Surface Optimization of Additively Manufactured (AM) Stainless Steel Components Using Combined Chemical and Electrochemical Post-Processing

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

The manuscript studies post-processing of AM 316/316L stainless steel using (i) electropolishing (EP), (ii) chemical polishing (CP), and (iii) electroless Ni–P plating (mid and high P), and applies a Taguchi L9 design to optimize factors including “nickel strike time,” surface preparation, build orientation, and bath phosphorus level. Surface roughness (Ra), scratch resistance (5 N), thickness, adhesion via ASTM B733 thermal shock, microscopy (KEYENCE), and SEM/EDS (Phenom XL) are reported.

• Taguchi design not fully/clearly executed. Several tables are inconsistent or contain placeholders/typos that make the L9 array unverifiable (e.g., “Table 1. 2, 3 for various impact factors,” repeated “Mid” under P level, confusing parenthetical numbers after “Surface Preparation,” and scrambled level labels). This prevents readers from reconstructing the DOE and the S/N and ANOVA analyses.
• Replication and error bars. Figures show single-value bars without explicit n, variance, or confidence intervals for Ra and scratch depth; Taguchi analysis requires replicated runs or at least clear S/N construction from repeated measures. The text later mentions “three new specimens” for validation, but full replicate counts per DOE cell are not provided.
• Scratch testing parameters incomplete. The 5 N load is given, but indenter type/radius, scratch length/speed, number of passes, and failure criteria are missing. The TABER 5900 reference is generic; standards (e.g., ASTM/ISO) for scratch should be cited and followed, or the method fully specified.
• Adhesion (ASTM B733 thermal shock) is described, yet only qualitative “no blistering” is reported; no micrographs, cross-sections, or quantitative adhesion (e.g., bend/peel) are provided, and cycle count deviates from the typical range without clear justification.
• Ni–P bath rate inconsistency. Earlier the mid-P bath is stated at 17 µm h⁻¹, while later Table A6 says 15 µm h⁻¹ average; thickness results (e.g., ~28–51 µm after 30 min) also appear incompatible with those deposition rates unless pre-existing layers or different calibration are involved. Clarify the actual plating time and thickness metrology (cross-section vs optical focus step).
• Roughness magnitudes and directionality. Ra values for “as-built” (~16–19 µm) dropping to 6–11 µm after EP/CP are plausible, but the increase of as-built Ra after Ni deposition (16.81 → 17.30 µm) attributed to “particular section area” implies high spatial heterogeneity; without areal maps and location-controlled sampling across orientations (XY/YZ/XZ), the Taguchi conclusions about “orientation” effects are weak.
• Method details missing/unsafe recipe reporting. EP bath is given as 70% H₃PO₄ / 30% H₂SO₄ at 75 °C and 70 A dm⁻²; this is extreme and warrants rigorous safety notes, agitation/cathode geometry details, and current distribution control. Similarly, CP bath lists wide ranges “10–30% H₃PO₄, 1–10% HCl, 1–10% HNO₃ + surfactants” at 75 °C—a mixture that can be exothermic and hazardous; exact compositions and stabilization protocols are essential for reproducibility.   

  

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript reports about the effect of different  (electropolishing, chemical polishing,. etc) post-processing methods for stainless steel that is additively manufactured.

I think that the topic is potentially interesting to the readers of Coatings,  that the method used to determine the best processing is sound and that the use of advanced statistical methods (ANOVA) to limit the number of experimental trials deserves consideration.

However the quality of the presentation is very poor and makes the manuscript hard to read and to follow. Several tables are mentioned in the text and are apparently not present due to wrong numbering.

Some important quantities are not explicitly defined (for example Rz, RzJis, Rp etc in several figures, S/N ratio which is negative in fig. 9 and positive in fig. 11 for the same variables !) so that it is difficult to assess the scientific soundness of the conclusions.

I report below a long list of comments that must be considered before the paper is given further consideration. I recommend a more careful presentation in the revised version.

1) Figure 3. Please describe in the caption in more details left and right panels and the meaning of orange, green, pink  reference points.

2) Fig. 4 is unclear. Clarify the meaning of Rz, Rzji, etc.
Only Ra seems to have been defined. The same comment holds also for fig. 5.

3) Line 314. Where is table A6 ?

4) Fig. 7. Why do the authors show only the results after Ni deposition for most samples  ?

5) Line 355. Where is table 3 ?
Use consistent numeration methods for tables (or Arabic or Roman, please not mixed !)

6) Fig. 9. The S/N ratio should be defined clearly. According to the usual definition (see e,g, https://real-statistics.com/design-of-experiments/taguchi-design-of-experiments/signal-to-noise-ratio/) the higher S/N the better is the behaviour. Why here the best conditions is identified with the less negative S/N?

Last but not least: how can S/N be negative ? Please clarify !

7) Fig. 11. The results shown in fig. 11 are quite different from those reported in Fig. 9 despite they apparently show the same information. I am confused and it is difficult to follow the arguments of the authors.

8) As for figs 4 and 5, also in fig. 12 and in fig. 13 the meaning of RZ, Rzijs,Rp and so on is not defined and not obvious. 

9) Table VI. What is the meaning of a negative improvement (-1.18 %) ?

10) Line 435. What is the sense of giving 4 digits in the values and in the error?

11) Table IX. What is the error on the atomic and weight concentrations ? I do not think the error is as low as 0.01 so also here the number of digits must be reduced.

 

Author Response

"Please see the attachment."

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

 In their reply the authors have answered all my questions satisfactorily an have revised the manuscripts considering my comments. 

The paper is quite long and a bit heavy to read but there is no doubt that its readability has improved with respect to the first version.

I think the authors should add as a reference also their recent paper:

The International Journal of Advanced Manufacturing Technology (2024) 134:1533–1546
https://doi.org/10.1007/s00170-024-14217-z

and briefly explain in their reply the novelty of the present manuscript with respect to this recent work.

Considering that the manuscript includes many details and a lot of informations potentially interesting for workers in the specific field I think it deserves to be published after this minor revision.

 

Author Response

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Author Response File: Author Response.pdf