Atomic Force Microscopy’s Application for Surface Structure Investigation of Materials Synthesized by Laser Powder Bed Fusion

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript gives a new microstructural characterization method by using AFM. The results are very interesting. I recommend to accept it for publication after minor revisions. Some comments are as follows:

1. It is suggested to add a brief introduction to the principles of AFM for application in LPBF-fabricated materials.

2. In Fig. 1, the authors said that the small grains detected by AFM. It is better to give the evidence by other traditional methods for these grains with nanometer size. 

Comments on the Quality of English Language

it is acceptable.

Author Response

Comment 0: This manuscript gives a new microstructural characterization method by using AFM. The results are very interesting. I recommend to accept it for publication after minor revisions.

Response 0: Authors would like to thank Reviewer for valuable comments which help to improve the manuscript.

Revised text in the manuscript concerning the comments is highlighted by green colour. 

Some comments are as follows:

Comment 1: It is suggested to add a brief introduction to the principles of AFM for application in LPBF-fabricated materials.

Response 1: Corresponding part was added to the Introduction section (see lines 80-87).

Comment 2: In Fig. 1, the authors said that the small grains detected by AFM. It is better to give the evidence by other traditional methods for these grains with nanometer size. 

Response 2: In previous studies authors have confirmed AFM results by X-ray diffraction, which showed good agreement:

https://doi.org/10.1016/j.jallcom.2016.04.228

https://doi.org/10.1134/S1063783416090079

Corresponding statement was added to the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

This work reported one interesting study by using the AFM to investigate the micro-structural character of LPBFed materials. Compared to the SEM observation, the AFM meausrement has its advantages and disadvantages. I think this study may be useful for the field of LPBF manufacturing. The detailed suggestions are in the below:

1. In Fig.1a, the authors should give the line correpsonding to Fig. 1b.

2. It seems a little vague for Fig.3a.

3. In all AFM pictures, there are the green cross-shaped signal. I suggest to delete them.

4. In the whole manuscript, there is no quantitative analyses. The authors should make some quantitative analyses and discussions. 

Comments on the Quality of English Language

English is OK.

Author Response

Comment 0: This work reported one interesting study by using the AFM to investigate the micro-structural character of LPBFed materials. Compared to the SEM observation, the AFM meausrement has its advantages and disadvantages. I think this study may be useful for the field of LPBF manufacturing.

Response 0: The authors are grateful to the reviewer for useful comments and additions.

Revised text in the manuscript concerning the comments is highlighted by blue colour. 

The detailed suggestions are  below:

Comment 1: In Fig.1a, the authors should give the line correpsonding to Fig. 1b.

Response 1:We agree with the suggestion, the line was added to Fig 1a with corresponding description.

Comment 2: It seems a little vague for Fig.3a.

Response 2: Fig.3a was taken with high resolution of the current AFM equipment to demonstrate the capabilities of the equipment using a real example. Moreover, comparison of Fig. 3a with Fig. 3b with higher sharpness was aimed to show wide possibilities of AFM combination with MFM.

Comment 3: In all AFM pictures, there are the green cross-shaped signal. I suggest to delete them.

Response 3: The signals were deleted.

Comment 4: In the whole manuscript, there is no quantitative analyses. The authors should make some quantitative analyses and discussions. 

Response 4: Quantitative analyses were not the aims of the manuscript study. The main goal was to compare AFM method with SEM and TEM in general. It is difficult to discuss quantitative characteristics and results since they are highly dependent on the specific equipment, the studied material, the conditions, etc. and vary widely. Therefore, in our opinion, it is not entirely correct to conduct quantitative analyses.

Reviewer 3 Report

Comments and Suggestions for Authors

The subject is worthy and interesting, and it is one to which the authors can add significant contributions, but the paper needs changes. To make this paper publishable the authors need to expand data analysis, rewrite a few sections of the results and discussion.

Here below my main comments:

The language of the manuscript should be significantly corrected; the paper would benefit from closer proof reading as it includes many linguistic errors, see few examples below:

“Attraction of AFM analysis is appropriate for this purpose due to>>>”

“Besides, SEM equipment price is order higher than AFM one.”, etc.

The authors stated “Besides, high cooling rates inherent in LPBF predetermine ultrafine grain structure of the material, including nano-sized grains and sub-grains, which are complicated to discover by ordinary analytical equipment such as SEM." please add pertinent references.

Please elaborate on the statement "Comparing AFM and ordinary SEM facilities, generally AFM possesses higher resolution without taking into account such rare and expensive equipment as high-resolution SEM."

The authors wrote "Expensive consumables (cantilevers)" and “Small size and affordable equipment” please explain and elaborate on the statements.

I would recommend adding to the experimental chapter further information on AFM characterization for the powders used for the study.

Some experimental observations are just described without proper scientific reasoning, e.g. the authors mentioned "Comparing AFM and ordinary SEM facilities, generally AFM possesses higher resolution >>>"

The authors should elaborate on accuracy and repeatability of the results, when applicable.

I hope the above comments help to improve a future version of the paper.

Comments on the Quality of English Language

no further comments

Author Response

Comment 0: The subject is worthy and interesting, and it is one to which the authors can add significant contributions, but the paper needs changes. To make this paper publishable the authors need to expand data analysis, rewrite a few sections of the results and discussion. 

Response 0: We would like to thank the reviewer for valuable comments which helped us improve the manuscript.

Revised text in the manuscript concerning the comments is highlighted by pink colour.

 Here below my main comments: 

Comment 1: The language of the manuscript should be significantly corrected; the paper would benefit from closer proof reading as it includes many linguistic errors, see few examples below:

“Attraction of AFM analysis is appropriate for this purpose due to>>>”

“Besides, SEM equipment price is order higher than AFM one.”, etc.

Response 1: The manuscript was revised from an English language perspective.

Comment 2: The authors stated “Besides, high cooling rates inherent in LPBF predetermine ultrafine grain structure of the material, including nano-sized grains and sub-grains, which are complicated to discover by ordinary analytical equipment such as SEM." please add pertinent references.

Response 2: Corresponding info and references were given.

Comment 3: Please elaborate on the statement "Comparing AFM and ordinary SEM facilities, generally AFM possesses higher resolution without taking into account such rare and expensive equipment as high-resolution SEM."

Response 3: The statement was revised to clarify it.

Comment 4: The authors wrote "Expensive consumables (cantilevers)" and “Small size and affordable equipment” please explain and elaborate on the statements. 

Response 4: These statements were explained in the text (see lines 197-202).

Comment 5: I would recommend adding to the experimental chapter further information on AFM characterization for the powders used for the study. 

Response 5: AFM characterization for the powders seems to be a complicated task since one of the main requirements for samples for AFM is flat surface. Considering powder samples, there are a few issues: i) preparation of powder layer with flat surface, ii) fixation of particles to prevent them from shifting, iii) visualization of spherical particles via AFM is difficult. Morphology of powder is much better to investigate using SEM, which allows visualization particles easily and with high resolution (taking into account 10-70 μm average particles’ size of powders for LPBF). Optimum way to define particle size distribution is laser particle analysis method. It is also should be noted, that powder characterization is usually required only once before series of printing experiments, while each printed sample needs to be analyzed. That is why the consideration of microstructural analysis by AFM method is a matter of greater practical demand.

Comment 6: Some experimental observations are just described without proper scientific reasoning, e.g. the authors mentioned "Comparing AFM and ordinary SEM facilities, generally AFM possesses higher resolution >>>"

Response 6: The statement was revised adding proper reasoning and reference.

Comment 7: The authors should elaborate on accuracy and repeatability of the results, when applicable. 

Response 7: The study concerns qualitative analysis of methods and their facilities, no quantitative analysis was not carried out. All qualitative results were based on a series of experiments and experience using different microscopes. Thus, in our opinion, there is no need to consider accuracy and repeatability in this specific case.

I hope the above comments help to improve a future version of the paper.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Please see the comments below.

Comments on the Quality of English Language

The quality of the language is still poor, the grammar has to be revised and improved.

Author Response

Thank you very much for highlighting the problem.

Comment 1: The quality of the language is still poor, the grammar has to be revised and improved.

Response 1: The manuscript was carefully revised. Please find all corrections in track changes in the re-submitted file.