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Study on Debinding and Sintering Conditions in Extrusion-Based Additive Manufacturing of 316L and 316L + Cu

Metals 2023, 13(11), 1858; https://doi.org/10.3390/met13111858

by Jean-François Silvain^1,2,*, Daniel Lincoln Gifford¹, Sébastien Fourcade¹, Laurent Cuzacq¹

, Jean-Luc Grosseau-Poussard³, Catherine Debiemme-Chouvy⁴

, Nicolas Tessier Doyen⁵ and Yongfeng Lu²

Reviewer 1:

Maksim Krinitcyn

Reviewer 2: Anonymous

Reviewer 3: Anonymous

Reviewer 4: Anonymous

Metals 2023, 13(11), 1858; https://doi.org/10.3390/met13111858

Submission received: 10 October 2023 / Revised: 2 November 2023 / Accepted: 3 November 2023 / Published: 7 November 2023

(This article belongs to the Special Issue New Trends of Powder Engineering and Additive Manufacturing (Editorial Board Members’ Collection Series))

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors presented a work on the material extrusion additive manufacturing (MEAM) of feedstock with 316L steel and copper. The work is relevant and presents significant results on the topic. However, the work requires serious adjustments.

A general notes about the article:

- It is necessary to expand section 2 and describe in more detail the methods used in the article.

- The graphical presentation of the results should be improved; in some places raw graphs and illustrations are provided. Also, some terms should be checked for correct application.

- The purpose of the work is not clear - many different tests of samples have been carried out, but integrity and logic are not obvious; it is necessary to more clearly formulate the purpose of the study and set the necessary objectives. For what applications is it planned to use the developed material? Based on this, you should select specific parameters to measure and their values, the shape of the samples, and so on. For example, might thermal conductivity be more important for samples than hardness or porosity?

In my opinion, the article is not yet ready for publication and needs to be seriously reworked. Here are some points I noted:

1) The title is long and confusing - the title should be shortened, focusing on one key feature of the manuscript.

2) The number of references to the literature needs to be increased; in particular, in the introduction there is little literature devoted specifically to the materials under study. Conclusions are drawn based on an analysis of a small number of relevant articles. It is recommended to expand the number of citations, in particular it is recommended to add the following articles:

https://doi.org/10.1016/j.prostr.2022.12.158

https://doi.org/10.1016/j.engfracmech.2023.109544

3) Line 166 – HOW?

4) Line 169-174 – it is necessary to quantitatively confirm the above conclusions, in particular, to provide the rheological properties of the compositions used.

5) Рисунок 1б – small pores have a repeating pattern. Accordingly, the reason is non-optimal printing parameters. It is necessary to vary printing parameters, in particular layer thickness and extrusion ratio. Have such studies been conducted? Printing parameters are not provided anywhere.

6) Line 196 – please provide TGA results (curves) in the manuscript.

7) Lines 86, 140, 198 – “ramp rate” is usually used for generators, “heating rate” is more suitable here I suppose.

8) Lines 194-202 – why 700 °C was the maximum investigated temperature?

9) How did you measure the carbon content? Please, describe in section 2.

10) Line 210 – please, specify the heating elements that you use in your furnaces. If you use LaCrO3 heating elements they may also cause the formation of chromium oxides on the surfaces.

11) The article provides few illustrations of the structure (SEM data). For example, in supplementary Figure S1, a color gradient is visible on the samples; accordingly, the structure should be different in different parts of the sample.

12) Line 238 – XRD pattern is mentioned, but only one XRD spectrum is provided. Please, provide all related XRD spectra to see the dynamics. In addition, the reflexes are not indexed (but (111) is mentioned in text), and the axes have incorrect designations.

13) In lines 241-245 the theory of silicon oxide formation is briefly discussed, however there are no proofs are provided. Please, add some experimental proofs or exclude this part.

14) Fig. 3 and before – you use “Relative density” but, however, do not provide the reference number for 100%. It is not an easy task to calculate relative density in composites with mutual dissolvable components. Please, specify the 100% density for all composites.

15) Lines 268-270 are ambiguous since EDS is not the best tool to proof diffusion of Cu to steel. TEM with SAED can proof it much better.

16) Please provide color legend for figure 4b and 4d, not only verbal description.

17) The load and dwell time for Vickers hardness is not provided. The method is not described in section 2 at all.

18) It is a fairly common fact that density is related to hardness. When measuring hardness, you are measuring the hardness of a sample, not the pure material. In this way, you characterize the material by understanding what hardness the sample has at a certain porosity. The authors did not set a goal to achieve maximum hardness; perhaps this is not necessary for certain tasks.

Author Response

Reviewer #1

Review comments:

A general note about the article:

- It is necessary to expand section 2 and describe in more detail the methods used in the article.

Reply: Done

- The graphical presentation of the results should be improved; in some places raw graphs and illustrations are provided. Also, some terms should be checked for correct application.

Reply: Done

Reply: The following sentences have been added in the introduction part in order to clarify the purpose of this study.

While a good deal of research has been conducted on printing 316L using EAM and MIM processes, most studies involve debinding steps with hazardous hexane or heptane solvents. Sintering temperatures for 316L powder are also above 1200 °C and close to 1400 °C under pure hydrogen atmosphere. In order to undergo that specific conditions, this paper studies variations in the post treatment of 316L extruded parts.

In my opinion, the article is not yet ready for publication and needs to be seriously reworked. Here are some points I noted

Reply: The authors would like to thank the reviewers for the positive feedback and time taken to review our manuscript.

Comment 1: The title is long and confusing - the title should be shortened, focusing on one key feature of the manuscript.

Reply: New title

Study on debinding and sintering conditions in extrusion-based additive manufacturing of 316L and 316L+Cu

Comment 2: The number of references to the literature needs to be increased; in particular, in the introduction there is little literature devoted specifically to the materials under study. Conclusions are drawn based on an analysis of a small number of relevant articles. It is recommended to expand the number of citations, in particular it is recommended to add the following articles:

https://doi.org/10.1016/j.prostr.2022.12.158

https://doi.org/10.1016/j.engfracmech.2023.109544

Reply: These references have been added.

Comment 3: Line 166 – HOW?

Reply: HOW has been removed

Comment 4: 4. Line 169-174 – it is necessary to quantitatively confirm the above conclusions, in particular, to provide the rheological properties of the compositions used.

Reply: The following sentences have been added in section 2.1.

Obtaining parts by AM by material extrusion requires that the feedstock exhibit appropriate rheological behavior throughout the shaping stage. During extrusion the material will undergo an intense shear gradient going from zero shear corresponding to the state of rest in the packaging container, to high shear as it passes through the nozzle and finally shear weak gravity induced on the extruded bead. The rheological properties that govern these transitions are: material viscosity, viscoelastic modulus, viscosity recovery behavior, and shear stress. From an experimental point of view, the higher the viscosity of a system, the higher the fidelity during deposition and the better the shape retention properties after extrusion. A material exhibiting ideal behavior must therefore have a low viscosity for shear rates (corresponding to the conditions of the extrusion shaping step) and a sufficiently high viscosity at rest (zero shear) to limit the deformation of the structure. All of the paste fabricated in this study have that particular behaviors.

Comment 5: Рисунок 1б – small pores have a repeating pattern. Accordingly, the reason is non-optimal printing parameters. It is necessary to vary printing parameters, in particular layer thickness and extrusion ratio. Have such studies been conducted? Printing parameters are not provided anywhere.

Reply: The purpose of this study and this paper is to work on debinding and sintering conditions. Printing parameters can be found in Table S1.

Comment 6: Line 196 – please provide TGA results (curves) in the manuscript.

Reply: Done in Figure S1

Comment 7: Lines 86, 140, 198 – “ramp rate” is usually used for generators, “heating rate” is more suitable here I suppose.

Reply: Ramp rate has been removed and change to heating rate

Comment 8: Lines 194-202 – why 700 °C was the maximum investigated temperature?

Reply: Samples debinded at 400 °C showed no discernable visual appearance and had the highest carbon content. Samples debinded at 700 °C showed a distinct dark blue color and a hard exterior. Carbon contents are also only slightly improved from 500 °C. In order to minimize this oxide growth, the temperature for subsequent thermal treatments was kept at 500 °C.

Comment 9: How did you measure the carbon content? Please, describe in section 2.

Reply: This sentence has been added:

Carbon contents were measured using a CS800 Carbon-Sulfur Determinator from Eltra. Initial carbon content for the 316L powder was 0.0301 wt.% +/- 0.002.

Comment 10: Line 210 – please, specify the heating elements that you use in your furnaces. If you use LaCrO3 heating elements they may also cause the formation of chromium oxides on the surfaces

Reply: The samples were placed in cylindrical alumina crucibles and the heating elements of the furnace are made of graphite

Comment 11: The article provides few illustrations of the structure (SEM data). For example, in supplementary Figure S1, a color gradient is visible on the samples; accordingly, the structure should be different in different parts of the sample.

Reply: Yes. Figure 5 shows SEM analysis of the sinter materials

Comment 12: Line 238 – XRD pattern is mentioned, but only one XRD spectrum is provided. Please, provide all related XRD spectra to see the dynamics. In addition, the reflexes are not indexed (but (111) is mentioned in text), and the axes have incorrect designations.

Reply: Authors have added XRD after sintering in Figure S3 in order to answer the demand of the reviewer

Figure S3. XRD spectra for (a) pure 316L powder, (b) sample before sintering, (c) sample after sintering for 5 hours

Comment 13: In lines 241-245 the theory of silicon oxide formation is briefly discussed, however there are no proofs are provided. Please, add some experimental proofs or exclude this part.

Reply: This part has been excluded

Comment 14: Fig. 3 and before – you use “Relative density” but, however, do not provide the reference number for 100%. It is not an easy task to calculate relative density in composites with mutual dissolvable components. Please, specify the 100% density for all composites.

Reply: Table 3 has been added in order to add the density of the different fabricated materials

		316L	316L + 10% Cu	316L + 20% Cu
0 hour	Relative density (%)	52.17	56.10	59.57
0 hour	Density (g/cm³)	4.12	4.43	4.70
5 hours	Relative density (%)	70.40	75.65	87.40
5 hours	Density (g/cm³)	5.36	6.05	6.99
10 hours	Relative density (%)	80.00	86.10	88.70
10 hours	Density (g/cm³)	6.49	6.98	7.19

Table 3. Relative density and density of the 316L, 316L + 10% Cu and 316L + 20% cu for the three-annealing time (0 hour, 5 hours and 10 hours)

Comment 15: Lines 268-270 are ambiguous since EDS is not the best tool to proof diffusion of Cu to steel. TEM with SAED can proof it much better.

Reply: Yes, you are wright. STEM (EDS) analysis will be a nice tool to analyze the diffusion behavior during sintering. However, lack of time didn’t allow us to perform that kind of study.

Comment 16: Please provide color legend for figure 4b and 4d, not only verbal description.

Reply: Legend of the different phases have been added on the figure (figure 5 now)

Comment 17: The load and dwell time for Vickers hardness is not provided. The method is not described in section 2 at all.

Reply: Method has been added in section 2

Hardness values are averages of 10 measurements determined by indenting a pyramidal diamond piece with force of 5 kgf (49 N) during 15 s, on polished surface (WILSON Hardness, Vickers 452 SVD). The dimension (D) of the imprint on the surface allow to determine the hardness of the composite material, using the following formula:

where HV is the hardness Vickers, F the force applied and D, the average dimensions of diagonals of imprint.

Comment 18: It is a fairly common fact that density is related to hardness. When measuring hardness, you are measuring the hardness of a sample, not the pure material. In this way, you characterize the material by understanding what hardness the sample has at a certain porosity. The authors did not set a goal to achieve maximum hardness; perhaps this is not necessary for certain tasks

Reply: Yes. We agree with the remark of the referee. Maximum hardness was not a final goal of this study.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Manuscript provides information on the new material for additive manufacturing and its properties. In my opinion manuscript needs improvement mainly in the methods description. It's impossible to review the results without properly described methods. Also, data presentation must be improved with additional statistical errors. Some other remarks:

1) Line 163 – what are hardness measurement conditions? The same with ultrasonic testing for yield strength.

2) Line 166 – HOW??? I think that you need to explain all the procedures in detail

3) Lines 169-174 Can you please show the results of this investigation?

4) Table 2 – what was the measurement procedure? According to the table, only one measurement per sample was made. If not, you need to include errors in the data.

5) For all figures – there are no errors in the data points. Please include error bars.

6) Line 306-307. Please provide a description of the ultrasonic method.

Author Response

Reviewer #2

Review comments: Manuscript provides information on the new material for additive manufacturing and its properties. In my opinion manuscript needs improvement mainly in the methods description. It's impossible to review the results without properly described methods. Also, data presentation must be improved with additional statistical errors.

Comment 1: Line 163 – what are hardness measurement conditions? The same with ultrasonic testing for yield strength.

Reply:

where HV is the hardness Vickers, F the force applied and D, the average dimensions of diagonals of imprint.

The Young E modulus of composite materials was determined by the ultrasound method This method makes it possible to measure the speed of propagation of longitudinal v_L and transverse v_T waves in a homogeneous, isotropic and non-dispersive material with density ρ. The measurement is carried out by transmission and requires a transmitter and a receiver including a longitudinal wave probe and a transverse wave probe. They will propagate an ultrasonic wave from its surface and determine the speeds v_L and v_T according to the ratio between the thickness e of the material and the transit time t of the ultrasonic wave.

From the longitudinal and transverse velocities, the Young modulus is determined by the following relationship

Comment 2: Line 166 – HOW??? I think that you need to explain all the procedures in detail

Reply: HOW has been removed from the text

Comment 3: Lines 169-174 Can you please show the results of this investigation?

Reply: The following sentence has been added:

For these compositions, the 316L and 316L+Cu pastes show a shear thinning behavior which is suitable for an extrusion shaping process.

Comment 4: Table 2 – what was the measurement procedure? According to the table, only one measurement per sample was made. If not, you need to include errors in the data.

Reply: The following sentence has been added:

Carbon contents were measured using a CS800 Carbon-Sulfur Determinator from Eltra. Initial carbon content for the 316L powder was 0.0301 wt.% +/- 0.002.

Comment 5: For all figures – there are no errors in the data points. Please include error bars.

Reply: Done

Comment 6: Line 306-307. Please provide a description of the ultrasonic method.

Reply: Done. The following sentence has been added

From the longitudinal and transverse velocities, the Young modulus is determined by the following relationship:

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

I certainly support the work done by the authors, that is, they conducted an examination of these two important procedures (sintering and debinding) in the production of metal products with extrusion additive manufacturing. But there are a lot of details missing in the paper and it would be good to do some things a little differently.

Here are my comments:

1. There is no need for the word HOW at the end of chapter 2 (line 166).

2. To avoid the appearance of air in the paste, there are nozzles on the market that have built-in vacuum pumps for extracting air. Such nozzles are widely used in food printing, and without it, the appearance of air is simply too big. You should use it in this work, or make such a nozzle yourself. Therefore, air must be drawn out of the paste itself before the material is dosed into the extruder to avoid the appearance of air. Were any methods used in this work?

3. I think that picture 1.a should be rotated by 180 degree.

4. Are the authors sure that it is called calendaring? I have to admit that this is the first time I have heard that word. Maybe the authors mean calendering? Calendering is mentioned throughout the paper in one sentence. It is not clear to me why it is necessary to state this in the title. The title should be changed.

5. Although the work is focused on sintering and debinding methods, I think that the processing parameters of the extrusion itself, i.e. the processing parameters of the mentioned samples, should be specified.

6. Line 264 mentioned Figure 6, but should be Figure 4.

7. Table S1 was made twice in the supplementary materials.

8. In line 338, a picture number 11 is mentioned. What is that picture? I'm assuming that's an S3?

9. In line 360, the authors forgot to list the literature.

10. Line 365 – literature 18 should be changed to a proper citation in bracket (18), not as a superscript. But in the list of literature there is no literature 18.

11. Standards for testing mechanical properties are not listed anywhere? What are the dimensions of the test specimens? I'm missing pictures of making test specimens by additive manufacturing, pictures of testing, etc...

12. What happens to the dimensions of the test specimens during the sintering and debinding process?

13. How was the Design of experiment (DoE) made? How were the combinations of parameters chosen according to table 2? I think this is bad – you should use a certain design of experiment and do statistical analysis. There are many softwares that allow you to create an experiment plan. And then the optimization of the results should be done with all the statistics as mentioned in line 229. Because without an experiment plan, the question arises as why exactly those parameter values (values of percentages of Ar and H2, values of temperatures and dwell time) were taken into consideration?

14. More comparison with other literature is missing in the Discussions chapter.

15. The authors did not fill: Author Contributions and Funding.

Author Response

Reviewer #3

Review comments:

Comment 1: There is no need for the word HOW at the end of chapter 2 (line 166).

Reply: It has been removed

Comment 2: To avoid the appearance of air in the paste, there are nozzles on the market that have built-in vacuum pumps for extracting air. Such nozzles are widely used in food printing, and without it, the appearance of air is simply too big. You should use it in this work, or make such a nozzle yourself. Therefore, air must be drawn out of the paste itself before the material is dosed into the extruder to avoid the appearance of air. Were any methods used in this work?

Reply:

To evaluate printability of the pastes, printing was conducted using a S600D professional 3D printer with a PAS11 toolhead both provided by Lynxter. Printing conditions have been added in Table S1

Comment 3: I think that picture 1.a should be rotated by 180 degree.

Reply: Figure has been changed

Figure 2. (a) as-printed sample. (b) cross-section of as-printed sample, (c) cross-section of sample formed using a cylindrical mold.

Comment 4: Are the authors sure that it is called calendaring? I have to admit that this is the first time I have heard that word. Maybe the authors mean calendering? Calendering is mentioned throughout the paper in one sentence. It is not clear to me why it is necessary to state this in the title. The title should be changed.1) Please move the two scale bars of "200 nm" in Figure 4(c) to the right position.

Reply: Title has been changed

Study on debinding and sintering conditions in extrusion-based additive manufacturing of 316L and 316L+Cu

Comment 5: Although the work is focused on sintering and debinding methods, I think that the processing parameters of the extrusion itself, i.e. the processing parameters of the mentioned samples, should be specified.

Reply: The purpose of this study and this paper is to work on debinding and sintering conditions. Another paper will be focused on the optimization of the printing conditions

Comment 6: Line 264 mentioned Figure 6, but should be Figure 4.

Reply: Yes, changed in the text to Figure 5a and 5c

Comment 7; Table S1 was made twice in the supplementary materials.

Reply: Yes removed

Comment 8: In line 338, a picture number 11 is mentioned. What is that picture? I'm assuming that's an S3?

Reply: Yes, figure number has been changed

Comment 9: In line 360, the authors forgot to list the literature.

Reply: References have been added in order to answer the remarks of most of the referees

Comment 10: Line 365 – literature 18 should be changed to a proper citation in bracket (18), not as a superscript. But in the list of literature there is no literature 18.

Reply: References have been added in order to answer the remarks of most of the referees

Comment 11: Standards for testing mechanical properties are not listed anywhere? What are the dimensions of the test specimens? I'm missing pictures of making test specimens by additive manufacturing, pictures of testing, etc...

Reply:

where HV is the hardness Vickers, F the force applied and D, the average dimensions of diagonals of imprint.

Comment 12: What happens to the dimensions of the test specimens during the sintering and debinding process?

Reply: Obviously a shrinkage of the materials after sintering append. Of course, shrinkage is higher when the relative density is higher. No evolution of the materials dimension can be observed after debinding

Comment 13: How was the Design of experiment (DoE) made? How were the combinations of parameters chosen according to table 2? I think this is bad – you should use a certain design of experiment and do statistical analysis. There are many softwares that allow you to create an experiment plan. And then the optimization of the results should be done with all the statistics as mentioned in line 229. Because without an experiment plan, the question arises as why exactly those parameter values (values of percentages of Ar and H2, values of temperatures and dwell time) were taken into consideration?

Reply:

As for the variables chosen, Literature showed different debinding atmospheres, and I recall that hydrogen was the most effective. Ar5H2 was chosen because it was a cost-effective, safer alternative to a debind in pure Hydrogen (so more likely to use in industry). In theory we could have studied variations in hydrogen content to binder removal, but that wasn't the research topic.

Comment 14: More comparison with other literature is missing in the Discussions chapter.

Reply: These sentences and table have been added

It is hard to compare our results obtained by AEM using bio-sourced paste with 316L materials from the literature due to the fact that base materials, and debinding and sintering conditions are different. Table 4 shows a comparison of 316L materials fabricated using Direct Laser Deposition (DLD), SLM, MIM and EAM with our materials. It has to be mentioned that literature materials are pure 316L where Cu can be added to our 316L in order to improve densification and that 316L materials from the literature are sinter at high temperature (close to 1400 °C) where our materials are sinter at much lower temperature (1200 °C).

Table 4. Overview of mechanical properties and porosity for 316L and 316L+Cu stainless steel produced using Fused Filament Fabrication (FFF), SLM and MIM.

Porosity (%)	Hardness	Yield strength	Method	Reference
< 0.5	240 HV 380 HV	2200 MPa 2300 MPa	DLD SLM	28
- - 10 4	213 HB 217 HB 126 HB -	375 MPa 533 MPa 153 MPa 170 MPa	SLM EOS SLM Renishaw FFF BASF MIM	29 29 29 30
1.6	200 HV	-	EAM	31
~ 21 ~ 14 ~ 12	65 85 85	140 150 150	EAM 316L EAM 316L+10%Cu EAM 316L+20%Cu	This work

Comment 15: The authors did not fill: Author Contributions and Funding.

Reply: Done

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The authors investigate the use of a methylcellulose binder in extrusion additive manufacturing of 316L as an alternative to common wax-based binders. The authors analyzed the influence of Cu content on densification, mechanical properties, microstructure, and corrosion resistance of 316L.

The manuscript should be thoroughly revised. The comments below should be incorporated.

1) What do you mean by the term "calendaring", which is also in the name of the manuscript? Please explain.

2) Section 2.1 (lines 115-116) should be supplemented with a histogram of the particle size distribution and an (SEM) image that confirms the spherical particles.

3) What did you mean by the term or sentence “HOW?” in line 166?

4) In Figure 1a, insert the scalebar. It would be advisable to use images that are of better quality.

5) Table 2 has a different text size than required.

6) In line 264, it is incorrectly stated "Figure 6". Figure 4 should be correct.

7) In Figure 4 a,c complete the scalebar.

8) Somewhere in the text, you mention Figure and somewhere Fig (line 276). Unite it.

9) You state that the material was hot-rolled (line 297). Complete the rolling data in section 2 Materials and methods. Indicate the name and type of rolling mill, rolling temperature, and deformation.

10) You state that after rolling, there was an increase in density respectively, a decrease in porosity in the investigated material (line 295). It would be convenient to document this by analyzing the porosity from the LOM images.

11) Please describe in section 2 Materials and methods the principle and conditions of the ultrasonic method for determining YS.

12) In the text in line 299, you state a densification of 95%, but in Figure 6, the value is 94%.

13) In section 2. Materials and methods, describe how the hardness was measured (device, conditions). It is not possible to provide hardness results if basic information about the test (load, time) is not provided.

14) What did you mean by "(Ref ?)" in line 360?

15) What does the "18" mean at the end of the sentence in line 365? Please unify the marking of literature sources.

16) Please compare the results from the other research in which the authors addressed the influence of Cu on mechanical properties in the discussion. A deeper connection between mechanical properties and microstructure is missing here (4.2. Mechanical properties).

17) The scientific intent should be supported by a greater number of literary sources than is the case in this manuscript (17).

18) In Figure S1, please complete the scalebar.

19) Figure S2 has illegible axes.

20) In Table S1, which lists “He et. al", this source is not mentioned in the bibliography.

21) Figure S4 does not have an X-axis.

22) The manuscript should be proofread and edited carefully to ensure clarity, accuracy, and consistency in language and formatting.

Based on the abovementioned comments, this manuscript is recommended for major revision. A revised version is required.

Comments for author File: Comments.pdf

Author Response

Reviewer #4

Review comments:

Comment 1: What do you mean by the term "calendaring", which is also in the name of the manuscript? Please explain.

Reply: New title has been proposed in order to answer the referee question

Study on debinding and sintering conditions in extrusion-based additive manufacturing of 316L and 316L+Cu

Comment 2: Section 2.1 (lines 115-116) should be supplemented with a histogram of the particle size distribution and an (SEM) image that confirms the spherical particles.

Reply: New figure has been added in order to answer the comment

Figure 1. (a) SEM micrograph of 316L particles formed by gas-atomization. (b) particle size distribution of those 316L particles

Comment 3: What did you mean by the term or sentence “HOW?” in line 166?

Reply: Mistake from ourself. This word has been removed.

Comment 4: In Figure 1a, insert the scalebar. It would be advisable to use images that are of better quality.

Reply: Figure has been changed

Figure 2. Photographs of (a) as-printed sample. (b) cross-section of as-printed sample, (c) cross-section of sample formed using a cylindrical mold.

Comment 5: Table 2 has a different text size than required.

Reply: Table has been changed

Table 2. C contents after debinding under various atmospheres, temperatures, and dwell times.

Gas composition Argon (%) H₂^(%)		Temperature (°C)	Dwell time (min)	Carbon content (wt.%)
316L powder (as received)				0 .03
100	0.0	400	90	0.130
100	0.0	500	90	0.127
100	0.0	500	300	0.125
95	5.0	500	300	0.125
95	5.0	500	900	0.123
100	0.0	700	300	0.122
95	5.0	700	300	0.117

Comment 6: In line 264, it is incorrectly stated "Figure 6". Figure 4 should be correct.

Reply: Yes, number was changed

Comment 7: In Figure 4 a,c complete the scalebar.

Reply: Yes, figure was changed in order to answer this comment

Figure 5. (a) 10 vol.% Cu, BSE micrograph, (b) 10 vol.% Cu EDS map, (c) 20 vol.% Cu BSE micrograph, (d) 20 vol.% Cu EDS map. For EDS maps, Fe is red, Cu is green, silicon at the pores is pink

Comment 8: Somewhere in the text, you mention Figure and somewhere Fig (line 276). Unite it.

Reply: When comparing the 20 vol.% Cu to 0 vol.%, the SEM micrographs in Fig. 6 show larger 316L particles in the 20 vol.% material (30% to 50% increase in average size).

Comment 9: You state that the material was hot-rolled (line 297). Complete the rolling data in section 2 Materials and methods. Indicate the name and type of rolling mill, rolling temperature, and deformation

Reply: Sentence added in section 2:

Hot rolled materials were placed in an oven, under neutral atmosphere, for 30 min at 500 °C and then immediately hot rolled at a speed close to 10^-2 m/s. The temperature of the roller is close to 100 °C. Each pass induces a thickness reduction of 10%.

Comment 10: You state that after rolling, there was an increase in density respectively, a decrease in porosity in the investigated material (line 295). It would be convenient to document this by analyzing the porosity from the LOM images.

Reply: Yes, referee comment is pertinent. However, this analysis has not been done

Comment 11: Please describe in section 2 Materials and methods the principle and conditions of the ultrasonic method for determining YS.

Reply: The sentences have been added:

Mechanical properties of the materials were determined by the ultrasound method. This method makes it possible to measure the speed of propagation of longitudinal v_L and transverse v_T waves in a homogeneous, isotropic and non-dispersive material with density ρ. The measurement is carried out by transmission and requires a transmitter and a receiver including a longitudinal wave probe and a transverse wave probe. They will propagate an ultrasonic wave from its surface and determine the speeds v_L and v_T according to the ratio between the thickness e of the material and the transit time t of the ultrasonic wave.

Comment 12: In the text in line 299, you state a densification of 95%, but in Figure 6, the value is 94%.

Reply: Value has been changed in the text to 94%

Comment 13: In section 2. Materials and methods, describe how the hardness was measured (device, conditions). It is not possible to provide hardness results if basic information about the test (load, time) is not provided.

Reply:

where HV is the hardness Vickers, F the force applied and D, the average dimensions of diagonals of imprint.

Comment 14: What did you mean by "(Ref ?)" in line 360?

Reply: This word has been removed

Comment 15: What does the "18" mean at the end of the sentence in line 365? Please unify the marking of literature sources.

Reply: This number has been removed

Comment 16: Please compare the results from the other research in which the authors addressed the influence of Cu on mechanical properties in the discussion. A deeper connection between mechanical properties and microstructure is missing here (4.2. Mechanical properties).

Reply: Yes, your remark is pertinent. However, we could not find article given the influence of Cu on 316L matrix on the mechanical behavior of 316L and 316L+Cu fabricated by additive extrusion manufacturing using bio-sourced gel. What we can say is that 316L grains are bigger when adding Cu and Cu help to get denser materials at low sintering temperature (1200 °C) compared with traditional temperature used to get dense 316L (around 1400 °C) and that mechanical properties like hardness and yield strength increase when Cu volume fraction inside 316L increases. We compare the mechanical properties of our material with 316L materials fabricated by additive manufacturing in the discussion section. Due to the fact that our materials have porosity level higher that materials find in the literature our materials have mechanical properties smaller than what we can find in the literature.

Comment 17: The scientific intent should be supported by a greater number of literary sources than is the case in this manuscript (17).

Reply: Done cf. references

Comment 19: In Figure S1, please complete the scale bar.

Reply: Done

Comment 20: In Table S1, which lists “He et. al", this source is not mentioned in the bibliography.

Reply: This Ref. has been added at the end of the SI (Table S2 in revised SI)

Comment 21: Figure S4 does not have an X-axis.

Reply: Figure S4 has been removed

Comment 22: The manuscript should be proofread and edited carefully to ensure clarity, accuracy, and consistency in language and formatting.

Reply: Done by Pr. Yongfeng Lu from the University of Nebraka Lincoln.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The article has improved in investigation material and is more logically correct. The article may be accepted for publication in this form.

Author Response

Thank you very much for your time dedicated to the reviewing of this paper

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear authors,

All my major questions were addressed. I can recommend this manuscript for publication.

Author Response

Thank you very much for your time dedicated to the reviewing of this paper

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Although the authors fixed some errors. Again, unanswered questions remain. I would like to point out that the standards by which the test was conducted were not specified, and the authors put an equation for hardness in the explanation. And according to what standard? What about the standard for yield strength? So I will repeat the question: What are the dimensions of the test specimens? I'm missing pictures of making test specimens by additive manufacturing, pictures of testing, etc...

Furthermore, what about the answer about removing the air. In what way were all the methods of air removal tried before the actual processing?

If there was a reduction in dimensions after sintering, this greatly changes the mechanical properties, because dimensions are needed to calculate strength. Put a table in the supplementary materials with data on dimensions and calculation of strength and hardness. Put also data for mean values and standard deviation.

As I stated for the first time, the comparison with previous literature should also be in the text itself. It is not enough to write through the table like this.

And I really think that this kind of testing should be done through a real design of experiment and statistical data processing through some software. But I know that for your paper it would mean starting all over again. But definitely think about it in the future.

Author Response

Review comments:

Reply: Sentences have been added in order to answer the comment

L172-174: Prior to any analysis samples were mirror polished on each side. The dimensions of the tested materials were 50 mm x 10 mm and 5 mm. in thickness.

L198-206: The measurement is carried out by transmission and requires a transmitter and a receiver including a longitudinal wave probe and a transverse wave probe. They will propagate an ultrasonic wave from its surface and determine the speeds v_L and v_T according to the ratio between the thickness e of the material and the transit time t of the ultrasonic wave [27]. The ultrasonic attenuation in the 316L and 316L+Cu samples were measured by pulsed-echo ultrasonic method as per ASTM E664/E664M-10: standard practice for the measurement of the apparent attenuation of longitudinal ultrasonic waves work [28]. Schematic representation of the ultrasonic method is shown in Fig. S1.

Figure S1. Representation of the ultrasonic method

The 2 following references have been added:

27 Tessier-Doyen, N. Etude experimentale et numerique du comportement thermomecanique de materiaux refractaires modeles. PhD thesis, Universite de Limoges, 2003

Aghaie-Khafri, M.; Honarvar, F.; Zanganeh, S. Characterization of grain size and yield strength in AISI 301 stainless steel using ultrasonic attenaution measurements. J. Non destruct. Eval 2012, 31, 191-196.

Review comments:

Furthermore, what about the answer about removing the air. In what way were all the methods of air removal tried before the actual processing?

Reply:

The Thinky ARE-250 Mixer allows for the process of mixing (accelerator of 400 GS) and bubble removal (accelerator of 510 GS) to be carried out simultaneously. Whatever the degassing time, the degassing configuration does help us to remove the air trapped inside the paste.

Review comments:

Reply: Sentences have been added in order to answer the comment

L172-174: Prior to any analysis samples were mirror polished on each side. The dimensions of the tested materials (316L, 316L + 10% Cu and 316l + 20% Cu) are 50 mm x 10 mm and 5 mm. in thickness after polishing.

The errors bars for the hardness values and the yield strengths are noted in Figure 7 and 8 respectively.

Review comments:

As I stated for the first time, the comparison with previous literature should also be in the text itself. It is not enough to write through the table like this.

Reply:

Yes I agree with the comment and this is why, in the revised 1 version, we have added sentences prior to the table in order to explain why the comparison with previous work is not easy due to the fact that experimental materials, apparatus and experimental procedure are different with what we have done. I do not see what we can add more

Review comments:

Reply: Thank you for your comment. Yes, in the future we will do it.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The authors have addressed the comments well. Just correct the following typos:

1) Please explain on what basis the heating temperature of 500 °C was chosen during rolling (literature). You state that the deformation was 10% for each pass. Nowhere do you state what the input thickness of the material was or the overall dimensions of the samples that were rolled. Please specify the following data: the input dimensions of the samples, how the temperature was measured on the sample during rolling and on the rolls (contact or non-contact), indicate the type and manufacturer of the used rolling mill.

2) The sentence in lines 190-194: "The dimension.......... imprint." is unnecessary. This is a generally known fact that does not need to be described.

3) Please state the name and type of equipment on which the mechanical tests were carried out using the ultrasound method.

Based on the abovementioned comments, this manuscript is recommended for minor revision. A revised manuscript is required.

Author Response

The authors have addressed the comments well. Just correct the following typos

Based on the abovementioned comments, this manuscript is recommended for minor revision. A revised manuscript is required.

Comment 1:

Please explain on what basis the heating temperature of 500 °C was chosen during rolling (literature). You state that the deformation was 10% for each pass. Nowhere do you state what the input thickness of the material was or the overall dimensions of the samples that were rolled. Please specify the following data: the input dimensions of the samples, how the temperature was measured on the sample during rolling and on the rolls (contact or non-contact), indicate the type and manufacturer of the used rolling mill.

Reply: Sentences have been added in order to answer the comment 1

L 172-174: Prior to any analysis samples were mirror polished on each side. The dimensions of the tested materials (316L, 316L + 10% Cu and 316l + 20% Cu) are 50 mm x 10 mm and 5 mm. in thickness after polishing

L177: 500 °C, according to Y. Dong et al work [26],

L177-178: hot rolled (Cavallin 130mm Rolling Mill)

L178-179: The temperature of the roller close to 100 °C was measured by thermocouple just prior to hot rolling

Comment 2:

The sentence in lines 190-194: "The dimension.......... imprint." is unnecessary. This is a generally known fact that does not need to be described.

Reply: The sentence has been removed

Comment 3:

Please state the name and type of equipment on which the mechanical tests were carried out using the ultrasound method.

Reply: This is a homemade apparatus. Sentence has been added on L195-196

L195-196: Mechanical properties of the materials were determined by the ultrasound method (homemade apparatus)

Author Response File: Author Response.pdf

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Study on Debinding and Sintering Conditions in Extrusion-Based Additive Manufacturing of 316L and 316L + Cu

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