Corrosion Resistance of a Plasma-Oxidized Ti6Al4V Alloy for Dental Applications

Round 1

Reviewer 1 Report

1. English needs a little amendment. There are typos and some wrong verb forms. Please also correct the name of Nyquist. Sometimes it is written Niquist.
2. In the abstract and the manuscript, it is written that the authors performed SEM analysis. There is no such thing. Surace, and more important, cross-section analysis must be reported so as the thickness of the oxide layers can be observed. This is mandatory. The whole manuscript is based on the assumption that the improvement of the anticorrosive properties of the metal is due to the formation of a thicker coating.
3. The exposition time in the caption of figure 5 must be reported. 100 h ?
4. Thus, on this base, obtained EIS results can be simulated by using electric circuit as shown on Fig. 8. Line 296. Figure 9.

Author Response

Reviewer 1:

1. English needs a little amendment. There are typos and some wrong verb forms. Please also correct the name of Nyquist. Sometimes it is written Niquist. Corrections have been done throughout the manuscript
2. In the abstract and the manuscript, it is written that the authors performed SEM analysis. There is no such thing. Surface, and more important, cross-section analysis must be reported so as the thickness of the oxide layers can be observed. This is mandatory. The whole manuscript is based on the assumption that the improvement of the anticorrosive properties of the metal is due to the formation of a thicker coating. Micrographs  showing cross section of the oxides have been included in Figure 1 and their discussion is on page 4, section 3.1
3. The exposition time in the caption of figure 5 must be reported. 100 h ?Done.
4. Thus, on this base, obtained EIS results can be simulated by using electric circuit as shown on Fig. 8. Line 296. Figure 9. Capacitances, C, have been replaced by Constant phase elements, CPE´s, on electric circuit shown on Fig. 9 and on table 2.

Author Response File: Author Response.pdf

Reviewer 2 Report

Before publication, several comments should be considered.

1. Considering the Tafel method discussion, at first at all, Fig.3 should be modified in order to demonstrate the anodic and cathodic branches utilized to determined Tafel parameters. Also, arrows should be included to indicate the "icorr" values. In fact, the Tafel area is absent in some plots.
2. The morphology of the samples before and after corrosion tests are suggested to be included. Some frequencies should be added to the Nyquist plots. The physical meaning of no and ni in Table 2 should be discussed. Can we use constant phase element instead of capacitor in the equivalent circuit model?. As the electrode has a heterogeneous structure, it would be better to use constant phase elements.
3. Since the authors discussed the two layers would be formed, the cross-section images should be added to show the inner and outer layers in the samples.
4. The introduction should be further improved by adding more references on Ti-6Al-4V alloy coated via other surface modification methods.
5. The introduction part should be further improved by discussing the influence of other surface modification methods, such as anodizing and plasma electrolytic oxidation on the corrosion behavior of Ti-6Al-4V alloy. 
6. The authors should describe clearly the novelty of this work in the introduction part.

Author Response

Reviewer 2

1. Considering the Tafel method discussion, at first at all, Fig.3 should be modified in order to demonstrate the anodic and cathodic branches utilized to determined Tafel parameters. Also, arrows should be included to indicate the "icorr" values. In fact, the Tafel area is absent in some plots. Scale in the Y-axis have been magnified and arrows have been included to illustrate how the calculationof the Icorr values were done.
2. The morphology of the samples before and after corrosion tests are suggested to be included. Some frequencies should be added to the Nyquist plots. The physical meaning of no and ni in Table 2 should be discussed. Can we use constant phase element instead of capacitor in the equivalent circuit model?. As the electrode has a heterogeneous structure, it would be better to use constant phase elements. Micrographs  showing cross section of the oxides have been included in Figure 1 and their discussion is on page 4, section 3.1. Micrographs of corroded specimens could not be taken since they have been left esxposed to the environment and are full of atmospheric oxides, and there are serous restrictions due to covid-19 to make new experiments. Some frequencies have been added to the Nyquist diagrams. Capacitances, C, have been replaced by Constant phase elements, CPE´s, on electric circuit shown on Fig. 9 and on table 2. Discussion for parameters n_o and n_i have been discussed on page 12, lines 10-15 from bottom.

1. Since the authors discussed the two layers would be formed, the cross-section images should be added to show the inner and outer layers in the samples. Micrographs  showing cross section of the oxides have been included in Figure 1 and their discussion is on page 4, section 3.1

1. The introduction should be further improved by adding more references on Ti-6Al-4V alloy coated via other surface modification methods. References 40-44 have been added and discussed on page 3, lines 8-30.
2. The introduction part should be further improved by discussing the influence of other surface modification methods, such as anodizing and plasma electrolytic oxidation on the corrosion behaviour of Ti-6Al-4V alloy. This has been done on page 3, lines 8-30
3. The authors should describe clearly the novelty of this work in the introduction part. Done.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors present in paper : Corrosion Resistance of a plasma oxidized Ti6Al4V alloy for dental applications some interesting results , electro-chemical analyze of a Ti6Al4V alloy with medical applications after few surface modification treatments. 

By my point off view the paper have two major problems and authors must clear this aspects: 

The main concern is that even if Ti6Al4V is still used as biomedical material in many applications V element is considered by more and more researchers as a dangerous element to human body, the authors must provide some arguments why did they continue with the investigation of this material. 

Second concern is that on Line 76 they mention about SEM analyze but no SEM images are presented in the paper. - there must be a mistake. 

Minor corrections: 

L68: mention the brand of Ti6Al4V you use for experiments â

L76: type of SEM equipment (Fei, Tescan etc. ) 

L77: model of Raman Equipment 

L77: what do you want to find/present through SEM and Raman analyses 

L83-85: type of potentiostat and did you perform OCP tests also ? 

L128: mention in text Mustafa at ref 32 or in ref 32 put Oteyaka 

L131: delete a dot . after solution.. 

L202: This figure, Fig. 4, clearly .. .. 

L230: al- at 

Author Response

Reviewer 3:

The authors present in paper : Corrosion Resistance of a plasma oxidized Ti6Al4V alloy for dental applications some interesting results , electro-chemical analyze of a Ti6Al4V alloy with medical applications after few surface modification treatments. 

By my point off view the paper have two major problems and authors must clear this aspects: 

The main concern is that even if Ti6Al4V is still used as biomedical material in many applications V element is considered by more and more researchers as a dangerous element to human body, the authors must provide some arguments why did they continue with the investigation of this material. Answer to this is on page 3, last part of the introduction, lines 19-22 from bottom.

Second concern is that on Line 76 they mention about SEM analyze but no SEM images are presented in the paper. - there must be a mistake. Micrographs  showing cross section of the oxides have been included in Figure 1 and their discussion is on page 4, section 3.1 

 Minor corrections: 

L68: mention the brand of Ti6Al4V you use for experiments â: Answer is on page 3, lines 15-16 from bottom.

L76: type of SEM equipment (Fei, Tescan etc. ): Answer is on page line 3, page 5 from bottom. 

L77: model of Raman Equipment : Answer is on page line 3, page 2-5 from bottom. 

L77: what do you want to find/present through SEM and Raman analyses. : Answer is on page 3, lines 2-6 from bottom.

L83-85: type of potentiostat and did you perform OCP tests also. Answer is on page 4, lines 11-12.

L128: mention in text Mustafa at ref 32 or in ref 32 put Oteyaka: Done 

L131: delete a dot . after solution. Done

L202: This figure, Fig. 4, clearly .. .. Done 

L230: al- at Done

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors, not to sound picky, but can you report cross-sections with higher magnification so as the thickness of the coating is well visible?

You reported, lines 131-132 "he oxide layer obtained after 3 hours is more uniform and homogeneous than the one oxidized during 8 hours.

But it is difficult to see it

Author Response

Reviewer 1

Dear Authors, not to sound picky, but can you report cross-sections with higher magnification so as the thickness of the coating is well visible?

You reported, lines 131-132 "he oxide layer obtained after 3 hours is more uniform and homogeneous than the one oxidized during 8 hours.

But it is difficult to see it

Answer: Micrographs of cross sections have been included in Figure 1.

Reviewer 2 Report

The answers provided by the authors are very poor, especially in the part related to icorr values, so I don't recommend this paper for publication

1.The quality of cross-sectional images is very poor. I can not see two layers, where are the substrate and the coatings.

2. The method used to calculate icorr is totally wrong ( as indicated in the revised version).  So, the results in table 1are  not correct.  The discussion of EIS is not enough and should be correlated to the morphology of the samples. The corrosion morphology should be presented. 

3. The quality of all figures is very poor

Author Response

Reviewer 2

1. The quality of cross-sectional images is very poor. I can not see two layers, where are the substrate and the coatings.

Answer: Micrographs of cross sections have been included in Figure 1.

2. The method used to calculate icorr is totally wrong ( as indicated in the revised version).  So, the results in table 1are  not correct.  The discussion of EIS is not enough and should be correlated to the morphology of the samples. The corrosion morphology should be presented.

Answer: Calculation of i_corr values have been corrected and explained, schematically, in Figure 4. Micrographs of corroded specimens are shown in Figure 11 and discussed on page 12, lines 7-14.

3. The quality of all figures is very poor:

Better figures quality have been included.

Reviewer 3 Report

Publish in this form

Author Response

Reviewer 3

Publish in this form