Re-Melting Nb–Si-Based Ultrahigh-Temperature Alloys in Ceramic Mold Shells
Round 1
Reviewer 1 Report
The manuscript entitled "Re-Melting Nb-Si Based Ultrahigh Temperature Alloys in Self-made Ceramic Mould Shells" is well structured and written. I suggest that the paper can be published in the journal.
Author Response
Responses to the Comments From Reviewer 1
We appreciate the reviewer very much for the affirmation on our work.
Reviewer 2 Report
This paper entitled “Re-Melting Nb-Si Based Ultrahigh Temperature Alloys in Self-made Ceramic Mould Shells", the authors investigated re-melting and solidification behavior of Nb-Si based ultrahigh temperature alloy during investment casting in different self-made ceramic mould shells. This topic is of interest to the Journal “Metals” readers that will help to understand the structures of the re-melted ceramic mould and the evolution of its microstructure. In my opinion, the research work is well structure and presented despite that the discussion is vague. Accordingly, I recommend the following comments to considered this paper for publication.
1 A lot of English mistake were found along the manuscript, especially in the abstract section. It is recommended to do short sentences and review the gramma.
2 In introduction, several referencing mistake were found, for example “Ma et al. [???] technically studied the…”
3 Figure 1 should be resized, besides the quality does not reach the required format.
4 Figure 2b needs an explanation what the authors want to indicate with the black circle.
5 A poor discussion has been done in this work. It is recommended to compare the results with previous authors to exhibit what is bringing new in this research work. A part from that, it is not commented the limitation of the re-melting cycles to the mechanical properties that seems to be crucial to the final purpose of these moulds.
Author Response
Responses to Reviewer 2 Comments
We appreciate the reviewer very much for the valuable comments on our manuscript entitled “Re-Melting Nb-Si Based Ultrahigh Temperature Alloys in Self-made Ceramic Mould Shells”. We have considered the comments carefully. Relevant revisions have been already made based on the comments. Detailed response has been made to the comments as follows.
Reviewer comments:
This paper entitled “Re-Melting Nb-Si Based Ultrahigh Temperature Alloys in Self-made Ceramic Mould Shells", the authors investigated re-melting and solidification behavior of Nb-Si based ultrahigh temperature alloy during investment casting in different self-made ceramic mould shells. This topic is of interest to the Journal “Metals” readers that will help to understand the structures of the re-melted ceramic mould and the evolution of its microstructure. In my opinion, the research work is well structure and presented despite that the discussion is vague. Accordingly, I recommend the following comments to considered this paper for publication.
Point 1: A lot of English mistake were found along the manuscript, especially in the abstract section. It is recommended to do short sentences and review the gramma.
Response 1: Thanks for the referee’s good comments which are valuable and very helpful for revising and improving our paper. We have reviewed the manuscript, especially the abstract section. Some English gramma mistakes have been modified and certain sentences have also been shorten in the current revised manuscript.
Point 2: In introduction, several referencing mistake were found, for example “Ma et al. [???] technically studied the…”
Response 2: Several analogous referencing mistakes have been corrected in the current revised manuscript.
Point 3: Figure 1 should be resized, besides the quality does not reach the required format.
Response 3: On your advice, Figure 1 has been remade in accordance with the required size and format in the current revised manuscript.
Point 4: Figure 2b needs an explanation what the authors want to indicate with the black circle.
Response 4: In the black circle is a eutectic cell. The further explanation has been given in the figure and the corresponding text in current revised manuscript.
Point 5: A poor discussion has been done in this work. It is recommended to compare the results with previous authors to exhibit what is bringing new in this research work. Apart from that, it is not commented the limitation of the re-melting cycles to the mechanical properties that seems to be crucial to the final purpose of these moulds.
Response 5: Previous similar work is mainly carried out in the furnace with tungsten heating element. On your advice to highlight novelty in this manuscript, the discussions regarding the various experiment phenomena of re-melting in the furnace with graphite heating element have been separated from "Results and discussion" section and constitutes new "Discussion" section. Comparison analysis with the re-melting experiment results carried out in the furnace with tungsten heating element has been strengthened and the corresponding modifications have been made in the revised manuscript.
The final purpose of the mould shells is confectioning and directional solidification of Nb-Si Based Ultrahigh Temperature Alloy turbine blades. For the experiment in this paper, re-melting the alloy using the mould shells with simple shape is just to evaluate the filling capability, microstructure homogeneity, elements segregation, casting defects, sand burning and the interactions between the mould shells and the alloy. These can be as reference for selecting technological parameter in further directional solidification of the turbine blades. We are concerned about the mechanical properties of the alloy only after directional solidification. Hence, the mechanical properties of the alloy is not commented in the manuscript. Indeed, the mould shells could exert impact on the mechanical properties of the directionally solidified alloy. But it needs to carry out the related experiment. Thank you for your valuable suggestion. This will be the next step of our work.
Reviewer 3 Report
I found this a difficult paper to read and understand. It is particularly over-long. The long discussion attempting to explain the chemical interactions is speculative, and in any case not helpful.
A central mis-translation which is unfortunately highly misleading seems to be the word 'electrode', implying contact or arcing with the melt. This seems to be incorrect. It seems from Figure 1 that the authors have used electrical resistance elements in the form of a winding around the charge to be melted. In place of the word 'electrode' used throughout the text, the word 'element' or 'resistance element' or 'heating element' should be used.
Figure 1 is also not described fully. Two crucibles are shown. However, if the figure is rotationally symmetric, 4, or 6 or more crucibles might be melted at the same time. I assume that the Mo tray is allowed to heat up to 1850 C (i.e. it is not water cooled).
Figure 4 is difficult to understand. Is there a very thick reaction layer? A magnification marker would be helpful on the photographic images.
The authors do not appear to give their target alloy composition in the experimental section. This would be helpful. Why this precise composition was chosen would also be of interest. Is it a composition defined as useful by other workers, for instance.
Figure 11 appears without any attribution, but appears to be from the work of other authors. If so a reference is necessary of course. If somehow defined from the text then clearly I have missed this.
Conclusion 2 finding that the structure of the investment casting is coarser than the vacuum arc remelted ingot is, frankly, obvious and hardly need be mentioned. The VAR ingot is cast into a water-cooled mold and freezes within seconds or minutes. The investment casting will take 10 to 100 times longer to freeze, and so be correspondingly coarser.
Each conclusion is mixed with results from W and Gr heating elements. It would be simpler and clearer for readers to give one conclusion for W reporting it to have future potential, and a separate conclusion for Gr, explaining how the use of this heating element gives unsatisfactory results.
Incidentally, it is very doubtful that the authors have used sand paper for the preparation of their metallographic studies. The use of silicon carbide paper is needed and its use in metallurgy and engineering is practically universal.
Author Response
Responses to Reviewer 3 Comments
We appreciate the reviewer very much for the valuable comments on our manuscript entitled “Re-Melting Nb-Si Based Ultrahigh Temperature Alloys in Self-made Ceramic Mould Shells”. We have considered the comments carefully. Relevant revisions have been already made based on the comments. Detailed response has been made to the comments as follows.
Reviewer comments:
Point 1: I found this a difficult paper to read and understand. It is particularly over-long. The long discussion attempting to explain the chemical interactions is speculative, and in any case not helpful.
Response 1: Thank you for pointing out the deficiencies in this work. We have made appropriate abridgement in the current revised manuscript. Besides, we have also re-discussed the results and made corresponding modifications. Please see the revised manuscript for details.
Point 2: A central mis-translation which is unfortunately highly misleading seems to be the word 'electrode', implying contact or arcing with the melt. This seems to be incorrect. It seems from Figure 1 that the authors have used electrical resistance elements in the form of a winding around the charge to be melted. In place of the word 'electrode' used throughout the text, the word 'element' or 'resistance element' or 'heating element' should be used.
Response 2: Thanks for your pertinent suggestion. The "electrodes" are all replaced by "heating element" in the revised manuscript. Please check them in the revised manuscript.
Point 3: Figure 1 is also not described fully. Two crucibles are shown. However, if the figure is rotationally symmetric, 4, or 6 or more crucibles might be melted at the same time. I assume that the Mo tray is allowed to heat up to 1850 C (i.e. it is not water cooled).
Response 3: Aiming at the problem you pointed out, Figure 1 has been remade. Please check it in the revised manuscript.
Point 4: Figure 4 is difficult to understand. Is there a very thick reaction layer? A magnification marker would be helpful on the photographic images.
Response 4: Figure 12(a) and (b) in the original manuscript (Figure 9(a) and (b) in the current revised manuscript) are the magnification of Figure 4(a) and (c). Figure 9 is to display the interfaces (including the reaction layers) between the alloy and the ceramic mould shells. Figure 4 is to display the macroscopic features of the samples after re-melting. Figure 4 (b) and (d) are the lateral surfaces of the re-melted alloy after removing the mould shells, which is for evaluation of the extent of sand burning and determination of the phase composition of the reaction layer using XRD methods.
Point 5: The authors do not appear to give their target alloy composition in the experimental section. This would be helpful. Why this precise composition was chosen would also be of interest. Is it a composition defined as useful by other workers, for instance.
Response 5: The target alloy composition is expressed as nominal composition of the alloy in the manuscript. It had been given in the experimental section of the original manuscript, which is Nb-20Ti-15Si-5Cr-3Hf-3Al (at%). The addition of various alloying elements is to balance the properties such as room temperature fracture toughness, high temperature strength, high temperature oxidation resistance and etc. Besides, the composition approximates to the eutectic composition in the arc melting situation, which had been also introduced in the original manuscript.
Point 6: Figure 11 appears without any attribution, but appears to be from the work of other authors. If so a reference is necessary of course. If somehow defined from the text then clearly I have missed this.
Response 6: Figure 11 in the original manuscript (Figure 12 in the current revised manuscript) is the activity coefficients changes of the elements Nb, Ti and Si. It is the work by our own. It was calculated with increase in carbon content in two simplified systems of Nb-Ti-C and Nb-Si-C based on Miedema formation heat model for a binary alloy and Kohler formulas, which had also been introduced in lines 312~315 in the original manuscript, lines 333~336 in the revised manuscript. Using Miedema formation heat model for a binary alloy and Kohler formulas is a general method to calculation the activity coefficients of elements in the alloy melt. Please refer to literatures [19] and [20] for more calculation details.
Point 7: Conclusion 2 finding that the structure of the investment casting is coarser than the vacuum arc remelted ingot is, frankly, obvious and hardly need be mentioned. The VAR ingot is cast into a water-cooled mold and freezes within seconds or minutes. The investment casting will take 10 to 100 times longer to freeze, and so be correspondingly coarser.
Response 7: Thanks for your valuable suggestion. The related conclusion has been deleted. Please check it in the revised manuscript.
Point 8: Each conclusion is mixed with results from W and Gr heating elements. It would be simpler and clearer for readers to give one conclusion for W reporting it to have future potential, and a separate conclusion for Gr, explaining how the use of this heating element gives unsatisfactory results.
Response 8: We have followed your suggestion and modified the conclusions in the revised manuscript. Thanks for your valuable advice.
Point 9: Incidentally, it is very doubtful that the authors have used sand paper for the preparation of their metallographic studies. The use of silicon carbide paper is needed and its use in metallurgy and engineering is practically universal.
Response 9: In this experiment, all samples after re-melting were cut on 10 mm distance from the bottoms. The cross section of the samples were indeed ground and polished, which can be seen from figure 2, figure 4(a), figure 4(c), figure 6(a), figure 6(b), figure 7 and figure 9. These procedures have been added into "Inspection of the samples" of the experimental section "Materials and methods". Thanks for your valuable advice.
Round 2
Reviewer 2 Report
The authors have properly addressed all my suggestion. Therefore, this article can be accepted in its present form.
Author Response
Responses to Reviewer 2 Comments (Round 2)
Thank you very much for your great efforts on our manuscript.
Reviewer 3 Report
The submission is much improved. The only recommendations for change include
Delete "Self made" from the title. It is not necessary, and is confusing.
In some figures its seems that mounting compound may have been used. If so, it is not easy to distinguish between the mount and the specimen. It would be helpful to the reader if the mount material were clearly labelled in every case. this may apply to figures 4, 6 and perhaps 9a and 9b.
Author Response
Responses to Reviewer 3 Comments (Round 2)
Reviewer comments:
The submission is much improved. The only recommendations for change include
Point 1: Delete "Self made" from the title. It is not necessary, and is confusing.
Response 1: On your advice, "Self-made" has been deleted from the title. Please see the current revised manuscript.
Point 2: In some figures its seems that mounting compound may have been used. If so, it is not easy to distinguish between the mount and the specimen. It would be helpful to the reader if the mount material were clearly labelled in every case. this may apply to figures 4, 6 and perhaps 9a and 9b.
Response 2: Thanks for your suggestion. The mounting materials are not displayed in figure 9(a) and (b), so we label the corresponding mounting materials in figures 4 and 6. Please see the current revised manuscript.
