Review Reports

Round 1

Reviewer 1 Report

The main function of the passive film of the 304L stainless steel is anti-corrosion capability. The authors had perform in depth surface and subsurface analyses. However, it lacks clear comparative conclusion in the respect. 

I would suggest the authors to perform salt water test which will be clearer and more useful for industrial applications.

Author Response

Thank you for your suggestion, we could effectively plan this kind of test.

Regarding the objective of this work, we have performed the same study with BWR and PWR environment to be more representative of industrial environment. According to your comment, we specify it in the conclusion part.

Reviewer 2 Report

This is a nice paper. The schematics in Figure 5 and Figure 6 are really useful and concisely tells the story of the paper.  I have a few suggestions which are not mandatory:

1. Increase the size of Figure 2. At present, it is hard to read the text embedded in the figures.
2. Did the authors measure the thickness of the ultrafine-grained region using TEM? If so, can the authors comment on the accuracy of the measurements, since the deposited Pt coating during FIB lift-out is going to affect the measured thickness, and what the authors are seeing may not be the actual thickness of the ultrafine-grained region? This can be seen in Figure 2a where the Pt-coating is curved. This may lead to misleading results!
3. Change the location of Table 1. At present, it is confusing as to how the authors measured the thickness of the ultrafine-grained region. It would make more sense if the table was placed after the TEM and residual stress measurement results are shown.
4. Can the authors comment on why the surface roughness between the 2400SiC paper and 1 mum diamond finish is within the scatter limits? Looking at the SEM micrographs there is a clear reduction in surface roughness (visually)
5. Please include the XPS spectra of the samples.
6. What was the rationale behind using a borate buffer? Please include that in the methods sections. 

Author Response

1. Increase the size of Figure 2. At present, it is hard to read the text embedded in the figures.

(A): Thank you for your comment. The Figure 2 has been modified for sake of clarity.

2. Did the authors measure the thickness of the ultrafine-grained region using TEM? If so, can the authors comment on the accuracy of the measurements, since the deposited Pt coating during FIB lift-out is going to affect the measured thickness, and what the authors are seeing may not be the actual thickness of the ultrafine-grained region? This can be seen in Figure 2a where the Pt-coating is curved. This may lead to misleading results!

(A): Indeed, it is difficult to measure accurately the thickness of the ultrafine-grained region, due to the roughness and the definition of the limit of this region. In these conditions we consider a trend which can be admit without doubt from several observations at different locations of the different treatments.

3. Change the location of Table 1. At present, it is confusing as to how the authors measured the thickness of the ultrafine-grained region. It would make more sense if the table was placed after the TEM and residual stress measurement results are shown.

(A): If it is clearer, we accept obviously to move the table 1 at another location. Editor will consider this modification regarding the publishing constrains.

4. Can the authors comment on why the surface roughness between the 2400SiC paper and 1 µm diamond finish is within the scatter limits? Looking at the SEM micrographs there is a clear reduction in surface roughness (visually)

(A): The roughness was measured by the 3D optical profilometer of the Micromap device. Root means square (RMS) parameter was selected as an adequate parameter to characterize roughness. However, corrugation and wave may introduce bias which explains the little discrimination between paper polishing and diamond paste.

5.Please include the XPS spectra of the samples.

(A): We have hesitate to introduce XPS spectra in the paper and decided to don’t introduce them to limit the size of the paper. These results obtained in the present paper were commonly admitted in the papers dedicated to the passive film studied on stainless steel. Moreover, there is not significant variation between the three surface finishing conditions. We consider that the spectra doesn’t give new information.

6. What was the rationale behind using a borate buffer? Please include that in the methods sections.

(A): This buffer solution has been chosen to stabilize the oxi-hydroxide nature of the passive film and minimize the solubility of the Cr-oxide. Moreover, it is close to the composition of the primary circuit corresponding to the nuclear environment which are considered in our global study. As proposed by reviewer, it is mentioned in the paper.

Reviewer 3 Report

Dear authors,

This paper is well written to explore the dependence of the surface state and passive performance of 304L stainless steel on the mechanical surface treatment. I would recommend this paper to be published after the following comments are considered.

(1) As your paper is public for researchers on different levels. it would be better if you can mark selected area electron diffraction and clarify which diffraction axis were used to get the SAED pictures in Fig. 2.

(2) Line 264-265: "In the present work, the assumption that the space charge capacitance is much smaller than the Helmholtz capacitance was made to relate the capacitance measured by EIS to the passive film capacitance." What possible results would you expect if you assume  the space charge capacitance is close to or a bit higher than the Helmholtz capacitance?

(3) Line 352 "both roughness and compressive residual stresses increase doping densities in the  passive film". It would be better if you could give reasonable explanation about this phenomenon here,

I would also advice authors to consider a comparative experiment by investigating the effect of heat treatment and mechanical treatment on the surface state, i.e. the influence of annealing on the release of surface stress by using laser scan confocal microscope.

Author Response

(1) As your paper is public for researchers on different levels. it would be better if you can mark selected area electron diffraction and clarify which diffraction axis were used to get the SAED pictures in Fig. 2.

(A): Thank you for your comment. The Figure 2 has been modified for sake of clarity.

(2) Line 264-265: "In the present work, the assumption that the space charge capacitance is much smaller than the Helmholtz capacitance was made to relate the capacitance measured by EIS to the passive film capacitance." What possible results would you expect if you assume  the space charge capacitance is close to or a bit higher than the Helmholtz capacitance?

(A): As at high frequency, the total capacitance takes into account the electrochemical double layer and space charge capacitance.

1/C = 1/C_SC + 1/C_dl

If the Csc is close to Cdl, we can’t neglect Cdl and Mott-Schottky theory is no more valuable. Generally, Cdl is at least ten times higher than Csc.

(3) Line 352 "both roughness and compressive residual stresses increase doping densities in the  passive film". It would be better if you could give reasonable explanation about this phenomenon here,

(A): Thank you for your comment, we added some clarifications in the text.

I would also advice authors to consider a comparative experiment by investigating the effect of heat treatment and mechanical treatment on the surface state, i.e. the influence of annealing on the release of surface stress by using laser scan confocal microscope.

(A): Thank you for this advice. We can precise that this work is inscribed in a global research concerning the effect of mechanical treatment for BWR and PWR systems after maintenance operations. Heat treatments and local mechanical treatments may have effectively a beneficial effect and have to be taken into account and validated from BWR and PWR environment exposure.