Pressing and Sintering of Titanium Aluminide Powder after Ball Milling in Silane-Doped Atmosphere

Round 1

Reviewer 1 Report

In this paper, pressing and sintering of titanium aluminide powder after ball milling in silane-doped atmosphere were investigated. I recommend the publication of this manuscript after minor revision.

 

1) Line 85 please provide more detailed information about argon-silane atmosphere.

2) In section 3.3, the pressability of powders may be related to the particle size distribution.

3) In section 3.6, the discreteness of hardness is a bit large. It’s better to test the strength of samples.

4) More discussion about the formation of MAX phase and the effect of atmosphere.

Author Response

Dear Reviewer,

Thank you for reading through and commenting on our manuscript. Your comments were very helpful and have been incorporated.

In the Materials and Methods section, from line 80 to 86, rewordings of the previous paragraph were made to improve the reading flow. In line 86, the achievable density of the material was mentioned, as in the section "Density" the relative density refers to this value. From line 87 to 92, the comment from Reviewer 1 was incorporated and the argon-silane atmosphere was explained in more detail. In addition, it was explained how this atmosphere is generated.

In the discussion it was mentioned that the particle size has an influence on the pressability (comment by reviewer 1).

In section 3.4, the strengths of the samples were examined as recommended by Reviewer 1.

In addition, the MAX phase (comment reviewer 1) was further explained.

Yours sincerely

Sebastian Döring

Reviewer 2 Report

This article is not acceptable in the current format due to poor discussion. Explanation of results is simple and short. I suggest authors to provide more scientific discussion on the results. Following are some comments to improve the manuscript:

1- Following statement is acceptable for conventional sintering but is not match with spark plasma sintering (SPS). Because using SPS fully dense titanium can be fabricated even containing high oxygen content. “During sintering, the oxide layers act as a diffusion barrier and therefore cause high porosities.” You can refer to the following reference: Ductility improvement of high-strength Ti–O material upon heteromicrostructure formation

2- How many indentations was applied to measure microhardness of each sample? and what was the indentation holding time? in addition, the detail of sintering method; facility, machine, model and parameters are missing in the methodology section.

3- Discussion on the density results is not clear. How density increase become 58% while no clear influence of oxygen-free processing and average density of all samples and reference are almost same. You are suggested to re-write this section and show the density of all samples in a table separately.

4- Poor discussion of microstructures in Fig.5 and 6. In addition, captions of figures 4,5 and 6 are not acceptable. You are suggested to mark the figures as (a),(c),… and explain in the caption properly.

Author Response

Dear Reviewer,

Thank you for reading through and commenting on our manuscript. Your comments were very helpful and have been incorporated.

In line 50 in the "Introduction" section, the comment from Reviewer 2 has been integrated by mentioning that the oxide layers are of secondary importance for the FAST process. 

In line 176 to 185 the comment from Reviewer was incorporated and the hardening process was explained in more detail. In line with Reviewer 2's comment, more details on sintering have been provided in lines 128 to 134.

In addition, the section on density was rewritten and further discussed. The influence of the atmosphere on density was described in the discussion (Reviewer 2 comment).  

The images have been revised as recommended by Reviewer 2. In addition, the microstructures (comment Reviewer 2) were further explained.

Yours sincerely

Sebastian Döring

Reviewer 3 Report

This work presents an interesting approach to the production of TiAl powders free from oxide surface films.

The paper was well prepared and gives a reader a very good impression. 

X-ray photoelectron spectroscopy was used to characterize the samples.

Overall, the submitted manuscript is worth publication in the Journal provided minor revision has been made.

1. I think that the term "silane-doped" should be replaced by "silane-containing".

2. In the Abstract, please provide the chemical formula of the compound and particle sizes of the ball-milled products.

3. All abbreviations should be explained upon their first use (in both main text and Abstract).

4. For the equipment manufacturing companies, the city and country information should be given, as required by MDPI Journals.

5. Hardness meanurements: how many measurements were done per sample? The hardness values should be rounded up, the decimal digits are not necessary.

6. How was the concentration of silane in the atmosphere of milling was selected? Please provide the concentrations used.

7. Please explain the phrase "Silane reacts with the residual oxygen of argon 5.0".

Author Response

Dear Reviewer,

Thank you for reading through and commenting on our manuscript. Your comments were very helpful and have been incorporated.

Reviewer 3's comment to change the word "silane doped" to "containing silane" was not incorporated, as this would be technically incorrect. By introducing monosilane (SiH4) for a short time to obtain the desired atmosphere, the gas reacts with the residual oxygen to form silica, which should not be called silane. Because we introduce monosilane this can be called "doped". However, since no monosilane is added after the desired atmosphere is reached, the term "silane-containing" would be incorrect.

The chemical formula symbols were added and the chemical reaction was described. 

Reviewer 3's comment to explain all abbreviations on first mention has been incorporated.

As noted in Reviewer 3's comment, the city and country information of the equipment suppliers has been added throughout the document. 

From line 176 to 185, comment 3 was incorporated and the hardening process was explained in more detail.

From line 105 to 110 comment from Reviewer 3 has been incorporated explaining the atmosphere at grinding.

The chemical reaction equation has been added to better show the influence of the monosilane and to explain how monosilane reacts with the residual oxygen from argon 5.0 (comment Reviewer 3).

Yours sincerely

Sebastian Döring

Reviewer 4 Report

he work is very well prepared in terms of editing and content. The introduction is concise and closely related to the topic of the work. The authors clearly justified the purpose of the research, which concerns a specific research problem. The experiment is described in detail, I like that the Authors give details such as Al-Kα radiation. The planned research is relatively simple to perform, but is adequate to solve the research problem. The description of the test results itself does not raise any objections, moreover, the authors provided hardness values with a measurement error. From a purely technical point of view, I suggest the Authors to separate a section "Conclusions" from the "Discussion" section. There are different styles in the references section, Authors should review the section and standardize the formatting.

In conclusion, the work is very well prepared and can be published without major changes.

Author Response

Dear Reviewer,

Thank you for reading through and commenting on our manuscript. Your comments were very helpful and have been incorporated.

As recommended by Reviewer 4, a Conclusion section has been added.

Yours sincerely

Sebastian Döring

Round 2

Reviewer 2 Report

I applaud the authors’ efforts on experimental research but unfortunately I do not recommend accepting this paper. The results does not show significant improvement on this experiment. Additionally, manuscript still has lack of strong scientific discussions.