Study on the Microstructure, Corrosion Resistance and Dielectric Properties of Atmospheric Plasma-Sprayed Y2O3 Ceramic Coatings
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
The paper titled «Study on the Microstructure, Corrosion Resistance and Dielectric Properties of Atmospheric Plasma Sprayed Y2O3 Ceramic Coatings» describes novel results on optimization of Atmospheric plasma spraying process to produce Y-bearing coating on aluminum alloy. The desired porosity, microstructure, dielectric strength and corrosion performance have been attained by variation of testing parameters. In general, the results are attractive and interesting for technical implementation of the APS approach. I have some comments devoting to the content and organization of the paper.
1) The abstract is well written, however some explanations or hypothesis responsible for the improvement of the corrosion resistance and dielectric properties should be proposed. It’s reasonable to discuss this issue in the separate section, if possible. Major microstructural details (either phase composition or crystallite size) would be valuable addition in this scope.
2) In the end of Introduction, it’s necessary to outline explicitly the main scientific goal of the study.
3) XRD pattern, given in Fig. 1, is advisably to describe separately in the section «Experimental results» rather than in the Methodology part. Lines (104-106) include the crystal phase of the bcc phase obtained by calibration. For what reason do the authors show Fig. 1 (c)? What does «calibration» mean in this context? It seems that this XRD investigation is not analyzed, so it does not build in the common description.
4) Lines 117-121. Please, add the manufacturer of SEM and parameters of EDS collection. Also, the XRD phase analysis is not trivial procedure, therefore the important details on peak fitting, background subtraction and method of phase analysis (using databases, any software etc.) should be completed.
5) Lines 127-128. What was the open circuit potential before measurements? It is not clear whether the used potential range (-0.8 and +0.8 V) is large enough to reveal the corrosion resistance of all studied samples.
6) Reorganization of the paper is required. The figures 3 and 4 include very important simulated results of the test parameters used for optimization. I recommend to remove this figures and corresponding description in the separate «results» section.
7) Lines 248-249. An optimal allocation value was verified by studying the dependencies of the current and spray distance. Due to the influence of many spraying parameters (current, Ar flow, distance) on the residual porosity, is it possible to adjust the procedure of the coating preparation in order to minimize the porosity level? Please, explain this issue more clearly and make some expressive conclusions on this moment.
8) Phase structure of the Y2O3 coating (Fig. 7) is not completely described. For identification of the phase, it’s required to notice the space group, Pearson symbol and lattice constant. I see that all XRD peaks are shifted to different direction relative to each other. What is the reason for (222) peak shifting? Residual stresses or variation of lattice parameters? The Scherer equation, to my knowledge, could be implemented for the materials with low internal stresses, because the physical contrition to the peak width (FWHM) includes both the size of the crystallites and lattice distortion.
9) Fig. 7, no other peaks are identified. Are there any other crystal modifications of Y2O3? Please, revise the peak indexing.
10) How do the authors prepare the cross-section for SEM? Did you use focused ion beam (FIB) procedure? Some explanations are required in the methodology section. In this regard, notify (by arrows and other graphics) the cracks and voids in the Fig. 8. The Arabic numerals (1, 2, 3, 4) are not good for visualization of the coatings defects.
11) The stresses induced via coating preparation are discussed in the lines 308-324. In this case, it’s reasonable to provide rough estimation of the residual stresses depending on the different parameter combinations.
12) Nyquist and Bode plots (Fig. 10) are shown without a proposed equivalent electrical circuit. No values of solution resistance, capacitance, charge transfer resistance and Warburg element are given with corresponding Pearson’s criterion (chi^2).
13) Conclusions seem to be one more description of the experimental results. They should be short, strong and expressive. Please, revise and outline the main achieving of your study more clearly (and avoid self-repetitions of the experimental results).
14) Discussion section is practically absent. I may suggest discussing the reason of enhancement of the corrosion resistance, influence of porosity or residual stresses for verification of the optimal parameters of the coatings fabrication.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors
Dear authors, the paper brings to attention an interesting idea, especially for researchers in the field of thermal spraying, concerning the statistical approach to the influence of parameters on coating quality. However, there are several aspects that I would like to ask you to correct/complete in order to make this article understandable to the mass of readers, but also to have uncompromising scientific value.
Also, the translation needs to be redone because there are many terms / expressions translated incorrectly. Some sentences are too long and no longer make sense, so they should be broken down into smaller and more to the point ones.
Comments:
- line 37: ``etch resistant`` what does it mean? probably corrosion resistant
- line 40: ``porosity structure`` should be ``porous structure``.
- line 42: ``tissue performance`` should be ``coating/layer performance``
- line 49: ``motor bearings`` what is the meaning?
- line 51 - 53: the underlined phrase makes no sense
- line 56: the underlined fragment does not make sense and the sentence from 55-59 does not make sense either as it is too long
- line 62 - 63: ``workpiece`` is repeated and must be replaced
- line 67: ``injection distance`` probably means spray distance (?)
- line 70: why is reference made to the development of high Ni alloyed cathode materials?
- line 72: ``8wtY2O3 stable ZrO2`` is not correctly translated
- line 73: what does ``increase of time in high temperature'' mean? Is it heat treatment?
- line 78-79: are you sure of the statement? The sentence 78-83 is too long and needs to be translated better
- line 99, 100 - to be corrected grammatically
- line 101: how was the particle size determined? As far as I know, it is provided by the manufacturer. Did you determine it yourself? How?
- line 108: ``spacing`` what does it mean?
- line 110: what does 30% mean? why is it specified?
- figure 1a,b: these are usually data supplied by the manufacturer. Have you analyzed them or taken them from the manufacturer?
- figure 1c: from whom are the smaller peaks between (400) and (622)?
- Chapter 2.2 - what ``performance''?
- line 130-134: the sentence is too long and loses its meaning
- figure 2b: nowhere is the test chip specified
- line 140: how is porosity determined? not explained so far...
- line 140: what does ``the center of the response`` mean? explain!
- Table 1: from what I have read (but I am not at all familiar with the PB method), the table should have 8 or 12 runs for the 4 variables, and yours has 9. Also, I don't understand the combination between the text defining the parameters and the significance of the factor: shouldn't only the significance (i.e. 0, -1 or +1) appear in the table? If you have worked in Minitab, perhaps it would be better to fill in the article with the initial table generated for the calculation. Or expand a bit the explanation of the method, because it is not very popular and becomes hard to understand for high mass readers, so it loses its trustworthiness.
- Table 1, Table 3: are the porosity values mentioned in this table measured on real samples, made by you in the experiment? I don't find this stated anywhere and it doesn't appear from what has been written so far. In fact, how many samples were actually made?
- line 267: I would like to ask you to clarify how many samples were actually taken and analysed. You put the term ``all`` but there are only 3 diffraction patterns.
- line 270: I think it should be smallest
- line 272 - 275: where do you draw this conclusion about the size of the gratings? Please explain.
- line 279: what does ``grain size of the coating`` mean?
- line 309: this is too general a statement - what is the performance?
- line 313: the parallel cracks marked with 4 are marked only at the interface with the substrate, so they cannot be defined as cracks but, more correctly, as areas of lack of adhesion to the substrate. In addition, these ``cracks'' may also originate from the method of making the metallographic sample in section, which involves cutting and grinding. For this reason I consider that they should not be considered in this way.
- line 320 - 322: this is a very theoretical explanation, but does not seem to have any basis in the evidence analysed. Please complete if you wish to maintain this paragraph.
- line 324: extrusion is not a phenomenon present in the thermal spraying mechanism.
- line 355: please translate this term better
- line 359: which amorphous phase is it?
- line 368: is the layer thickness obtained from deposition or is it processed to this value? I ask because, in figure 8, the thickness of the 3 samples shown seems different, relative to the measuring bar (the layer thickness on the SEMs should also be put in this figure).
- line 388, 392: to be corrected from a grammatical point of view
- line 396: in the above conclusion you did not mention the influence of flow rate.
- line 401 - 405: please revise this statement as it is purely theoretical and speculative. Furthermore, I do not believe that the large pores come from ``air being covered by the post - sprayed coating``...
- line 420-422: is this statement valid for the same coating thickness? Please confirm in the text.
Comments for author File: Comments.pdf
Comments on the Quality of English Language
Also, the translation needs to be redone because there are many terms / expressions translated incorrectly.
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors
The revised manuscript and author's response make a good expression. So, many experimental details were included in the final version, as well as the description of the XRD and corrosion results was improved. Overall, I may recommend this paper for publication.
