Influence of Processing Conditions on the Mechanical Properties of 17-4PH Specimens Produced by Additive Manufacturing

Round 1

Reviewer 1 Report

The paper presents interesting results and I think it is suitable for publication in this special issue of the journal. Improvements are needed, especially in the way the results are presented:

- Abbreviations must be detailed on first use, including in the abstract. Figures and tables should be positioned next to the paragraph in which they are cited.

- I think the introduction needs to be improved. Citations 4-11 are some general ones. It should be detailed what the authors conclude. Could the bibliography be improved?

- The diagrams in figure 7 are difficult to analyse because of the positioning of three different scales. I think different diagrams can be generated for each parameter.

-Interpretation of the scatter of the results is needed (from 614 MPA to 1074 MPa, UTS, samples 2.1, 2.2 and 2.3 ???).

-Tables 2 and 3 show the same data as figures 7 and 8?

Author Response

Dear Reviewer,

1. “The paper presents interesting results and I think it is suitable for publication in this special issue of the journal.”

AR: Thank you very much for your comment.

2. “Improvements are needed, especially in the way the results are presented.”

AR: We have improved the data presentation; we hope everything is clearer now.

3. “Abbreviations must be detailed on first use, including in the abstract.”

AR: Thank you for your observation, the manuscript has been revised to detail every abbreviation.

4. “Figures and tables should be positioned next to the paragraph in which they are cited.”

AR: We appreciate the comment, we found some mistakes with the numbering of the figures.

5. “I think the introduction needs to be improved.”

AR: Thank you very much for noticing this. We have added the objectives of this research to the introduction, it is indeed true that the introduction was missing one main and important paragraph (displayed in comment number 7). This new paragraph has been incorporated.

The bibliography has also been improved with more specific and recent references.

“The aim of this research has been the development of specimens made from starting powders with a chemical composition similar to the 17-4PH steel, produced under different manufacturing conditions via PMD, to determine the influence of their operational parameters and thermal treatments in their final properties.”

6. “Citations 4-11 are some general ones.”

AR: As previously commented, we have added more specific and recent references. Here down below, the new bibliography in this section is displayed:

9. Jessy Michla, J.R.; Ravikumar, B.; Ram Prabhu, T.; Siengchin, S.; Arul Kumar, M.; Rajini, N. Effect of nitriding on mechanical and microstructural properties of Direct Metal Laser Sintered 17-4PH stainless steel. J Mater Res Technol 2022, 19, 2810–2821. doi:10.1016/J.JMRT.2022.05.198
10. Yang, K.T.; Kim, M.K.; Kim, D.; Suhr, J. Investigation of laser powder bed fusion manufacturing and post-processing for surface quality of as-built 17-4PH stainless steel. Surf Coat Technol 2021, 422, 127492. doi:10.1016/J.SURFCOAT.2021.127492
11. Guennouni, N.; Maisonnette, D.; Grosjean, C.; Poquillon, D.; Blanc, C. Susceptibility to Pitting and Environmentally Assisted Cracking of 17-4PH Martensitic Stainless Steel Produced by Laser Beam Melting. Materials 2022, 15(20), 7121. doi:10.3390/ma15207121
12. “It should be detailed what the authors conclude.”

AR: As specified in your suggestion number 5, we have added a paragraph with the main goals to achieve with this research.

“The aim of this research has been the development of specimens made from starting powders with a chemical composition similar to the 17-4PH steel, produced under different manufacturing conditions via PMD, to determine the influence of their operational parameters and thermal treatments in their final properties.”

8. “Could the bibliography be improved?”

AR: We have updated the bibliography with more specific and recent references. The ones added are the following ones:

2. Ding, H.; Bao, X.; Jamili-Shirvan, J.; Jin, J.; Deng, L.; Yao, K.; Gong, P.Wang, X. Enhancing strength-ductility synergy in an ex situ Zr-based metallic glass composite via nanocrystal formation within high-entropy alloy particles. Mater Des 2021, 210, 110108. doi: 1016/j.matdes.2021.110108
3. Thawon, I.; Fongsamootr, T.; Mona, Y.; Suttakul, P. Investigation of the Mechanical Properties of Additively Manufactured Metal Parts with Different Relative Densities. Appl Sci 2022, 12(19), 9915. doi:10.3390/app12199915
4. Jessy Michla, J.R.; Ravikumar, B.; Ram Prabhu, T.; Siengchin, S.; Arul Kumar, M.; Rajini, N. Effect of nitriding on mechanical and microstructural properties of Direct Metal Laser Sintered 17-4PH stainless steel. J Mater Res Technol 2022, 19, 2810–2821. doi:10.1016/J.JMRT.2022.05.198
5. Yang, K.T.; Kim, M.K.; Kim, D.; Suhr, J. Investigation of laser powder bed fusion manufacturing and post-processing for surface quality of as-built 17-4PH stainless steel. Surf Coat Technol 2021, 422, 127492. doi:10.1016/J.SURFCOAT.2021.127492
6. Guennouni, N.; Maisonnette, D.; Grosjean, C.; Poquillon, D.; Blanc, C. Susceptibility to Pitting and Environmentally Assisted Cracking of 17-4PH Martensitic Stainless Steel Produced by Laser Beam Melting. Materials 2022, 15(20), 7121. doi:10.3390/ma15207121
7. Bouaziz, M.A.; Djouda, J.M.; Chemkhi, M.; Rambaudon, M.; Kauffmann, J.; Hild, F. Heat treatment effect on 17-4PH stainless steel manufactured by Atomic Diffusion Additive Manufacturing (ADAM). Procedia CIRP 2021, 104, 935–938. doi:10.1016/J.PROCIR.2021.11.157
8. “The diagrams in figure 7 are difficult to analyse because of the positioning of three different scales. I think different diagrams can be generated for each parameter.”

AR: We agree that it could be complicated to find the results with so many axes. To simplify, the authors decided this kind of representation. If more detail info is necessary, Table 2 lists all the properties values.

10. “Interpretation of the scatter of the results is needed (from 614 MPA to 1074 MPa, UTS, samples 2.1, 2.2 and 2.3 ???).”

AR: It is discussed in the manuscript the problem that we found with the specimens built under argon and the post thermal treatment TT1. Those samples showed a fragile behaviour, the elongation values fluctuated around 0.35% and 3.47%. As you have pointed out, we find commendable to extend the “non-representative” note for the other properties values in these specimens.

11. “Tables 2 and 3 show the same data as figures 7 and 8?”

AR: This affirmation is true, but we find figures and tables, both necessary. Within the figures, the comparison among the values could be easily done; the tables show the exact values and their deviations, otherwise, in the figures would be very complicated to get these results.

We hope, after all the corrections that we have applied, this manuscript could be found satisfactory and considered for publication.

  Sincerely yours,

The Authors

Reviewer 2 Report

The paper is totally fine. It can be accepted for publication after major revision.

Some suggestions:

1. The abstract and conclusion parts are too long. They should be condensed.

2. More details about the experiments should be given. e.g., the scanning speed for the XRD tests, etc.

3. What are the main scientific contributions of this paper? The authors have to mentioned this point in the introduction.

4. What are the main reasons selecting the parameters for additive manufacturing?

5. Figure 7: it is better to provide the corresponding stress-strain curves.

6. Figure 5 and Figure 6 can be merged.

7. The caption for Figure 10: there are two e).

8. Figure 11, the label is too small.

9. The discussion part is too short. More discussions in depth should be given.

10. It is better to cite some recent papers about powder metallugy for metals and alloys .e.g., Material and design, 2021, 210:110108

Author Response

Dear Reviewer 

1. “The abstract and conclusion parts are too long. They should be condensed.”

AR: The abstract is limited by the journal to 200 words, and ours is 197. Regarding the conclusions, we agree with your comment and some of the paragraphs have been moved to the discussion section. The discussions and the conclusions now stay as follows:

“4. Discussions

The manufacturing parameters were suitable to produce specimens as-built that exhibited both an appropriate densification and an imperceptible segregation phenomenon, being the hardness measured in the specimens as-built in agreement with the reference values. Moreover, the XRD patterns of the as‑built specimens resembled previous results, confirming in this way the validity of the PMD parameters.

The behaviour of the as-built specimens was close to the standard values of those specimens manufactured by traditional techniques. The PMD technique might then be used in the case when an improvement in the manufacturing procedure with respect to traditional techniques can be observed and a favourable cost-benefit ratio.

The microstructural study and the XRD analysis confirmed the presence of martensitic phase, delta ferrite, and austenite, which affected the final properties of the specimens. Austenite was primarily encountered in argon processed samples, which confirms the initial results that these specimens are less hard than those conformed in air, despite the subsequent treatment applied. Regarding the ferrite phase, when comparing the content in each set of samples, a clear pattern can be discerned; this is in accordance with what was presented in the mechanical properties: the more ferrite phase, the less bending behaviour can be found. In as-built and TT1 samples, a decrease in elongation can be reported in argon walls compared to those manufactured in air; the opposite case is given in the TT2 samples, as the elongation is greater in the argon samples congruent with the decrease in the ferrite phase. It is noticeable that the presence and amount of the retained austenite phase may significantly influence the strength, toughness, strain hardening, and elongation to failure of the specimen, as previously reported [37].

The apparition of austenite could present cracks due to a phase transformation provoked by the shift in volume. Copper precipitates are not observed after hardening treatments sponsored by the TT1 thermal treatment.

Regarding TT2, as mentioned earlier, a significant increase in the percentage of elongation has been reported in both air and argon manufactured walls. This elongation improvement can be extremely useful when the piece made under this thermal treatment is placed in a critical or sensitive position. Before breaking, it will be misshaped as a warning signal of a nearby failure, in contrast to hard materials, which can break in a fragile way without any previous notice.

The above mentioned can be crucial in, for example, the aerospace sector, which demands an extensive safety and certain level of flexibility. This new method, alongside others that are currently under study and perfection, can prove invaluable in the outcome of new material developments and composites, which are constantly demanded for future developments in material engineering research and industrial applications.

5. Conclusions

In this research, two walls of a powder with the same composition as the 17-4PH steel were used as raw material to perform an advanced and newfangled additive manufacturing technique known as PMD in air and argon surrounding atmospheres. Furthermore, two thermal treatments (TT1 and TT2) were performed on various to evaluate the improvement or worsening of certain mechanical properties. After a detailed characterization and study of their measured properties and the analysed microstructures, the following conclusions can be drawn:

• The specimens processed in air showed less content of the austenitic retained phase, which addresses mechanical properties better than those produced in argon. Furthermore, the embrittlement effect of interdendritic δ ferrite was detected in specimens that suffered TT1.
• In the framework of thermal treatments, due to variations in phases during processing and thermal treatments, the mechanical properties of the specimens were affected by these treatment effects: i) TT1 was suitable to achieve improvements in Young’s modulus and yield strength values of the specimens, at the cost of elongation decrement; ii) TT2 was successful in improving the elongation, contributing to the remaining acceptable UTS values.
• Consistent with the mechanical and physical properties, the tribological behaviour in the TT1 treated samples matches the hardness values obtained.”

2. “More details about the experiments should be given. e.g., the scanning speed for the XRD tests, etc.”

AR: We agree your comment. We have added the required information:

“XRD analysis was carried out on a Bruker D8 Advance A25 equipment (Billerica, MA, USA) with Cu-K_α radiation of wavelength 1.5418 Å at scanning angle (2θ) in the range of 0° to 120°.”

3. “Abbreviations must be detailed on first use, including in the abstract.”

AR: Thank you for your comment, the manuscript has been revised to detail every abbreviation.

4. “What are the main scientific contributions of this paper? The authors have to mentioned this point in the introduction.”

AR: Thank you very much for noticing this. We have added the objectives of this research to the introduction, it is indeed true that the introduction was missing one main and important paragraph. Accordingly, we have added a paragraph with the main goals to achieve with this research.

“The aim of this research has been the development of specimens made from starting powders with a chemical composition similar to the 17-4PH steel, produced under different manufacturing conditions via PMD, to determine the influence of their operational parameters and thermal treatments in their final properties.”

5. “What are the main reasons selecting the parameters for additive manufacturing?”

AR: They were selected according to the authors’ background.

6. “Figure 7: it is better to provide the corresponding stress-strain curves.”

AR: Due to the embrittlement of the specimens, some of the curves were not easily intelligible.

7. “Figure 5 and Figure 6 can be merged.”

AR: The figures have been merged as requested. Thank you very much for your recommendation.

8. “The caption for Figure 10: there are two e).”

AR: Thank you very much for noticing this mistake. It has been corrected; indeed, the second “e” was really an “f”.

9. “Figure 11, the label is too small.”

AR: We agree with your comment. The figure has been improved.

10. “The discussion part is too short. More discussions in depth should be given.”

AR: Thank you for your observations. Regarding to the discussion of the results, there was an improvement of this section of the manuscript in order to clarify the understanding of the achieved results.

“4. Discussions

The manufacturing parameters were suitable to produce specimens as-built that exhibited both an appropriate densification and an imperceptible segregation phenomenon, being the hardness measured in the specimens as-built in agreement with the reference values. Moreover, the XRD patterns of the as‑built specimens resembled previous results, confirming in this way the validity of the PMD parameters.

The behaviour of the as-built specimens was close to the standard values of those specimens manufactured by traditional techniques. The PMD technique might then be used in the case when an improvement in the manufacturing procedure with respect to traditional techniques can be observed and a favourable cost-benefit ratio.

The microstructural study and the XRD analysis confirmed the presence of martensitic phase, delta ferrite, and austenite, which affected the final properties of the specimens. Austenite was primarily encountered in argon processed samples, which confirms the initial results that these specimens are less hard than those conformed in air, despite the subsequent treatment applied. Regarding the ferrite phase, when comparing the content in each set of samples, a clear pattern can be discerned; this is in accordance with what was presented in the mechanical properties: the more ferrite phase, the less bending behaviour can be found. In as-built and TT1 samples, a decrease in elongation can be reported in argon walls compared to those manufactured in air; the opposite case is given in the TT2 samples, as the elongation is greater in the argon samples congruent with the decrease in the ferrite phase. It is noticeable that the presence and amount of the retained austenite phase may significantly influence the strength, toughness, strain hardening, and elongation to failure of the specimen, as previously reported [37].

The apparition of austenite could present cracks due to a phase transformation provoked by the shift in volume. Copper precipitates are not observed after hardening treatments sponsored by the TT1 thermal treatment.

Regarding TT2, as mentioned earlier, a significant increase in the percentage of elongation has been reported in both air and argon manufactured walls. This elongation improvement can be extremely useful when the piece made under this thermal treatment is placed in a critical or sensitive position. Before breaking, it will be misshaped as a warning signal of a nearby failure, in contrast to hard materials, which can break in a fragile way without any previous notice.

The above mentioned can be crucial in, for example, the aerospace sector, which demands an extensive safety and certain level of flexibility. This new method, alongside others that are currently under study and perfection, can prove invaluable in the outcome of new material developments and composites, which are constantly demanded for future developments in material engineering research and industrial applications.”

11. “It is better to cite some recent papers about powder metallugy for metals and alloys .e.g., Material and design, 2021, 210:110108.”

AR: In this regard, the recommended reference has been added, as long with others in the bibliography.

2. Ding, H.; Bao, X.; Jamili-Shirvan, J.; Jin, J.; Deng, L.; Yao, K.; Gong, P.Wang, X. Enhancing strength-ductility synergy in an ex situ Zr-based metallic glass composite via nanocrystal formation within high-entropy alloy particles. Mater Des 2021, 210, 110108. doi: 1016/j.matdes.2021.110108
3. Thawon, I.; Fongsamootr, T.; Mona, Y.; Suttakul, P. Investigation of the Mechanical Properties of Additively Manufactured Metal Parts with Different Relative Densities. Appl Sci 2022, 12(19), 9915. doi:10.3390/app12199915
4. Jessy Michla, J.R.; Ravikumar, B.; Ram Prabhu, T.; Siengchin, S.; Arul Kumar, M.; Rajini, N. Effect of nitriding on mechanical and microstructural properties of Direct Metal Laser Sintered 17-4PH stainless steel. J Mater Res Technol 2022, 19, 2810–2821. doi:10.1016/J.JMRT.2022.05.198
5. Yang, K.T.; Kim, M.K.; Kim, D.; Suhr, J. Investigation of laser powder bed fusion manufacturing and post-processing for surface quality of as-built 17-4PH stainless steel. Surf Coat Technol 2021, 422, 127492. doi:10.1016/J.SURFCOAT.2021.127492
6. Guennouni, N.; Maisonnette, D.; Grosjean, C.; Poquillon, D.; Blanc, C. Susceptibility to Pitting and Environmentally Assisted Cracking of 17-4PH Martensitic Stainless Steel Produced by Laser Beam Melting. Materials 2022, 15(20), 7121. doi:10.3390/ma15207121
7. Bouaziz, M.A.; Djouda, J.M.; Chemkhi, M.; Rambaudon, M.; Kauffmann, J.; Hild, F. Heat treatment effect on 17-4PH stainless steel manufactured by Atomic Diffusion Additive Manufacturing (ADAM). Procedia CIRP 2021, 104, 935–938. doi:10.1016/J.PROCIR.2021.11.157

We hope, after all the corrections that we have applied, this manuscript could be found satisfactory and considered for publication.                                           

Sincerely yours

The authors

Round 2

Reviewer 1 Report

The authors have improved the paper, taking into account most of the suggestions from the first review.

I think the introduction and the way of citing references could be improved.

Author Response

Dear Reviewer 

these are the required changes:

1. “The authors have improved the paper, taking into account most of the suggestions from the first review.”

AR: Thank you very much for your comment.

2. “I think the introduction and the way of citing references could be improved.”

AR: We have improved the introduction and our way of citing, as you requested. Here down you can find attached the sentences modified:

“The literature shows that the nature of the initial condition of the 17-4PH powder feedstock has a direct impact on the final properties of the additive-manufactured deposited material [1].”

“Moreover, in AM, the use of powders as raw materials and the possibility of making parts with near-net shapes encourage the use of this technique as a promising alternative to conventional manufacturing routes, improving the fabrication of final components in terms of sustainability and reducing the environmental impact [3-5].”

“This technique can open up a wide range of possibilities in the field of engineering, as it allows extremely complex patterns to be obtained in a single piece, which would be inconceivable in traditional machining proceedings, as conformal cooling channels [18].”

“Although the 17-4PH alloy is commonly used in many industrial applications and that the mentioned thermal treatments generally improve its mechanical properties [20-21], up to this point, no comparisons have been reported among specimens produced by PMD under different environmental conditions (air and argon), nor post-production treatment.”

18. Pragana, J.P.M; Braganca, I.M.F; Silva, C.M.A; Martins, P.A.F. Hybrid Wire-Arc Additive Manufacturing od Conformal Cooling Channels: A Feasibility Study. International Journal of Precision Engineering and Manufacturing-Green Technology 2022. doi: 10.1007/s40684-022-00436-w.

Reviewer 2 Report

Thanks for the nice revision.

Author Response

Dear Reviewer,

We really appreciate your words, thank you very much.