Powder Injection Molding of Ti-Al-W Nano/Micro Bimodal Powders: Structure, Phase Composition and Oxidation Kinetics
Round 1
Reviewer 1 Report
The authors presented a report on the powder injection molding process on Ti-Al-W powders before and after HIPping. The results are well described but the article clearly lacks in reviewing relevant literature to show the importance of Ti-Al-W alloys and discussing the results.
I recommend authors to pay more attention towards discussing the appropriateness of the observed results in relation to the relevant literature to show the novelty in the work. So far, I couldn't figure out any novelty in the work and clear discussion of any observations.
Author Response
Dear Reviewer!
Thank you for your valuable comments. Thank you for your time and attention to our article. We have carefully read your comment. As for the remark about the novelty of the work, the article deals with Ti-Al materials reinforced with tungsten. In our case, the material is obtained by the method of electric explosion of wire. Bulk samples contain both elemental Ti and Al and their intermetallic compounds. Tungsten is used as an additional hardening element, articles on this issue are also given in the manuscript. In the introduction, these are references 33-40, in the results - 68 and 69. In addition, we already have conducted a study on the production of powders based on Ti-Al with the addition of Mo, W and Cu (reference 53) where the advantages of such systems are also considered in detail. As mentioned in the end of the introduction, the main purpose of this work is to show feasibility of PIM production of bulk samples using EEW Ti-Al-W powders. Products from these materials are planned to be used by us in further studies. This study allowed us to understand which EEW and sintering parameters should be used in the future in terms of providing the required properties.
Reviewer 2 Report
The authors present a work entitled "Powder injection molding of Ti-Al-W nano / micro bimodal powders: structure, phase composition, and oxidation kinetics." Powder composites Ti-48Al-4W with different powder size distribution obtained by electric explosion of wire (EEW) method were investigated. This work is interesting, but some improvements should be made before it can be accepted for publication.
1. Abstract section. Please describe the specific effects of size distribution and sintering method on mechanical properties and particle size distribution on oxidation resistance more clearly.
2. Introduction section. Spark plasma sintering is also a vital powder metallurgy process. Recent studies have found that using amorphous powder as a precursor can significantly promote densification, like thermoplastics. It is a primary method for preparing micro/nano bimodal microstructure. Please add some discussions about the spark plasma sintering of amorphous powders. Here is some literature that can help with this process.
[1] "Enhancing strength-ductility synergy in an ex-situ Zr-based metallic glass composite via nanocrystal formation within high-entropy alloy particles." Materials & design 210 (2021): 110108.
3. Introduction section. A mixture of particles with a bimodal size distribution has a higher flowability and forms a bimodal grain structure that will affect the deformation process and, thus, the mechanical properties. Please briefly describe the relevant studies.
4. In the present study, the authors obtained powders with different powder size distributions by the electric explosion of wire (EEW) method. Did the authors measure the particle size distribution of the powder obtained with different EEW parameters? If so, please show the corresponding particle size distribution as this is a crucial experimental result to help the readers understand this study.
5. Figure 4, Please show the stress-strain curves of TAW1, TAW2, and TAW3 samples prepared by different sintering methods. The parameters of the three-point bending test should be added, such as the loading speed.
Author Response
Dear Reviewer!
Thank you for your valuable comments. Thank you for your time and attention to our article. We have carefully read your comments, our responses can be found below:
1) The abstract had been modified.
2) Indeed, SPS is a very powerful tool for obtaining bulk products from powders. In addition to it, there are other compaction methods, and there are other methods for obtaining bulk samples along with PIM and MEAM. Since the article does not aim to review technologies, we consider it irrelevant to include articles on SPS and other technologies in the introduction. However, we are currently preparing an article on SPS samples prepared from preceramic papers and will take the provided article into consideration.
3) This point have been added and highlighted in Introduction.
4) The main idea is that EEW energy input correlates with the average particle size and amount of microparticles. This is why Table 1 brings the information about particle size distribution. The particle size distribution in EEW technology is the separate study that was conducted before (see references 51-53).
5) Fig.4 had been modified. The bending test parameters have been added and highlighted.
Reviewer 3 Report
This work presents the use of EEW to prepare Ti-Al-W powders for the PIM process. A wide range of analysis were covered to evaluate the manufacturing performance. The work is a good match with this journal, while some more details need to be more clearly provided to better support the conclusion.
On the first paragraph of Page 2, when introducing EEW, it is suggested to add some literature citations for EEW which proved that it is more promising than other techniques of mixture preparation.
In Section 3.1, only microstructure for TAW1 and XRD for TAW2 are shown in Figure 2 and Figure 3. The results of other samples are needed to better support the conclusion that all samples have nearly the same structure. For the EDX, is there any point analysis to obtain atomic percentages of elements for phases such as TiAl?
In Section 3.3, authors mentioned that vacuum-sintered and HIP samples show the same kinetics, while the data of the vacuum-sintered samples were not found in the manuscript, which are relevant information for the conclusion that the oxidation resistance is largely independent of sintering methods.
Author Response
Dear Reviewer!
Thank you for your valuable comments. Thank you for your time and attention to our article. We have carefully read your comments, our responses can be found below:
- On the first paragraph of Page 2, when introducing EEW, it is suggested to add some literature citations for EEW which proved that it is more promising than other techniques of mixture preparation.
The literature was added.
- In Section 3.1, only microstructure for TAW1 and XRD for TAW2 are shown in Figure 2 and Figure 3. The results of other samples are needed to better support the conclusion that all samples have nearly the same structure. For the EDX, is there any point analysis to obtain atomic percentages of elements for phases such as TiAl?
Since the structure and XRD patterns are very similar, we decided not to add all the figures and spectra for all samples in order to not overload the paper and improve readability. EDX from area demonstrates the nearly 50 : 50 (±5%) Ti to Al ratio for big areas, point analysis also demonstrates the same values. In areas where both titanium and aluminum are present, the ratio is also about 50 to 50. However, the areas are quite narrow, and the measurement error is ±9%. Mapping allows to more clearly see the areas enriched and depleted in titanium and aluminum. However, the point analysis values, even taking into account deviations, do not show the formation of other phases, such as TiAl3 or Ti3Al. These results correlates with XRD data since patterns for TiAl3 and Ti3Al differ significantly from each other.
- In Section 3.3, authors mentioned that vacuum-sintered and HIP samples show the same kinetics, while the data of the vacuum-sintered samples were not found in the manuscript, which are relevant information for the conclusion that the oxidation resistance is largely independent of sintering methods.
By "show the same kinetics" we mean that the ΔW/A values differ by less than 2 mg/cm2 for all points. Thus, we are faced with the problem of presenting the results obtained, since the graphs are overlapped. In this regard, we refused to present data for both sintering methods and limited ourselves to indicating the same kinetics in the discussion.
Round 2
Reviewer 2 Report
The authors have tried to improve the manuscript. However, I have some more concerns.
1. Experimental: more details should be added. E.g., target and scanning speed for XRD, etc
2. Figure 4: the error bar of the hardness for the vacuum sintering sample is larger than that of HIP. What is the possible reasons? How about the relative density?
3. Figure 5: it is better to provide results for TAW1 and TAW3 for comparison. Same problems in Figure 2.
4. About the oxidation behavior, it is better to provide more results e.g., the XRD, SEM, to find out the oxidation mechanisms (Only the XRD patter for TAW2 was provided). Only Figure 7 is not enough.
Author Response
Dear Reviewer!
Thank you for your valuable comments. Thank you for your time and attention to our article. We have carefully read your comments, our responses can be found below:
- The experimental details have been added.
- We did at least 50 indentations per sample. On average, the indentation size made it possible to indent regions containing several phases. The error values of hardness depends on the phases present on the cross section of the sample where the indentation was carried out. In some cross-sections, tungsten particles were more common, in some - an intermetallic shell. However, the trend towards a decrease in hardness with decreasing particle size from TAW1 to TAW3 is observed even with the error bars taken into account. If we compare the scatter values ​​for one sample but sintered in vacuum and by the HIP method, then the values ​​differ insignificantly.
- All necessary figures have been added.
- In this work, a preliminary study was carried out to understand the kinetics of the oxidation of the samples. In fact, when examining the results of microscopy of oxidized samples, interesting results were found. We decided not to present these results in this article and to separate them into a separate, deeper study on the oxidation of the obtained samples. Research is currently underway on oxidation under different conditions. These results will be accompanied by a deeper study of microscopy, including SEM and TEM. in the present work, the aim was to show that the oxidation kinetics is more dependent on the particle size and it differs for different samples. At the same time, HIP does not significantly affect the oxidation kinetics. This conclusion is important to us for our next article, where we will abandon the use of the HIP. Explanation of this added to the article.
Round 3
Reviewer 2 Report
accept it
