Effect of Lateral Laser-Cladding Process on the Corrosion Performance of Inconel 625
, Amirhossein Aboutorabi Sani 2, Mohammad Talafi Noghani 2, Morteza Saghafi Yazdi 2, Morteza Taheri 3, Amirhossein Moghanian 2, Mohammad Abedini Mohammadi 2, Mahmoud Moradi 4, Antonio Manuel Mateo García 1,5 and Hossein Besharatloo 1,5,6,*
Masatoshi Sakairi
Round 1
Reviewer 1 Report
The manuscript investigates the process of obtaining Inconel 625 alloy coating by laser cladding method. The topic is interesting, but serious drawbacks are present in the manuscript, so the major revision is required, as follows:
Introduction: it is claimed several times that Inconel 625 nickel-based superalloy may be used as a protection of gas turbine against high temperature and gas corrosion. However, the work describes the corrosion tests in NaCl electrolyte. Some other corrosion tests should have been chosen, more related to the gas corrosion of turbines, instead of simple immersion in NaCl.
Page 4: “A current difference was applied between the two electrodes, and the developed current between the reference electrode (Inconel 738) and work electrode (Inconel 625) was measured.” Explain this statement. In previous paragraph, calomel electrode is mentioned as reference electrode.
Figure numeration in the text is erroneous throughout the whole manuscript. Some figures are missing.
Page 4: “Figure 2 shows the corrosion zone (CZ) and heat-affected zone (HAZ) within the cross-sectional view of the studied coatings after the corrosion test.” Provide more information: what is the thickness of the coatings? What corrosion test has been performed and for which time period? Define corrosion zone and heat affected zone. Explain the unusual shape of the corrosion zone. Provide significant literature support.
“Section 2.1. Corrosion behavior of Inconel 625 coating”, should be completely rewritten, with additional experiments. This section is very baffling and inconsistent.
2.1. Corrosion behavior: since the alloy investigated contains significant amount of Cr, Ni, Mo, why did the authors choose to perform a simple ASTM-G102 test? There are more appropriate corrosion tests for alloys containing these elements, which are known to provide surface passivation.
Table 5: there is no information after which immersion period in NaCl, the polarization test was performed.
Table 5: provide and explain the equation used for calculation Rp from jcorr. For very high corrosion current density (2.28 A m-2), a very high Rp is calculated (2.094×104 Ω/cm2). This seems odd.
Page 7, “The passive layer formation in sample S2 took place more quickly as a consequence of a lower corrosion current density”. Better explain this statement. How is passive layer formed? Is passive layer the consequence of low current density, or is it the opposite?
Page 7, authors state that passive layer is formed on the samples. Yet, the corrosion current densities are extremely high (85,9 A m-2 and higher), pointing to the very fast corrosion. Explain this.
Page 7, “The presented Tafel diagram displayed that the change in potential has led to a sudden change in the current density value, which verifies the inappropriateness of the passive layer formed on the Inconel 625 coating.” Explain better this sentence. It is related to which samples?
Figure 3, Tafel curves: give current density values in Am-2 or Acm-2, not just current (ampere). What was the potential sweep rate?
Figure 4 is missing. Figure numeration in text is erroneous.
Page 8: “Accordingly, the surface corrosion rate decreased for the S2 sample as it contains a higher amount of chromium and molybdenum within the electrolyte solution (See Tables 5 and 6). In addition, the amount of these protective coating elements in the uncoated sample is remarkable.” My question is, if the amount of Cr and Mo is already remarkable in the uncoated sample, what is the point of adding the coating that also contains Cr and Mo?
Page 10: “The pH of the polarization solution is increased when nickel ions are added to the polarization solution”. This statement is incorrect. Please check data on pH change after Ni ion addition to water solution.
Page 10, “…the coated sample S2 has a lower corrosion rate than the uncoated substrate owing to a proper formation of a passive nickel layer…” but in page 9, it was “…the surface corrosion rate decreased for the S2 sample as it contains a higher amount of chromium and molybdenum within the electrolyte solution...”. Please better clarify which elements are responsible for better corrosion resistance of sample S2. Provide more literature data and make comparation with previous works.
Figure 6: there is no information after which immersion period in NaCl, the impedance test was performed.
Impedance spectroscopy: data representation in Table 7 and their discussion in page 12, point to the fact that the authors are not familiar even with basic knowledge related to electrochemical impedance spectroscopy. This part must be rewritten.
Conclusion, sentence 5: “…reducing the amount of CPE prevents the creation of defects and cavities on the surface of the sample.” Explain this statement because it does not make sense.
Author Response
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Reviewer 2 Report
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Comments for author File: Comments.pdf
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Reviewer 3 Report
The introduction needs to increase more
Fig.1 Resolution and writing is not good.
revise all numbering of titles 2.1 is repeated and others...
FeCl3 (1 g), HNO3 revise 3 is subscript.
Equation 1 put as (1), revise within all the manuscript.
These parameters Ecorr: Corrosion potential (V), Icorr: Corrosion current density (A/m2), Rp: Polarization resistance (Ω), ba: anodic branch slope, bc: Cathodic branch slope, C. Rate: Corrosion rate (mm/year) should be written in the discussion and you must put the figures.
Fig.3 for polarization in writing not Fig.4 …..
Figure 5 shows SEM micrographs ….. is Fig.4
Revise Figures numbers all are inxcorrect in the discussion?
Where is alpha values accompanied with the CPE
Where is the average error for fitting?
No data in the conclusion
Really, the article needs major revision.
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Reviewer 4 Report
This paper reported corrosion performance of Inconel 625. The results may important for corrosive environment usage of Inconel 738 or other structural metals.
However, it is not well organized. Some comments are as follows.
No need "and" after " Hossein Besharatloo1, 5, 6".
Table 1: Powder Inconel "62" is Powder Inconel "625".
There are many typos.
If authors use sandpaper, "polish" may be "grind".
Caption of Figure 1 is not correct.
OLYMPUS model BX-51M (PA, USA): Is it correct?
"Followingly, copper wires were joined into samples with the help of a soldering machine."
Copper wire may not in the sample. It may be on the sample, so, the sentence should modify.
" A current difference was applied between the two electrodes, and the developed current between the reference electrode (Inconel 738) and work electrode (Inconel 625) was measured."
The explanation is not correct. Potential was applied and obtain the current between tow electrodes. Moreover, what does the "developed current" mean?
Results and discussion is not "2". It is "3".
It must explain more in detail of potentiodynamic polarization tests.
In Table 5; what is the V/dey? What kind of electrochemical reaction involve over 200 mV/dec?
Moreover, no Tafel region can be seen in Figure 3, so, no Tafel slope may not observe.
No explanation was made for Figure 3. Moreover, explanation of Figures 4, 5, 6, 7 are wrong.
Figure 6: Why uncoated sample results is different from other samples. Why R1 is changed with specimen?
More in detail of each experiment must be written in the experimental section.
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Round 2
Reviewer 1 Report
The manuscript investigates the process of obtaining Inconel 625 alloy coating by laser cladding method. The topic is interesting, but serious drawbacks are present in the manuscript, so the major revision is required, as follows:
page 10: “The pH of the Inconel 738 substrate greatly affects the corrosion of the Inconel 625 coating [60].” I don’t understand this sentence. How the pH of a substrate is measured?
page 10: “The pH of the polarization solution is increased when nickel ions are added to the polarization solution.” I don’t understand this sentence. Is it an observation from the pH measurement, or an assumption? How pH changes when Ni ions are added to water solution? Please use literature to support your answer. For example, read reference “J. Chem. Educ. 1996, 73, 6, 516, All Positive Ions Give Acid Solutions in Water”.
page 11, 12: discussion of impedance spectroscopy does not make sense in many points. Include in your team a person who is familiar with this experimental method.
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Reviewer 2 Report
After major correction, the present formal manuscript can be accepted.
Reviewer 3 Report
The impedance data should be revised again.
You see the diameter of S1 is larger for the semicircle than S2 in Fig.7.
How you said that it is of lower resistance. This is wrong. Revise this part and check if you write the symbols wrong on the graph.
after correction, it can accepted.
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Reviewer 4 Report
The paper is important for corrosion research. However, present style of the paper is not suitable for publication. Comments are as follows.
Not organized explanation was made in the manuscript. It must improve explanation level.
Fig. 2: It must show in detail of corrosion tests
"Various forms of corrosion are evident in the microscopic images, which apply to pitting corrosion. The through pits were seen as shallow and elliptical, and sideway pits occurred in the subsurface due to the increase in average laser power [42]."
It must show the results in the manuscript.
From Fig. 4, no Tafel region in anodic polarization curves is obtain. So, Table 5 may not correct.
It must show fitted data in Fig. 7.
"In the standard state, the resistance of the coating is higher than the resistance of thesolution; in other words, the values of Rs against Rct should be smaller."
It is difficult to follow this explanation. Rct may not be resistance of coating. Rct is related to corrosion reaction.
Table 7: Unit for CPE is wrong. Moreover, it must show value of CPE in the Table.
Author Response
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Round 3
Reviewer 1 Report
I believe the manuscript has been sufficiently improved to warrantpublication in Metals.
Prior the publication, rewrite the sentence "Due to the presence of nickel,
molybdenum, and niobium - which has a non-conductive nature [74]
- sample S2 has not passed much electrical potential,
which has increased the initial resistance of the solution to almost
9000 O.Cm-2."
Several statements are incorrect here:
1. nickel, molybdenum, and niobium DO NOT have non-conductive nature
because they are metals.
2. "sample S2 has not passed much electrical potential" - what does
it mean? Potential may not pass, current passes.
3. "resistance of the solution to almost 9000 O.Cm-2" so high solution
resistance is nonsense.
Author Response
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Reviewer 4 Report
It is better to check unit of CPE.
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