Combination of Electron Beam Surface Structuring and Plasma Electrolytic Oxidation for Advanced Surface Modification of Ti6Al4V Alloy
, Ricardo Buzolin 3,4, Marta Mohedano 1, Raúl Arrabal 1, Fernando Warchomicka 3 and Endzhe Matykina 1
Round 1
Reviewer 1 Report
REVIEW REPORT
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The objective of this work is to study the combination of electron beam (EB) surface structuring and plasma electrolytic oxidation (PEO) of the Ti6Al4V alloy for biomedical applications. The selected material is Ti64 (it is required to add the chemical composition) the results have a clear indication that the PEO coatings effectively prevented the crevice corrosion.
Some Comments:
1 Pag.2- 1.1. Material and electron beam surface structuring
The authors indicate that material selected for this investigation was the α+β alloy Ti6Al4V.
It is suggested to add a table with the chemical composition and in particular with the O/N/H content, because these entrapped gasses (interstitial or the form of oxides) can have a deleterious effect on coatings quality.
The Author state : Prior to the EB processing, the surface contaminations were removed mechanically,
But what kind of mechanical operation? What was the final resulting roughness? Is this roughness correlated with the final roughness/results?
At pag 9, last sentences is reported: The roughness parameters of the B1 and B2 samples in Table 4 correspond primarily to the bridge structures. There was an increase in area ratio, Sa, Sq and S10z in the B2.
It is suggested to put in relation and report the initial roughness before and after the treatment. Moreover table 4 I svery risch of data, it is suggested to introduce a column with the description of the main characteristics of the various specimens in order to facilitate the reader. Moreover, the authors are kindly invited to consider if several parameters can be, considered not prioritary and negletted?
Dear Author, You report in Table 1: a frequency = 1000 KHz? Are You Sure..it seems a little bit high…please explain.
Author Response
The authors would like to thank the editors and reviewers for their time and efforts. Please notice that during the revision process sections and tables numbering were modified. Also, references were modified. Response to the reviewers’ comments can be found below.
#Reviewer 1:
The objective of this work is to study the combination of electron beam (EB) surface structuring and plasma electrolytic oxidation (PEO) of the Ti6Al4V alloy for biomedical applications. The selected material is Ti64 (it is required to add the chemical composition) the results have a clear indication that the PEO coatings effectively prevented the crevice corrosion.
The authors appreciate the considerations and comments from the reviewer. Reviewers’ comments are addressed in the following:
- 2- 1.1. Material and electron beam surface structuring. The authors indicate that material selected for this investigation was the α+β alloy Ti6Al4V. It is suggested to add a table with the chemical composition and in particular with the O/N/H content, because these entrapped gasses (interstitial or the form of oxides) can have a deleterious effect on coatings quality.
Thank you for your appreciation. However, the authors believe that the particular O, N and H contents are rather irrelevant to the aim and results of the article.
The high density heat input and vacuum atmosphere of the EB processing used to obtain the presented surface topographies changed the initial composition of the alloy. In vacuum-based melting processes, elements (especially oxygen, nitrogen and hydrogen) evaporate with a high saturated vapor pressure, and there is a significant loss of evaporation during processing. The amount is difficult to determine because in the present case the surface modification and melting was limited to a ~50-150 microns on the surface (see example in Figure 5l for the revised article). Normally, expensive LECO measurements, e.g. LECO 836, would be needed to determine such interstitials, but the amount of material required to measure it would include the influence/composition of the base material. Moreover, Al evaporation would be of much greater concern in terms of coatings composition since it is generally incorporated from the substrate (Table 6 in the manuscript). However, Al loss during EB surface structuring is not significant, keeping the overall content of Al within the specification of Ti-6Al-4V.
Regarding the negative effect on the coatings quality of entrapped gases from the alloy O/N/H contents, to the best knowledge of the authors, there has not been reported in the literature any chemical, electrochemical or mechanical concerns related to neither N or H entrapped gases. As for the O, oxygen evolution takes places during the PEO process and leads to the formation of entrapped gas which ultimately results in internal porosity. However, the origin of this O is the oxidation of water of the electrolyte and not the substrate. The authors consider that, if any, the effect of entrapped gasses from N or H impurities in the alloy would be insignificant when compared with the defects produced during the process itself such as porosity arising from entrapped oxygen bubbles.
Finally, defects on the surface of the alloy, such as grain boundaries, may influence the coating growth during the early anodic stage of the process. In this sense, the authors believe that the density and nature of grain boundaries have a predominant effect over O/N/H interstitials.
The authors believe that such interstitials might be of great concern on other processes such as atomic layer deposition but not for PEO coatings.
- The Author state: Prior to the EB processing, the surface contaminations were removed mechanically. But what kind of mechanical operation? What was the final resulting roughness? Is this roughness correlated with the final roughness/results?
Prior to EB processing, surface contamination and intrinsic oxide layer was eliminated with a metallic brush which is a standard procedure that formed a stochastic roughness. The following sentence has been added to the first paragraph of the 2.1 Material and electron beam surface structuring: Prior to the EB processing, the surface contaminations were removed mechanically, generating a surface roughness (Sa) of approximately 4 μm, and the surface was subsequently cleaned with isopropanol.
As it can be appreciated in the 3D reconstructions in Figures 2c and 3d, the flat surface previous to EB surface structuring was completely modified and its roughness was not significant compared to the surface structuring scales. Also, SEM images did not reveal any sign of stochastic ploughed grinding-like roughness. Structured surfaces according to the design were found. Figure R1 shows an example before the final topography design, where the brushed surface can be compared with the structured area. This was due to the fact that the surface of the material during the EB was melted down to a depth between 50 to 150 μm. Henceforth, the authors believe that the roughness after EB processing is not correlated to the roughness after mechanical removal but to the EB scan parameters and input energy.
Figure R1. SEM image of a structure used for parameter optimization. On the left side the brushed surface is observed.
- At pag 9, last sentences is reported: The roughness parameters of the B1 and B2 samples in Table 4 correspond primarily to the bridge structures. There was an increase in area ratio, Sa, Sq and S10z in the B2. It is suggested to put in relation and report the initial roughness before and after the treatment.
In relation to comment number 2, the increase in the values of surface descriptors for the B2 structure is related to the larger amount of material displaced and piled up at the centreline of the structure due to a higher energy input (480 and 960 J/m, B1 and B2 structures, respectively, Table 3 in the manuscript) and it is not related to the initial roughness of the specimens.
- Moreover table 4 I svery risch of data, it is suggested to introduce a column with the description of the main characteristics of the various specimens in order to facilitate the reader. Moreover, the authors are kindly invited to consider if several parameters can be, considered not prioritary and negletted?
The authors appreciate the appreciation of the reviewer. The Authors believe that the EB structures are sufficiently well described in section 3.1. Notice that B1-B, B1-C, B2-B and B2-C are described in the text and in Figure 4b, e and f as profiles. The caption of Table 4 has been completed with the following sentence to facilitate the reader: B1-B, B1-C, B2-B and B2-C stand for the profiles B and C specified in Figure 4b, e and f.
The parameters presented in Table 2 (notice that table numbers were changed in the last version of the manuscript due to a request from other reviewer) are typically reported surface descriptors. Nevertheless, the authors acknowledge that there was a mistake in the table since Sa, Ssq, S10z, Ssk and Sku were taken from area measurements for all the EB structures (G1, G2, B1 and B2) while B1-B, B1-C, B2-B and B2-C correspond to profiles (as indicated in Figure 4) and henceforth the values presented in the table correspond to R10z. These values have been marked with * and the following has been added to the caption in Table 2: *: R10z values.
- Dear Author, You report in Table 1: a frequency = 1000 KHz? Are You Sure..it seems a little bit high…please explain.
This frequency is the so-called "read frequency", i.e. how many coordinates can be read per second, and can be considered as the beam deflection frequency. Each figure consists of a certain number of coordinates. In the Figure 1 of the revised manuscript, the strategy for the molten surface (M) contains 1000 elements/coordinates. It means the beam figure is passed through 1000 times per second. Such a high deflection was required because the aim was melt a large area at the surface, using higher beam current to avoid expulsion of the melt pool due to evaporation. For surface structuring, the read frequency was reduced to 10 and 20 kHz and the number of coordinates was increased to promote a specific topographic features. For G1 and G2 the figures were swept at 0.25 Hz and for C1 and C2 at 0.5 Hz.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Interesting article. It presents many of the results of current research. The weakness is formatting. Numerous errors in numbering. No descriptions of drawings. After applying corrections, in my opinion, it is ready for publication.
Remarks:
Page 1. Point 1, 1st paragraph. You wrote 10-40 GPa. I think should be 10÷40 GPa. Please use that mark (÷) in the whole article when you show numerical interval.
Page 2. 1. Materials and experimental procedures. That point should have number 2.
Page 2. Not point 1.1. only 2.1. Please correct numbering in the whole article.
Page 3. Fig. 1. Does not have description.
Page 5. Fig. 2. Incorrect description.
Page 6, Point 1.1., 2nd paragraph, should be 23oC not 23oC.
Page 9. Fig. 4 is not 4 only 3. Does not have description. Please correct numbering and description all figures in whole article (also in the text).
Page 18. Fifth and fourth verse from the end. Use identical font and size. You wrote e.g. 1.5·10-6 instead of 1.5·10-6.
Page 25. It is necessary put here figure captions? Bibliography is the end of article.
Author Response
#Reviewer 2
Interesting article. It presents many of the results of current research. The weakness is formatting. Numerous errors in numbering. No descriptions of drawings. After applying corrections, in my opinion, it is ready for publication.
The authors greatly appreciate the remarks of the reviewer. The authors would like to state that the numbering of the sections was correct in the original manuscript submitted to the application. When revising the journals’ version there were several errors found regarding this, including missing section titles and in particular Figure 3. Although recommended, it was not required to submit the manuscript in the journals’ template.
The errors in numbering have been corrected.
Regarding the figure captions, indeed, there was a mistake. Figure captions can be found at the end of the article since a standard submission format was used where figure captions were listed at the end of the article as the reviewer pointed out in their last remark. It should have been specified by the authors in the comments section during the submission phase.
Remarks:
Page 1. Point 1, 1st paragraph. You wrote 10-40 GPa. I think should be 10÷40 GPa. Please use that mark (÷) in the whole article when you show numerical interval.
This has been corrected.
Page 2. 1. Materials and experimental procedures. That point should have number 2.
This has been corrected.
Page 2. Not point 1.1. only 2.1. Please correct numbering in the whole article.
This has been corrected.
Page 3. Fig. 1. Does not have description.
This has been corrected.
Page 5. Fig. 2. Incorrect description.
This has been corrected.
Page 6, Point 1.1., 2nd paragraph, should be 23oC not 23oC.
This has been corrected.
Page 9. Fig. 4 is not 4 only 3. Does not have description. Please correct numbering and description all figures in whole article (also in the text).
This has been corrected.
Page 18. Fifth and fourth verse from the end. Use identical font and size. You wrote e.g. 1.5·10-6 instead of 1.5·10-6.
This has been corrected.
Page 25. It is necessary put here figure captions? Bibliography is the end of article.
Figure captions can be found at the end of the article since a standard submission format was used where figure captions were listed at the end of the article as the reviewer pointed out in their last remark. It should have been specified by the authors in the comments section during the submission phase. This has been corrected.
Author Response File: Author Response.docx
Reviewer 3 Report
The manuscript presents an interesting study about the different coatings deposited by EB and PEO on the surface of Ti6Al4V alloy. The paper needs major revisions before it is processed further, some comments follow:
Abstract:
The abstract must be improved. The abstract must contain information about:
- Background: Please highlight the novelty of the study;
- Methods: Describe briefly the main methods used to obtain and characterize the coating.
- Results and conclusions: Indicate the main conclusions or interpretations.
Materials and experimental procedures
Change the name of this section to Materials and methods.
Electrochemical characterization. Please introduce the software used. Also, add the surface exposed to the solution.
Results and discussion
Figures 9, 10, 11, 12. Introduce figure labels in order to highlight the interest zone for the reader.
Calculate the corrosion rate and polarization resistance and discussed them, see an example: DOI: 10.3390/ma13153410
The discussion is poor. Add discussion by comparing the obtained results with other types of coatings.
Conclusions
The conclusion must be improved. Add quantitative results, limitations and suggestions.
General
Revise the numbering of the sections and subsections.
Introduce figures titles in the entire manuscript.
Author Response
Please see attachment
Author Response File: Author Response.docx
Reviewer 4 Report
Review of paper ‘Combination of Electron Beam Surface Structuring and Plasma Electrolytic Oxidation For Advanced Surface Modification of Ti6Al4V Alloy’ prepared by Hugo Mora-Sanchez, Florian Pixner, Ricardo Buzolin, Marta Mohedano, Raúl Arrabal, Fernando Warchomicka, and Endzhe Matykina.
The manuscript coatings-1952145 is focused on the presentation of modification of Ti materials used, for example, as medical implants. I have some suggestions that authors may consider before publishing this work:
1. The work requires editorial revision, including the correction of chapter numbering.
2. In my opinion, Tables 1-3 should be merged into one: It will be easier to refer to and compare parameters for each of the three solutions. In addition, duplication of the same information (columns 1, 2 and 4) will be avoided.
3. The authors should address the proposed PEO modification in more detail, addressing how it relates to the parameters obtained before and after and whether it is worthwhile, for example by discussing the differences in the parameters obtained in Tables 4 and 7.
4. In the figures in which the connection of points is used, the way in which the lines are drawn should be changed. At present, in several cases the way in which points are connected is not justified, for example, in Figure 14 points B1 or in Figure 17 points M - pH 7.5.
5. After conducting the study, should identify the most optimal solution, as well as refer to the parameters of the implants used, to indicate the advantages and disadvantages of their own solution.
6. References: 10, 12, 13, 14, 19, 20, 21, 22, and 26 (9 out of 30). This represents 30% of all citations, which is very high. Authors should minimise references to their own publications or clearly indicate the necessity of citing them.
Author Response
Please see the attachment
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
The manuscript can be published in the present form.
Reviewer 4 Report
The authors have corrected the text as recommended. I have no further comments.
