Effect of Molybdenum Content on Microstructure and Mechanical Properties of Ti-Mo-Fe Alloys by Powder Metallurgy

Round 1

Reviewer 1 Report

This article should be of great interest to the researchers and engineers in this field. I suggest that it be accepted after some revision. The specific comments are as below:

1.     The written English should be improved for better readability. For example, the sentence “At this time, the human-friendly Ti-Mo-Fe ternary beta tita- 10 nium alloy is an alloy in which V, Nb, and Zr, which are expensive alloying elements, are replaced with Mo and Fe” is obscure.

2.     However, a powder metallurgy (PM) process is easy to manufacture complex parts[22]. Is it easy to prepare Ti parts with complex shape?

3.     Please explain why Mo stabilizes beta phase.

4.     Any evidence of the claim that the pores are due to Kirkendal effect.

5.     The last paragraph of Section 3-1 should be relocated just after the first paragraph of Section 3-1.

6.     The influences of porosity on the micro-hardness should be taken into consideration.

7.     The stress-strain curves rather than stress-strain curve should be used.

8.     The oxidation of powder should also be considered in the explanation of fracture as it affects the bonding between particles.

 

 

Author Response

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Reviewer 2 Report

It would be good to expand the review a little: to describe in more detail the achievements of the researchers and the content of their work to which you refer. The number of sources, however, can not be increased.

It would be good to indicate the phases with the arrows in Figure 2.

 

In conclusion 1, indicate the cost of what can be reduced. And in general, a little more describe the findings. Maybe add a comparison to the conclusions with those already available from other authors' achievements.

In general, the paper and the study were performed at a high level. Article subject devoted to the study of biocompatible Ti-Mo-Fe is hugely relevant. The authors contribute a fairly significant contribution to the development of this area by adding new elements to this material.

To improve the paper can be recommended, as I wrote earlier, a little to expand the introduction and the conclusions to add a comparison with the already existing results of third-party researchers.

 

Author Response

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Round 2

Reviewer 1 Report

This article should be of great interest to the researchers and engineers in this field. I suggest that it be accepted after some revision. The specific comments are as below:

1.      The written English should be improved for better readability. For example, the sentence “At this time, the human-friendly Ti-Mo-Fe ternary beta tita- 10 nium alloy is an alloy in which V, Nb, and Zr, which are expensive alloying elements, are replaced with Mo and Fe” is obscure.

2.      However, a powder metallurgy (PM) process is easy to manufacture complex parts[22]. Is it easy to to prepare Ti parts with complex shape?

3.      Please explain why Mo stabilizes beta phase.

4.      Any evidence of the claim that the pores are due to Kirkendal effect.

5.      The last paragraph of Section 3-1 should be relocated just after the first paragraph of Section 3-1.

6.      The influences of porosity on the micro-hardness should be taken into consideration.

7.      The stress-strain curves rather than stress-strain curve should be used.

8.      The oxidation of powder should also be considered in the explanation of fracture as it affects the bonding between particles.

 

Author Response

[Response to Reviewer 1 Comments]

According to the Reviewer’s comments, the quality of this manuscript can be improved. Thanks very much for your comments.

 

Point 1: The written English should be improved for better readability. For example, the sentence “At this time, the human-friendly Ti-Mo-Fe ternary beta tita- 10 nium alloy is an alloy in which V, Nb, and Zr, which are expensive alloying elements, are replaced with Mo and Fe” is obscure.

Response 1: According to the Reviewer’s comment, we revised the manuscript.

 

Point 2: However, a powder metallurgy (PM) process is easy to manufacture complex parts[22]. Is it easy to prepare Ti parts with complex shape?

Response 2: Due to its high chemical activity, titanium has a problem of high-temperature oxidation when the process is performed at a high temperature. However, 'simpler work processes and facilities are used for comparing it with the ingot process.’ mentioned in the text is not a comparison with other materials, but it is a description of “relatively easy” compared to the ingot process.

We revised the sentence.

 

Point 3: Please explain why Mo stabilizes beta phase.

Response 3: Molybdenum has a body-centered cubic structure and is a strong β-stabilizer for the formation of titanium alloys. According to the literature, when increasing the Mo content to 10 wt.% and above, the phases become entirely converted into the beta phase. Also, the addition of molybdenum is known to decrease the beta transition temperature of titanium.

 

Point 4: Any evidence of the claim that the pores are due to Kirkendal effect.

Response 4: The Kirkendall effect is the motion of the interface between two atoms that occurs as a consequence of the difference in diffusion rates of the metal atoms. This means pore formation due to the difference in diffusion rate between the two atoms. The diffusivity of molybdenum atoms into titanium is much lower than that of self-diffusion of titanium, and this unbalance of mass transfer results in pore formation.

 

Point 5: The last paragraph of Section 3-1 should be relocated just after the first paragraph of Section 3-1.

Response 5: According to the Reviewer’s comment, we revised the manuscript.

 

Point 6: The influences of porosity on the micro-hardness should be taken into consideration.

Response 6: Thank you for your good comment. We explained the influences in the text, followed as; “In general, it is known that as the Mo content increases, the hardness value increases due to the solid-solution strengthening effect [35], but when the Mo content increases, the hardness value increases due to the decrease in the thickness of widmanstätten α-lath, and the pore fraction increases (2.1% à 3.5%). As a result, the effect of decreasing the hardness value was largely affected, and it is considered that the hardness value of TMF 54 P/M was similar to the hardness value of TMF 34 P/M.”

~~~

“ In addition, the P/M alloy has a hardness value lower than that of I/M with the same composition, and the hardness of the P/M alloy is decreased due to pores in the P/M alloy. Thus, it is considered that the hardness value of the P/M alloy is lower than that of the ingot alloy.”~~~

 

Point 7: The stress-strain curves rather than stress-strain curve should be used.

Response 7: According to the Reviewer’s comment, we revised the manuscript. Thank you for your kind comment.

“The tensile stress-strain curves obtained from the room temperature tensile test conducted on four types of the TMF beta alloys were shown in Figure 8~”

 

Point 8: The oxidation of powder should also be considered in the explanation of fracture as it affects the bonding between particles.

Response 8:  As you know, titanium has very high chemical activity. So all processes were woked under high vacuum atmosphere including the storage of titanium powder. Also, room-temperature quasi-static tensile fracture is mainly affected by microstructure, pore distribution, etc, so the oxidation was not considered in this manuscript.

 

Reviewer 2 Report

The authors have made the necessary changes. Thanks to the authors for their work. Article in my opinion can be published.

Author Response

The quality of this manuscript can be improved by the Reviewer’s helpful comments. Thanks very much for your comments.