Effect of La₂O₃ on Microstructure and Properties of Laser Cladding SMA Coating on AISI 304 Stainless Steel

Round 1

Reviewer 1 Report

Dear authors, I consider that your manuscript needs major revision. Please see the remarks presented in the attached review document.

Comments for author File: Comments.pdf

Author Response

Dear Editor and Reviewers of the Journal of Coatings,

 

It is great thanks to you for the consideration of our manuscript “Effect of La₂O₃ on microstructure and properties of laser cladding SMA coating on AISI 304 stainless steel” (No. Coatings-1808577), and for giving us an opportunity to revise our manuscript.

 

The suggestions of editor and referees have been seriously considered and the manuscript has been further experimented, analyzed and revised based on these comments. The revised manuscript, a copy of the revised version in which all revised contents have been marked red, a supporting information document and the point-by-point response to referees’ comments are resubmitted using your online submission.

 

Please let me know any decisions you have made on the manuscript.

 

Thanks again for your and the referees’ advice.

 

 

Yours Sincerely,

Dr. Peng Xu

College of Materials and Metallurgy,

Guizhou University, Guiyang, 550025, China,

E-mail: pxu2@gzu.edu.cn.

 

 

 

 

 

 

Response to the editor and reviewers’ comments

About the questions and advices from Reviewer #1' comments:

The article is a research paper which studies the effect of La₂O₃ on microstructure and properties to enhance the microhardness and anti-corrosion of shape memory alloy coatings deposited on 304 stainless steel matrix and it is in accordance with journal topics.

The title reflects the article content and the abstract it is well structured, concise and summarizes the purpose of the research. After the introduction on the state of the art on different shape memory alloy coatings used in the literature(Fe-Mn-Si, Mn-Si-Ni-Cr, etc.), authors present subsequently the materials and methods used in this research, results and short discussion on microstructure, chemical composition, microhardness, wear resistance and anti-corrosion of 304 stainless steel by adding different amounts La₂O₃ in SMA coatings. The complex experiments,mechanical properties and microstructural investigation presented in this manuscript shows the efforts made by the authors.

However, some statements are unclear and the manuscript needs revision and improvement.

 

Reply to Reviewer:

Thank you very much for your approval. We have revised the manuscript as required.

Remark 1:

For a better understanding of readers, replace ss in the title with text: stainless steel!!!

The acronyms must be explained where appear for the first time in the text.

SMA - in abstract section (shape memory alloy)

Please verify all acronyms in the article!!!!

 

Reply to Reviewer:

Thanks very much for your suggestion and we have replaced ss in the title with stainless steel.

Modification of Manuscript:

• Title: Effect of La₂O₃on microstructure and properties of laser cladding SMA coating on AISI 304 stainless steel
• Meanwhile, SMA (shape memory alloy) has been explained in abstract section.

Abstract: Known as stress self-accommodation characteristic, the laser cladding shape memory alloy (SMA) coatings have been widely used in material failure repair.

• In general, the smaller self-corrosion current (I_corr) is, the smaller the corrosion rate is, and the greater self-corrosion voltage (E_corr) is,

Remark 2:

Keywords must indicate the main materials tests, and methodology used in the study. However, it is required to revise the keywords and write based on the points mentioned above.

 

Reply to Reviewer:

Thank you very much for your valuable comments. We have made changes to the keywords as required.

Modification of Manuscript:

Keywords: Shape memory alloy; La₂O₃; Laser cladding; Microstructure; Anti-corrosion.

Where the materials are shape memory alloy and La₂O₃, the method is laser cladding, and the microstructure and corrosion resistance are studied.

Remark 3:

On the line 38 of the manuscript,the reference [13] is wrong mentioned; the reference [15] it is by Ferretto et al.

Also, the references are numbered twice in References section.Remove the number in straight brackets.

 

Reply to Reviewer:

Thank you very much for your valuable comments. This is indeed the problem that we did not carefully check the manuscript, and we have corrected this mistake in time, thank you again.

Modification of Manuscript:

Ferretto et al. [12] prepared Fe17Mn5Si10Cr4Ni SMA parts by LPBF for the first time, which further promotes the development of SMA.

 

[12]Ferretto, I.; Kim, D.; Della Ventur, N.M.; Shahverdi, M.; Lee, W.; Leinenbach, C. Laser powder bed fusion of a Fe-Mn-Si shape memory alloy. Addit. Manuf. 2021, 46, 102071.

Remark 4:

Section 4 is missing in the manuscript!!!!!!!

Conclusions section must be number 4!!!!!!!

 

Reply to Reviewer:

Thank you very much for your valuable comments. We have corrected this mistake. Thank you again.

Modification of Manuscript:

4. Conclusions

In this paper, SMA/La₂O₃ composite coating was prepared on AISI 304 SS by laser cladding technology, so as to improve the microhardness and anti-corrosion of SMA coating.

Remark 5:

In figure 7 are presented the friction coefficient variation and wear resistance of samples used in this study. It's clear from results that SMA coating without adding La₂O₃ present the high values of friction coefficient and wear volume loss. For a better comprehension of wear resistance, I think that instead of wear volume loss, the authors should consider the intensity of wear resistance.

 

Reply to Reviewer:

Thank you very much for your valuable comments. We are very sorry that the abrasion resistance of the coating are not clearly expressed. Due to the lack of relevant experimental equipment, the intensity of wear resistance cannot be carried out. Nevertheless, we believe that the description of wear volume loss can also explain the wear resistance of coating, which has been done in many articles [1]-[4]. To better understand wear resistance, we supplement the description of the wear mechanism.

Modification of Manuscript:

As shown in Figure 9. the wear width of SMA coating reaches 956 um, while the width of SMA/(La₂O₃)_{0.9 wt.%} composite coating is only 867 um, indicates that the composite coating has better wear resistance. Furthermore, plenty of furrow marks, which are caused by the falling off of particles on the surface and continued to wear the surface, was observed in both SMA coatings, which is called abrasive wear. However, the wear scars depth of the SMA coating is significantly deeper than that of SMA/La₂O₃ composite coating (the arrow of Figure 9b) owing to the lower microhardness. Moreover, a large area of spalling on the surface was observed in Figure 9b, which is a typical adhesion wear, also a more serious wear form than abrasive wear. On the contrast, the wear marks of SMA/La₂O₃ composite coating is more smooth and flat, although there are some spalling, the area is smaller compared with the SMA coating.

 

Figure 9. SEM micrographs of the wear scar (a)-(b) SMA coating; (c)-(b) SMA/(La₂O₃)_{0.9 wt.%}.

• Aydin, F.; Durgut, R. Estimation of wear performance of AZ91 alloy under dry sliding conditions using machine learning methods. T. Nonferr, Metal Soc. 2021, 31, 125-137.
• Xu, Z.; Li, D.Y.; Chen, D.L. Effect of Ti on the wear behavior of AlCoCrFeNi high-entropy alloy during unidirectional and bi-directional sliding wear processes. Wear. 2021, 476, 203650.
• Katinas, E.; Chotěborský, R.; Linda, M.; Kuře, J. Sensitivity analysis of the influence of particle dynamic friction, rolling resistance and volume/shear work ratio on wear loss and friction force using DEM model of dry sand rubber wheel test. Tribol Int. 2021, 156, 106853.
• Zhou, M.; Meng, M.; Chai, Z.G.; Zhang, Y.M.; Li, D.; Niu, L.N.; Jia, Y.M.; Zhang, S,F.; Wang, F. Dynamic wear characteristics and fracture strength of high-translucent monolithic zirconia crowns. Ceram. Int. 2022, 48, 11298-11303.

Remark 6:

The conclusions are very general and need to be revised and improved. Please make sure the conclusion section underscores the scientific value added by the article and the applicability of the findings/results.Do not number every conclusion presented in this section!!!!

 

In conclusion, I consider that the article have some errors and present a medium level of novelty. Due to remarks presented above, I recommend major revision of the manuscript.

 

Reply to Reviewer:

Thank you very much for your valuable comments. We have revised the conclusions section based on the suggestions above, emphasizing the scientific value and the applicability of the findings/results.

Modification of Manuscript:

4. conclusion

In this paper, SMA/La₂O₃ composite coating was prepared on AISI 304 stainless steel by laser cladding technology so as to improve the microhardness and anti-corrosion of SMA coating. The result shows that the phases of all coatings are composed of Nb phase, thermoelastic ε-martensite, non-thermoelastic α'-martensite and γ-austenite phases. The presence of thermoelastic ε-martensite proves that γ-austenite transformation occurs in the SMA coatings, which is the characteristic of SMAs, and it is also the key to shape memory effect. The advantage of using rare earth oxide as heterogeneous nucleation site can increase the probability of heterogeneous nucleation and refine the grain. Based on the Hall-Petch formula, The smaller the grain size, the higher the microhardness. When doping with 0.9 wt.%, the average grain size of the composite coating decreases to only 3.03 um, and the refinement rate reaches 19%, which greatly improves the microhardness and anti-wear of the coating. Due to the low microhardness of SMA coating, the surface has a large area of peeling, and the wear pit is larger and deeper after friction test, which is corresponding to abrasive wear and adhesive wear. On the contrary, the surface of composite coating is only abrasive wear, and the wear scars are shallower.

The E_corr and I_corr of the composite coating are significantly improved, this is attribute to the addition of La₂O₃ in the alloy can not only refine the grain but also generate inclusions with impurity element S and Al, which can be purified the microstructure and improved the anti-corrosion. Compared with SMA coating, the Cdl of the composite coating decreases by 1-2 order of magnitude, and the Rct increases by 3-6 times, indicating that the corrosion of the coating is more difficult.

Author Response File: Author Response.pdf

Reviewer 2 Report

The article deals with an interesting topic and I think that it will enrich readers' knowledge.

I recommend the following modifications to the authors:

- the abstract is insufficient, it needs to be expanded (it contains only 115 words)

- Figure 2 is unclear

- figure 3, 5 - magnification is missing

- literature in the text is not cited correctly or is not cited at all (literature number 15, 19, 20, 21, 24, 27, 30, 31)

- the conclusion and the results presented in it need to be extended and specified.

After these corrections, the article could be published.

Author Response

Dear Editor and Reviewers of the Journal of Coatings,

 

It is great thanks to you for the consideration of our manuscript “Effect of La₂O₃ on microstructure and properties of laser cladding SMA coating on AISI 304 stainless steel” (No. Coatings-1808577), and for giving us an opportunity to revise our manuscript.

 

The suggestions of editor and referees have been seriously considered and the manuscript has been further experimented, analyzed and revised based on these comments. The revised manuscript, a copy of the revised version in which all revised contents have been marked red, a supporting information document and the point-by-point response to referees’ comments are resubmitted using your online submission.

 

Please let me know any decisions you have made on the manuscript.

 

Thanks again for your and the referees’ advice.

 

 

Yours Sincerely,

Dr. Peng Xu

College of Materials and Metallurgy,

Guizhou University, Guiyang, 550025, China,

E-mail: pxu2@gzu.edu.cn.

 

 

 

 

 

 

About the questions and advices from Reviewer #2' comments:

1. The article deals with an interesting topic and I think that it will enrich readers' knowledge.I recommend the following modifications to the authors:

 

Reply to Reviewer:

Thank you very much for your approval. We have revised the manuscript as required.

 

2. the abstract is insufficient, it needs to be expanded (it contains only 115 words)

 

Reply to Reviewer:

Thanks very much for your valuable suggestion. We supplement the background, methods, results and conclusions of the abstract. Now the abstract has 176 words, and the content is more abundant, thank you again for your suggestion.

Modification of Manuscript:

Abstract: Known as stress self-accommodation characteristic, the laser cladding shape memory alloy (SMA) coatings have been widely used in material failure repair. Nevertheless, its further development is greatly limited by the low microhardness (250 HV_0.2) and corrosion resistance. Benefiting from the capability of refined grain and adjusted microstructure, rare earth oxides play a key role in improving the properties of materials. Herein, to improve the microhardness and anti-corrosion of laser cladding SMA coatings, different amounts of La₂O₃ were doped in SMA coating. The influence of the different La₂O₃ doping amounts on the phases, grain size and microhardness was studied. The anti-corrosion of the SMA/La₂O₃ composite coating was explored in 3.5 wt.% sodium chloride solution. Result showed that the grain of the SMA/La₂O₃ composite coating is significantly refined. When doping with 0.9 wt.%, the refinement rate reaches 19%. Furthermore, based on the Hall-Petch effect, the microhardness of the SMA/La₂O₃ composite coating is increased to 450 HV_0.2. At the same time, the anti-corrosion of the composite coating is enhanced due to the smaller grain size and fewer defects.

 

3. Figure 2 is unclear

 

Reply to Reviewer:

Thank you very much for your valuable comments. We re-analyzed the XRD from phase, peak shift, and split the original Figure 2 into two figures for easier understanding.

Modification of Manuscript:

The XRD patterns of La₂O₃ doped with different amounts are shown in Figure 2a. There is no obvious difference in the XRD patterns, all of which are composed of Nb phase, thermoelastic ε-martensite, non-thermoelastic α'-martensite and γ-austenite phases. The presence of ε-martensite proves that γ-austenite transformation occurs in the SMA coating, which is the characteristic of SMAs. Furthermore, thermoelastic ε-martensite is also key to shape memory effect. Meanwhile, the γ-austenite of the composite coatings are all shifted to high angles, whcih indicates that the interplanar spacing d decreases based on the Bragg equation (2dsinθ=nλ).

In addition, Figure 3 exhibits a lot of white area on the surface (white circle), and EDS analysis indicates that the Nb phase is precipitated in this area, which is consistent with the XRD pattern.

 

 

Figure 2. The XRD patterns of coatings

 

 

Figure 3. The elements of coating surface.

 

4. figure 3, 5 - magnification is missing

 

Reply to Reviewer:

Thank you very much for your valuable comments. We have replaced the original Figure and re-marked the scale.

Modification of Manuscript:

 

Figure 4. The microstructures of (a) SMA; (b) SMA+0.3 wt.% La₂O₃; (c) SMA+0.6 wt.% La₂O₃; (d) SMA+0.9 wt.% La₂O₃; (e) SMA+1.2 wt.% La₂O₃.

 

5. literature in the text is not cited correctly or is not cited at all (literature number 15, 19, 20, 21, 24, 27, 30, 31)

 

Reply to Reviewer:

Thanks very much for your valuable suggestion. We have revised the references mentioned above. Thank you again for your careful reading.

Modification of Manuscript:

• Benefiting from its good chemical and physical properties as well grain refinement, rare earth elements, honored as industrial vitamins, has a vital role in improving the microhardness, wear resistance and anti-corrosion of materials [15-16].
• Liu et al. [19] doped different amounts of CeO₂in TiC/Ti₂Ni coating.
• The frequency range from 100-106 HZ and the amplitude is 0.005 V [20].
• The presence of thermoelastic ε-martensite proves that γ-austenite transformation occurs in the SMA coating, which is the characteristic of SMAs [21-22].
• This is because the rare earth oxides act as heterogeneous nucleation sites, increase the probability of heterogeneous nucleation, and refine grains [24-25].
• This is attributed to the segregation of excess La₂O₃at the grain boundaries, which is weakening refining effect and increasing the average grain size [26-27].
• Based on the Hall-Petch formula [30-31].

 

6. the conclusion and the results presented in it need to be extended and specified.

 

Reply to Reviewer:

Thank you very much for your valuable comments. We have revised the conclusions section, emphasizing the scientific value and the applicability of the findings/results.

Modification of Manuscript:

4.conclusion

In this paper, SMA/La₂O₃ composite coating was prepared on AISI 304 stainless steel by laser cladding technology, so as to improve the microhardness and anti-corrosion of SMA coating. The result shows that the phases of all coatings are composed of Nb phase, thermoelastic ε-martensite, non-thermoelastic α'-martensite and γ-austenite phases. The presence of thermoelastic ε-martensite proves that γ-austenite transformation occurs in the SMA coatings, which is the characteristic of SMAs, and it is also the key to shape memory effect. The advantage of using rare earth oxide as heterogeneous nucleation site can increase the probability of heterogeneous nucleation and refine the grain. Based on the Hall-Petch formula, The smaller the grain size, the higher the microhardness. When doping with 0.9 wt.%, the average grain size of the composite coating decreases to only 3.03 um, and the refinement rate reaches 19%, which greatly improves the microhardness and anti-wear of the coating. Due to the low microhardness of SMA coating, the surface has a large area of peeling, and the wear pit is larger and deeper after friction test, which is corresponding to abrasive wear and adhesive wear. On the contrary, the surface of composite coating is only abrasive wear, and the wear scars are shallower.

The E_corr and I_corr of the composite coating are significantly improved, this is attribute to the addition of La₂O₃ in the alloy can not only refine the grain but also generate inclusions with impurity element S and Al, which can be purified the microstructure and improved the anti-corrosion. Compared with SMA coating, the Cdl of the composite coating decreases by 1-2 order of magnitude, and the Rct increases by 3-6 times, indicating that the corrosion of the coating is more difficult.

 

7. After these corrections, the article could be published.

Reply to Reviewer:

Thank you very much for your approval.

Author Response File: Author Response.pdf

Reviewer 3 Report

 

This paper investigates the microstructure and corrosion behavior of a La2O3-containing SMA coatings. Authors have investigated the influence of the different La2O3 doping amounts on the phases, grain size, microhardness and anti-corrosion characteristics of the coating. Results showed that the grain of the SMA/La2O3 composite coating is significantly refined. The paper is well-written and well-organized. Also, it has its own novelty in this field. I suggest this paper for publication after taking following comments into consideration:

-        In Figure 6: what is the error range? Is it possible that all these data are within the error range and are just scattering in measurements?

-        What is the reason for the observed increase in the friction coefficient, when the addition is 1.2%?

-        If possible, please provide pictures from the wear tracks. Also, I suggest authors give a brief overview of wear mechanisms. Following manuscripts can be used:

-        Corrosion and wear resistance characterization of environmentally friendly sol–gel hybrid nanocomposite coating on AA5083, Journal of Materials Science & Technology 29 (7), 603-608, 2013

-        Wear Induced Failure of Automotive Disc Brakes—A Case Study, Materials 12 (24), 4214, 2019

-        Could this increase in mechanical properties be ascribed to the dispersion hardening? Nothing is said about dispersion hardening. Please explain different strengthening mechanisms and mention that dispersion hardening can also attribute to final properties. Following papers are suggested:

-        Microstructure and Mechanical Properties of Spark Plasma Sintered Nanocrystalline TiAl-xB Composites (0.0< x< 1.5 at.%) Containing Carbon Nanotubes, Journal of Materials Engineering and Performance 30 (6), 4380-4392, 2021

-  Mechanical property evaluation of corrosion protection sol–gel nanocomposite coatings, Surface Engineering 29 (4), 249-254, 2013

-          Please make sure you use “AISI 304 SS” In the title and in the text.

Author Response

Dear Editor and Reviewers of the Journal of Coatings,

 

It is great thanks to you for the consideration of our manuscript “Effect of La₂O₃ on microstructure and properties of laser cladding SMA coating on AISI 304 stainless steel” (No. Coatings-1808577), and for giving us an opportunity to revise our manuscript.

 

The suggestions of editor and referees have been seriously considered and the manuscript has been further experimented, analyzed and revised based on these comments. The revised manuscript, a copy of the revised version in which all revised contents have been marked red, a supporting information document and the point-by-point response to referees’ comments are resubmitted using your online submission.

 

Please let me know any decisions you have made on the manuscript.

 

Thanks again for your and the referees’ advice.

 

 

Yours Sincerely,

Dr. Peng Xu

College of Materials and Metallurgy,

Guizhou University, Guiyang, 550025, China,

E-mail: pxu2@gzu.edu.cn.

 

 

 

 

 

 

About the questions and advices from Reviewer #3' comments:

 

1. This paper investigates the microstructure and corrosion behavior of a La₂O₃-containing SMA coatings. Authors have investigated the influence of the different La₂O₃doping amounts on the phases, grain size, microhardness and anti-corrosion characteristics of the coating. Results showed that the grain of the SMA/La₂O₃ composite coating is significantly refined. The paper is well-written and well-organized. Also, it has its own novelty in this field. I suggest this paper for publication after taking following comments into consideration:

 

Reply to Reviewer:

Thank you very much for your approval. We have revised the manuscript as required.

 

2. In Figure 6: what is the error range? Is it possible that all these data are within the error range and are just scattering in measurements?

 

Reply to Reviewer:

Thank you very much for your valuable comments. We calculated the error range based on the original data and redrew Figure 6 (updated to Figure 7). According to our calculation results, the error range is within 0-12 HV_0.2.

Modification of Manuscript:

 

Figure 7. The microhardness changes of cross-section.

 

3. What is the reason for the observed increase in the friction coefficient, when the addition is 1.2%?

 

Reply to Reviewer:

Thank you very much for your valuable comments. When the addition is 1.2 wt.%, a large amount of La₂O₃ will be segregated at the grain boundary, thus weakening the refining effect. It can also be seen from the Figure 5 and Figure 7 that the composite coating of the average grain size increases to 3.12 um, and the microhardness also decreases, so the friction coefficient increases.

 

 

Figure 5. The average grain size of (a) SMA; (b) SMA+0.3 wt.% La₂O₃; (c) SMA+0.6 wt.% La₂O₃; (d) SMA+0.9 wt.% La₂O₃; (e) SMA+1.2 wt.% La₂O₃.

 

 

Figure 7. The microhardness changes of cross-section.

 

4. If possible, please provide pictures from the wear tracks. Also, I suggest authors give a brief overview of wear mechanisms. Following manuscripts can be used:

 

(1)-Corrosion and wear resistance characterization of environmentally friendly sol–gel hybrid nanocomposite coating on AA5083, Journal of Materials Science & Technology 29 (7), 603-608, 2013

 

(2)-Wear Induced Failure of Automotive Disc Brakes—A Case Study, Materials 12 (24), 4214, 2019

 

Reply to Reviewer:

Thank you very much for your valuable comments. We provide the wear tracks of SMA coating and SMA/(La₂O₃)_{0.9 wt.%} composite coating, and the wear mechanism has been analyzed by referring to two recommended papers.

Modification of Manuscript:

As shown in Figure 8. the wear width of SMA coating reaches 956 um, while the width of SMA/(La₂O₃)0_{.9 wt.%} composite coating is only 867 um. Plenty of furrow marks, which are caused by the the falling off of particles on the surface and continued to wear the surface, was observed in both SMA coatings, which is called abrasive wear. However, the wear scars depth of the SMA coating is significantly deeper than that of SMA/La₂O₃ composite coating (the arrow of Figure 8b) owing to the lower microhardness. Moreover, a large area of spalling on the surface was observed in Figure 8b, which is a typical adhesion wear, but also a more serious wear form than abrasive wear. On the contrast, the wear marks of SMA/La₂O₃ composite coating is more smooth and flat, although there are some spalling, but the area is smaller compared with the SMA coating [34-35].

 

[34]Rahimi, H.; Mozaffarinia, R.; Najafabadi, A.H. Corrosion and Wear Resistance Characterization of Environmentally Friendly Solegel Hybrid Nanocomposite Coating on AA5083. J. Mater. Sci. Technol. 2013, 29, 603-608.

[35]Mohammadnejad. A.; Bahrami, A.; Goli, M.; Nia, D.H.; Taheri, P. Wear Induced Failure of Automotive Disc Brakes—A Case Study. Materials, 2019, 12, 4214.

 

 

Figure 8. SEM micrographs of the wear scar (a)-(b) SMA coating; (c)-(b) SMA/(La₂O₃)_{0.9 wt.%}.

 

5. Could this increase in mechanical properties be ascribed to the dispersion hardening? Nothing is said about dispersion hardening. Please explain different strengthening mechanisms and mention that dispersion hardening can also attribute to final properties. Following papers are suggested:

 

(1)-Microstructure and Mechanical Properties of Spark Plasma Sintered Nanocrystalline TiAl-xB Composites (0.0<x<1.5 at.%) Containing Carbon Nanotubes, Journal of Materials Engineering and Performance 30 (6), 4380-4392, 2021

(2)-Mechanical property evaluation of corrosion protection sol–gel nanocomposite coatings, Surface Engineering 29 (4), 249-254, 2013.

 

Reply to Reviewer:

Thank you very much for your valuable comments.

Dispersion hardening is a strengthening method by adding hard particles to a uniform material. In this paper, when doping with 0.3 wt.%, 0.6 wt.% and 0.9 wt.%, no fine particles were observed in the composite coating, as shown in Figure. 4. However, when doping with 1.2 wt.%, some fine particles can be observed in the microstructure (red circle of Figure 4d), which may contain dispersion hardening. Importantly, we found the two articles you recommended helpful for our understanding and have been cited in the article. Thanks again for your valuable comments.

 

 

Figure 4. The microstructures of (a) SMA; (b) SMA+0.3 wt.% La₂O₃; (c) SMA+0.6 wt.% La₂O₃; (d) SMA+0.9 wt.% La₂O₃; (e) SMA+1.2 wt.% La₂O₃.

 

[33]Mohammadnejad, A., Bahrami, A., Tafaghodi Khajavi, L. Microstructure and Mechanical Properties of Spark Plasma Sintered Nanocrystalline TiAl-xB Composites (0.0<x<1.5 at.%) Containing Carbon Nanotubes. J. Mater. Eng. Perform. 2021, 30, 4380-4392.

[36]Hojjati Najafabadi, A., Mozaffarinia, R., Rahimi, H., Shoja Razavi, R., Paimozd, E. Mechanical property evaluation of corrosion protection sol-gel nanocomposite coatings. Surf. Eng. 2013, 29, 249-254.

 

6. Please make sure you use “AISI 304 SS” In the title and in the text.

 

Reply to Reviewer:

Thanks very much for your suggestion and we have replaced 304 ss in the title with AISI 304 SS.

Modification of Manuscript:

• Materials and Methods: AISI 304 stainless steel (SS) as the matrix.
• The composition ofAISI 304 SS and experimental powder (50-100 μm) were shown in table 1.
• Conclusions: In this paper, SMA/La₂O₃composite coating was prepared on AISI 304 SS by laser cladding technology.

Author Response File: Author Response.pdf

Reviewer 4 Report

The manuscript presents an interesting study about the effect of La₂O₃ on characteristics of SMA/Na coating deposited on steel. The paper needs major revisions before it is processed further, some comments follow:

Abstract:

The abstract is too short. The abstract must contain information about:

-       Background: Please highlight the novelty of the study.

-       Methods: Describe briefly the main methods used to obtain and characterize the coating.

-       Results and conclusions: Indicate the main conclusions or interpretations.

 

Introduction:

The introduction section must be improved.

In the introduction section, a comprehensive and exhaustive review of the state of the art in the field of the study must be provided. Please introduce and discuss more previous works, and highlight the experiments and results published previously.

Also, in the last paragraph please highlight the novelty and importance of this study and introduce the methods with which the characteristics of the coating were investigated.

 

Materials and methods

Line 77. The Potentiodynamic polarization and EIS are two different methods used to study the corrosion behaviour of materials. The authors must introduce the parameters of the Potentiodynamic polarization and EIS used to analyze the samples as type and material of electrodes, scan rate, working temperature, potential field, the exposed surface etc. Also, must be introduced information about the soft used to obtain the polarization curves and the soft used to obtain the equivalent circuit.

Regarding EIS, the Nyquist plots are not enough, in order to do the characterization, the authors need Bode too. A

Results and discussion

Subsection 3.1. The discussion about XRD patterns is poor. Please compare with other studies and introduce more comments.

Figures 3 and 5. Introduce figure labels to highlight the interest zone for the reader.

Why the grain is refined with doping of La₂O₃? Introduce discussion about this.

How was the chemical composition from Table 2 studied? Write in the Materials and Methods section. Also, Table 2 is not discussed in the text.

Subsection 3.4. Discuss these two methods separately and after that, the authors can compare the results. For the polarization method, the authors must introduce a table with the parameters obtained/calculated and discuss them (polarization resistance, corrosion rate etc.), please see DOI:10.3390/ma13153410.

Also, for the EIS the authors must introduce also the Bode plots and discuss them. Also, the discussion of EIS analysis was just a theoretical explanation. The impedance behaviour was not sufficiently discussed. The physical meanings of CPE parameters should be discussed and correlated with the results.

The results and discussion section must be improved. The results are discussed vague, introduce more comments and provide a comparative discussion between the obtained results and the literature.

Conclusion

The conclusion section should be improved. Conclusions present some of the results discussed above in the paper with very limited discussion.

References

There are too many self-citations (over 6) please remove the unnecessary ones.

Author Response

Dear Editor and Reviewers of the Journal of Coatings,

 

It is great thanks to you for the consideration of our manuscript “Effect of La₂O₃ on microstructure and properties of laser cladding SMA coating on AISI 304 stainless steel” (No. Coatings-1808577), and for giving us an opportunity to revise our manuscript.

 

The suggestions of editor and referees have been seriously considered and the manuscript has been further experimented, analyzed and revised based on these comments. The revised manuscript, a copy of the revised version in which all revised contents have been marked red, a supporting information document and the point-by-point response to referees’ comments are resubmitted using your online submission.

 

Please let me know any decisions you have made on the manuscript.

 

Thanks again for your and the referees’ advice.

 

 

Yours Sincerely,

Dr. Peng Xu

College of Materials and Metallurgy,

Guizhou University, Guiyang, 550025, China,

E-mail: pxu2@gzu.edu.cn.

 

 

 

 

 

 

 

About the questions and advices from Reviewer #4' comments:

 

1. Abstract:

The abstract is too short. The abstract must contain information about:

Background: Please highlight the novelty of the study.

Methods: Describe briefly the main methods used to obtain and characterize the coating.

Results and conclusions: Indicate the main conclusions or interpretations.

 

Reply to Reviewer:

Thanks very much for your valuable suggestion. We supplement the background, methods, results and conclusions of the abstract. Now the abstract has 176 words, and the content is more abundant, thank you again for your suggestion.

Modification of Manuscript:

Abstract: Known as stress self-accommodation characteristic, the laser cladding shape memory alloy (SMA) coatings have been widely used in material failure repair. Nevertheless, its further development is greatly limited by the low microhardness (250 HV_0.2) and corrosion resistance. Benefiting from the capability of refined grain and adjusted microstructure, rare earth oxides play a key role in improving the properties of materials. Herein, to improve the microhardness and anti-corrosion of laser cladding SMA coatings, different amounts of La₂O₃ were doped in SMA coating. The influence of the different La₂O₃ doping amounts on the phases, grain size and microhardness was studied. The anti-corrosion of the SMA/La₂O₃ composite coating was explored in 3.5 wt.% sodium chloride solution. Result showed that the grain of the SMA/La₂O₃ composite coating is significantly refined. When doping with 0.9 wt.%, the refinement rate reaches 19%. Furthermore, based on the Hall-Petch effect, the microhardness of the SMA/La₂O₃ composite coating is increased to 450 HV_0.2. At the same time, the anti-corrosion of the composite coating is enhanced due to the smaller grain size and fewer defects.

 

2. Introduction:

The introduction section must be improved. In the introduction section, a comprehensive and exhaustive review of the state of the art in the field of the study must be provided. Please introduce and discuss more previous works, and highlight the experiments and results published previously. Also, in the last paragraph please highlight the novelty and importance of this study and introduce the methods with which the characteristics of the coating were investigated.

 

Reply to Reviewer:

Thank you very much for your valuable comments. We present more previously published papers and highlight the results. The novelty and importance of our research and the method of coating preparation are also emphasized in the last paragraph.

Modification of Manuscript:

Introduction

As the conditions of service become more stringent, materials are put forward higher demands and the problem of material failure becomes more and more severe [1-2]. Based on the advantages of the small heat-affected zone and metallurgical bonding [3-4], laser cladding technology is widely applied in material failure repair [5]. Nevertheless, the residual stress caused by the extremely fast cooling rate will affect the service life. In order to better apply laser cladding technology in material failure repairing, how to further reduce the residual stress has become an urgent problem to be solved [6].

Over the past few decades, extensive amounts of studies have been carried out in the field of residual stress release due to its crucial role in practical application [7-8]. The heat treatment was used to reduce the residual stresses by Park [9], and the residual stress was reduced by 50% after 700 ℃ treatment. Roehling [10] developed an in situ annealing method to weaken residual stresses in coating fabricated by LPBF (laser powder bed fusion). The result shows that the residual stress decrease of 90% was achieved in the coating. However, these methods mentioned above have a complex process and high production costs.

Recently, Fe-Mn-Si shape memory alloy (SMA) has attracted more and more attention owing to the stress self-accommodation characteristic. Xu et al. [11] fabricated Fe-Mn-Si-Ni-Cr SMA coating using laser cladding technology, which greatly weakens the residual stress of the coating. Ferretto et al. [12] prepared Fe17Mn5Si10Cr4Ni SMA parts by LPBF for the first time, which further promotes the development of SMA. But the anti-corrosion and lower microhardness (only 250 HV_0.2) are two key factors that limit its industrial application. To strengthen the performance of SMA coating, the PZT, Ti, WC and Nb were used for modification. The corrosion resistance and microhardness were enhanced significantly. But there is still a certain gap from the practical application [13-14].

Benefiting from its good chemical and physical properties as well grain refinement, rare earth elements, honored as industrial vitamins, has a vital role in improving the microhardness, wear resistance and anti-corrosion of materials [15-16]. Rare earth elements can purify molten steel, improve inclusions and refine grains, which is an effective method for adjusting the microstructure and enhancing the mechanical properties of steel. Du et al [17] prepared Y₂O₃ doped WC reinforced coating by laser cladding technology. The result showed that the addition of Y₂O₃ promoted the metallurgical bonding between the coating and the substrate, and also improved the weldability and laser absorption rate of Invar alloys. By adding different amounts of La₂O₃, Y₂O₃ and CeO₂, the grains of Ni60 coating were significantly refined and the microhardness was significantly improved [18]. Liu et al. [19] doped different amounts of CeO₂ in TiC/Ti₂Ni coating. The result showed that the microhardness and wear resistance of the composite coating was greatly enhanced. Therefore, rare earth elements alloying is an effective method to improve the properties of materials.

To further strengthen the properties of Fe-Mn-Si shape memory alloy composite coating, The FeMnSiCrNiNb/(La₂O₃)x (x= 0.3, 0.6, 0.9, 1.2 wt.%) composite coating was prepared via laser cladding technology. The XRD, Vickers hardness tester, the MFT-5000 Tribometer and electrochemical workstation were applied to explore the phases, microhardness and anti-corrosion of coatings.

 

3. Materials and methods

Line 77. The Potentiodynamic polarization and EIS are two different methods used to study the corrosion behaviour of materials. The authors must introduce the parameters of the Potentiodynamic polarization and EIS used to analyze the samples as type and material of electrodes, scan rate, working temperature, potential field, the exposed surface etc. Also, must be introduced information about the soft used to obtain the polarization curves and the soft used to obtain the equivalent circuit.

Regarding EIS, the Nyquist plots are not enough, in order to do the characterization, the authors need Bode too. A

 

Reply to Reviewer:

Thank you very much for your valuable comments. We have introduced the experimental parameters in detail in the Materials and Methods section, including electrode type, scanning rate, working temperature, working area and frequency. Polarization curve testing software and equivalent circuit software are also introduced.

The description of bode plot is added in the Results and Discussion section. Thank you again for your advice.

Modification of Manuscript:

(1)-Materials and Methods

The polarization plots was measured by the three-electrode system of electrochemical workstation (CHI660D; CH Company, Ltd) in 3.5 wt.% sodium chloride solution (macklin, AR) at 25 ℃. The Pt electrode and saturated calomel electrode were used as counter electrode (the area of Pt is 1 cm²) and reference electrode, respectively. Voltage range from -2 V to 2 V, scan rate is 0.01 V/s and the sample exposure area is 0.49 cm². The electrochemical impedance spectroscopy (EIS) was used to test the impedance of the coating. The frequency range from 10⁰-10⁶ HZ and the amplitude is 0.005 V [20]. ZView software was used to simulate the equivalent circuit.

 

(2)-Results and Discussion

Figure 10c shows the bode plot of coatings. The |Z| can be applied to evaluate the anti-corrosion of the coatings in low frequency. When the doping amounts exceeds 0.6 wt.%, the |Z| of the composite coating is higher than that of the SMA coating from high frequency to low frequency, indicating that doping La₂O₃ is an effective method to improve corrosion resistance. Figure 10d shows the frequency-phase plot. Obviously, there is only one weav peak, indicating that coatings has only one time constant.

 

Figure 10. (a) Polarization curve; (b) Nyquist plot; (c)-(d) Bode plot.

 

4. Results and discussion

 

4.1 Subsection 3.1. The discussion about XRD patterns is poor. Please compare with other studies and introduce more comments.

 

Reply to Reviewer:

Thank you very much for your valuable comments. We re-analyzed the XRD from phase, peak shift, and split the original Figure 2 into two figures for easier understanding.

Modification of Manuscript:

The XRD patterns of La₂O₃ doped with different amounts are shown in Figure 2a. There is no obvious difference in the XRD patterns, all of which are composed of Nb phase, thermoelastic ε-martensite, non-thermoelastic α'-martensite and γ-austenite phases. The presence of thermoelastic ε-martensite proves that γ-austenite transformation occurs in the SMA coating, which is the characteristic of SMAs [21-22]. Furthermore, thermoelastic ε-martensite is also key to shape memory effect. Meanwhile, the γ-austenite of the composite coatings are all shifted to high angles, whcih indicates that the interplanar spacing d decreases based on the Bragg equation (2dsinθ=nλ).

In addition, Figure 3 exhibits a lot of white area on the surface (white circle), and EDS analysis indicates that the Nb phase is precipitated in this area, which is consistent with the XRD pattern [23].

 

Figure 2. The XRD patterns of coatings

 

 

Figure 3. The elements of coating surface.

 

 

4.2 Figures 3 and 5. Introduce figure labels to highlight the interest zone for the reader.

 

Reply to Reviewer:

Thank you very much for your valuable comments. We are very sorry for not describing Figures 3 (Updated to Figure 4) and 5 (Updated to Figure 6) clearly. Firstly, Figure 3 is a description of the grain size, the reader only needs to know its grain size, so we did not mark Figure 3. But we found that the scale of the original image was not clear, so we supplemented the scale and replaced the new image. Secondly, we supplemented the markup in Figure 5 to help readers understand. Thanks again for your valuable comments.

 

 

Figure 4. The microstructures of (a) SMA; (b) SMA+0.3 wt.% La₂O₃; (c) SMA+0.6 wt.% La₂O₃; (d) SMA+0.9 wt.% La₂O₃; (e) SMA+1.2 wt.% La₂O₃.

 

 

Figure 6. The eutectic microstructures (arroy) of (a) SMA+0.3 wt.% La₂O₃; (b) SMA+0.6 wt.% La₂O₃; (c) SMA+0.9 wt.% La₂O₃; (d) SMA+1.2 wt.% La₂O₃.

 

4.3 Why the grain is refined with doping of La₂O₃? Introduce discussion about this.

 

Reply to Reviewer:

Thank you very much for your valuable comments. The grain refining mechanism is described in the 3.2 section.

Modification of Manuscript:

This is because the rare earth oxides act as heterogeneous nucleation sites, increase the probability of heterogeneous nucleation, and refine grains [24-25].

 

4.4 How was the chemical composition from Table 2 studied? Write in the Materials and Methods section. Also, Table 2 is not discussed in the text.

 

Reply to Reviewer:

Thank you very much for your valuable comments. We supplement how to study chemical composition in the Materials and Methods section. The description of Table 2 is also added in the paper. Thank you very much for your reminding.

Modification of Manuscript:

(1)-Elemental analysis of the samples was performed using Energy-dispersive X-ray spectroscopy (EDS, Oxford instruments).

 

(2)-Besides, as shown in Figure 6 [28-29], plenty of eutectic microstructures containing Fe, Si, Mn and Nb elements were also formed on the grain boundary of the SMA/La₂O₃ composite coating, as shown in Table 2.

 

4.5 Subsection 3.4. Discuss these two methods separately and after that, the authors can compare the results. For the polarization method, the authors must introduce a table with the parameters obtained/calculated and discuss them (polarization resistance, corrosion rate etc.), please see DOI:10.3390/ma13153410.

Also, for the EIS the authors must introduce also the Bode plots and discuss them. Also, the discussion of EIS analysis was just a theoretical explanation. The impedance behaviour was not sufficiently discussed. The physical meanings of CPE parameters should be discussed and correlated with the results.

 

Reply to Reviewer:

Thank you very much for your valuable comments. Firstly, We have supplemented the corrosion rates in Table 3, and thank you very much for your suggestion. Secondly, we supplement the description of the bode plot in Section 3.4, and further describe the EIS curve. Finally, we reanalyze CPE and further elucidate its physical significance.

Modification of Manuscript:

Table 3 EIS parameters

wt.%	Ecorr	Icorr	Rate (gram/hr)	Rate (mil/year)
0	-0.81	4.733*10-5	3.296*10-5	29.52
0.3	-0.67	4.710*10-6	3.280*10-6	2.937
0.6	-0.64	4.556*10-6	3.173*10-6	2.842
0.9	-0.65	1.462*10-5	1.018*10-5	9.118
1.2	-0.72	1.345*10-5	9.367*10-6	8.388

 

(1)-Figure 10c shows the bode plot of coatings. The |Z| can be applied to evaluate the anti-corrosion of the coatings in low frequency. When the doping amounts exceeds 0.6 wt.%, the |Z| of the composite coating is higher than that of the SMA coating from high frequency to low frequency, indicating that doping La₂O₃ is an effective method to improve corrosion resistance. Figure 10d shows the frequency-phase plot. Obviously, there is only one weav peak, indicating that they have only one time constant.

 

Figure 10. (a) Polarization curve; (b) Nyquist plot; (c)-(d) Bode plot.

 

(2)-In order to more accurately describe the anti-corrosion, the equivalent circuit was used to simulate EIS parameters. As shown in Figure 11, the EIS data are shown in Table 4. Where Rct, Rs, Rf and CPE represent the film resistance charge transfer resistance, solution resistance, coating resistance and constant phase element, respectively. The CPE is applied to compensate the non-uniformity of the system instead of capacitors. The CPE is defined using the equation of Z_CPE= [Y(jω)n]^-1,where n present the dimensionless index, ω present the frequency and Y present the CPE constant. If n=1, the CPE is equivalent capacitor; if n=0, the CPE is equivalent resistance [43].

The capacitance (C) of the coating is calculated by resistance R and CPE (Q) respectively [44]:

Rs of all coatings are lower 2 Ω, which will not affect the results. Benefiting from the grain refinement, the Cdl of the composite coating decreased by 1-2 orders of magnitude, and the Rct increased by 3 to 6 times, compared with SMA coating. Especially, the SMA/(La₂O₃)_{0.9 wt.%} composite coating processes the minimum Cdl and maximum n value, proving that the corrosion of the composite coating was more difficult. When the doping with 1.2 wt.%, the Cdl gradually increased and n decreased. This is consistent with the previous results.

 

4.6 The results and discussion section must be improved. The results are discussed vague, introduce more comments and provide a comparative discussion between the obtained results and the literature.

 

Reply to Reviewer:

Thank you very much for your valuable comments. We have modified the XRD, microstructure and polarization curve according to the above requirements. Thank you again for your careful reading.

 

5. Conclusion

 

The conclusion section should be improved. Conclusions present some of the results discussed above in the paper with very limited discussion.

 

Reply to Reviewer:

Thank you very much for your valuable comments. We have improved our conclusions.

Modification of Manuscript:

4. conclusion

In this paper, SMA/La₂O₃ composite coating was prepared on AISI 304 stainless steel by laser cladding technology, so as to improve the microhardness and anti-corrosion of SMA coating. The result shows that the phases of all coatings are composed of Nb phase, thermoelastic ε-martensite, non-thermoelastic α'-martensite and γ-austenite phases. The presence of thermoelastic ε-martensite proves that γ-austenite transformation occurs in the SMA coatings, which is the characteristic of SMAs, and it is also the key to shape memory effect. The advantage of using rare earth oxide as heterogeneous nucleation site can increase the probability of heterogeneous nucleation and refine the grain. Based on the Hall-Petch formula, The smaller the grain size, the higher the microhardness. When doping with 0.9 wt.%, the average grain size of the composite coating decreases to only 3.03 um, and the refinement rate reaches 19%, which greatly improves the microhardness and anti-wear of the coating. Due to the low microhardness of SMA coating, the surface has a large area of peeling, and the wear pit is larger and deeper after friction test, which is corresponding to abrasive wear and adhesive wear. On the contrary, the surface of composite coating is only abrasive wear, and the wear scars are shallower.

The E_corr and I_corr of the composite coating are significantly improved, this is attribute to the addition of La₂O₃ in the alloy can not only refine the grain but also generate inclusions with impurity element S and Al, which can be purified the microstructure and improved the anti-corrosion. Compared with SMA coating, the Cdl of the composite coating decreases by 1-2 order of magnitude, and the Rct increases by 3-6 times, indicating that the corrosion of the coating is more difficult.

 

6. References

There are too many self-citations (over 6) please remove the unnecessary ones.

 

Reply to Reviewer:

Thank you very much for your valuable comments. We have reduced self-citation to five now.

Modification of Manuscript:

[6]Liu, C.Y.; Xu, P.; Zheng, D.Y.; Liu, Q.B. Study on microstructure and properties of a Fe-based SMA/PZT composite coating produced by laser cladding. J. Alloys. Comp. 2020, 831, 154813.

[11]Xu, P.; Ju, H.; Lin, C.X.; Zhou, C.Y.; Pan, D.W. In-situ synthesis of Fe-Mn-Si-Cr-Ni shape memory alloy functional coating by Laser cladding. Chin. Optic Lett. 2014, 12, 041403.

[13]Tian, J.Y.; Xu, P.; Chen, J.H.; Liu, Q.B. Microstructure and phase transformation behaviour of a Fe/Mn/Si/Cr/Ni alloy coating by laser cladding. Opt. Lasers.Eng. 2019, 122, 97-104.

[14]Liu, C.Y.; Xu, P.; Zha, G.Q.; Ouyang, Z. Microstructure and properties of a Ti doped Fe based SMA coating produced by laser cladding. J. Mater. Res. Technol. 2021, 14, 2441-2450.

[21]Tian, J.Y.; Xu, P.; Liu,Q.B. Effects of stress-induced solid phase transformations on residual stress in laser cladding a Fe-Mn-Si-Cr-Ni alloy coating. Mater. Design. 2020, 193, 108824.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear authors, I see major improvements of your manuscript. You answered clearly and satisfactory to all my review remarks. I see that you didn't taking account of this remark: the references are numbered twice in References section. Remove the number in straight brackets!!!!

Reviewer 3 Report

Thanks for addressing all my comments. The paper can be published in my opinion.

 

Reviewer 4 Report

The manuscript can be published in the present form.