Wear Behavior Assessment of New Wire-Arc Additively Manufactured Surfaces on AA6061 and AA5086 Alloys through Multi-Walled Carbon Nanotubes and Ni Particles Inducement
, Junzhou Yang 4 and Muhammad Ahmed Raza 1
Yusuf Usta
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
Overall, the study has been organized very well. Necessary tests and their parameters are correctly assigned. Results are discussed in detail, and even the highlights are depicted clearly. The study's outcomes show that this coating method can be implemented in industrial applications, an important aspect.
I only need to remind the authors that the manuscript has missing figures. It would have occurred due to the software on which the text has been prepared. There are a few mistakes that need to be fixed. All my notes are in the attached PDF file; please read and take the necessary steps to submit the revised version. I want to read the revised version before making my final decision.
Comments for author File: 
Comments.pdf
Author Response
A separate PDF is attached to answer all the questions of Reviewer 1.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe article is poorly prepared and requires significant revision for its normal review. Authors should prepare their manuscript better.
1. The first section presents a literature review on the issue of using aluminum alloys in industry. The possibility of increasing their tribological properties by surface modification is being considered. Much attention is paid to the laser sintering/melting method.
2. The second section provides a description of the materials used and research methods.
The description of the materials is satisfactory. The description of the methods is not satisfactory.
Notes:
1. The review pays a lot of attention to laser melting and only a few references to work in the field of the electric-arc method of modifying the surface of aluminum alloys. Why do the authors make so many references to work done in a different way, and which then does not appear in the discussion of the results of the work?
2. The description of the research methods is not complete. There is no key information about the material and properties of the counterbody used, as well as about friction modes.
3. In dry sliding friction, an important task is to evaluate the adhesion and formation of mass transfer layers. The authors of this work completely ignore this issue.
4. Figure 5 described in subsection 3.1 is missing.
5. In section 2, the microhardness measurement method is indicated according to Vickers, and in subsection 3.2 the results are presented according to Rockwell.
6. The graph shown in Figure 6 (page 10) is completely incorrectly constructed. There should be a diagram in its place.
Author Response
A separate pdf file is uploaded in the reply to questions of Reviewer 2.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsIn this work, a layer with added MWCNTs and Ni particles was deposited on two series of aluminum alloys by using a WAAM with the TIG welding power source, and that layer was assessed by hardness and wear tests. After review, this work is not recommended for publication, owing to (a) not well organized and important figures loss, (b) not clear experimental details description and an apparent lack of experimental data to support the view, (c) need to improve on the mechanism discussion. Detailed comments are provided below:
1. Page 1-Line-38 Page1, “nontoxicity” of aluminum is questionable, and it must need to be supported by the literature. The toxicity is highly related to factors, like composition, morphology and size... Please provide relevant references.
2. Page 2-Line 133-135, (1) why did the authors select MWCNTs? No background was introduced. (2) why was Ni powder? Other materials, such as Ti, SiC, were also mentioned in the Introduction. (3) why did the authors design them by hybrid, rather than individual one? Please demonstrate them in the manuscript.
3. Page 4-Line 158-160, (1) typo of 20mml, (2) the authors prepared two solutions with the addition of MWCNTs and Ni nanoparticles. Is there an agglomeration problem? Does agglomeration affect final deposition? (3) the dimensions of MWCNT are 35 nm and 30 um in length, but the described dimensions are not consistent with the morphology in Figure 2. Please clarify them in the manuscript.
4. Page 5-Line 167-179, (1) please give the details of welding process parameters, (2) what is deposited coating thickness? (3) surface roughness is important for further hardness and wear tests. Please give the surface roughness values after sample manufacturing. (4) I recommend the authors improve the resolution of Figure 3, especially the first and second photos.
5. Page 5-Line 185, the authors applied the Vickers hardness testing, but the results are converted to HRB (Rockwell B) in section 3.2-line255 and figure 5. Has the probe been replaced? What was the normal load and dwell time used during measurement? Please clarify in the manuscript.
6. Page 6-Figure 4, (1) what is the pin made of and size? (2) line 193-197, please give the rotation speed and respective time.
7. Page 6-section 3.1, (1) the figures of radiographic testing results are lost, causing the disordered figure numbers in the following sections and, to some extent, the entire manuscript is unreadable. Please check carefully and revise them!! (2) the absent experiment description of RT is suggested to be provided in the manuscript. (3) RT may not be suitable for planar defect detection (depending on the direction). Please discuss it.
8. Page 8-Line 291, (1) Figure 7 is also lost! (2) What do the colors and arrows in Figure 5 indicate? (3) the hardness variation with and without the addition of MWCNT and Ni particles is one of the important study points in this work. However, the discussion on the mechanism of hardness improvement is scarce and weak, and there is insufficient experimental evidence to support the authors' statement.
9. Page 10-Figure 6, (1) the authors repeated the test twice for each sliding distance, and I suggested that the authors plot histograms with standard deviations rather than line plots. (2) the mass loss of Al 6061 (without) is obviously higher than the Al 5086(without), particularly in 17R and 30 R. Why? (3) Is the third-body abrasive wear likely to occur, due to the addition of MWCNTs and Ni particles?
10. Page 10-Line 342-346, the high mass loss of control samples is ascribed to the dissolution of the precipitates. Furthermore, the precipitate generation is also responsible for the hardness improvement in the samples with the addition. If so, why do the precipitates not dissolve in the samples with the MWCNTs and Ni addition? No further relevant discussion in the manuscript.
11. Page 11-Line 362-363, please provide relevant evidence to support the statement “This percentage improvement is supported by the formation of hard nickel aluminates and aluminum carbides in the matrix that increased the wear resistance.”
12. Page 11-section 3.4. In this section, the authors mentioned “deep” multiple times, how to confirm the deep or shallow depth of the wear track if there is no surface profile measurement? The judgment based on the contrast of SEM images is not accurate. Similar questions for the claim in adhesive wear. This section was suggested to be reorganized and rewritten with a reasonable discussion.
Author Response
A separate file is uploaded in the reply to all questions and queries of Reviewer-3.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThe following comments/suggestions need to be incorporated into the manuscript.
1. The abstract should be more quantitative in terms of improvements. Also, the author needs to mention the equipment used in the investigation.
2. From Fig 2, the particles are observed as flak structures but the author has mentioned it diameter of 35 nm 155 and a length of 30μm. Justify.
3. The author should also report the purity of MWCNT. It can be only evaluated by the raman. Add the Raman spectrum of MWCNT.
4. On which equipment, the author conducted the microhardness test and what parameters? Further, the surface hardness of the interface is missing in the Pin-on-disk test. Also, include the contact pressure.
5. The heading should be Results and Discussion.
6. The Radiographic Resting Results figure is missing. The author must add the same.
7. Figure 5 should be Figure 6. The author must check the figure number that is wrongly presented.
8. Figure 7 is missing.
9. The author should also add the friction coefficient raw data. That is highly important to investigate the wear.
10. The author should include the possible wear mechanism in this work. Further, they have to add the scientific discussion on each obtained result.
Author Response
A separate file is provided to answer all the queries of Reviewer-4.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsI have studied the authors' responses to the comments of all reviewers and evaluated the corrections made.
I believe that all the main shortcomings have been eliminated by the authors. The structure of the work and its content now correspond to the level of a good scientific publication. In its current form, their manuscript can be accepted for publication in the Coverage journal.
Author Response
A separate file is attached against the positive remarks of Reviewer 2.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThank you for the authors’ revisions and the provided responses. After reviewing, I decided to maintain my initial decision. Several comments can be found below:
1. Please clarify the meaning of the white arrows in Fig. 2.
2. Previous #4-(3) comment, I agree with the authors’ response, “the surface is machined for all the specimens before hardness measurement and wear testing.” But in Fig. 3-finishing photo, the authors applied the abrasive paper to grind and polish the surface. I recommend that the authors provide the grade of abrasive paper in the manuscript, which will help the audience to roughly estimate the level of surface roughness. Or, please provide the exact surface roughness value. This is important for hardness and wear testing. That was the purpose of my previous comment.
3. The authors neglected my previous comment #7-(3) comment, please respond to it or talk about the limitations of radiographic testing in this work, although it is a common NDT in welding. Fig. 5 (b), is not a photo of the entire disk, please replace it or explain why it was used. In addition, why did the authors only detect the sample with 0.02 g MWCNT?? What about samples with 0.01g MWCNT? Samples with 0.01 g MWCNT were also tested for hardness and wear tests.
4. Previous comment # 8-(2) comment, please simply label what the color means. For example, blue: center ......, otherwise it may cause confusion.
5. Previous comment # 9 comment, (1) please give the standard deviation in Fig. 8. (2), the authors deposited a welded layer (ER4043) on AA6061 and AA5086, without NANOMATERIALS. It implies the deposited layers in AA 5086 (without) and AA6061 (without) should be quite similar. But why is there such a big difference in mass loss (Fig. 8)? In addition, the authors neglected my #9-(3) comment. Please respond to it.
6. Fig. 10 and lineS 427-430, the statement “Fig. 10 shows the macro cross-sections images after the wear tracks developments from all the four radii on the without inducement and with 0.02 grams of MWCNTs in AA5086.” is not consistent with the figure caption. It is confusing. What are the exact samples, AA 5086 or AA 6061? Again, in Fig. 10 (b) 17R, why is the depth quite deeper than others 25R, 30R, 37R? As my previous comment #9-(2). I realized the authors explained it in Lines 484-486. Why is higher contact stress developed at the 17 mm wear track? If according to Fig. 10, the contact area should become larger during the test, resulting in a lower contact stress.
7. Previous comment #12, I still have questions about the claims of adhesive wear in this work and the authors' responses are not convincing. I understand “the adhesive type of wear is the prevalent wear mechanism, which is visible in the obtained SEM images, Figure 11-14. The extreme plastic deformation and the material build-up sideways are the features, which are visible in the images.” and also believe the occurrence of adhesive in this tribopair (Deposited layer vs. tungsten carbide pin) used in this work. I was wondering why “The extreme plastic deformation and the material build-up sideways” are considered the features of adhesive wear. These features seem to be related to the hardness and ductility of materials. In other words, extreme plastic deformation and material pile up in the edges of the wear track are the results of the softer and more ductile deposited layer, compared with the pin. Do the authors characterize chemical information, e.g., EDS or XPS? Do the authors observe the pin surface as well? What about the friction change?
Author Response
A file is attached in the reply to Revision 2.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsNo Comments
Author Response
The authors would like to express their gratitude to Reviewer-4 for pointing out positive and significant details for the improvement of the manuscript in Round-1 and further acknowledged the provided Revision in Round-2.
Regards,
Dr. Muhammad Muzamil
