Robust γ-TiAl Dual Microstructure Concept by Advanced Electron Beam Powder Bed Fusion Technology

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Present paper is focused on the electron beam powder bed fusion of TiAl and shows perspective possibilities of additional parameters tuning by changing the voltage (from 60 to 150 kV), electron beam intensity distribution and size. The paper is well written and structured, methods are clearly described and results are nicely represented. There are several minor corrections and one major comment to this work.

Lines 14-16: “the difference between the designed aluminum-rich and aluminum-lean regions of the part is increased. Moreover, the aluminum content is more homogenous.” – this is a bit unclear. Do the authors mean that the difference in aluminum content between aluminum-rich and aluminum-lean regions is increased, whereas each of these regions have more homogenous aluminum distribution?

Line 107: “The particle size distribution is 45 µm to 150 µm” – what exactly are these values?  d10 and d90 or others? Please indicate. Also, please provide a median particle size (d50).

Lines 117-121: please, check the consistency between variable names in the text and in Equation 1 (either uppercase or lowercase).

Line 135: “20 images with 100x magnification are analyzed” – this parameter is not informative, please provide the size of the analyzed area (in the same way as written further in paragraph).

Lines 177-179: The equation 2 (and corresponding sentence) states that the area of the beam can be calculated from the beam diameter d as (d/2)^2. Should not there be a pi in the formula of circular area? Circular area = pi*r^2 = pi*(d/2)^2. Thus equation 2 should be then q = P / (pi*(d/2)^2)

Line 227: “the mappings show 500 μm in the build direction” – please, rephrase, it is unclear how micrometers can have a direction.

Line 228: “no boundaries between these layers or differences between the layers can be found in the aluminum content” – actually, one can see laminar inhomogeneities, which indicates that there are differences in Al content between the layers. For example, there are yellow and orange areas in the upper row, violet and dark orange in lower row. This corresponds to around 0.5-1% of difference between areas within a single 500 um^2 area.

Line 230: Figure 4 – please, indicate clearly the building direction on the image (for example, with an arrow)

Major comment:

One of the main subjects in present paper is the homogeneity of Al distribution: authors state as the main outcome of the work that using 150 kV instead of 60 kV provides better homogeneity. To support this statement, the authors demonstrate color maps of Al distribution on Fig 4 and 7. However, (1) one could see inhomogeneity on Fig 4 (as was mentioned previously) and (2) no quantitative calculation of local interlayer inhomogeneity is provided. Thus, speaking of better or worse homogeneity is subjective and unclear. To overcome this uncertainty the authors are asked to calculate Al content on subimages of Figures 4 and 7 along the building direction. This can be done by summing up (integration) all the pixel values in each row and plotting this summed Al content along the z axis (build direction) near each mapping subfigure. By doing so, authors would obtain quantitative measurement of inhomogeneity in contrast to subjective observation of colors. The example of such integration curve is shown on Fig S1 (attached).

Comments for author File: Comments.zip

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The present study reports the article entitled “Robust γ-TiAl dual microstructure concept by advanced electron beam powder bed fusion technology” and authors need to consider following comments.

-I’m not agree with the term ‘have been shown in previous studies’ in Abstract; I think Introduction is a suitable section for such expressions.

-I see similar publications from the authors such as references 10, 12, 13, and 15, etc. But what is No 19 ‘revised under review’? how you can reference to article which is not published!

-The phrase ‘dual microstructure concept’ is addressed many places, but need to elaborate it in Introduction section’ what is it? I understand it may be introduced in previous articles of authors but still need to appropriate some lines for theory. I think it named Dual Microstructure Heat Treatment (DMHT) in some literatures.

-Number of references are less for such article, whereas the named ones also more and less belong to the authors.

-Such spherical powder materials named Ti-Al-Nb in most of literatures, is there any reason you call it γ-TiAl? Also, I think laser powder bed fusion is more known than electron beam powder bed fusion.

-In section materials and methods, you say you’re using a prototype PBF-EB machine which has no information in an article which is not published! At least you can introduce some specifications about it.

-It would be good if a SEM micrograph and a photograph of sample was available to see in figures.

- Except for the aspect that the work continues or replicates the author's previous efforts, the article's structure is sound and consistently guides towards its objective.

Author Response

Please see attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for your corrections, there are no more comments from my side

Reviewer 2 Report

Comments and Suggestions for Authors

Manuscript is modified in the line of the comments and can be published by the opinion of the Editor.