Features of Cathodic Plasma Electrolytic Nitrocarburizing of Low-Carbon Steel in an Aqueous Electrolyte of Ammonium Nitrate and Glycerin

Round 1

Reviewer 1 Report

Performed experiment shows promising results of described method for low-carbon steel treatment, based on measured key features. In a conclusion section, it could be noted, if this research can be the basis for further follow-up researches. In the "2. Material and Methods" section would be appropriate, to acquaint the reader about the number of experimental samples.

Which sample is depicted in Figure 9?

Which PENC time could be optimal for used material, according to obtained resulting data of experiment?

Beside the improvement of enviromental friendliness of production, are there any other positives of application of used electrolyte for cathodic PENC, in comparison with anodic PENC? 

 

 

 

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

1. It is hard to find the top surface boundaries of the “oxide layer” in Fig.4, which should be marked or shown clearly. Especially, the thickness of the top surface compound layers and the diffusion layers should be marked clearly in the Fig.4 and the values should be stated in the text.

2. The definition of the “oxide layer” is questionable, there should also be the existence of carbon and nitrogen in the top layer.

3. For comparison, the whole track morphologies of untreated and cathodic PENC treated samples should be given in Fig.9.

4. In Kinetic calculations, how to choose the concentration of carbon and nitrogen on the top surface (C^s)?

5. There will be a big error for the concentration of carbon or nitrogen obtained from EDAX, some other methods, such as EPMA is recommended.

6. Is it possible to get the surface hardness? Surface hardness should be more important to influence the wear resistance of the cathodic PENC treated samples.

7. Except for corrosion current density, there is no corrosion potential and other parameters, therefore, it is hard to say that the corrosion resistance of the sample treated for 20 min is good or not.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Thanks for the improvement. There are still some questions need to be considered:

1. In Fig.4, top surface of the oxide layers for PENC 15min and PENC 20min samples can not be seen, which should be displayed clearly for determining the thicknesses of the oxide layers. Thickness of the oxide layer seems not to increase evidently with the treated time. Moreover, (a), (b), (c) and (d) should be marked in each of the image.

2. Since the contents of carbon and nitrogen tested by EDX are only semi-quantitatively, the calculated diffusion coefficients of carbon and nitrogen will be less meaningful.

3. In the present investigation, the out oxide layers (over 100um) should be characterized in detail, which should play vital effects on the wear resistance and corrosion resistance of the modified layer. As for the inner diffusion layer, its influence may be limited.

4.The XRD spectra in Fig.2 should mainly come from the oxide layers. Moreover, the distribution of oxygen and the hardness distribution along the oxide layer should be characterized.

5. From Fig.10, the corrosion potentials of all the modified samples (including the sample treated for 20min) decrease apparently, which should indicate the deterioration of the corrosion resistance. That is, it is questionable to say the corrosion resistance improvement for the PENC sample treated for 20 min, though its corrosion current density decreased. Some other method, such as EIS is recommended for further study.

 

Author Response

Dear Reviewer

We answered your questions and improved the manuscript. Please see the attachment.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

Thanks for the improvement.