Study on Microstructure and Tribological Performance of Diamond/Cu Composite Coating via Supersonic Laser Deposition

Round 1

Reviewer 1 Report

Comments are in the attachment.

Comments for author File: Comments.pdf

Author Response

(1) At the same time, it is known that in the coatings of instruments such physical and mechanical properties of diamond as high hardness and cutting ability with a low coefficient of friction, wear resistance and thermal conductivity are used inefficiently. From 30 to 95% of diamonds fall out of the matrix, without reaching boundary wear. Therefore, it is important to securely fix the grains in the metal bundle of the tool. Reliability of diamond fixing and tool performance are largely determined by the nature of the transition layer between the diamond and the matrix.

The microstructures and interface bonding between the diamond particles (for minimal, average and minimal sizes) and Cu matrix could be analysed using indentation test and/or SEM.

• Thanks for the reviewer’s suggestion. The microstructures and interface bonding between diamond particles and Cu matrix have been investigated using SEM as shown in Fig.7-Fig.9. We are now also conducting experiments about the effects of diamond particles with different sizes on the microstructures and interface bonding between the diamond particles and Cu matrix. The results are now being analyzed and will be published in other paper.

(2) Diamond grains are large enough, why? How was choosed and justified the size of diamond grains? Perhaps it was worth using nanodiamonds?

• The particles with average size of 10-30 μm are usually used to achieve high particle velocity in cold spraying. The diamond particles used in this study are irregular in shape, with an average size of 17.76 μm. Due to the light weight and thus small momentum, it is difficult to for nanoparticles to overcome the de-acceleration effect by shock wave on the surface of substrate and reach the substrate to achieve effective deposition.Corresponding revision have been made in the revised manuscript (line 98-102).

(3) For a better understanding of the wear mechanisms, it would be useful to make a 3-D profilogram of the wear surface, Figure 15. This would be systematizing the wear mechanisms. An example of such asystematization can be found at https://www.sciencedirect.com/science/article/abs/pii/S1350630715301412

• Thanks for the reviewer’s suggestion. 3-D profilogram is a very useful method and extensively used to investigate the wear surface and related wear mechanism. We are currently conducting relevant research, and the results will be reported in subsequent article.The citation of this technology has been added in the revised manuscript (line 451-455, 591-592).

（4） What can be said about the value of residual stresses in a coating.

• In CS coating, as the high-speed particles continue to impact the substrate or deposited particles, the compressive stress rather than tensile stress is generally formed in the coating, which is conducive to additive manufacturing and improve the fatigue performance. In SLD technology, due to the introduction of laser irradiation, how laser heating affects the stress distribution in the coating is a content worthy of in-depth study, which is also the focus of our follow-up work.

（5） For what temperature conditions will be used this coating?

• The temperature conditions of the coating should be determined according to the specific application conditions, and the phase transformation of diamond particles in the composite coatings should also be taken into consideration. The composite coating is suitable for wrapping copper workpieces which are vulnerable to wear.

 

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript reports on microstructure and tribological performance of Diamond/Cu composite coating via supersonic laser deposition

The experimental results are interesting and proposed  a new method for fabrication Diamond/Cu composite coating via supersonic laser deposition.

But there are things which I would like to clarify before paper submission:

 

1) The language of the paper should be improved and many sintaxis typos must be corrected, before the manuscript can be accepted for publication.

2) Then, in paper's Experimental Setup laser parameters are not outlined properly.

 

3) EDS images shoud be done properly, peaks of C and O2 are almost invisible. Maybe It will be nice to extend left part of graphs.

 

Author Response

(1) The language of the paper should be improved and many sintaxis typos must be corrected, before the manuscript can be accepted for publication.

Thanks for the reviewer’s suggestion. We have carefully checked and corrected grammatical errors in the paper.

（2）Then, in paper's Experimental Setup laser parameters are not outlined properly.

In Experimental Setup, we have added detailed laser parameters in the revised manuscript.Corresponding revision have been made in the revised manuscript (line 121-122, 135-136).

（3）EDS images shoud be done properly, peaks of C and O₂ are almost invisible. Maybe It will be nice to extend left part of graphs.

Thanks for the reviewer’s suggestion. We have rearranged the graphs by Origin. Corresponding revision has been made in the revised manuscript (Fig.11).

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript can be accepted after following major corrections:

1. Line 103: why the substrate surface was grit blasted before coating?
2. Figure 4.: The figures are not clear, difficult to understand that these are cross-sections. It is better if authors show substrate also at the cross section to visualize. Also, why there is peak in the coating that authors measured as thickness, are the coatings not uniform?
3. Table 1: How many times the tests were conducted? The Rd values for SLD 1, 1,5, 2 2.5 are close, provide standard deviations to the Δm, Rd and DE.
4. Figure 10: why diamond peaks are missing in XRD spectrum of CS coating?
5. Figure 12: what is the laser intensity for SLD diamond/Cu coating on which hardness test were performed? Please include in caption as per sample designation.
6. line 400: Please explain, how the wear rates are measured.
7. Line 444: Furthermore, the uniformly distributed diamond particles in the SLD diamond/Cu specimen (Fig.14b) can also improve the tribological performance of the coating.

The increase in hardness itself is due to the two factors: i) work hardening of copper and ii) diamond particles. These leads to lesser wear. The above sentenced is not required since diamond particle’s contribution is already included in hardness.

 

Author Response

(1) Line 103: why the substrate surface was grit blasted before coating?

• Grit blasting has been extensively used to increase the surface roughness of substrate in cold spray and thermal spray process. The increased surface roughness is reported to be beneficial for interfacial bonding between coating and substrate.Corresponding revision has been made in the revised manuscript (line   103-106).

(2) Figure 4: The figures are not clear, difficult to understand that these are cross-sections. It is better if authors show substrate also at the cross section to visualize. Also, why there is peak in the coating that authors measured as thickness, are the coatings not uniform?

• The interfaces between coatings and substrates have been highlighted by dotted line in Fig.4 so as to clearly distinguish the coatings from substrates in the cross section.Corresponding revision has been made in the revised manuscript (line 161-163 and Fig.4)

• Cold-sprayed coatings usually have symmetric pyramidal morphologies due to the different velocities of the spraying particles accelerated by a de Laval nozzle. Prior to hitting the substrate, the spraying particles have to be accelerated by a de Laval nozzle. Because of the disturbance effect of nozzle wall, the particles close to the nozzle wall have lower velocities than those close to the nozzle axis. As the deposition efficiency is proportional to the impacting velocity for given particle and substrate materials, particles with higher impacting velocities (close to the nozzle axis) have higher deposition efficiencies (viz. coating thickness) than those with lower impacting velocities (close to the nozzle wall). As a result, the CS tracks exhibit symmetric pyramidal shapes due to the distribution of particle impact velocities along the nozzle diameter. Therefore, peak coating thickness is usually employed to evaluate deposition efficiency. This has been reported in our previous paper.Corresponding revision has been made in the revised manuscript (line 167-170)
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• (3)Table 1: How many times the tests were conducted? The R_d values for SLD 1, 1,5, 2 2.5 are close, provide standard deviations to the Δ_m, R_d and DE.

• Each sample was tested for three times and the results were obtained by calculating the average value of three time tests for each sample. And the standard deviations have been added in Table 1 in the revised manuscript.Corresponding revisions have been made in the revised manuscript (line 203-205 and Table 1)

(4) Figure 10: why diamond peaks are missing in XRD spectrum of CS coating?

• Due to the lattice distortion caused by severe plastic deformation of Cu powder, the XRD diffraction peaks of Cu become wider in CS coating, which may cover and thus lead to the disappearance of the weaker diffraction peaks of diamond. For SLD coating, because the laser is reported to have annealing effect on the deposited coating, diffraction peak broadening of Cu will be partly eliminated, so the diffraction peak of diamond can observed in this coating.Corresponding revision has been made in the revised manuscript (line 355-360).

(5) Figure 12: what is the laser intensity for SLD diamond/Cu coating on which hardness test were performed? Please include in caption as per sample designation.

• Both SLD Cu and SLD diamond/Cu are prepared with laser power of 2 kW. The laser parameter have provided in the revised manuscript (line 392-392).

（6）line 400: Please explain, how the wear rates are measured.

• The wear rates are calculated via dividing wear track volume by wear time and load. This explanation has been added in the revised manuscript (line 420-421).

（7）Line 444: Furthermore, the uniformly distributed diamond particles in the SLD diamond/Cu specimen (Fig.14b) can also improve the tribological performance of the coating.

The increase in hardness itself is due to the two factors: i) work hardening of copper and ii) diamond particles. These leads to lesser wear. The above sentenced is not required since diamond particle’s contribution is already included in hardness.

• This sentence has been deleted in the revised manuscript.