The Effect of Incorporating Ceramic Particles with Different Morphologies on the Microstructure, Mechanical and Tribological Behavior of Hybrid TaC_ BN/AA2024 Nanocomposites

Round 1

Reviewer 1 Report

This paper presents a method to improve the properties of aluminum alloy by incorporating a hybrid of heavy particles, tantalum carbide (TaC), and light nanoparticles, boron nitride (BN), into the AA2024 alloy sheets by friction stir processing (FSP) technique. It shows reinforcement particles play an important role in improvement in the mechanical and tribological behavior. But the analysis are often based on visual observations and remain too superficial on several points.

Before publication, I think it is important to give more information on the following points:

1. How to determine the uniform distribution of grains? Figure 5 is very unclear and no information such as grains is marked.
2. Why chose these two particles? How to ensure the principle of single variable to analyze their respective effects?
3. “Due to the plastic deformation and the produced heat flux, the thermo-mechanically affected zone displays recrystallised grains partly.” How to know the density and volume fraction of the reinforcements after thermo-mechanically affecting?
4. As a polycrystalline material, the effect of crystal orientation on hardness should be considered.
5. Figure 6 shows that the hardness fluctuates greatly at different positions. How to explain?
6. The mechanism of the changes of the mechanical and wear resistance is not explained clearly. It is important to see the change of grain or grain boundary during the test.
7. The author should also check the full text carefully to avoid grammatical errors, such as so many section "3.1" in “3. Results and discussion”. The font size of Figure 2 and Figure 6 shall be consistent, etc.

Author Response

Dear Prof.

We would thank the Editor and Reviewers for their insightful comments on our manuscript. We have considered all the comments, and we have marked changes in the manuscript (marked-up version) with tracking changes.

Please contact us if any further clarification is required.

Kind regards,

Authors

Reviewers' comments:

Reviewer #1:

This paper presents a method to improve the properties of aluminum alloy by incorporating a hybrid of heavy particles, tantalum carbide (TaC), and light nanoparticles, boron nitride (BN), into the AA2024 alloy sheets by friction stir processing (FSP) technique. It shows reinforcement particles play an important role in improvement in the mechanical and tribological behavior. But the analysis are often based on visual observations and remain too superficial on several points.

Before publication, I think it is important to give more information on the following points:

1. How to determine the uniform distribution of grains? Figure 5 is very unclear and no information such as grains is marked.

Answer: thank you very much for your comment. With reference to Fig. 5, the image SEM illustrates the distribution of the reinforcement particles in the stirred zone. The particles appear as white and gray dots, while Fig. 4 shows the uniform distribution and equiaxed size of the grains. The uniform distribution of the grains was also confirmed by the uniform hardness and wear in the SZ.

2. Why chose these two particles? How to ensure the principle of single variable to analyze their respective effects?

Answer: We selected TaC particles for their excellent hardness and strength properties, while BN was chosen for its tribological effect, i.e., the boron nitride improves wear resistance. Therefore, the incorporation of these different particles can improve the overall physical and mechanical properties of the resulting hybrid composite. Regarding the second question to ensure the principle of single variable to analyze their respective effects, the previous work obviously examined the single additive and the hybrid composite, and this is addressed in the literature.

3. “Due to the plastic deformation and the produced heat flux, the thermo-mechanically affected zone displays recrystallised grains partly.” How to know the density and volume fraction of the reinforcements after thermo-mechanically affecting?

Answer: Thank you very much for your valuable comment. First, the thermo-mechanically affected zone (TMAZ) is the transition region between the SZ and the BM, where the elongated grains of the parent metal are deformed in an upward flowing pattern around the SZ. We believe that for a surface composite, the volume fraction and density must be uniform throughout the fabricated composite. Therefore, we focused on the study of the SZ. Overlapping passes can be processed in the SZ for the fabrication of a large area composite. Moreover, the TMAZ can be considered as a region with free reinforcements.

4. As a polycrystalline material, the effect of crystal orientation on hardness should be considered.

Answer: We agree with you. The crystal orientation due to the plastic deformation after FSP can be analyzed by advanced tools a, EBSD technique, this tools not available in our lab. Moreover, the limitation in time to do this.

5. Figure 6 shows that the hardness fluctuates greatly at different positions. How to explain?

Answer: Thank you for your valuable comment. The hardness depends on the microstructure. As mentioned in Figure 3, according to the FSP, there are different regions besides the BM. SZ contains the particles that lead to high hardness. HAZ and TMAZ do not have any particles, which leads to low hardness. The explanation is attached to the manuscript.

6. The mechanism of the changes of the mechanical and wear resistance is not explained clearly. It is important to see the change of grain or grain boundary during the test.

Answer: We agree with you. Actually, in this work we aimed to study the effects of these particles on the behavior of this alloy. Thus, the wear test was performed by the weight loss method; therefore, it is necessary to confirm the hardness results and the general behavior of the wear rate. In the further work, we will focus on the wear behavior of the hybrid composite via the surface morphology. ‎

7. The author should also check the full text carefully to avoid grammatical errors, such as so many section "3.1" in “3. Results and discussion”. The font size of Figure 2 and Figure 6 shall be consistent, etc.

Answer: Thank you for your valuable comment. The manuscript has been proofread and the Figures were revised 

Reviewer 2 Report

The manuscript of Ghandourah et al. evaluates the effect on the microstructure, mechanical and tribological properties of incorporating tantalum carbide and boron nitride nanoparticles into AA2024 alloy by friction stir processing. The manuscript is sound, nevertheless some improvements are necessary before publication, as discussed below.

1. Especially for in the case of the SEM images identifiying the different grain size of the initial AA2024 alloys sheet and the stirred zone (Fig 3,b) and of the different hybrid coatings in Fig 4, it would help if authors could provide a higher magnification optical image and indicate roughly the grain size.
2. It is very difficult to differentiation or to categorize the dispersion of the particles in the SEM images of the stirred zone. Based on the average particle size (100nm for BN and 300nm for TaC) authors should also provide higher magnification SEM images. If still not clear author could evaluate by EDX mapping of the coatings, and check the distribution of TaC or BN (at least Ta and B should be differentiated in EDX maps).
3. Authors state in conclusion (lines 225-227) that from SEM the dispersion of the reinformcement as well as less acolumution was revealed as well as the appearance of nanoclusters on reinforcing ceramic particles. Actually the SEM data of Figure 5 does not confirm these - as mentioned in previous comments, EDX mapping and higher magnifications are required. Authors should also indicate the agglomeration points on the lower magnification SEM images
4. A proofreading of the manuscript is necessary. For example, figure captions (there are two different Figures denoted as Figure 2), numbering of sections (there are two different subsections 3.1)

Author Response

Dear Prof.

We would thank the Editor and Reviewers for their insightful comments on our manuscript. We have considered all the comments, and we have marked changes in the manuscript (marked-up version) with tracking changes.

Please contact us if any further clarification is required.

Kind regards,

Authors

Reviewers' comments:

Reviewer #2:

The manuscript of Ghandourah et al. evaluates the effect on the microstructure, mechanical and tribological properties of incorporating tantalum carbide and boron nitride nanoparticles into AA2024 alloy by friction stir processing. The manuscript is sound, nevertheless some improvements are necessary before publication, as discussed below.

1. Especially for in the case of the SEM images identifiying the different grain size of the initial AA2024 alloys sheet and the stirred zone (Fig 3,b) and of the different hybrid coatings in Fig 4, it would help if authors could provide a higher magnification optical image and indicate roughly the grain size.

Answer: Thank you for your comment. The Figures have been modified.

2. It is very difficult to differentiation or to categorize the dispersion of the particles in the SEM images of the stirred zone. Based on the average particle size (100nm for BN and 300nm for TaC) authors should also provide higher magnification SEM images. If still not clear author could evaluate by EDX mapping of the coatings, and check the distribution of TaC or BN (at least Ta and B should be differentiated in EDX maps).

Answer: We agree with you. We have demonstrated here the even distribution of TaC and BN in two ways. The first by the provided SEM. The second way was after the hardness measurements and wear test. The uniform hardness and wear in the SZ confirmed the uniform distribution of the particles. Of course, you are absolutely right, the EDX can easily confirm the distribution of particles in the SZ. But due to the insufficient equipment of our laboratory in our country, we cannot do this at present. But we have confirmed the uniformity by the above two methods.

3. Authors state in conclusion (lines 225-227) that from SEM the dispersion of the reinformcement as well as less acolumution was revealed as well as the appearance of nanoclusters on reinforcing ceramic particles. Actually the SEM data of Figure 5 does not confirm these - as mentioned in previous comments, EDX mapping and higher magnifications are required. Authors should also indicate the agglomeration points on the lower magnification SEM images

Answer: Thank you for your comment. This sentence has been deleted. But the uniform hardness in SZ (the hardness does not vary) proves the uniform distribution of particles without any nanoclusters

4. A proofreading of the manuscript is necessary. For example, figure captions (there are two different Figures denoted as Figure 2), numbering of sections (there are two different subsections 3.1)

Answer: Thank you for your valuable comment. The manuscript has been proofread and the captions of the Figures have been revised.

Round 2

Reviewer 1 Report

The manuscript is revised carefully and can be accepted.

Author Response

Thank you very much for your valuable comments which helped us to improve our manuscript.

We have reviewed the manuscript for all grammatical errors and mistakes and corrected all problems.

Reviewer 2 Report

The authors have attempeted to revise the manuscript, however except for proofreading and English corrections, authors did not properly address the comments.

The lack of ease of access to EDX can be understood and the manuscript can be brought to a proper shape without. Nevertheless, the author modifications on the first two comments were not satisfactory.

Figures 3-5 were just made bigger. This is not the same with higher magnification images. Even with enlarging the figures, only Figure 3 is partly improved. Grain boundaries and particles, respectively, can be easily indicated on the images with arrows. There is no additional higher magnification for Figure 4. With respect to Figure 5 (SEM) and possible EDX, higher magnification images should at least be provided. As long as authors have the initial SEM images, higher magnifications of areas from those could be provided.

Author Response

Dear Prof.

We would thank the Editor and Reviewers for their insightful comments on our manuscript. We have considered all the comments, and we have marked changes in the manuscript (marked-up version) with tracking changes.

Please contact us if any further clarification is required.

Kind regards,

Authors

Reviewers' comments:

Reviewer #2:

• The authors have attempted to revise the manuscript, however except for proofreading and English corrections, authors did not properly address the comments.

Answer: the manuscript has been carefully proofread. We have checked the manuscript for all grammatical errors and mistakes.

• The lack of ease of access to EDX can be understood and the manuscript can be brought to a proper shape without. Nevertheless, the author modifications on the first two comments were not satisfactory. Figures 3-5 were just made bigger. This is not the same with higher magnification images. Even with enlarging the figures, only Figure 3 is partly improved. Grain boundaries and particles, respectively, can be easily indicated on the images with arrows. There is no additional higher magnification for Figure 4. With respect to Figure 5 (SEM) and possible EDX, higher magnification images should at least be provided. As long as authors have the initial SEM images, higher magnifications of areas from those could be provided.

Answer: Thank you for your valuable comments which helped us to improve our manuscript. Figures 3 and 4 have been changed and modified.