Erosion Behavior of Stellite-6 and WC-12Co Coatings on SA213-T22 Boiler Steel
Round 1
Reviewer 1 Report (Previous Reviewer 2)
This paper has been significantly improved. However, there are still a few concerns that need to be clarified.
1, the erosion rates the authors used is ‘mg/g’, which is fine if the target materials have the same solid density. However, compared to steel, Co-28Cr has a close solid density (8.56 g/cm3) but WC-12Co has a big difference (17.2 g/cm3). Now the concern is the erosion rates in Fig. 5, where the WC-12Co has the highest erosion rate. In principle, the WC-12Co has the highest hardness in Fig. 4, which should have the lowest erosion rate. The harder materials used to have a good erosion resistance. The results showed here are against the common sense. This could be due the erosion rate used here. If it converts to a volumetric erosion rate (mm3/gram erodent), which may give a true result. The complexity of coating material erosion can be another reason, but the authors did not show here or explain it.
2, how many targets do the authors use in the study? What is the measurement error? The error analysis has not been addressed in the manuscript.
Other minor corrections are suggested as:
1, Line 19: ‘The Stellite-6 coating showed some ductile erosion…’ should be clarified.
2, Section 2.1: solid densities for the substrate material and coating materials.
3, Line 103: manufacturer for the ‘laser Doppler anemometer’ should give.
4, Line 271-305: Discussion on the erosion characteristics needs to be clarified. The erosion on coatings is complicated compared to pure materials, but the propose of coating is to improve the erosion resistance of a pure material. If a simple coating process can give a much better erosion life of a pure material, the coating is novel and significant. The discussion should address this point.
The English has been significantly improved, but it still needs to be checked. There are some minor errors and format problems.
Author Response
August 9th, 2023
Dear Reviewer 1
Submission of the revised manuscript
We have completed the revision of the manuscript entitled “Erosion behaviour of Stellite-6 and WC-12Co coatings on SA213-T22 boiler steel” authored by Aumpava Kiatisereekul, Asst. Prof. Dr. Thamrongsin Siripongsakul and Asst. Prof. Dr. Kittichai Fakpan (the corresponding author).
Let me send to you the revised manuscript, the revised highlights and response to reviewer and thank you very much for your kind work as the reviewer.
Yours sincerely
Kittichai Fakpan
Author Response File: 
Author Response.doc
Reviewer 2 Report (Previous Reviewer 3)
The authors studied the Erosion behaviour of Stellite-6 and WC-12Co coatings on 2 SA213-T22 boiler steel with high velocity oxy-fuel (HVOF) thermal spray technique. The research findings are interesting. Some of the important need to be addressed to improve the quality.
1. Add the novelty statement at the end of the introduction section
2. In Fig 4, WC-12Co coatings exhibited high hardness. But in Fig. 5 indicated the erosion wear is high in WC-12Co when compared to stellite 6 coating results. please justify it with references.
3. In conclusions, better erosion resistance of Stellite-6 due to low porosity of the coating. But In the paper, what is the porosity and how did you measure . it is not clear, please include it.
Author Response
August 9th, 2023
Dear Reviewer 2
Submission of the revised manuscript
We have completed the revision of the manuscript entitled “Erosion behaviour of Stellite-6 and WC-12Co coatings on SA213-T22 boiler steel” authored by Aumpava Kiatisereekul, Asst. Prof. Dr. Thamrongsin Siripongsakul and Asst. Prof. Dr. Kittichai Fakpan (the corresponding author).
Let me send to you the revised manuscript, the revised highlights and response to reviewer and thank you very much for your kind work as the Reviewer.
Yours sincerely
Kittichai Fakpan
Author Response File: Author Response.doc
Reviewer 3 Report (New Reviewer)
This paper introduced the HVOF process used to deposit Stellite-6 and WC-12Co coatings on SA213-T22 steel. The coated surfaces demonstrated high hardness, low porosity, and denseness. Erosion testing with SiC revealed that uncoated steel exhibited ductile erosion with SiC embedment, while Stellite-6 and WC-12Co coatings resisted SiC embedment due to their high hardness. Stellite-6 showed some ductile erosion, whereas WC-12Co demonstrated only brittle erosion. Stellite-6 exhibited better erosion resistance than WC-12Co due to its strong and tough metal matrixed composite structure and lower porosity. Further optimization is suggested for WC-12Co coating. Overall the claim is clear and straight. I only have some small comments about the experimental design.
1. In figure1, is it possible to show the EDS mapping of the SEM image? I think the mapping result is more straightforward compared with the EDS line scan.
2. Is it possible to show the surface roughness data of the coating film of the steel before and after Stellite-6 and WC-12Co coatings? It is hard to see the surface morphology (microcrack or micro-cutting) directly from the SEM image.
Author Response
August 9th, 2023
Dear Reviewer 3
Submission of the revised manuscript
We have completed the revision of the manuscript entitled “Erosion behaviour of Stellite-6 and WC-12Co coatings on SA213-T22 boiler steel” authored by Aumpava Kiatisereekul, Asst. Prof. Dr. Thamrongsin Siripongsakul and Asst. Prof. Dr. Kittichai Fakpan (the corresponding author).
Let me send to you the revised manuscript, the revised highlights and response to reviewer and thank you very much for your kind work as the reviewer.
Yours sincerely
Kittichai Fakpan
Author Response File: Author Response.doc
Round 2
Reviewer 1 Report (Previous Reviewer 2)
Line 136: the target material density should be given.
It is fine, but it needs to double check.
Author Response
August 10th, 2023
Corrosion, Wear and Erosion Section
Assistant Editor, Coatings
Dear Reviewer 1,
Submission of the revised manuscript
We have completed the minor revisions of the manuscript entitled “Erosion behaviour of Stellite-6 and WC-12Co coatings on SA213-T22 boiler steel” authored by Aumpava Kiatisereekul, Asst. Prof. Dr. Thamrongsin Siripongsakul and Asst. Prof. Dr. Kittichai Fakpan (the corresponding author).
Let me send to you the revised manuscript, the revised highlights and response to reviewer and thank you very much for your kind work as the reviewer.
Yours sincerely
Kittichai Fakpan
Enc. The revised manuscript and response to reviewer
Author Response File: Author Response.doc
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Paper shows the results of an investigation into the erosion of cobalt and cermet coatings. Results are comparatively analyzed in relation to the steel substrate. Erosion tests and results analysis is accurate. But novelity of the paper, chemical composition and coatigns characterisation should be improved. Comments on the paper:
1. Introduction should better be shown the gaps in knowledge and paper novelty.
2. Clarify this phrase: Furthermore, it has been reported that cobalt is one of the 62 important elements affecting the hardness and toughness of the materials. - its meaning is unclear and not adhere to plot of introduction. Please improve it.
3. In Table 1 provide also the nominal chemical composition of steel according to the international standard requirements.
4. In table 2 - instead of "Heat source temperature" write "Maximal heat source temperature".
5. In fig 1 the SEM micrograph of SiC is missing.
6. Explain in methodology why SiC has been used as erodent material? It is relatively hard, harder than corundum which is usually used. Take into consideration that other lower hardness erodent material were used to simulate the real working environment like those reported by Hejwowski in works https://doi.org/10.12913/22998624/140200 and https://doi.org/10.1016/j.vacuum.2008.04.004
7. The standoff between the nozzle and test sample should be added in the paper (write it in tab. 3 or in fig 1).
8. The nominal chemical composition of the feedstock powders must be added in the paper. The chemical composition of Co-28Cr is unclear... EDS suggests other chemical elements than Co or Cr... It must be clarified.
Authors wrote: "
| The line scanning element analysis of the coating is shown in figure 3 (c) exhibiting the presence of W, Co Cr and C, while oxide is less detected compared to the Co-28Cr | 139 |
"
9. Were the spray parameters optimised. Justify the spray parameters selection.
10. Figuer 2c and 3c should be enlarged to improve the readability of the EDS results.
11. Ithink that XRD analysis should be repeated and taking into account the nominal chemical composition of the feedstock powders. Diffractogram shown in fig 2 provides unkward results. If you detected by EDS also W and C why only chromium oxide and cobalt solid solution are visible? These elements should form a carbides... Maybe you deposited satellite 6 -type coating? Explain it.
12. Where the XRD measurements were done, in the coatings cross sections or top surface? State it in the text.
13. What was the surface preparation prior erosion testing? Were the surfaces prepared by grinding or tested in as spray conditions?
14. You must inform in the paper that you obtained relatively low hardness of WC-12Co coatigns which could strongly affect the wear results and hardness of coatings. These type of coatings sprayed with appropriate parameters with low porosity should provide hardness at the level of approx 16 GPa (or approx 1300 HV), see exemplary Jonda group reports: https://doi.org/10.1016/j.apsusc.2022.155071 https://doi.org/10.12913/22998624/135979
These examples are useful to support this claim "However, the difference in hardness among research works could be attributed by 172
decarburization, carbide grain size and density of the coating which are generated by 173
various conditions in the HVOF process.
"
15. Erosion results are accurately stated. Hovewer, after improving the coatings characterisation please improve this part. Expecially comment on the selection of such a hard erodent mateiral, which is harder than ceramics reported in fly ash.
Reviewer 2 Report
This paper shows an interesting study on erosion behaviour of Co-28Cr and WC-12Co coatings on steel. However, a few concerns need to be clarified.
1, The novelty of this study is a concern. Any purposes of coatings should be to improve the wear resistances of substrate materials such as steels. In this study, the erosion rates of the coatings are significantly higher than the substrate material (boiler steel). If anti-erosion is a requirement, it is unnecessary to go for a coating process.
2, The results in Table 4 show that the velocity exponent (n) for Co-28Cr is less than 2. This is weird as previous studies show that the n is always bigger than 2. For any ductile materials, the n should be between 2.3 and 2.8. for any brittle materials, the n should be between 3 and 6. The results showed here do not follow the traditional rules, maybe because erosion of the coatings does not behave as any pure materials. Coatings on a ductile substrate may behave like a composite. The coatings can be removed quickly and then it suffers the erosion as it behaves the substate material.
3, The surface morphology does not show the depth of the caters. It is hard to identify whether the erosion only happens on the coatings or coatings were removed and damaged area was entered the substate material. Because the coatings are likely to be brittle, the adhesion between the coatings and the substrate can also play an important role. When the coatings are cracked, more debris can be off from the substrate and cause a high erosion rate.
4, The interpretation using the ratio of erodent particle hardness to target surface hardness (Hp/Ht) may be not correct as the ratio of Hp/Ht must be bigger than 1 if an erosion happens. Otherwise, there is not erosion happened. Higher ratio causes more damages to ductile materials as a result of cuttings, but maybe the same actions to brittle materials.
5, In Fig. 9, it does not consider the influence of the fluid. For the ASTM tester, the distance between the nozzle and the target (not indicated in the text) must be small. The air stream has strong influences on the impact angles. However, the authors did not describe it clearly including the calibration of particle velocity as required in the standard.
Reviewer 3 Report
The authors investigated the Erosion behaviour of Co-28Cr and WC-12Co coatings on SA213-T22 boiler steel. The research finding and outcomes are interesting. however, some of the points need to address to improve the quality of the manuscript.
1. Erosion rates of SA213-T22 steel is lower than Co-28Cr and WC-12Co coated specimens. Any specific reason for it? (is it porosity in coating or any adhesive strength of bonding materials)
2. Please include the surface preparation on or before coating
3. plastic deformation of materials occurs due to high hardness of SiC, is it true, Please check the sentance
