Enhanced Tribological Properties of LA43M Magnesium Alloy by Ni60 Coating via Ultra-High-Speed Laser Cladding

Round 1

Reviewer 1 Report

The manuscript deals with novel ultra-high speed laser cladding method and it's use for modification of magnesium alloy. The topic can be interesting for Coatings readers.

• The Introduction is well written and highlights the goal of research. I just would recommend to add more details about the selection of the Ni alloy for coating. Also, the part about the method (lines 51-81) sounds too long.
• Materials and experimental procedures part is a little bit messy. Please add at.% in tables 1 and 3. A method of powder size determination is not mentioned. In chapter 2.4 the manufacturers of equipment are missing. SEM machine name and name of the country are wrong. What is "surface comprehensive performance tester"?  Name of three-
  dimensional laser microscopic system is missing. Why the authors selected Si3N4 counterpart for room temperature tests? It is not a common material for low-temperature friction.
• Line 165. What is "The back secondary electron image view"? Is this the correct term?
• Lines 173-177 sound speculative without proofs. 
• Line 184. Any pieces of evidence of the presence of a solid solution? XTD, TEM?
• Lines 207-208. EDS mapping is mandatory
• XRD. Please doublecheck the whole interpretation of XRD pattern. For example, FeNi3 (220) is missing, the intensity of (111) is much lower that (200). It is strange
• Lines 245-251 - general words that give no valuable data to readers
• Line 253 - the relationship between friction coefficient and grain size is unclear.  
• Lines 263-265.  A crack formation was not studied in the manuscript
• Line 286. What kind of harsh environment was mentioned?
• Lines 290, 300. The authors speculate about wear modes. "very severe kind of abrasive wear" - what is it? Please revise the description. Also, from the reviewer's point of view, fig.7b shows nothing from adhesive wear mode.
• line 262. Check values
• line 303. Not clear what these references say to the readers. Please, be more specific  
• In general, there is a lack of deep scientific discussion in some parts, please add relevant references. 

Author Response

Respected reviewer,

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors,

thank you for sharing your original research with this journal.

The subject fits to the journal‘s scope.

However, there is no information on how you approached the parameter set you finally used and hence the publications ends up being a simple phenomenological comparison of a Mg-Li substrate with a Ni coating. Thus, the conclusion, that the laser cladded coating is more hard and abrasion resistant, is not really surprising.

In addition, when using the claim that this process enables new material properties for specific fields of application, mechanical testing alone will not be sufficient. You will need to evaluate the influence on the corrosion resistance, especially as Mg-Li alloys are prone to galvanic corrosion. Otherwise, it will only be tribological assessment of this approach (what actually does fit well with the title though).

Finally, there is no evaluation or discussion on the binding mechanism between the substrate and the coating. Is it a metallic bound or mechanical cramping? Why are there no signals in the XRD indicating intermetallics of Ni and Mg phases?

Please try to implement this ideas and the answers to those questions to your concept.

Good luck!

Minor comments:

37 of “other” magnesium alloys

38 „primary choice for application in aviation, aerospace, defense or 3C.“

47 electro plating is missing, what is “surface treatment” in particular referring to, what is “thermal”?

65/66 please cite an original work or reference instead of naming the ILT

73 introduce abb. HAZ

87/88 if you claim to unwind current restrictions, you will have to show a) that there is no egg shell effect and b) the influence of the cladding layer on the corrosion properties; otherwise you need to change your claim (and limit on tribological properties as the title indicates)

109 how was the particle size distribution measured? If visually via SEM, one would expect rather a bar chart than a curve (state method)

122ff give more detail on the design of experiments, which parameters were varied, which criteria were used to evaluate the optimised set of parameters?

236 please indicate, why a thinner HAZ (200/300 down to 140 my) would contribute to process as being promising..

278/279 please give a reference

Author Response

Respected reviewer,

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I think that the authors mostly corrected the weak parts of the manuscript.

I'd like to point at two comments that were ignored (or it was just misunderstanding):

1) Tables 1 and 3 should contain atomic %, not wt.% (or both if you like) 

2)EDS mapping is not the same as point analysis, so it is necessary to add it

Author Response

Thank you so much for your precious time to review our revised manuscript entitled “Enhanced tribological properties of LA43M magnesium alloy by Ni60 coating via ultra-high speed laser cladding” (coatings-847552). We really appreciate all your comments and suggestions!

Thanks once again.

I think that the authors mostly corrected the weak parts of the manuscript.

I’d like to point at two comments that were ignored (or it was just misunderstanding):

Point 1: Table 1 and 3 should contain atomic %, not wt % (or both if you like).

Response 1: Thank you so much again for your comment. The result recorded in the both table 1 and 3 were recorded in terms of wt% instead of at% that’s why reported table contain wt % instead of at%. Some research studies also validated the substrate and coatings in term of wt% rather than at%.

Lu, F. F., Ma, K., Li, C. X., Yasir, M., Luo, X. T., & Li, C. J. (2020). Enhanced corrosion resistance of cold-sprayed and shot-peened aluminum coatings on LA43M magnesium alloy. Surface and Coatings Technology, 125865.

30. Yao, J., et al., Characteristics and performance of hard Ni60 alloy coating produced with supersonic laser deposition technique. Materials & Design, 2015. 83: p. 26-35

Li-Yan, L., Yu, Z., Yun-Jie, J., Yan, L., Hong-Fang, T., Yu-Jun, C., & Cheng-Xin, L. (2020). High speed laser cladded Ti-Cu-NiCoCrAlTaY burn resistant coating and its oxidation behavior. Surface and Coatings Technology, 125697.

Point 2: EDS mapping is not the same as point analysis, so it is necessary to add it.

Response 2: Thank you so much again for your comment. The author just wants to report that from color and morphological observation in contrast as shown in inset of Fig 3(e), fully dense Ni60 coating is composed of mixture of two distinct phases; light gray region (A1) and dark gray region (A2). So main concern was to find out which elements are present in those distinct region EDS point scans were carried out and found that A1 consist of higher quantity of carbon, chromium and silicon whereas A2 has higher iron and nickel contents. In accordance with XRD pattern and EDS area scan, it can be inferred that area 1 mainly comprises of Cr7C3, CrB and Ni31Si12 whereas A2 contains FeNi3/Fe31Si12 eutectic and γ-Ni solid solution. Meanwhile many researchers have concluded the same things after just carrying out point scan analysis instead of EDS mapping which cannot be performed yet because of present pandemic situation.

30. Yao, J., et al., Characteristics and performance of hard Ni60 alloy coating produced with supersonic laser deposition technique. Materials & Design, 2015. 83: p. 26-35

Li-Yan, L., Yu, Z., Yun-Jie, J., Yan, L., Hong-Fang, T., Yu-Jun, C., & Cheng-Xin, L. (2020). High speed laser cladded Ti-Cu-NiCoCrAlTaY burn resistant coating and its oxidation behavior. Surface and Coatings Technology, 125697.

Finally, we appreciate again for your warm work earnestly, and hope that the correction above will meet with approval. Once again, thank you very much for your comments and suggestions on our revised manuscript.

Yours sincerely,

Cheng-Xin Li

Reviewer 2 Report

Dear authors,

thank you for your extensive answers to my criticism. You appropriately addressed all concerns. Hence, I recommend publication of the revised manuscript.

Kind regards.