Corrosion Behavior of Cr19Fe22Co21Ni25Mo13 Alloy in 1M Nitric Acid and 1M Hydrochloric Acid Solutions
Round 1
Reviewer 1 Report
The manuscript presents some experimental results related to the corrosion behavior of Cr19Fe22Co21Ni25Mo13 alloy in two aggressive electrolytes based on HNO3 and HCl solutions.
Samples of Cr19Fe22Co21Ni25Mo13 were prepared by arc-melting and their morphology, structure and corrosion resistance in two acid solutions were determined by different techniques. The work is a continuation of the studies performed by the authors regarding high-entropy alloys CrFeCoNi with addition of different metals (Nb, Mo) and corrosion tests were previously performed in sulfuric acid and NaCl media.
-Actually, the present work is a short communication, containing only few experimental results and interpretations.
The manuscript requires significant improvement and some recommendations are shown below.
In the actual form it is not recommended for publication.
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The title “Corrosion behaviors …in 1N nitric acid and 1N hydrochloric acid solutions” is inadequate to be published in Crystals because of the profile of this journal. I mention that the term normality (1 N) concentration in title and inside the text (see line 97) is used for chemical analysis (papers in the field of analytical chemistry), the usual being molarities (1 M). In addition, the correct formulation is “Corrosion behavior…..”
Comments of data from literature are very few; you can mention your own articles published in 2017 (Tsau et al. Microstructures and corrosion behaviors of FeCoNi and CrFeCoNi equimolar alloys; Tsau et al. Microstructures and corrosion behaviors of FeCoNi and CrFeCoNi equimolar alloys); you can cite several recent published articles, for example: (1) E.M. Godlewska et al, Corrosion of Al(Co)CrFeNi high-entropy alloys, Front. Mater., 2020; doi: 10.3389/fmats.2020.566336 and (2) P. Lyu et al., Surface modification of CrFeCoNiMo high entropy alloy induced by high-current pulsed electron beam, Appl. Surf. Sci., 504(8) 2019, 144453; doi: 10.1016/j.apsusc.2019.144453
- In section Materials and Methods: lack of information (type, company) about the used equipment for arc-melting (operating conditions), SEM/EDS, XRD, potentiodynamic polarization curves
- In section Results and discussion:
(1) English grammar must be corrected; there are a lot of mistakes (see lines 75, 76, 80, 82, 83 as example)
(2) Mention in line 77: face-centered cubic (FCC) phase
(3) How the values of lattice constants of FCC and SC phases from XRD pattern were determined; is it a preferred orientation growth to an orientation plane in XRD patterns?
(4) Many mistakes related to terminology in corrosion part: In line 96 (also in line 63) it must mention the correct name of corrosion test: potentiodynamic polarization curves; it must mention which was the procedure to determine values of Ecorr and icorr, because the sentence “The corrosion potential (Ecorr ) means the potential of each polarization curve with the lowest current density” in line 98 is wrong
(5) There are no comments for cathodic branches on polarization curves
(6) The corrosion potential may be more positive (more noble) or more negative, not lower or higher, see lines 99,100, 109, 123, 146); also it not be increased (lines 102, 158); similar for standard potential (line 154)
(7) The sentence in lines 104, 111, 125: “.. the polarization curve has no anodic peak” must be replaced by ‘it has not a passivation potential”
(8) Correct …chloride ions (line 132)
(9) Comment of Figures 4 must mention the time of corrosion test, because the attack may be more intense in other immersion times (in other papers you wrote “The immersion time before the experiment was fixed at 900 s for stabilizing the open circuit potential (EOC)”
(10)) Comparison with commercial 304 stainless steel was made only at 30oC; similarly at 40-60 oC ?
(11) No comment regarding the breakdown potential (the end of passivation); is it oxygen evolution in acid media
Comments for author File: 
Comments.pdf
Author Response
According to reviewer’s commands, we modified the title of our manuscript, added the references and improved the section of “Materials and method”.
In section Results and discussion:
(1) English grammar must be corrected; there are a lot of mistakes (see lines 75, 76, 80, 82, 83 as example)
Reply: We have corrected those mistakes.
(2) Mention in line 77: face-centered cubic (FCC) phase
Reply: We have modified it.
(3) How the values of lattice constants of FCC and SC phases from XRD pattern were determined; is it a preferred orientation growth to an orientation plane in XRD patterns?
Reply: According to Bragg’s law, we select the four peaks of each phase to calculate the average value. The diffraction planes of the peaks are shown in the XRD pattern. The SC phase has been identified in our previous study by HREM.
(4) Many mistakes related to terminology in corrosion part: In line 96 (also in line 63) it must mention the correct name of corrosion test: potentiodynamic polarization curves; it must mention which was the procedure to determine values of Ecorr and icorr, because the sentence “The corrosion potential (Ecorr ) means the potential of each polarization curve with the lowest current density” in line 98 is wrong
Reply: We have corrected them.
(5) There are no comments for cathodic branches on polarization curves
Reply: Because we studied the corrosion properties of the alloy, thus the cathodic brabches were not included in this manuscript.
(6) The corrosion potential may be more positive (more noble) or more negative, not lower or higher, see lines 99,100, 109, 123, 146); also it not be increased (lines 102, 158); similar for standard potential (line 154)
Reply: We have corrected those.
(7) The sentence in lines 104, 111, 125: “.. the polarization curve has no anodic peak” must be replaced by ‘it has not a passivation potential”
Reply: We have modified those.
(8) Correct …chloride ions (line 132)
Reply: We have corrected it. Thank you.
(9) Comment of Figures 4 must mention the time of corrosion test, because the attack may be more intense in other immersion times (in other papers you wrote “The immersion time before the experiment was fixed at 900 s for stabilizing the open circuit potential (EOC)”
Reply: The corrosion test was 1500 sec, scanning range was from Eoc to Eoc+1.5V, and scanning rate was 1mV/s, line 166 and Figure 4.
(10)) Comparison with commercial 304 stainless steel was made only at 30oC; similarly at 40-60 oC ?
Reply: Yes, they were similar, so we did not show the other results.
(11) No comment regarding the breakdown potential (the end of passivation); is it oxygen evolution in acid media
Reply: The description has been added in the manuscript, line 127 and 139.
Reviewer 2 Report
The manuscript studied the microstructures of Cr19Fe22Co21Ni25Mo13 alloy and the corrosion behavior of this HEA in deaerated 1N nitric acid and 1N hydrochloric solutions at different temperatures. It is an interesting material but I consider that can be published only after major revision.
Comments for author File: Comments.pdf
Author Response
- The introduction is very poor: there is a lot of literature on new HEA and a good revision has to be made and the references list should be improved.
Reply: We improved our manuscript.
- The experimental part is also poor: details of the equipment used and the conditions under which the mentioned techniques have been applied should be given.
Reply: We have improved the section of “Materials and Method”.
- I consider it very important to relate the structure and composition of the phases with their microhardness, so I recommend to complement the obtained results with those of microhardness.
Reply: We have added the description of microhardness of the alloy in our manuscript, both of “Materials and Method” (line 67) and “Results and discussion” (line 100).
- Is necessary to explain the anodic peaks in the polarization curves.
Reply: We have modified the description.
- Please indicate the reference patterns and lattice parameters for XRD results.
Reply: According to Bragg’s law, we select the four peaks of each phase to calculate the average value. The diffraction planes of the peaks are shown in the XRD pattern. The SC phase has been identified in our previous study by HREM.
- Please add the atoms distribution of main elements of HEAs micro-area maps.
Reply: The mapping of the micro-area cannot clearly display the atoms distribution of this five elements, because the difference of element-content of FCC and HCP phases are not apparent except the molybdenum. So we choice the SEM/EDS results.
- I suggest the authors to analyze and determine the fraction of phases presence in the AlCrFeCoNi system.
Reply: We do not have the equipment to analyze the fraction of the phases in Cr19Fe22Co21Ni25Mo13 alloy. We do not think that it is necessary to analyze the fraction of each phase.
- The conclusions must be improve
Reply: We have improved our manuscript.
Round 2
Reviewer 1 Report
The authors have made the most of the recommended corrections.
In Table 2 the correction of the electrolytes concentrations has not been operated (1M instead of 1N).
Reviewer 2 Report
I consider that now the manuscript can be published !
