Research on Laser Cladding Co-Based Alloy on the Surface of Vermicular Graphite Cast Iron

Round 1

Reviewer 1 Report

Figure 11 needs a scale or a dimension reference

increases the number of micro-batteries: what is this…what is batteries.

Figure 10…how many repetitions did you perform?

Stent was one key application in some printing. I did not know that steels were allowed if a high purity is not achieved. Is this a demonstrator or a real part?
Amazing work, my questions are about the joints of several line-shape with others, as it is also studied in below work. Anisotropy and microstructural heterogeneity are commonly regarded as two of the primary drawbacks to be rectified in metal AM processes.
You missed https://doi.org/10.1016/j.eng.2020.02.013 and some comparison with Bioresorbable stents (BRS), they were introduced with important advantages: complete bioresorption, mechanical flexibility, does not produce imaging artefacts in non-invasive imaging modalities, etc. BRS are an alternative to yours.
1. There are new works recently published about how small and other aspects of auxetic structures, using LPBF, you did not read: A New Approach in the Design of Microstructured Ultralight Components to Achieve Maximum Functional Performance. Materials 2021, 14, 1588. https://doi.org/10.3390/ma14071588 you can see how small the printing is here, perhaps the alloy is not the same but the concept is. This is the only paper I found.
2. Please include, only a few are working on the topic.
3. Figure 14 shows thicker corners, did you check structures in the 316 steel?
4. You define 3 ways to remove support structures. Did you compare them in one single case?
5. The microstructure of the LPBF-ed components depends on three main aspects: the solidification mode, LSS and volumetric energy density (VED). Moreover, these features depend on the following specific parameters: the laser power (P), layer thickness (t), hatching space (h) and laser speed (Vb). Perhaps you can extend the discussion about the influence of the parameters on stent quality.
6. By the way, you missed one line of research, A sustainable process for material removal on pure copper by use of extremophile bacteria, Journal of cleaner production 84, 752-760 there are people working with bacteria for removing and polishing micro-printed components. Please include.

 

Author Response

Figure 11 needs a scale or a dimension reference

      

Modifications have been made in the article, and a ruler has been added to the picture.

 

increases the number of micro-batteries: what is this…what is batteries.

When the surface of the cladding layer is in contact with the electrolyte solution, there are many tiny cathodes and anodes on the entire metal surface under the comprehensive influence of material unevenness, uneven surface state and uneven structure, thereby forming many tiny short-circuit batteries that undergo corrosion. These tiny batteries are called micro-batteries.

Figure 10…how many repetitions did you perform?

The shear strength was repeated 4 times for each sample.

Stent was one key application in some printing. I did not know that steels were allowed if a high purity is not achieved. Is this a demonstrator or a real part?

Did not find the corresponding part in the article
Amazing work, my questions are about the joints of several line-shape with others, as it is also studied in below work. Anisotropy and microstructural heterogeneity are commonly regarded as two of the primary drawbacks to be rectified in metal AM processes.

Did not find the corresponding part in the article
You missed https://doi.org/10.1016/j.eng.2020.02.013 and some comparison with Bioresorbable stents (BRS), they were introduced with important advantages: complete bioresorption, mechanical flexibility, does not produce imaging artefacts in non-invasive imaging modalities, etc. BRS are an alternative to yours.

Did not find the corresponding part in the article
1. There are new works recently published about how small and other aspects of auxetic structures, using LPBF, you did not read: A New Approach in the Design of Microstructured Ultralight Components to Achieve Maximum Functional Performance. Materials 2021, 14, 1588. https://doi.org/10.3390/ma14071588 you can see how small the printing is here, perhaps the alloy is not the same but the concept is. This is the only paper I found.

Did not find the corresponding part in the article
2. Please include, only a few are working on the topic.

Did not find the corresponding part in the article
3. Figure 14 shows thicker corners, did you check structures in the 316 steel?

Did not find the corresponding part in the article
4. You define 3 ways to remove support structures. Did you compare them in one single case?

Did not find the corresponding part in the article
5. The microstructure of the LPBF-ed components depends on three main aspects: the solidification mode, LSS and volumetric energy density (VED). Moreover, these features depend on the following specific parameters: the laser power (P), layer thickness (t), hatching space (h) and laser speed (Vb). Perhaps you can extend the discussion about the influence of the parameters on stent quality.

Did not find the corresponding part in the article
6. By the way, you missed one line of research, A sustainable process for material removal on pure copper by use of extremophile bacteria, Journal of cleaner production 84, 752-760 there are people working with bacteria for removing and polishing micro-printed components. Please include.

Did not find the corresponding part in the article

Author Response File: Author Response.docx

Reviewer 2 Report

The present study investigated the effect of the Co/Ni metal cladding layer on the wear characteristics of Cast iron. The topic is interesting and can be valuable to the coating development community. However, there are many flaws in data analysis and presentation. So, this manuscript can be accepted only after major revision.

1. The author did a very good literature survey. However, there are some investigations on the wear behavior of cast iron that can be included.

https://doi.org/10.1016/B978-0-12-803581-8.10460-6

doi:10.4028/www.scientific.net/AMR.264-265.1928

https://doi.org/10.1108/ILT-03-2011-0019

 

2. The experimental is not clear. Please describe the detailed steps of the materials processing and characterization. Such as is the powder coaxially feeder with laser or first feed the powder and then melted with a laser. A schematic may provide a nice visualization.
3. Characterization: Such as -XRD data acquisition parameter need to be provided.
4. Results: what was the thickness of the clad layers. Please add a cross-sectional image.
5. The EDS data is hard to read. I recommended exporting the EDX line scan to a text file and plot it manually using Matlab/Excel.
6. Usually, EDX cannot provide C content accurately as there would always be contamination. So, better not to present the C data.
7. The XRD data analysis needs to be revised. It is not possible to overlap 7 phases in one peak. What is the 2q angles for each phase? What is the volume fraction of the phases? What is the XRD detection limit you used?
8. The figure captions should be comprehensive. Such as “Load-displacement curve”-what does it mean? Load-displacement curve of ...?
9. Please add scale bars in Fig. 11.
10. Please add more references. They are very limited.

Author Response

1.The author did a very good literature survey. However, there are some investigations on the wear behavior of cast iron that can be included.

https://doi.org/10.1016/B978-0-12-803581-8.10460-6

doi:10.4028/www.scientific.net/AMR.264-265.1928

https://doi.org/10.1108/ILT-03-2011-0019

Thank you for your comments. We have added the suggested references to the article introduction

1.The experimental is not clear. Please describe the detailed steps of the materials processing and characterization. Such as is the powder coaxially feeder with laser or first feed the powder and then melted with a laser. A schematic may provide a nice visualization.

 

Schematic diagram of laser cladding

 

2. Characterization: Such as -XRD data acquisition parameter need to be provided.

XRD data acquisition parameter:The phase identification was characterized by an X-ray diffractometer (D/max-rA), which worked under Cu K-α radiation (λ=1.54Å, 40 kV, 40 mA). The XRD pattern collection range was 10◦≤2θ ≤100◦, and the scanning velocity was 4°/min). The dimension of the test specimens was 15mm×15mm×10mm.

3.Results: what was the thickness of the clad layers. Please add a cross-sectional image.

The cross-sectional image is shown below

Fig.2 shows the macro morphology of the cross section of the cladding layer. Fig.2 shows that the two cladding layer structures are dense and uniform, with a small amount of pores and no obvious cracks. The existence of a small amount of pores in the cladding layer is due to the rapid heating and cooling characteristics of the laser cladding process, which makes the amorphous powder insufficiently meltedand some space among the filled powders is remained^[1]. In addition, there is a clear macroscopic boundary between the cladding layer and the substrate, and the boundary line is a curve close to the horizontal on the left and right sides. A metallurgical bond is formed between the cladding layer and the substrate. The average thickness of the two different cladding layers is about 2mm.

Figure 2. Macro morphology of the cross section of the cladding layer

4. The EDS data is hard to read. I recommended exporting the EDX line scan to a text file and plot it manually using Matlab/Excel.

The EDX line scan has been corrected as follows

 

5. Usually, EDX cannot provide C content accurately as there would always be contamination. So, better not to present the C data.

EDX line scan graph has deleted C data

6. The XRD data analysis needs to be revised. It is not possible to overlap 7 phases in one peak. What is the 2q angles for each phase? What is the volume fraction of the phases? What is the XRD detection limit you used?

XRD data has been changed.

The 2q angles is 3-70°.  The phase identification was characterized by an X-ray diffractometer (D/max-rA), which worked under Cu K-α radiation (λ=1.54Å, 40 kV, 40 mA). The XRD pattern collection range was 10◦≤2θ ≤100◦, and the scanning velocity was 4°/min). The XRD detection limit is 5%.

 

7.The figure captions should be comprehensive. Such as “Load-displacement curve”-what does it mean? Load-displacement curve of ...?

Modifications have been made in the article to the load-displacement curve of the cladding layer.

8.Please add scale bars in Fig. 11.

Modifications have been made in the article, and a ruler has been added to the picture.

9.Please add more references. They are very limited.

Added references in the introduction

Reviewer 3 Report

- Abstract must contain brief and highlight achievements of research, not general discussion. Re-organization of abstract is needed.
- All the abbreviations need to be introduced in the main text (for example MMAM).
-The sentence must be referenced; “The parameters of the experiment are the parameters of good surface condition and good quality in the previous experiments.”
- The sentence must be corrected; “inert nitrogen gas…”
- The sentence must be corrected; “The length and width of the cladding layer were 40mm respectively”
- The sentence must be corrected; “When cladding the next cladding layer. According to heat transfer,…”
- In Figure 2, the image quality is low and the text is not clear and legible
- The interface between the clad layer and the cast iron substrate needs to be further investigated.
- Investigating the distribution and composition of the phases formed in the clad layer requires more evidence.
- The novelty of your work should be presented better at the end of the introduction part. This should be presented with more details
-Literature review is not sufficient and authors must review and cite more papers in the field and especially newly published ones. Doing this, review and citing the following refs could be helpful:
[a] Ceramics International 41 (2015) 9350-9360
[b] Journal of Alloys and Compounds 822 (2020) 153708
[c] Surface and Coatings Technology 339 (2018) 37-47
[d] Neural Computing and Applications 23 (2013) 779-786
[e] Optics & Laser Technology 134 (2021) 106619
[f] Surface and Coatings Technology 347 (2018) 20-28
- Conclusion part must be rewritten in such a quantitative way rather than a qualitative report.

Author Response

1.Abstract must contain brief and highlight achievements of research, not general discussion. Re-organization of abstract is needed.

The summary content has been reorganized as follows：“To further improve the hardness of the laser cladding layer on the surface of the vermicular graphite cast iron, the structural parameters of the laser cladding Co-base were designed and optimized, and the properties of the clad layer were evaluated using optical microscopy (OM), scanning electron microscopy (SEM), energy spectroscopy (EDS), X-ray diffractometer (XRD), electrochemical workstation, and friction wear equipment. The results show that the average hardness of the molten layer of Ni and Co-based composite cladding layer is 504 HV_0.5, which is 0.64 times that of the Co-based cladding layer due to the combined factors of Ni-Cr-Fe equivalent to the dilution of the Ni-based cladding layer to the Co-based cladding layer. Due to the potential difference of the Ni, Cr, and Co elements on the surface of the cladding layer, the self-corrosion potential of the Ni and Co-based composite cladding layer is 1.08 times that of the Co-based cladding layer, and the self-corrosion current density is 0.51 times. Laser cladding Co-based cladding layer has high corrosion resistance. Under the influence of plastic deformation and oxidative wear of the cladding layer of the Ni and Co-based composite cladding layer, the wear amount of the cladding layer of the Ni and Co-based composite cladding layer is less”.

2.All the abbreviations need to be introduced in the main text (for example MMAM).
     Abbreviations MMAW has been corrected to “manual metal arc welding”

3.The sentence must be referenced; “The parameters of the experiment are the parameters of good surface condition and good quality in the previous experiments.”

Modifications have been made in the article to:“In order to obtain a cladding layer with good surface condition and good quality forming, the parameters were optimized.”
4. The sentence must be corrected; “inert nitrogen gas…”

Modifications have been made in the article to:“Nitrogen is used as the protective gas, and the flow rate is 18L/min.”
5.The sentence must be corrected; “The length and width of the cladding layer were 40mm respectively”
    Modifications have been made in the article to:“Two layers of cobalt-based materials with a length and a width of 40 mm were cladding on the substrate.”

6. The sentence must be corrected; “When cladding the next cladding layer. According to heat transfer,…”

The sentence has been corrected to “Fig.6 (b) shows the lateral hardness distribution on the surface of the cladding layer. Fig.6 (b) shows that the lateral hardness has periodic fluctuations. The periodic hardness fluctuations are due to the use of multiple laser cladding for each cladding layer. The second irradiation of the laser causes the grains in the remelting zone to grow up by heating, and the structure to coarsen ^[21].”

7.In Figure 2, the image quality is low and the text is not clear and legible

The changed picture is shown below

8.The interface between the clad layer and the cast iron substrate needs to be further investigated.

A cross-sectional image has been added to study the interface between the cladding and the substrate

Fig.2 shows the macro morphology of the cross section of the cladding layer.  Fig.2 shows that the two cladding layer structures are dense and uniform, with a small amount of pores and no obvious cracks. The existence of a small amount of pores in the cladding layer is due to the rapid heating and cooling characteristics of the laser cladding process, which makes the amorphous powder insufficiently meltedand some space among the filled powders is remained^[15]. In addition, there is a clear macroscopic boundary between the cladding layer and the substrate, and the boundary line is a curve close to the horizontal on the left and right sides. A metallurgical bond is formed between the cladding layer and the substrate. The average thickness of the two different cladding layers is about 2mm.

Figure 2. Macro morphology of the cross section of the cladding layer

9.Investigating the distribution and composition of the phases formed in the clad layer requires more evidence.

It has been corrected to the following:Table 2 demonstrates that the surface structure of the Ni-based transition layer is enriched in Fe, Co and Ni in the Crystal nucleus, and C and Cr are enriched in the intergranular. The surface structure without the Ni-based transition layer is rich in Co and Fe in crystal nucleus, and C and Cr in the intercrystalline. According to the literature^[18-20], the Cr, Mo, Fe and C elements enriched in the dendrites mainly exist in the form of carbides. The surface structure with the transition layer is rich in Ni element between the nuclei. According to the intercrystalline enrichment of C and Cr elements, and combined with XRD analysis, the main carbides are Cr23C6 and Cr7C3.

10.The novelty of your work should be presented better at the end of the introduction part. This should be presented with more details

The content at the end of the introduction has been rewritten as follows:“Although there has been some research on laser cladding on cast iron, the issue of how to further improve the quality of the cladding remains a hot issue of engineering concern. In this paper, the structural design of the laser cladding layer is optimized and its performance is evaluated. The research results provide support for the optimization of process parameters in engineering”.

11.Literature review is not sufficient and authors must review and cite more papers in the field and especially newly published ones. Doing this, review and citing the following refs could be helpful:
[a] Ceramics International 41 (2015) 9350-9360
[b] Journal of Alloys and Compounds 822 (2020) 153708
[c] Surface and Coatings Technology 339 (2018) 37-47
[d] Neural Computing and Applications 23 (2013) 779-786
[e] Optics & Laser Technology 134 (2021) 106619
[f] Surface and Coatings Technology 347 (2018) 20-28

The newly published papers are reviewed and cited at the beginning of the introduction and the literature review section. The details are as follows:“Vermicular graphite cast iron has good thermal conductivity and thermal fatigue properties, and is often used to manufacture cylinder heads for engines^[1-4]. In engineering, in order to achieve the engine intake and exhaust function, the cylinder head is designed with intake and exhaust holes and an upper valve seat is mounted. The traditional inlay valve seat way in the service process, by the valve high-frequency impact effect, valve seat off failure frequently. In order to improve the durability of the valve seat in the service process, the new power is integrated with a cylinder head and a valve seat. Since valve seats require a material surface resistant to wear, the overall valve seat surface needs to increase its abrasion resistance using the modified process. The main methods used to modify and improve the hardness of valve seats are high frequency induction phase change hardening, laser phase change hardening, laser melting and laser cladding^[5-6]. The use of high-frequency induction phase hardening, which requires the development of special induction coils for the shape of the valve seat, a method that primarily involves heating ductile iron above the phase hardening hardness and using rapid cooling in phase change hardening regions to form martensite tissue. Laser phase hardening and high-frequency induction phase hardening are basically the same in principle, also generating a layer of high hardness martensite tissue on the surface. Laser melting is the use of high power density laser to generate a layer of high hardness Leylandite on the surface of the material, but the Leylandite organization is brittle and affects the service life of the valve seat in the service environment^[7]. Martensite generated by phase hardening method, when the valve seat temperature reaches 500°C under service conditions, the martensite will experience hardness deterioration^[8]. ”“ Li^[9]et al investigated the effect of different structural designs of the substrate on the properties of the cladding layers and obtained a cladding layer structure that reduces stress. Liu^[10] prepared multilayer cladding layers on the surface of ductile iron by using laser cladding in order to solve the problem of bond interface brittleness and evaluated the properties of the cladding layers.”

12.Conclusion part must be rewritten in such a quantitative way rather than a qualitative report.

The conclusion of the article has been reorganized as follows：

1)The self-corrosion potentials of the Co-based cladding layer and the Ni and Co-based composite cladding layers are -0.896V and -0.964V, respectively, and the self-corrosion current density is 2.469×10^-4 A·cm^-2 and 3.547×10^-4 A·cm^-2. Due to the inhomogeneity of the material and the structure and the potential difference between the elements, the micro-batteries are formed. Compared with the Ni and Co-based composite cladding layer, the surface of the Co-based cladding layer has better corrosion resistance.

2)The wear of Ni and Co-based composite cladding layer is 0.72 times higher than that of Co-based cladding layers due to the combination of different compounds generated by the different elemental contents and the different degrees of plastic deformation, fatigue wear and oxidative wear occurring on the surface of the cladding layers.

3)The average hardness value of the cladding region of the Co-based cladding layer is 788HV_0.5, and the average hardness value of the cladding region of the Ni and Co-based composite cladding layer is 504HV_0.5.

4)Due to the excellent mechanical properties of the Co-based cladding layer prepared by laser, the shear strength of the cladding layer is greater than that of the base material.

 

Author Response File: Author Response.docx

Reviewer 4 Report

It is a very interesting topic concerning the production of a coating using the laser cladding method on vermicular cast iron.
However, I am missing a few things and therefore have some comments:
1. Please check the English language carefully. It will be good when the manuscript will checked by native speaker.
2. The Abstract section is a bit chaotic, it can be slightly shortened.
3. The Introduction section is interesting. It can be see that the authors have a practical approach to the topic. However, I propose to extend this section a little to Co-based coatings produced on other substrates. 
4. How the amount of powder feeding per 18 g/min was determined?
5. Did the drying of powder take place from the moment of reaching the temperature or from putting the powder into the dryer?
6. What was the TEM of the laser beam?
7. The authors write that the SEM photos were taken using Phenom XL, while the photos have the ZEISS logo
8. I miss pictures of the coating morphology on the cross-section, so that I can evaluate the entire coating from surface to substrate.
9. Punctuation errors, eg line 162 - no spaces
10. Are you able to estimate the composition of complex carbides? Have you analyzed the equilibrium diagrams for the coating elements?
11. You write "hardness" in one place and "microhardness" in another. Of course, "hardness" is correct, because the microhardness is less than 200 g of load. Load above 200 g will be hardness.
12. When entering the hardness value, you must enter the load, ie instead of 825 HV, it will enter 825 HV0.5
13. Although, in my opinion, the results of the research are interestingly described, please refer to the results of other researchers more often in the research results.
14. Did you monitor the mass loss during the test or only have the final results. Perhaps it would be better to plot a weight loss versus time graph.
15. What do you mean by micro-batteries
16. Conclusions match the content
My opinion: Major revision 

Author Response

1. Please check the English language carefully. It will be good when the manuscript will checked by native speaker.

Thanks for your comments. We have checked the content of the article in detail and checked the sentence of the article.

2. The Abstract section is a bit chaotic, it can be slightly shortened.

The summary content has been reorganized as follows：“To further improve the hardness of the laser cladding layer on the surface of the vermicular graphite cast iron, the structural parameters of the laser cladding Co-base were designed and optimized, and the properties of the clad layer were evaluated using optical microscopy (OM), scanning electron microscopy (SEM), energy spectroscopy (EDS), X-ray diffractometer (XRD), electrochemical workstation, and friction wear equipment. The results show that the average hardness of the molten layer of Ni and Co-based composite cladding layer is 504 HV_0.5, which is 0.64 times that of the Co-based cladding layer due to the combined factors of Ni-Cr-Fe equivalent to the dilution of the Ni-based cladding layer to the Co-based cladding layer. Due to the potential difference of the Ni, Cr, and Co elements on the surface of the cladding layer, the self-corrosion potential of the Ni and Co-based composite cladding layer is 1.08 times that of the Co-based cladding layer, and the self-corrosion current density is 0.51 times. Laser cladding Co-based cladding layer has high corrosion resistance. Under the influence of plastic deformation and oxidative wear of the cladding layer of the Ni and Co-based composite cladding layer, the wear amount of the cladding layer of the Ni and Co-based composite cladding layer is less”.

3. The Introduction section is interesting. It can be see that the authors have a practical approach to

The research of other authors on cast iron and cobalt-based has been added to the introduction as follows：“ Li^[9]et al investigated the effect of different structural designs of the substrate on the properties of the cladding layers and obtained a cladding layer structure that reduces stress. Liu^[10] prepared multilayer cladding layers on the surface of ductile iron by using laser cladding in order to solve the problem of bond interface brittleness and evaluated the properties of the cladding layers. Ding^[11] prepared a Co-base protective layer on a steel valve seat and evaluated the performance of the protective layer. S. Selvi^[12] carried out a study on the preparation of protective layers on mild steel valve seats using the manual metal arc welding process. Paczkowska^[13] et al evaluated the possibility of laser melting of Co-based on the surface of ductile cast iron and also carried out the surface modification of ductile cast iron valve seats to study the organization and hardness of the clad layer by varying different cooling rates and thus obtaining a clad layer with high hardness, fine organization, and high-temperature resistance. Bourahima^[14] et al investigated the effect of process parameters on the Ni-based cladding layer and cast iron substrate, using a combination of experimental and numerical analysis to vary the process parameters and finally prepare a crack-free cladding layer with the desired geometry on the cast iron surface”.

4. How the amount of powder feeding per 18 g/min was determined?

Modifications have been made in the article to read: After setting the parameters of the powder feeder, after 5 minutes of continuous powder feeding, use an analytical balance to weigh the powder, and the average powder feeding amount is measured to be 18-20g/min.
5. Did the drying of powder take place from the moment of reaching the temperature or from putting the powder into the dryer?

Modifications have been made in the article to read: "After reaching the drying temperature, the heat preservation calculation time will begin."
6. What was the TEM of the laser beam?

Modifications have been made in the article to read:The laser beam TEM distribution is TEM00

7.The authors write that the SEM photos were taken using Phenom XL, while the photos have the ZEISS logo

For the SEM logo in the text has been changed to “Use the scanning electron microscope ZEISS integrated with the energy spectrometer to observe the structure of the coating and measure the elemental composition.” 

8.I miss pictures of the coating morphology on the cross-section, so that I can evaluate the entire coating from surface to substrate.

The following cross-sectional image has been added to the text

Fig.2 shows the macro morphology of the cross section of the cladding layer.  Fig.2 shows that the two cladding layer structures are dense and uniform, with a small amount of pores and no obvious cracks. The existence of a small amount of pores in the cladding layer is due to the rapid heating and cooling characteristics of the laser cladding process, which makes the amorphous powder insufficiently meltedand some space among the filled powders is remained^[15]. In addition, there is a clear macroscopic boundary between the cladding layer and the substrate, and the boundary line is a curve close to the horizontal on the left and right sides. A metallurgical bond is formed between the cladding layer and the substrate. The average thickness of the two different cladding layers is about 2mm.

Figure 2. Macro morphology of the cross section of the cladding layer

9.Punctuation errors, eg line 162 - no spaces

The punctuation problem has been corrected.

10.Are you able to estimate the composition of complex carbides? Have you analyzed the equilibrium diagrams for the coating elements?

The complex carbide composition is Cr7C3, Cr23C6.

Table 2 demonstrates that the surface structure of the Ni-based transition layer is enriched in Fe, Co and Ni in the Crystal nucleus, and C and Cr are enriched in the intergranular. The surface structure without the Ni-based transition layer is rich in Co and Fe in crystal nucleus, and C and Cr in the intercrystalline. According to the literature^[18-20], the Cr, Mo, Fe and C elements enriched in the dendrites mainly exist in the form of carbides. The surface structure with the transition layer is rich in Ni element between the nuclei. According to the intercrystalline enrichment of C and Cr elements, and combined with XRD analysis, the main carbides are Cr23C6 and Cr7C3.

11.You write "hardness" in one place and "microhardness" in another. Of course, "hardness" is correct, because the microhardness is less than 200 g of load. Load above 200 g will be hardness.

3.1. Hardness of the cladding layer

The “microhardness” in the article has been corrected to “hardness”

Fig.6 (a) shows the hardness distribution from the surface of the cladding layer to the substrate. It can be observed from Fig.6 (a) that the average hardness of the laser cladding Co-based cladding layer is 788HV_0.5. The average hardness of the Ni and Co-based composite cladding layer is 504HV_0.5. What's more, there is a hardness peak at the interface between the cladding layer and the substrate. The hardness of the laser cladding Co-based cladding layer is higher than that of the Ni and Co-based composite cladding layer. This is because the content of Cr and C in the laser cladding Co-based powder is higher than that in the Ni-based powder. And C and Cr elements have a strong affinity. After high temperature melting, the solidification process creates conditions for the formation of carbides. The formation of carbides (Cr23C6, Cr7C3) was also observed in XRD. In the Ni and Co-based composite cladding layer, the hardness of the cladding layer would be reduced due to the dilution effect of the Ni-based transition layer on the Co-based cladding layer, and the intermediate Cr-Ni-Fe generated. In the heat-affected zone, the hardness of the two cladding layers increased to 825 HV_0.5 and 676 HV_0.5, respectively. This is due to the formation of high-carbon martensite and ledeburite in the heat-affected zone.

Fig.6 (b) shows the lateral hardness distribution on the surface of the cladding layer. Fig.6 (b) shows that the lateral hardness has periodic fluctuations. The periodic hardness fluctuations are due to the use of multiple laser cladding for each cladding layer. The second irradiation of the laser causes the grains in the remelting zone to grow up by heating, and the structure to coarsen^[21].

12.When entering the hardness value, you must enter the load, ie instead of 825 HV, it will enter 825 HV0.5

The 825HV in the article has been corrected to 825HV_0.5, and other hardness values have also been corrected.

13.Although, in my opinion, the results of the research are interestingly described, please refer to the results of other researchers more often in the research results.

The conclusion of the article has been reorganized as follows：

1)The self-corrosion potentials of the Co-based cladding layer and the Ni and Co-based composite cladding layers are -0.896V and -0.964V, respectively, and the self-corrosion current density is 2.469×10^-4 A·cm^-2 and 3.547×10^-4 A·cm^-2. Due to the inhomogeneity of the material and the structure and the potential difference between the elements, the micro-batteries are formed. Compared with the Ni and Co-based composite cladding layer, the surface of the Co-based cladding layer has better corrosion resistance.

2)The wear of Ni and Co-based composite cladding layer is 0.72 times higher than that of Co-based cladding layers due to the combination of different compounds generated by the different elemental contents and the different degrees of plastic deformation, fatigue wear and oxidative wear occurring on the surface of the cladding layers.

3)The average hardness value of the cladding region of the Co-based cladding layer is 788HV_0.5, and the average hardness value of the cladding region of the Ni and Co-based composite cladding layer is 504HV_0.5.

4)Due to the excellent mechanical properties of the Co-based cladding layer prepared by laser, the shear strength of the cladding layer is greater than that of the base material.

14. Did you monitor the mass loss during the test or only have the final results. Perhaps it would be better to plot a weight loss versus time graph.

Thanks for your comments.

We mainly evaluate the amount of wear in a fixed time, so we draw a graph of the amount of wear.

 

15. What do you mean by micro-batteries

When the surface of the cladding layer is in contact with the electrolyte solution, there are many tiny cathodes and anodes on the entire metal surface under the comprehensive influence of material unevenness, uneven surface state and uneven structure, thereby forming many tiny short-circuit batteries that undergo corrosion. These tiny batteries are called micro-batteries.

16. Conclusions match the content

Thank you for your comments. Conclusion match the content.

17.My opinion: Major revision 

Thank you for your comments. Detailed changes have been made to the article.

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Research on Laser Cladding Co-based Alloy on the Surface of 2 Vermicular Graphite Cast Iron

Partially improved was the paper, but some points are to be making better.

• It is mandatory. Many works without discussion is against the quality standards.
• Well done the conclusions
• Why GUO is in capital letters?
• New and recent advances about ADI castings are missed, such as: The International Journal of Advanced Manufacturing Technology 110 (3), 899-907 or Isotropic finishing of austempered iron casting cylindrical parts by roller burnishing, The International Journal of Advanced Manufacturing Technology 110 (3), 753-761 both are about ADI after treating ductile iron and in competition with vermicular. I think you must include a reference to ADI in introduction, CGI or vermicular are les resistant.
• I must confess that I did not see any aspect in paper relative to Taylor or laser effects on grain orientation, I read a new work in the topo journal: https://doi.org/10.1016/j.ijmachtools.2021.103801 the grain orientation is well explained, so in yours it must be discussed. An application is not enough for the journal.
•  

Author Response

Partially improved was the paper, but some points are to be making better.

It is mandatory. Many works without discussion is against the quality standards.

Well done the conclusions

Why GUO is in capital letters?

Thanks for your comments and suggestions! It was our mistake not to notice the capitalization problem in the references, and now GUO has been revised to Guo, and other similar problems have also been corrected.

New and recent advances about ADI castings are missed, such as: The International Journal of Advanced Manufacturing Technology 110 (3), 899-907 or Isotropic finishing of austempered iron casting cylindrical parts by roller burnishing, The International Journal of Advanced Manufacturing Technology 110 (3), 753-761 both are about ADI after treating ductile iron and in competition with vermicular. I think you must include a reference to ADI in introduction, CGI or vermicular are les resistant.

Thanks for your comments and suggestions! Relevant references have been added to show that cast iron is not wear-resistant in harsh service environments and needs to be comprehensively improved.

I must confess that I did not see any aspect in paper relative to Taylor or laser effects on grain orientation, I read a new work in the topo journal: https://doi.org/10.1016/j.ijmachtools.2021.103801 the grain orientation is well explained, so in yours it must be discussed. An application is not enough for the journal.

Thanks for your comments and suggestions! I have added the analysis related to grain orientation to the microstructure and added the reviewer's recommendation to the references.

 

 

We tried our best to improve the manuscript and made some changes to the manuscript. These changes will not influence the content and framework of the paper. And here, we marked in red in the revised manuscript. We appreciate for Editors/Reviewers’ warm work earnestly and hope that the correction will meet with approval. Once again, thank you very much for your comments and suggestions.

Author Response File: Author Response.docx

Reviewer 3 Report

The revised manuscript could be considered for publication in Coatings.

Author Response

The revised manuscript could be considered for publication in Coatings.

Thanks for your comments and suggestions! We appreciate for Reviewers’ warm work earnestly. Once again, thank you very much for your comments and suggestions.

Reviewer 4 Report

Thanks for the detailed answer. In my opinion - Accept 

Author Response

Thanks for the detailed answer. In my opinion - Accept 

Thanks for your comments and suggestions! We appreciate for Reviewers’ warm work earnestly. Once again, thank you very much for your comments and suggestions.

Round 3

Reviewer 1 Report

Good work.