Corrosion Resistance Properties of As-Sintered 17-4 PH Samples Additive-Manufactured Through Binder Jetting

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article investigates the corrosion properties and microstructural characteristics of steel 17-4 PH, made by the method of inkjet printing with the use of a metallic binder. Studies including cyclic potentiodynamic tests, open-circuit potential measurements, SEM-EDX microscopy, optical microscopy, and X-ray diffraction revealed that the sintered samples demonstrate isotropic corrosion behavior at various assembly orientations and directions. CPP tests indicate the formation of a passive film with limited stability, and OCP monitoring demonstrates initial instability followed by stabilization over time. Analysis of the microstructure revealed the presence of micropores and a structure consisting of martensitic and ferritic grains, as well as segregation of copper and niobium at grain boundaries, which can affect local susceptibility to corrosion. The study emphasizes the influence of microstructure on electrochemical characteristics and the need for targeted heat treatment to increase corrosion resistance. The results show comparable corrosion behavior with steel 17-4 PH, made by other methods of additive manufacturing, which use the sintering process.
At the same time, the article needs some improvement.
1. The article represents a valuable contribution to the understanding of the corrosion properties of 17-4 PH steel produced by the Metal Binder Jetting method. However, to increase its significance, it is necessary to more clearly define the research niche in the context of existing works on additive manufacturing and corrosion (Lines 52-60). Comparison with other technologies of additive manufacturing and emphasizing the uniqueness of MBJ will better indicate the novelty of this work. It should also be indicated what gaps in knowledge this research seeks to fill.
2. The authors should more clearly indicate the goals and objectives of the research, as well as specify what specific questions they plan to solve. For example, it is possible to specify that the goal is to determine the influence of the orientation of the seal and directionality on the corrosion resistance of steel 17-4 PH, made by the MBJ method, under certain environmental conditions.
3. The introduction does not contain a clear justification for the choice of steel 17-4 PH as a research object. It is important to indicate why this material is of interest from the point of view of corrosion resistance and additive manufacturing. It is also necessary to mention the areas of application of steel 17-4 PH, where corrosion resistance is a critically important parameter.
4. It is necessary to provide more detailed information about printing parameters, such as power, scanning speed, distance between layers, etc. These parameters can significantly affect the microstructure and properties of the material.
5. The authors should specify which criterion was used to determine the moment when the current density reached 0.1 mA·cm-2 in the CPP experiment, and also justify the choice of this criterion.
6. It is necessary to discuss in more detail the results of XRD analysis and explain why only peaks of the BCC phase are observed in as-sintered samples, and peaks of FCC and BCC phases are observed in wrought samples. It is also important to specify what factors can affect the phase composition of the material during additive manufacturing.
7. In addition, a more detailed analysis of the microstructure of the material should be provided, including grain size, grain shape, phase distribution, and the presence of defects. It is also important to indicate how these parameters can affect the corrosion resistance of the material.
8. Why is there no clear anodic passive region on the CPP curves? It is also necessary to discuss the possible causes of this phenomenon and its influence on the corrosion resistance of the material.
9. Possible reasons for the observed instability of the open circuit potential (OCP) in as-sintered samples should be discussed in more detail. It is also important to indicate what factors can affect the stability of the passive film.

Author Response

Notes and replies are in the pdf file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript addressed the important aspect of additive manufacturing methods – orientation of sample and direction of injection on protection against corrosion. The authors examined the electrochemical stability using electrochemical tests and microstructure analysis, including SEM-EDX and XRD. The manuscript is well-organized and clearly written. However, motivation to work, comparison with other groups, and some details need clarification. I recommend a minor revision before publishing.

Comments

1. Why did you conducted the investigation is unclearly stated in introduction. What is the motivation to consider different orientations of samples with respect to particles beam? Did you want to apply it on corrugated substrates? Clear statement is needed.
2. Abstract (L. 2729): “the as-sintered 17-26 4 PH fabricated through MBJ exhibits comparable corrosion behavior to 17-4 PH additive manufactured through other techniques in which the sintering process is involved. Further improvement of the localized corrosion resistance properties may be obtained through post-processing heat treatments.” I did not find any results on heat treatment and other techniques. These sentences are misleading and must be removed.
3. You are comparing the result with your previous publications. How does it compare with works by other groups? Comparison of electrochemical parameters such as corrosion current density and nobler corrosion potential with the-best-practice data is necessary. You may add the information in a form of a table.
4. L278: “... attacks at porosities or copper and niobium segregations is also unclear”. What did you want to emphasized? Also, references to a similar conclusion are needed.
5. L.328 : “While A45B45 shows 328 a higher instability, no surface corrosion was observed, suggesting… ” How did you decide it ?

Technical deficiency:

L.200: “revealed using Kalling’s (Fig. 3a) are characteristic of martensitic grains, in agreement” Missing word.

L275- “although it was not uncertain whether” (English?)

 

Author Response

Notes and replies are in the pdf file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript presents a comprehensive study on the corrosion behavior of 17-4 PH stainless steel fabricated via Metal Binder Jetting (MBJ), focusing on the effects of build-up orientation and direction on corrosion resistance. Electrochemical techniques, including cyclic potentiodynamic polarization (CPP) and open-circuit potential (OCP) monitoring were employed, supported by microstructural characterization (SEM-EDX, XRD, optical microscopy). There are some interesting observations. Many ambiguous points and mistakes need to be revised and clarified. The comments are as follows.
1.    Expand the literature review to cover the above points. A dedicated paragraph discussing the comparative corrosion performance of 17-4 PH stainless steel fabricated via BJM, PBF, ME, and traditional methods would improve the context and underscore the novelty of this study. This will also help readers better appreciate the observed isotropic behavior and the relevance of microstructural findings.
2.    The manuscript does not provide sufficient detail about the binder system composition, curing chemistry, or binder saturation parameters used in the Binder Jetting Manufacturing (BJM) process. Since the binder type and content significantly influence green part integrity, sintering behavior, residual carbon, and ultimately corrosion resistance, this information is critical for reproducibility and interpretation of results.
3.    Figure 3 presents optical micrographs of the A0B0 sample etched with Kalling’s and Vilella’s reagents. While the figure is described as revealing martensitic and ferritic grains, no direct phase labeling or microstructural annotations are provided in the images, which limits the clarity and usefulness of the figure for readers.
4.    The porosity fraction, pore size distribution, and grain size metrics are not quantitatively presented. These parameters are essential for understanding corrosion initiation and progression.
5.    In its current form, Table 2 reports the average chemical compositions of martensitic and ferritic grains, but Figure 4(a) does not clearly indicate which areas were analyzed to generate these data. This lack of visual correlation between the tabulated values and the microstructural features undermines the transparency and reproducibility of the analysis.
6.    “The CPP curves shown in Fig. 5 indicate a corrosion behavior similar to that of as-sintered 17-4 PH samples fabricated using the ME technique, as reported in a previous investigation [21].” However, no quantitative data or specific electrochemical characteristics from the ME-fabricated 17-4 PH samples are summarized or compared in the current manuscript. This makes it difficult for readers to assess the basis of the stated similarity or understand the extent to which the MBJ corrosion behavior aligns with or differs from the ME counterpart.
7.    Although EIS was mentioned in the methods, its data and discussion are absent. EIS could provide deeper insights into the passive film characteristics and support the CPP/OCP interpretations.
8.    “Although significant differences can be observed in the average values of icorr shown in Fig. 6, these values range between 0.1 and 0.9 µA·cm⁻², comparable to those of stainless steel passive films in neutral pH sodium chloride solutions, as reported in another study [21]. This indicates that a protective passive film may still form on the material surface despite the absence of a clear anodic passive trait of the CPP curves.” The formation of a passive film is usually supported not only by low icorr but also by a well-defined passive region in the anodic polarization curve and/or low passive current densities (ipass). Since no distinct passive plateau is observed in the CPP curves, additional evidence (e.g., EIS phase angle, XPS surface chemistry, or long-term OCP stabilization trends) would more robustly support the claim of passive film formation.
9.    The microstructural characterization is only performed on one build configuration (A0B0). This is insufficient to generalize claims about isotropy, especially given that other configurations may exhibit localized heterogeneities.
10.    While the manuscript attributes some instability to Cu/Nb segregation, the exact electrochemical mechanisms remain speculative. The role of these segregates as anodic/cathodic sites should be probed further by using EPMA.

Comments on the Quality of English Language

None

Author Response

Notes and replies are in the PDF file.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This is a well-made paper on Corrosion Resistance Properties of As-Sintered 17-4 PH Samples Additive-Manufactured through Binder Jetting. The paper is scientifically solid and well suited to the scope of the journal and the field of interest. The presentation is good, but more details are needed.

In general, the paper does a good job and is well suited to the scope of the journal and the field of interest.

Comment 1: In lines 187 and 188, the meanings of the FCC and BCC are missing.

Comment 2: In Figure 4 it is necessary to identify ferrite and martensite in the figure.

Comment 3: In the section Results and Discussion, the results obtained for CPP curves need to be better discussed, for example, the authors do not discuss how the parameters E_corr and E_pit vary.

 

Author Response

Notes and replies are in the PDF file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors of the article have done a significant job of addressing my comments, but in a number of areas the corrections require further clarification and depth.

Printing and sintering parameters. Even if the parameters are not disclosed by the system, the authors should at least indicate the temperature range and typical heating profile (from the literature or Desktop Metal technical documentation).

Quantitative microstructural assessment. The lack of data on grain size, porosity, phase density, and inclusion distribution limits the depth of analysis. Without these data, it is difficult to judge the influence of microstructure on electrochemical properties.

Early OCP. Although instability after 24 h is assessed, the analysis of the passive film behavior at the early stage (0–6 h) remains insufficiently detailed. It would be useful to correlate the initial instability peaks with the observed microstructural defects.

Author Response

Notes and replies are in the pdf file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The revision adds useful background text, labels several figures, and supplies some new electrochemical data, yet several core issues raised by the reviewer remain unanswered or only partially addressed. In particular (1) key experimental parameters for Binder-Jetting (BJ) and sintering are still missing, (2) critical quantitative microstructural metrics are not supplied, and (3) mechanistic evidence for passive-film formation and the role of Cu/Nb segregates is still largely speculative. The replies often defer requested work to “future studies”; this is not acceptable for a final revision.

Author Response

Notes and replies are in the PDF file.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript has been revised to meet the comments' requirements. It can be accepted.