Microstructure and Wear Resistance of TiCp/Ti6Al4V Composite Coatings by Follow-Up Ultrasonic-Assisted Laser Additive Manufacturing

Round 1

Reviewer 1 Report

The Authors have succeeded to show the novelty of their research work in a scientific professional way, in which they showed that under the effect of ultrasonic cavitation and acoustic streaming, the content of unmelted TiC was reduced, the dendritic primary TiC in solidification process was broken, and the distribution uniformity of primary TiC was improved. Also, they proved that the content of unmelted TiC in the composite coating decreased significantly under ultrasonic.

Meanwhile, the authors investigated the average size of dendritic primary TiC in the composite coating, which was decreased from 61.59 μm to 27.04 μm, in addition the average microhardness of the composite coating reached the maximum of 656.70 HV0.2 under ultrasonic.

They also, proved that due to ultrasonic cavitation and acoustic streaming effect, the content of unmelted TiC decreases obviously, so the average friction coefficient of the composite coating increased, and the wear mechanism changed from abrasive wear to adhesive wear.

In my opinion the research article is well written and from my point of view the results are well illustrated, in general the whole proposed research work is novel and highly recommended for the scientific community. 

Author Response

Thanks for the reviewer’s advice.

Reviewer 2 Report

Study on Microstructure and wear resistance of TiCp/Ti6Al4V composite coatings by follow-up ultrasonic assisted laser additive manufacturing is worthfull. However the Experimental Materials and process can be reinforced with some informations as below:

--> the distance between the ultrasonic impingement diameter and matreials deposition diameter

--> If it ultrasonic application distance will be varied with the laser scanning diametert, then what will be the effect

correct typos present in the manuscript like ...putting the references

Author Response

1. the distance between the ultrasonic impingement diameter and matreials deposition diameter

Answer: Thanks for the reviewer’s advice.

In our preliminary test, the ultrasonic effect has its own strengths and weaknesses, we choose the nearest point of effect for the experiment, the distance is 10 mm. We have modified and adjusted the relevant content.

2. If it ultrasonic application distance will be varied with the laser scanning diametert, then what will be the effect

Answer: Thanks for the reviewer’s advice.

The method we propose is follow-up ultrasound, so the distance will not change. When the distance changes, the effect will be greatly reduced when encountering the weakness of ultrasonic action. Continue to the next advantage point, the effect is still obvious, we also carry out Some simple observations in this regard, but ultrasonic has distance attenuation, when the distance continues to increase, its effect will become less and less obvious, so the experimental results are based on the selected advantages of the effect, just follow-up ultrasonic can be very good Take advantage of ultrasound advantages.

3.correct typos present in the manuscript like ...putting the references

Answer: Thanks for the reviewer’s advice.

We have modified and adjusted the relevant content.

Reviewer 3 Report

The work presents the studies on the fabrication of 30 wt.%TiC/Ti6Al4V composite coating on Ti6Al4V by ultrasonic-assisted laser additive manufacturing. Mainly the effect of different ultrasonic power on the microstructure and wear resistance of the composite coating was studied. Even though this investigation is very detailed and the results are interesting. Here I listed several points which must be improved before the publication:

- Introduction: this part is very poor. Only 5 literature references are given in the main body of the introduction; the authors should perform a more detailed literature review.

- Experimental part: what grade of sandpaper was used? please provide this information; The SEM images of the powders should not be presented in the Experimental part - please move it to the Results part or to the Supplementary content; What is the company of the printer etc. ?

- Text editing/errors: please provide uniform nomenclature of the Figures in the whole manuscript: not e.g. Figure 6, Fig.8 etc.; moreover, the citation of the references in the whole manuscript is wrong, sometimes there are only some numbers given randomly in the text or number with and without the brackets etc.; another issue: please check the whole manuscript with regard to the text editing: there are many words without space etc.  

Author Response

1. Introduction: this part is very poor. Only 5 literature references are given in the main body of the introduction; the authors should perform a more detailed literature review.

Answer: Thanks for the reviewer’s advice.

We have added corresponding literature readings for the background of application limitations of Ti6Al4V materials and the research on ultrasonic effects. At the same time, the original citations in 6-9 of the article are also background descriptions.

We have modified and adjusted the relevant content.

[1]Xing Y Z, Jiang C P, Hao J M. Time dependence of microstructure and hardness in plasma carbonized Ti-6A1-4V alloys[J]. Vacuum, 2013,95:12-17.

[2]Xiao L, Tian S G, Bao X Y, et al. Creep properties and effect factors of hot continuous rolled Ti-6Al-4V alloy[J]. Materials Science and Engineering: A, 2011, 526: 452-458.

[3]Hao Y J, Liu J X, Li J C, et al. Rapid preparation of TiC reinforced Ti6Al4V based composites by carburizing method through spark plasma sintering technique[J]. Materials & Design, 2015,65:94-97.

[4] Chen C Y, Deng Q L, Song J L. The effect of Ultrasonic Vibration on Laser Cladding Process [J]. Electromech Mould, 2005(3): 37-39.

[5] Cong WL, Ning FD. A fundamental investigation on ultrasonic vibration-assisted laser engineered net shaping of stainless stee. Int J Mach Tool Manufact 2017;121:61–9.

 

2.Experimental part: what grade of sandpaper was used? please provide this information; The SEM images of the powders should not be presented in the Experimental part - please move it to the Results part or to the Supplementary content; What is the company of the printer etc. ?
Answer: Thanks for the reviewer’s advice.

In the experiment, the following sandpapers were mainly used, 320#, 600#, 1000#, #1500, 2000#, and finally 1.5 um diamond polishing paste was used to polish the section.

The SEM image of the powder is placed in the experimental part mainly based on this consideration, the powder is the material of the experiment, and the shape and specifications of TC4 and TiC are observed under the SEM to be mixed, which better shows the experimental material part, which does not belong to the results of the experiment.

Ultrasonic vibration equipment(including ultrasonic generator and ultrasonichead, Hangzhou Fansonic Ultrasonic Technology Co., Ltd)， and Nd: YAG continuous laser device (JK1002, GSI Lumonics).

 

3.Text editing/errors: please provide uniform nomenclature of the Figures in the whole manuscript: not e.g. Figure 6, Fig.8 etc.; moreover, the citation of the references in the whole manuscript is wrong, sometimes there are only some numbers given randomly in the text or number with and without the brackets etc.; another issue: please check the whole manuscript with regard to the text editing: there are many words without space etc.

Answer: Thanks for the reviewer’s advice.

The paper format may have been converted incorrectly, we have carefully changed the format.

We have modified and adjusted the relevant content.

Reviewer 4 Report

Dear authors. You have prepared a well written manuscript, which is rich in results, but I have a few comments.

1. First of all, I would recommend checking the English with a specialist to correct many deficiencies, for example, missing articles and incorrectly worded sentences.

2. References to literature sources should be in square brackets, like [1], but there are often references without brackets throughout the text, as in lines 35, 42, 54, 375, 377, and others.

3. In many places the use of subscripts is necessary, e.g., La2O3 in line 65, or HV0.2 in line 364.

4. In Section 2, the description of the friction tests needs to be in a separate paragraph, since it represents a separate experiment. Also, the equipment names and manufacturer's information should be correctly stated according to the manuscript preparation requirements.

5. In line 119 it is written "100 r/min". The generally accepted form of writing the dimension of rotational speed is rpm.

6. In what fraction was the content of unmelted TiC measured? Volume fraction, weight fraction?

7. You talk about areas of large and small temperature gradient, but do not give values. Did you determine its values experimentally or theoretically? If not, you should at least give literature data.

8. In Figure 10, the arrows show alpha-Ti. It is not clear from the figure whether the morphology of this phase is globular or lamellar. In this regard, further reasoning about the size of the alpha-phase grains does not look correct. It is necessary to give enlarged images with demonstration of alpha-phase, and if it is represented by a lamellar structure, then we should talk about the plate size, not grains.

9. Figures 11 and 12 lack descriptions of designations (a)-(e). It is necessary to add a description in the figure caption.

10. Table 3 does not seem necessary because microhardness values are discussed in the manuscript text and can be seen in Figure 15. I would recommend removing this table.

11. The results of tribological tests show that the friction characteristics of the coating worsen with increasing ultrasound power, but there is no discussion of this fact in the manuscript. It is necessary to consider this fact in more detail in connection with process parameters and mechanical characteristics to determine the best option for ultrasonic effect to improve the material friction characteristics.

12. In this work, the material studied was used as a pin for friction testing. Have similar tests been performed where the material under study would act as a disk? In my opinion, such an approach would give more thorough results about the wear of the coating. Maybe if similar studies have been performed by other researchers, it would be helpful to compare your results with those of other works.

13. The conclusions state a transition from abrasive wear to adhesive wear, but the data given is not sufficient for such a conclusion. On the wear surface, it can be seen that material adhesion is more pronounced at lower ultrasonic powers. If possible, it would be useful to see a three-dimensional image of the wear surface or wear surface profiles.

Author Response

1. First of all, I would recommend checking the English with a specialist to correct many deficiencies, for example, missing articles and incorrectly worded sentences.
   Answer: Thanks for the reviewer’s advice.

We have modified and adjusted the relevant content.

2. References to literature sources should be in square brackets, like [1], but there are often references without brackets throughout the text, as in lines 35, 42, 54, 375, 377, and others.
   Answer: Thanks for the reviewer’s advice.

We have modified and adjusted the relevant content.

3. In many places the use of subscripts is necessary, e.g., La2O3 in line 65, or HV0.2 in line 364.
   Answer: Thanks for the reviewer’s advice.

We have modified and adjusted the relevant content.

4. In Section 2, the description of the friction tests needs to be in a separate paragraph, since it represents a separate experiment. Also, the equipment names and manufacturer's information should be correctly stated according to the manuscript preparation requirements.
   Answer: Thanks for the reviewer’s advice.

More consideration for friction and wear is based on a performance test, such as tensile and hardness, by testing friction and wear properties to infer the effect of ultrasound.

5. In line 119 it is written "100 r/min". The generally accepted form of writing the dimension of rotational speed is rpm.
   Answer: Thanks for the reviewer’s advice.

We have modified and adjusted the relevant content

6. In what fraction was the content of unmelted TiC measured? Volume fraction, weight fraction?
   Answer: Thanks for the reviewer’s advice.

The content of unmelted TiC was investigated around 30% by mass.

7. You talk about areas of large and small temperature gradient, but do not give values. Did you determine its values experimentally or theoretically? If not, you should at least give literature data.
   Answer: Thanks for the reviewer’s advice.

The detection of the determined value of the temperature gradient is very difficult and troublesome, but in the laser additive process, due to the characteristics of the laser, the area with a large temperature gradient can be judged. The closer to the deposition point, the greater the temperature gradient. This is due to the fact that after the laser moves, the temperature of the molten pool reaches the highest, and it contacts with the environment, and the temperature drops rapidly to maximize the temperature gradient.

8. In Figure 10, the arrows show alpha-Ti. It is not clear from the figure whether the morphology of this phase is globular or lamellar. In this regard, further reasoning about the size of the alpha-phase grains does not look correct. It is necessary to give enlarged images with demonstration of alpha-phase, and if it is represented by a lamellar structure, then we should talk about the plate size, not grains.
   Answer: Thanks for the reviewer’s advice.

The grain size is counted by the line intercept method in the horizontal direction. The statistical results are meaningful for experimental research and verification. The effect of ultrasound is further illustrated by the statistics of the average grain size.

 

9. Figures 11 and 12 lack descriptions of designations (a)-(e). It is necessary to add a description in the figure caption.
   Answer: Thanks for the reviewer’s advice.

We have modified the image tag, mainly on the image, to tag specific elements.

 

10. Table 3 does not seem necessary because microhardness values are discussed in the manuscript text and can be seen in Figure 15. I would recommend removing this table.
    Answer: Thanks for the reviewer’s advice.

We have modified and adjusted the relevant content.

11. The results of tribological tests show that the friction characteristics of the coating worsen with increasing ultrasound power, but there is no discussion of this fact in the manuscript. It is necessary to consider this fact in more detail in connection with process parameters and mechanical characteristics to determine the best option for ultrasonic effect to improve the material friction characteristics.
    Answer: Thanks for the reviewer’s advice.

Compared with no ultrasonic application, the friction performance was improved after ultrasonic application. When the ultrasonic power reached 1800 W, the friction coefficient fluctuated due to the uneven distribution of TiC.

12. In this work, the material studied was used as a pin for friction testing. Have similar tests been performed where the material under study would act as a disk? In my opinion, such an approach would give more thorough results about the wear of the coating. Maybe if similar studies have been performed by other researchers, it would be helpful to compare your results with those of other works.
    Answer: Thanks for the reviewer’s advice.

In friction and wear testing, testing the material under study as a friction pin is the same as testing the testing material as a friction disc. Based on the following judgments, we first select a harder material for friction and wear testing. , the second contact surface is the same, and the final detection environment, detection time, loading force, etc. are the same.

13. The conclusions state a transition from abrasive wear to adhesive wear, but the data given is not sufficient for such a conclusion. On the wear surface, it can be seen that material adhesion is more pronounced at lower ultrasonic powers. If possible, it would be useful to see a three-dimensional image of the wear surface or wear surface profiles.

Answer: Thanks for the reviewer’s advice.

We are very sorry that in our original idea, we detected a change in the friction coefficient and observed the surface wear pattern under the electron microscope, and judged a change in wear by the surface wear pattern and the number of weld nodules. The wear debris that falls off when there is no power is squeezed and deformed during wear, and adheres to the friction surface, so it seems that the material adhesion is stronger. The obtained results can illustrate the relevant information, so three-dimensional images of the worn surface profile were not performed.

Round 2

Reviewer 4 Report

Dear authors,

I have to recommend your manuscript be rejected because you have not made any substantive revisions and the responses provided were not convincing.

I am very glad that you decided to revise this manuscript. I have read the responses and revisions, and I am ready to recommend the manuscript for publication after the few additional comments listed in the attached file have been addressed. These comments relate directly to the corrections made by the authors at the previous stage, which in my opinion are not quite accurate.

Dear authors,

You have done a good job in correcting the manuscript, but I have a few more comments.

 

1. Make your corrections more carefully. On line 124 you put "rpm/min" whereas "rpm" is rates per minute.  Remove "/min" and leave only "rpm".

 

2. You corrected the large and small temperature gradient in the text, but not in Figure 8. Correct the figure so there is no dissonance.

 

3. In section 3.2.3 I would still recommend writing not alpha-Ti grains, but alpha laths or alpha-phase laths. I have read the papers you pointed out, and they deal with primary beta-phase grains and alpha laths, which are inside the beta grains. Therefore, it is incorrect to write alpha grains in this case. Judging by the order of values measured, you are considered the average thickness of the alpha laths, as in the work of Ma G, Yu C, Tang B, et al.

I believe this is the most important factor in describing the microstructure, and specifying alpha grains rather than alpha laths will mislead the reader about the real morphology of the alloy structure.

Author Response

Thank you very much for your comments on our manuscript entitled "Microstructure and wear resistance of TiCp/Ti6Al4V composite coatings by follow-up ultrasonic assisted laser additive manufacturing" (Manuscript ID: coatings-1763940). We have carefully revised.

1. Make your corrections more carefully. On line 124 you put "rpm/min" whereas "rpm" is rates per minute.  Remove "/min" and leave only "rpm".

 Thanks for the reviewer’s advice.

We have removed duplicates in the manuscript.

2. You corrected the large and small temperature gradient in the text, but not in Figure 8. Correct the figure so there is no dissonance.

 Thanks for the reviewer’s advice.

Thanks for the reminder, we have revised the description of the "region" in the figure.

3. In section 3.2.3 I would still recommend writing not alpha-Ti grains, but alpha laths or alpha-phase laths. I have read the papers you pointed out, and they deal with primary beta-phase grains and alpha laths, which are inside the beta grains. Therefore, it is incorrect to write alpha grains in this case. Judging by the order of values measured, you are considered the average thickness of the alpha laths, as in the work of Ma G, Yu C, Tang B, et al.

I believe this is the most important factor in describing the microstructure, and specifying alpha grains rather than alpha laths will mislead the reader about the real morphology of the alloy structure.

 Thanks for the reviewer’s advice.

Based on your suggestion, we have reconsidered the relevant description in the manuscript, and the original description was not rigorous enough. In conjunction with your suggestion, we have revised the description of the relevant content in the manuscript for the convenience of readers.