Carbon Nanotubes (CNTs) Reinforced CoCrMoNbTi_0.4 Refractory High Entropy Alloy Fabricated via Laser Additive Manufacturing: Processing Optimization, Microstructure Transformation and Mechanical Properties

Round 1

Reviewer 1 Report

In this manuscript, the authors presented a laser melting deposition (LMD) technology applied to the fabrication of CNTs/CoCrMoNbTi_0.4 alloy. The surface morphology, microstructure, and mechanical properties were investigated as function of LMD process parameters. The authors showed many results. Some are interesting. However, the discussion is somewhat poor and could be improved and there are some conclusions not supported by the results. Also, authors could improve the figures’ caption. Some comments are listed below.

Introduction is clear and concise, and it was able to contextualize the reader about the subject of the manuscript.

The authors said that “The optimal ball-processing parameters were determined as follows: the ball-to-powder of 1:2; the rotation speed at 400 rpm; the milling time of 10 h. Among which, after each 2 h, the interval of 30 min was set, for the purpose of avoiding damaging the structural integrity of CNTs due to overheating of powder”. How did the authors determine these optimal parameters?

The English of the subsection “2.2. Microstructure and mechanical properties tests” is poor. I was not able to understand the methodology.

In line 142, the authors explained the reason why the low-density energy of the laser generated a low relative density. However, could the authors explain why the relative density decrease again for laser density higher than 3.6 J/mm?

In line 187, authors claimed that “…the surface quality of the obtained CoCrMoNbTi_0.4 RHEA is relatively excellent after adding 0.8 wt.% CNTs…”. Not only this is a subjective analysis but also it is not clear how the authors made this analysis to reach these qualitative conclusions on the morphology. What was the parameter analyzed? Did the authors compare the sample with and without 0.8 wt.% CNTs? The capture on the figure do not help to understand the image.

The discussion on the surface roughness behavior was not convincing. Also, the roughness varies with laser density inversely when compared to the relative density. Authors did not explore this, which may be related. The discussion could be improved.

There is no Figure 5f, as pointed in line 208.

How did the authors conclude that specimen at 3.6 J/mm has “excellent” appearance? This is a subjective analysis and there is no discussion on how the authors came to that. Could the surface roughness be related to the cracks and defects after LMD forming?

The graph on Figure 8a do not need the crack. It could be presented from the 800 or 850 value of HV_0.5.

Author Response

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Reviewer 2 Report

The paper is well written and the authors selected the eminent Refractory heavy alloys field as a research work and processed via LMD technique. I have noticed that almost all the reference from one geographical location. I request the authors to consider the author location where good no of review article on RHEA and which can be included in the abstract.

 

A Review of the Latest Developments in the Field of Refractory High-Entropy Alloys      May 2021     Crystals 11(6):612  DOI:10.3390/cryst11060612

Why did the authors choose the ball to powder ratio 1: 2?

 

TEM image may be good to consider for CNT! The tdensity of the alloy is not full. What is the reason. any impact on sample size. kindly discuss.

 

The importance of surface morphology discussion is missing. OM image is before etching? Conclusion can be represented in paragraph

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Author Response

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Reviewer 3 Report

The authors have studied the processing parameters, microstructure evolution and mechanical properties of the carbon nanotubes reinforced CoCrMoNbTi_0.4 refractory high entropy alloy (CNTs/CoCrMoNbTi_0.4 RHEA) prepared via laser melting deposition (LMD) technology. The research is well designed and presented clearly. A good comparative analysis of existing publications concerning the tasks set in the work is performed. The methodological section of the manuscript is presented in sufficient detail. The explanation for the microstructure evolution in the investigated samples is reasonable. However, some minor shortcomings should be corrected to make the manuscript acceptable for publication in Crystals.

(1) Throughout the manuscript, especially in the abstract and conclusions, the authors should replace “fraction strength, fraction strain” (incorrect terms) with “fracture strength, fracture strain” (correct ones).

(2) In the Introduction, the sentence “At present, the improvement of the quality of formed parts mainly focuses on optimization of component design [11-14], combination with the heat treatment process [15] and introduction of second phase materials [16-19]” (Lines 60–62), the authors should add more references to articles related to laser melting technologies (for example https://doi.org/10.3390/met11030434), this will increase the weight and significance of the research.

(3) The phrase “… a unite” is incorrect. It should be “… a unit” (Line 105), (Line 106, double mistake).

(4) The sentence in Lines 111–113 is confusing and should be rewritten (check the word order!).

(5) The caption to Figure 4 should be corrected as follows: “Two-dimensional morphology profile and three-dimensional morphology surface morphologies of RHEA specimens corresponding to the linear energy densities of (a) E_l = 2.8 J/mm, (b) …”

(6) In many places in the text, the authors should correct the use of subject “powder” (singular) with corresponding predicate (singular, not plural) and also with a possessive determiner “its” (not “their”).

(7) Line 269: It should be “… microhardness, as shown in Figure 8a” instead of “… microhardness, as shown in Figure 8b”.

(8) Figure 9 should be placed after its description in the manuscript.

(9) Throughout the manuscript, the authors should check the word form “was/were” for the singular/plural cases.

(10) To emphasis the microstructural peculiarity of the optimized LMD-processed alloy, it is proposed to correct “Conclusions” section (Lines 342–343) as follows: “(2) Both the high densification level and significant grain refinement due to CNTs mainly distributed within the dendrites contributed to the high microhardness (1015 HV_0.5) of LMD-processed …”

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Round 2

Reviewer 1 Report

The authors have answered this reviewer's questions. Manuscript can be publish in the present form.

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Reviewer 3 Report

Almost all the reviewer’s comments were taken into account by the authors.

(1) The authors should complete the sentence in the corrected “Conclusions” section in the revised manuscript (Lines 358–360) as follows: “(2) Both the high densification level and significant grain refinement due to CNTs mainly distributed within the dendrites contributed to the high microhardness (1015 HV_0.5) of LMD-processed CNTs/CoCrMoNbTi_0.4 alloy.”

(2) In Reference 10, the authors should correct the authors’ names as follows:

10. Duriagina, Z.; Kulyk, V.; Kovbasiuk, T.; Vasyliv, B.; Kostryzhev, A. Synthesis of functional surface layers on stainless steels by laser alloying. Metals 2021, 11, 434. https://doi.org/10.3390/met11030434.

The manuscript can be accepted for publication in Crystals after correction of the shortcomings.

Author Response

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