Study of Coatings Formed on Zirconium Alloy by Plasma Electrolytic Oxidation in Electrolyte with Submicron Yttria Powder Additives
Round 1
Reviewer 1 Report
The work by Savushkina et al. evaluates the coatings formed on zirconium alloys by plasma electrolytic oxidation, when PEO is performed in an electrolyte with submicron Yttria power additives. Results and discussion are well written and the data supports the conclusion. Nevertheless, there are some aspects that need improvement, as mentioned below.
- Regarding the potentiodynamic polarization data, an additional reference has to be added for both the measurement at room temperature and at 100°C. Authors should include the measurement and data for a PEO coating obtained in one of the conditions without the Yttria added into the electrolyte - this to further emphasize on the effect of the Yttria addition.
- For better clarity, authors could indicate the interface between the PEO coating and the alloy, as well as the different layers (top, middle and boundary) – in Figure 3. Also the arrangement of the figure could be improved to present the data in a more clear-cut rate (e.g. mention first the different coatings in a column, and then focus on the layer morphology – and so on).
- Figure 4: it is very difficult to see the absence of Y in the alloy as it is the bottom most part of the image and very small at that.
- Overall quality of figures can be improved. For example, XRD (Fig 6) – due to the small nature of the XRD peaks not optimal to overlay them, but it is quite difficult to compare the intensities and peak positions when a different 2theta range is used (also size of the annotated text can be increased).
- There is a slight coagulation of the yttria particles during the plasma electrolytic process, as the authors mention in the experimental part. Do the yttria particles suffer also some chemical modification?
Author Response
We thank the Reviewer for their detail consideration of the paper. The changes have been highlighted in colour through the text of the revised manuscript. The questions of reviewers with our comments are given below.
Best regards, Dr. S.V. Savushkina
1. Regarding the potentiodynamic polarization data, an additional reference has to be added for both the measurement at room temperature and at 100°C. Authors should include the measurement and data for a PEO coating obtained in one of the conditions without the Yttria added into the electrolyte - this to further emphasize on the effect of the Yttria addition.
The purpose of this work in accordance with the title of the article (Study of Coatings Formed on Zirconium Alloy by Plasma Electrolytic Oxidation in Electrolyte with Submicron Yttria Powder Additives) was study of coatings formed precisely in electrolyte with powder. The introduction contains references [33–36], from which it follows that the addition of oxide powders to the electrolyte reduces corrosion currents by 3-4 orders of magnitude compared to uncoated samples. PEO in electrolytes without powders reduces corrosion currents by only 2 orders of magnitude.
2. For better clarity, authors could indicate the interface between the PEO coating and the alloy, as well as the different layers (top, middle and boundary) – in Figure 3. Also the arrangement of the figure could be improved to present the data in a more clear-cut rate (e.g. mention first the different coatings in a column, and then focus on the layer morphology – and so on).
Figure 3 has been corrected. The layers marks has been added. The arrangement of the figure has been improved The image of boundary and middle layer microstructure of PEO coating formed at 30 A / dm2 has been added.
3.Figure 4: it is very difficult to see the absence of Y in the alloy as it is the bottom most part of the image and very small at that.
We have added a table 2 of PEO coatings elemental composition (EDX data). Figure 4 has been corrected. The boundary and layers have indicated.Enlarged image of barrier layer microstructure and elements distribution along linein this area have been added.
4. Overall quality of figures can be improved. For example, XRD (Fig 6) – due to the small nature of the XRD peaks not optimal to overlay them, but it is quite difficult to compare the intensities and peak positions when a different 2theta range is used (also size of the annotated text can be increased).
Figure 6 (Figure 7 in new version) has been corrected. 2 theta scales of XRD patterns were matched. Size of the annotated text has been increased
5. There is a slight coagulation of the yttria particles during the plasma electrolytic process, as the authors mention in the experimental part. Do the yttria particles suffer also some chemical modification?
Y2O3 forms a solid solution with ZrO2 in accordance with the ZrO2 – Y2O3 phase diagram. At the same time, X-ray phase analysis did not reveal the formation of compounds with yttrium oxide. Analysis of scientific works on this topic also did not reveal any mention of yttrium oxide particles chemical modification during the plasma electrolytic process.
Reviewer 2 Report
This work studied the properties and behaviour of coatings formed on the Zr-1Nb alloy by plasma electrolytic oxidation at different current densities in the slurry electrolyte with the addition of submicron yttria powder. The paper is well-written and conclusions made are clear however there is the need for some minor corrections before the paper is accepted. The following corrections should be considered:
- Reviewing minor grammar mistakes throughout
- Writing abbreviations in full the first time they appear e.g. PVD
- Methodology details need to be improved. There are no details to DLS and SEM settings. The number of runs and instrument settings should all be included.
- EDS would have helped to confirm Yttria. Why was this not done?
- How was Figure 4 achieved? There is no explanation or methodological detail. Also there is no explanation to the colour coding.
- Figure 2a is unclear and needs to be replaced.
- Figures 6-8 would have benefitted from keys rather than simply captions.
Author Response
We thank the Reviewer for their detail consideration of the paper. The changes have been highlighted in colour through the text of the revised manuscript. The questions of reviewers with our comments are given below.
Best regards, Dr. S.V. Savushkina
1. Reviewing minor grammar mistakes throughout.
Some mistakes have been corrected in the text.
2. Writing abbreviations in full the first time they appear e.g. PVD
Abbreviations PVD and CVD have been written in full.
3. Methodology details need to be improved. There are no details to DLS and SEM settings. The number of runs and instrument settings should all be included.
DLS, SEM details, and number of runs have been added. The instruments settings was included.
4. EDS would have helped to confirm Yttria. Why was this not done?
The elemental composition of PEO coatings layers according with EDX data has been added (Table 2).
5.How was Figure 4 achieved? There is no explanation or methodological detail. Also there is no explanation to the colour coding.
Figure 4 has been corrected. The mapping details has been added.
6. Figure 2a is unclear and needs to be replaced.
Figure 2a has been replaced by another one.
7. Figures 6-8 would have benefitted from keys rather than simply captions
We have added additional marks in Figures 6-8 (Figures 7-9 in new version).
Reviewer 3 Report
Dear Authors
congratulations for the work done and all the information gathered and explained in the manuscript. I think that the paper has clear merits in terms of providing new, experimental data in order to advance the state of the art in the field. A few comments from my side:
- Please ensure that the same measurement units system is used across the manuscript; current density in “A/dm2” is , at least, un usual;
- Your figure 3 images; if possible, please ensure that you have same magnification for a, c, and d. For fig 3b, I do not see how relevant is such a high magnification coefficient, doubled compared with the other two figures (c and d).
- The non uniformities, in terms of the distribution of the chemical elements, can be seen without problems; any information relating the colour intensity with the concentrations provided by the Energy dispersive x-ray analyser measurements would be relevant for the reader.
- Please add units cu Igi in table 2.
- In figure 2 b, e, and f you are claiming an agglomeration of submicronic yttrium particles; it would be nice if you could confirm that these agglomerations have been identified using EDAX measurements and to provide a "colour" map of their distribution, similar to the one presented in fig. 4.
Author Response
We thank the Reviewer for their detail consideration of the paper. The changes have been highlighted in colour through the text of the revised manuscript. The questions of reviewers with our comments are given below.
Best regards, Dr. S.V. Savushkina
1. Please ensure that the same measurement units system is used across the manuscript; current density in “A/dm2” is , at least, un usual;
The current density in "A / dm2" is a quite common unit of measurement in works on plasma-electrolytic processes. For example, it was used in these works devoted to PEO of zirconium alloys (Matykina E., Arrabal R., Skeldon P., Thompson G.E., Wang P., Wood P. Plasma electrolytic oxidation of a zirconium alloy under AC conditions Surf. Coat. Technol. 2010, 204, 2142–2151, 10.1016/j.surfcoat.2009.11.042; Farrakhov, R. G.; Parfenov, E. V.; Mukaeva, V. R.; Gorbatkov, M.V.; Tarasov, P.V.; Fatkullin, A.R.; Rameshbabu, N.; Ravisankar, B. Effect of Electrolyte Composition on Protective Properties of the PEO Coating on Zr-1Nb Zirconium. Alloy Surf. Eng. Appl. Electrochem., 2019, 55 (5), 514–521, 10.3103/S106837551905003X)
2. Your figure 3 images; if possible, please ensure that you have same magnification for a, c, and d. For fig 3b, I do not see how relevant is such a high magnification coefficient, doubled compared with the other two figures (c and d).
Figure 3 has been corrected. Figure 3b was replaced. The magnifications in the figures are different to represent equally clearly all layers and the interface with the alloy of PEO coatings with thickness from 40 to 150 microns
3. The non uniformities, in terms of the distribution of the chemical elements, can be seen without problems; any information relating the colour intensity with the concentrations provided by the Energy dispersive x-ray analyser measurements would be relevant for the reader.
The elemental composition of PEO coatings according to EDX data has been added (Table 2).
4. Please add units cu Igi in table 2.
The units of Igi have been added in table 2 (table 3 in new version).
5. In figure 2 b, e, and f you are claiming an agglomeration of submicronic yttrium particles; it would be nice if you could confirm that these agglomerations have been identified using EDAX measurements and to provide a "colour" map of their distribution, similar to the one presented in fig. 4.
An accelerating electron voltage of at least 20 keV was used to identify yttrium during X-ray microanalysis (to obtain a peak corresponding to the K line), since the L line of yttrium coincides with the L line of zirconium. Due to the impossibility of reducing the voltage, the depth of analysis was quite high. In addition, there was a drift due to the charging of the surface of the oxide coating, which was especially evident when analyzing small areas and collecting a map for a long time. As a result, small features of the structure as submicron particles in the EDX map of PEO coating structure are not apparent.
Round 2
Reviewer 1 Report
The authors have included the suggested modification and significantly impoved the manuscript.
A suggestion would be also to improve the annotation of the curves in Figures 8 and 9.
