Diffraction Line Profile Analysis of 3D Wedge Samples of Ti-6Al-4V Fabricated Using Four Different Additive Manufacturing Processes
Round 1
Reviewer 1 Report
In this paper microstructural features of Ti6Al4V samples manufactured by LBM, EBM, DED and WAAM are investigated. Properties like sub-grain size, dislocation density as well as type and percentage of different Burgers vectors have been obtained using diffraction line profile analysis. The results are backed by the experimental data. Still the quality of this paper should be improved, and for this I have the following comments:
- generally I am missing the link of the results to the actual microstructure, e.g. with respect to the consituent phases, which might lead to different conclusions. Example: to my knowledge, EBM samples rarely contain the martensite phase, which authors claim to be the main source of dislocations. Therefore, a different conclusion on the low dislocation density could be the absence of that phase.
- generally the paper is difficult to follow at some points for someone, who is not skilled in the field of diffraction line profile analysis. A more detailed desciption on how the obtained results are linked to the analysis would help
- the authors chose neutron diffraction due to the comparatively large volumes that can be analyzed. Nevertheless I am missing a discussion on how representative the results are, because to me it seems that they were obtained on only one sample. Process variations, which are a known issue in AM, would therefore not have been considered appropriately.
- Fig.4 is meaningless without the link to the actual consituent phases. please leave it out or add the respective data.
Author Response
The authors are very grateful for the feedback and comments given by the reviewers. We have used this feedback to make revisions which has improved the quality of the manuscript. All of the comments made by the reviewers have been addressed in detail. The changes and modifications have been highlighted in colour in the revised manuscript. Details of the actions taken with regard to the reviewers' comments are given below.
Yours truly,
Ryan Cottam
Suresh Palanisamy
Maxim Avdeev
Tom Jarvis
Chad Henry
Dominc Cuiuri
Levente Balogh
Rizwan Abdul Rahman Rashid
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The study is on line broadening analysis of four samples produced by different additive manufacturing methods. The authors focus on the density of dislocations that each material, produced by different methods, exhibits. The results clearly show less density of dislocations for the SLM methods, which is expected to result in higher cooling rates followed by methods with slower cooling rates, e.g. EBM or WAAM. However, the findings are not sufficiently discussed, in specific topics, which should be thoroughly covered in the discussion:
· Page 7, Line 231: “plastic deformation due to residual stress formation as the sample cools after deposition”. The authors use neutron diffraction method, which is perhaps the most essential method for residual stress (RS) characterization. Do they have any RS values between the different methods? How much higher is the RS (e.g. in SLM) than the yield strength of the material so that so high density of dislocations is produced?
Although it is generally seen that high compressive RS build up along the building direction in SLM and EBM components have in general lower RS, they are highly dependent on the building direction/methods/parameters etc. It is thus crucial to know the differences in RS between these samples.
· Page 7, Line 233: It is further stated that the formation of martensite can induce more dislocations. The authors used a diffraction technique and obtained the diffraction profiles along a large range of 2-theta. They should be able to assess the phase fractions of alpha+beta phases in the different samples. By doing this they can associate, partially, the difference in the density of dislocations to the presence of martensite and the corresponding dislocations.
· Page 8 Lines 251-259: The authors discuss briefly the observed differences between the different types of Burger’s vectors of slip seen in the different materials. It is known that the hcp crystals can exhibit different slip systems depending on their orientation with respect to the loading direction. The authors should discuss how the crystallographic texture, the residual stress magnitude and direction, can affect the activated slip systems and thus the Burger’s vectors in association with the different AM techniques.
Moreover the following should be addressed:
· In the experimental description it is stated that wedge shaped samples were produced to contain heterogeneous microstructures due to varying cooling rates, however it is later said that the entire sample was irradiated by neutron, thus the results represent an average along a heterogeneous microstructure. What is the reason for doing this? Moreover the WAAM sample is produced as a block and then cut in a wedge shape, this means that this particular sample has more homogeneous microstructure that the rest. How much does this affect the average results over the entire sample and to what extent can it explain the large difference seen, compared to the rest of the wedge samples?
· It is strange that the building condition are disclosed, in principal the conditions and parameters should be given so that these building conditions are reproducible.
· Indexing of the diffraction peaks in Figure 2a are missing.
Author Response
The authors are very grateful for the feedback and comments given by the reviewers. We have used this feedback to make revisions which has improved the quality of the manuscript. All of the comments made by the reviewers have been addressed in detail. The changes and modifications have been highlighted in colour in the revised manuscript. Details of the actions taken with regard to the reviewers' comments are in the attached file.
Yours truly,
Ryan Cottam
Suresh Palanisamy
Maxim Avdeev
Tom Jarvis
Chad Henry
Dominc Cuiuri
Levente Balogh
Rizwan Abdul Rahman Rashid
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors have revised the manuscript according to the remarks of the first review round. The manuscript is missing a short description (maybe in the experimental part) on how the new residual stress data (Figure 3 and the corresponding text in page 9 lines 297-310) was obtained (is it a contour method?).
Author Response
The authors are very grateful for the feedback and comments given by the reviewers. We have used this feedback to make revisions which has improved the quality of the manuscript. All of the comments made by the reviewers have been addressed in detail. The changes and modifications have been highlighted in colour in the revised manuscript. Details of the actions taken with regard to the reviewers' comments are provided in the letter.
Yours truly,
Ryan Cottam
Suresh Palanisamy
Maxim Avdeev
Tom Jarvis
Chad Henry
Dominc Cuiuri
Levente Balogh
Rizwan Abdul Rahman Rashid
Author Response File: Author Response.pdf
