD processing assisted by ultrasounds for metal deposition. Therefore it should be improved also to better highlight the novelty of the work. The research design requires further information about the choice of the process parameters and the replications carried out to define the repeatibility of the process itself. This will further support the explanation of the findings, which need to be compared with the literature results. Finally, conclusions are adequate.

In the following, the authors can find some comments/suggestions that should be addressed before reconsidering the article for publication in the international journal Metals:

1. The Introduction should be improved by discussing the state-of-the-art on metal DLD and US-assisted metal DLD.
2. Line 52: please, modify "for example:" with "e.g."
3. Line 106: why did you use 28 kHz? Did you perform any previous test to define it? Please, explain.
4. Line 110: do you mean Fig. 3c?
5. Lines 118-127: why did you adopt such process parameters for fabrication and heat treatments? Did you perform any previous test? Please, explain. Moreover, how many replications did you perform? How do you evaluate the repeatibility of the process? This aspects are of major concern about this work
6. Line 167: do you mean (b,d)?
7. Line 170: you mention (e,f), but it does not appear in any figure. Please, verify.
8. Lines 194 and 200: do you mean DLD?
9. Line 203: maybe it is better to say "US-assisted".
10. Line 210: please, verify the unit of measure moving the 3 as a power.
11. Line 249: Please, verify the last sentence.
12. Line 283: the hardness is also reported as HRC. This is a useful information to compare steels hardness. Please, add this information also within the discussion of the results in Section 3.3.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Authors present work concerning multi-track samples from AISI H13 tool steel manufactured by a ultrasound assisted direct laser deposition (DLD) process using a specially designed cooling system. After reading the manuscript I have following comments/questions:

• In the context of the information presented in the introduction on the use of the ultrasound assisted direct laser deposition method for the production of bulk materials from powders of various types of steel, what is the main novelty of the submitted manuscript? Is it only the fact of using AISI H13 steel powder?
• Do the authors have the consent of the authors/publisher to include Figure 1 in the prepared manuscript?
• What is the wavelength of the ytterbium fiber laser IPG LS-3?
• Is printing only one sample with and without US exposure a good basis for the conclusions presented in the paper?
• How was estimated coherent scattering region?
• Figure 7 and 8 - How US exposure influence on overlapping tracks during DLD process?
• The hardness results from Figures 13 and 14 could be presented in one graph (histogram).
• What does XRD spectra look like after the heat treatment process?
• Do the authors have any (quantitative) knowledge about internal stresses in the analyzed samples?
• How did the external dimensions of prints change after the heat treatment process?
• Please remember about subscripts while editing your text - example, line 131 of the text.

Concluded, the manuscript after major correction (additions) maybe be published in the Metals.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Accept. 

Author Response

Reviewer 2 accepted the article

Reviewer 3 Report

The authors greatly improved the overall quality of the work by strictly following the comments/suggestions of the reviewers, therefore now meeting the high standard quality requirements of the journal.

Author Response

Reviewer 3 accepted the article

Reviewer 4 Report

The manuscript after minor correction (keywords - the word "direct laser deposition" remained while in the revised work it was replaced by "Laser Directed Energy Deposition") should be published in the Metals.

Author Response

1. The word "direct laser deposition" remained while in the revised work it was replaced by "Laser Directed Energy Deposition"

Thank you, we've fixed the keyword